Symposium SB08—Bioelectronics—Materials and Interfaces

Reaction Centers (RCs) are specific transmembrane proteins of photosynthetic microorganisms that convert photons into charge separated states, with extremely high photoconversion efficiency. Our research group has demonstrated that bioconjugation of tailored molecular organic antennas represents an efficient strategy to enhance the light harvesting capability of RC extracted from Rhodobacter sphaeroides R26 photosynthetic bacterium [1-3]. Moreover, RC based photoelectrochemical cells [4,5], photosensors [6] and photoactive transistors [7] have been developed. RCs have been also integrated in semiconducting thin films deposited onto metal electrodes [8], and stabilized in soft structures like vesicles and polymersomes [9] before integration in electronic systems. Recently, we have developed chemical methods to optimize the interface of Rhodobacter sphaeroides RCs with electrodes, avoiding protein denaturation. To this aim, an adhesive biocompatible polymer, polydopamine (PDA), has been used. PDA can be easily produced by oxidative polymerization of dopamine in mild aqueous aerated conditions. It acts as an efficient coating layer for RC photoenzymes, improving the electrode/protein interface without altering the enzyme photoactivity [10]. PDA can be further functionalized to improve its light transmittance, allowing an increase of photocurrent generation of PDA coated RCs [11]. Hence, this polymer can be envisaged as a promising biocompatible adhesive material to efficiently interface photoenzymes with electrodes in bioelectronic devices for solar energy conversion.

[1] F. Milano, R.R. Tangorra, O. Hassan Omar, R. Ragni, A. Operamolla, A. Agostiano, G.M. Farinola, M. Trotta, Angew. Chem. Int. Ed., 51(44), 11019-11023 (2012).
[2] O. Hassan Omar, S. La Gatta, R.R. Tangorra, F. Milano, R. Ragni, A. Operamolla, R. Argazzi, C. Chiorboli, A. Agostiano, M. Trotta, G. M. Farinola, Bioconjugate Chem. 27, 1614-1623 (2016).
[3] S. la Gatta, F. Milano, G. M. Farinola, A. Agostiano, M. Di Donato, A. Lapini, P. Foggi, M. Trotta, R. Ragni, Biochimica et Biophysica Acta-Bioenergetics, 1860 (4), 350-359 (2019).
[4] F. Milano, F. Ciriaco, M.Trotta, D. Chirizzi, V. De Leo, A. Agostiano, L.Valli, L. Giotta, M.R. Guascito, Electrochim. Acta, 293, 105-115 (2019).
[5] F. Milano, A. Punzi, R. Ragni, M. Trotta, G. M. Farinola, Adv. Funct. Mater., 29 (21), 1805521, (2019).
[6] M. Chatzipetrou, F. Milano, L. Giotta, D. Chirizzi, M. Trotta, M. Massaouti, M.R. Guascito, I. Zergioti, Electrochemistry Communications, 64, 46-50 (2016).
[7] M. Di Lauro, S. la Gatta, C.A. Bortolotti, V. Beni, V. Parkula, S. Drakopoulou, M. Giordani, M. Berto, F. Milano, T. Cramer, M. Murgia, A. Agostiano, G.M. Farinola, M. Trotta, F. Biscarini, Adv. Electronic Mater. 6 (1), 1900888 (2020).
[8] E. D. Glowacki, R. R. Tangorra, H. Coskun, D. Farka, A. Operamolla, Y. Kanbur, F. Milano, L. Giotta and N. S. Sariciftci, J. Mater. Chem. C, 3 (25), 6554-6564 (2015).
[9] R. R. Tangorra, A. Operamolla, F. Milano, O. Hassan Omar, J. Henrard, R. Comparelli, F. Italiano, A. Agostiano, V. De Leo, R. Marotta, A. Falqui, G.M. Farinola, Trotta M., Photochem Photobiol Sci., 14(10), 1844-1852 (2015).
[10] M. Lo Presti, M. M. Giangregorio, R. Ragni, L. Giotta, M. R. Guascito, R. Comparelli, E. Fanizza, R. R. Tangorra,
A. Agostiano, M. Losurdo, G. M. Farinola, F.Milano, M. Trotta Adv. Electron. Mater. 2000140, (2020).
[11] G. Buscemi, D. Vona, R. Ragni, R. Comparelli, M. Trotta, F. Milano, G. M. Farinola, Adv. Sustain. Syst., doi.org/10.1002/adsu.202000303 (2021).

Applying organic electronics technology to biological systems, such as cells and neuronal tissue, is a promising strategy to answer many of the long-standing questions of biology and neuro-signaling. Further, such approach may also provide new solutions for therapy and prosthesis applications, especially to combat neurodegenerative disorders or diseases. The fidelity of such methodology depends heavily on the quality of interfacing foreign device technology with soft and complex biological systems. Several approaches have been conducted in the past to improve the matching between organic electronics and biology with respect to mechanical, chemical, electrical and signaling characteristics. Here, a novel approach is reported where organic electronic materials is applied to the biological system in the form as monomers, followed by bio-interfacing and in-situ polymerization. The resulting system is a self-organized electrode and device technology that integrates and interfaces with cells and tissues in a highly conformable and tight manner. The chemical approach, electrical characteristics as well as the performance when operating such in vivo-manufactured organic bioelectronics will be reported.

Biological tissues are multiscale, cooperative across different components, dynamically responsive, and in many cases strain-stiffening. One key challenge in creating bioelectronic devices with tissue-like features is to recapitulate the multiscale tissue architectures and the unique dynamic mechanical responsiveness. If these could be achieved, the bioelectronic devices would allow for seamless biointerfaces and the sensing or modulating of the biological signals with high efficiency. In this work, we designed a granules-enabled hydrogel composite, with multiple naturally occurring biopolymers and synthetic hydrogels as the key components. Mechanical and in-situ x-ray characterizations reveal that the strong inter-molecular and inter-granular interactions between the components give rise to the exceptional tissue-like strain-stiffening behaviors. Due to mechanical match with the real tissues, our tissue-like materials have enabled the pneumatically actuated bioelectronic devices for applications such as the recording of the heart electrocardiogram (ECG) signal ex-vivo.

Functional polymer semiconductors based on π-conjugated structures have shown distinct promise for the development of human-integrated electronics, owing to their solution processability for large-area fabrication, mechanical softness and even stretchability, as well as low cost. However, among the wide range of functional properties required for this application domain, which include, but not limited to, biochemical sensing, chemotherapeutic property, bio/immune-compatibility, micro-patternability, tissue/skin adhesion, stimuli-responsiveness, numerous of them face synthetic challenges to be imparted onto conjugated polymers and thus combined with efficient charge-transport property. Currently, the absence of these functional properties poses the major obstacle for taking advantage of the unique properties of conjugated polymers to benefit the development of human-integrated electronics. Here, we establish a “click-to-polymer” (CLIP) synthesis strategy for conjugated polymers, which enables the use of a click reaction for the facile and versatile attachment of diverse types of functional units to a pre-synthesized conjugated-polymer precursor. This can be utilized to realize both bulk and surface functionalization in/on the deposited thin films. Through demonstrating the applicability on four types of functional groups that each carry distinct emerging properties, for instance, ion conduction and immune-modulation, we show that functionalized polymers from this CLIP method can still retain good charge-carrier mobility above 0.1 square centimeters per volt per second. The obtained electrical performance is much higher compared to that from conventional synthesis approach for the incorporation of long polar groups. On the other hand, the surface functionalization does not cause any influence on the mobility while bringing in new surface properties. To demonstrate the usefulness of this CLIP strategy, we realized two highly desired functions on conjugated polymers: the direct photo-patterning with sub-10 μm resolution enabled by the incorporation of benzophenone groups; and the amplified biomolecular sensing enabled by the incorporation of N-hydroxysuccinimide (NHS) ester that can conjugate with enzymatic bioreceptors. Both the performances advance the state of the art of realizing these two types of functions on conjugated polymers. We expect the expanded use of this synthesis approach will largely enrich the functional properties from conjugated polymers and facilitate the electronic-biological interfacing in the future.
(Under revision)

Soft actuators are garnering considerable attention, due to their ability to perform tasks that are difficult or impossible for traditional electromechanical robotic technologies. The flexibility and control exerted by soft actuators is ideal for biomimicking of the complex and delicate movements emerging from soft muscles. These soft actuators are often fabricated from smart materials, being able to respond and actuate when exposed to a specific external stimulus. With such advantages as flexibility, lightweight, and deliverance of a wide range of movement, smart materials based soft actuators can be utilized in applications from satellite mirror control to miniaturized medical devices and biomimetic robotic grippers.
This study reports a novel soft actuator that combines the advantages of pneumatic and magnetic responsive systems for achieving a multi-directional actuation behaviour. The fabricated Fe₃O₄/silicone hybrid actuator balances the two distinct pneumatic and magnetic stimuli responses by allowing each stimuli to overcome each other’s disadvantages and optimizing these components. The micro soft pneumatic actuator is fabricated utilizing 3D printed wires to create unique singular motions, forming unique “S”, “L”, or a hook shape. The magnetic actuation is integrated into the silicone soft body through Fe₃O₄ nanoparticles and complements this pneumatic movement. It was reported that the Fe₃O₄ had a significant impact on the mechanical property of the silicone matrix, the incorporation reducing the elastic modulus of the silicone elastomers. This was favorable overall, allowing the pneumatic actuation to occur under a lower pressure requirement while producing a high blocking force. Additionally, it was observed that the magnetic nanoparticles alignment within the samples enhanced the magnetic deflection and susceptibility at a lower magnetic field. The demonstrated hybrid soft actuators could lift objects 3.4 times its own weight. Furthermore, a gripper system was designed with two operational soft actuators in parallel configuration. It could grab objects larger than the gripper width due to a secondary magnetic actuation. Using the advantage of the multi-directional pneumatic/magnetic actuation, such hybrid soft actuator has the capability to be utilized in biomimicking or biomedical applications where unique maneuverability and force control is required.

Mixed electron/ion transport in organic materials is enticing due to the potential applications in electrochemical transistors, bioelectronics, printed electronics, and sensors. PEDOT:PSS is a model mixed conductor with a morphology consisting of PEDOT:PSS-rich gel particles embedded within a PSS matrix. Our previous study reported heterogeneous ion mobility. However, the origins behind this heterogeneity were not explored in detail. We present the existence of two separate ion channels in PEDOT:PSS originating from a bilayer morphology that naturally forms from the differing surface energies of the two components during solution casting. A higher ion mobility occurs in a PSS-rich ~10 nm top channel versus a slower PEDOT-rich bulk. We demonstrate the ability to gate ion flow by using different ion barrier materials of increasing hydrophobicity that drives ions out of the top channel. By increasingly removing the PSS top channel, the ion mobility approaches that of the bulk. These results reveal that the measured ion mobility can be skewed without taking surface layers into effect. Finally, we demonstrate sensing of UV exposure over time through switching a hydrophobic barrier layer to hydrophilic, an effect that attracts ions into the fast channel and increases ion transport. Understanding how polymer nanostructure and hydrophobicity can control ion mobility and potentially transduction to electron transport will enable these devices to be used in wide-ranging sensing applications.

NSF, Electronic and Photonic: Grant#1905790

Intracortical microelectrode arrays (MEAs) used for diagnostic and treatment purposes, such as prosthetic devices, are currently limited in their chronic reliability. Several biotic and abiotic factors have been identified that lead to device failure in vivo. Abiotic causes of failure include delamination, metal corrosion, and insulation damage. At the biotic level, failure occurs as a result of initial tissue damage caused by insertion and the immune response elicited by the chronic persistence of a foreign object, which leads to glial scarring and neuronal death. This foreign body response of the tissue leads to disruptions in the functionality of the implanted devices, interfering with their ability to stimulate or record. We are developing shape-changing, liquid crystal polymer (LCP) based ultramicroelectrode arrays where probes of minimal cross-sectional area deploy to predetermined locations, away from the site of implantation and the associated foreign body response. We hypothesize that the deployment of these flexible probes with subcellular dimensions will mitigate the foreign body response, allowing for a more successful long-term implantation. We have shown that liquid crystal polymers are highly resistant to degradation when exposed to accelerated aging conditions. Prior work demonstrated liquid crystal polymer-based electrodes deploying distances of hundreds of micrometers away from the site of implantation in agar brain phantom and rodent brain tissue. However, one limitation of this work was that due to the low elastic modulus of the liquid crystal polymer, the devices were of mm-scale (0.07 mm²). Here, we aim to describe a novel approach to synthesize a semicrystalline liquid crystal polymer with increased elastic modulus, that may allow for the deployment of electrodes of much smaller size in a volume of cortical tissue. We employ a thiol-ene approach to synthesize liquid crystal polymer networks that crystallize after polymerization. Directed self-assembly can be used to pattern the molecular orientation of the liquid crystal monomer mixture prior to crosslinking. This alignment of molecular order enables controlled deployment of the device after insertion. Liquid crystal polymer substrates are synthesized where the crosslinker content is varied from 0% to 40% to optimize the mechanical properties. At 40% crosslinker content, Young’s modulus of the liquid crystal polymer is 400 MPa, with an actuation strain of up to 130%. Electrode arrays can be fabricated on these crystalline liquid crystal polymer substrates using photolithography. We envision, that this approach to develop deployable neural interfaces will overcome some critical challenges that currently hinder the chronic functionality and longevity of intracortical devices.

Photo-stimulation of neurons allows optogenetics to evoke and probe cellular activity with high spatial and temporal resolution. Light-responsive proteins are genetically expressed across the plasma membrane to control fluxes of ions in response to light with specific wavelength and intensity. Recently, light-sensitive proteins that combine two separate photosensitive cores into a single domain have been developed by covalent linking of a cation-conducting and an anion-conducting channel, to provoke neuronal excitation and inhibition with a single optogenetic tool¹. Traditionally, light sources such as lasers or LEDs are used for addressing biological targets. Although these devices are adequate for in vitro studies, their bulkiness, low biocompatibility, and poor mechanical matching with biological systems make them less appealing for in vivo applications. Organic LEDs (OLEDs) may overcome these limitations, since they offer mechanical flexibility, excellent optical tunability, and can be patterned on the micron scale. Thus, OLEDs have the potential to increase the precision of optogenetic targeting while providing also a softer interface between light source and tissue². Here, we present two stacked OLED architectures that can emit light with two different emission colors from the same pixel³, addressing the single domains of bidirectional ion channels expressed in Drosophila melanogaster larvae and ND7/23 cells. Tuning of the OLED layers' thicknesses allowed us to well match the OLED emission spectra to the activation spectra of the tandem photo-sensitive proteins GtACR2-Chrimson and GtACR2-ChRmine. Our work shows that OLEDs can provide narrowband light emission with minimal crosstalk between sub-pixels, enabling us to switch between optogenetic activation and inhibition of Drosophila larvae and ND7/23 cells.

1. Vierock, J. et al. BiPOLES: a tool for bidirectional dual-color optogenetic control of neurons. bioRxiv 2020.07.15.204347 (2020) doi:10.1101/2020.07.15.204347.
2. Kim, D. et al. Ultraflexible organic light-emitting diodes for optogenetic nerve stimulation. Proceedings of the National Academy of Sciences of the United States of America 117, 21138–21146 (2020).
3. Fröbel, M. et al. Get it white: Color-tunable AC/DC OLEDs. Light: Science and Applications 4, 247 (2015).

Biocompatible and leadless stimulation is the ongoing goal of bioelectronics research with a broad potential for clinical translation. New soft, thin, and efficient materials must be developed to achieve biological modulation suitable for medical treatments. Photosensitive semiconductor nanowires and patterned membranes were found to be suitable materials for wireless optical modulation. However, the preparation of p-i-n junctions is time-consuming, requires dedicated instrumentation, and may need additional metal modifications to achieve sufficient photoelectrochemical activity in saline. To this end, we sought a new approach for the generation of highly photoelectrochemically active materials fabricated directly from a thin crystalline silicon substrate. In this presentation, I will discuss our recent advances in the synthesis of nanoporous/non-porous silicon membranes and their application for remote non-genetic biological modulation with light. Specifically, we have developed a simple, wet processing technique to generate nanoporous silicon-based photoelectrochemical devices. We have shown how nanostructuring of the material surfaces can improve the modulation efficiency and biocompatibility at the device and tissue interfaces. We have successfully applied silicon devices to stimulate hearts and nerves in a rat model using light pulses. We have achieved highly efficient modulation in which the radiant exposure necessary for the modulation is on the same scale as in the approaches based on optogenetics. We hope that our materials designs and synthetic methods enable new tools for bioelectronic research and future clinical therapies.

Significant advances have been made in the last two decades in interfacing electronic devices with the nervous system. Organic electronic materials in particular have emerged as ideal materials for interfacing with the neural tissues due to their flexibility, biocompatibility and moreover their electronic and ionic conductivity. To that end, significant research efforts are being pursued to develop minimally invasive, implantable organic electronic devices integrating recording, stimulating, and drug delivery features. Here we report recent developments towards such dynamic devices for neural interfacing that take full advantage of the favorable properties offered by conducting polymers and polymer substrates. It is shown that thin, flexible devices can incorporate microfluidic channels to enable actuated shape control. Furthermore, we show such features open the door to novel implantation strategies that can reduce the surgical footprint required for implantation of large bioelectronic devices. We anticipate this work will accelerate the development of a new generation of minimally invasive implants for neural interfacing.

The vast amount of biological mysteries and biomedical challenges faced by human provide a prominent drive for seamlessly merging electronics with biological living systems (e.g. human bodies) to achieve long-term stable functions. Towards this trend, one of the key requirements for electronics is to possess biomimetic form-factors in various aspects for achieving the long-term biocompatibility. To enable such paradigm-shifting requirements, polymer-based electronics are uniquely promising for combining advanced electronic functionalities with biomimetic properties. In this talk, I will introduce our new molecular-design, chemical-synthesis and physical-processing concepts for polymer semiconductors, which enabled the incorporation of multiple biomimetic properties with advanced electronic functionalities. Fundamental understandings that have been obtained about the structure property relationship on these unprecedented material designs are serving as the foundation for opening up this new research direction for polymer semiconductors. Furthermore, enabled by these new materials, we have also created new device designs and fabrication processes for building unprecedented functional devices (i.e., sensors and circuits) that are intrinsically stretchable with unperturbed performance when operating conformably on human bodies. Collectively, our research is opening up a new generation of electronics that fundamentally change the way that the humans interact with electronics.

The past decade has delivered unprecedented speed of development of neurotechnologies. Modern complimentary metal-oxide-semiconductor (CMOS) fabrication has yielded high-resolution electrophysiology and robust back-end interfaces for probes implanted in the brains of rodents and even non-human primates. Combining electrophysiology with modern opto- and chemogenetic approaches, as well as with the emergence of photopharmacological tools remains a challenge. Furthermore, multifunctional neural interfaces with organs other than the brain present additional challenges associated with dimensions, reduced redundancy, vascularization, and susceptibility to the immune response. In this talk, I will discuss our recent efforts in multi-material fiber design that address some of the challenges of the neurobiological complexity and create stable multifunctional interfaces to the central and peripheral nervous systems.

The informational density and relative accessibility of the peripheral nervous system make it an attractive site for therapeutic intervention. Although electrode-based electrophysiological interfaces for peripheral nerves have been under development for over half a century, achieving spatial specificity and minimally invasive devices remains challenging. The value in tackling this challenge lies in the possibility to treat disorders such as, for example, chronic pain, overactive bladder, depression, and epilepsy. We aim to improve peripheral nerve interfaces through the use of wired flexible electrode arrays to intelligently design wireless organic electrolytic photocapacitor (OEPC) stimulation devices. Through the use of OEPCs we achieve capacitive stimulation pulses delivered by non-toxic materials as tissue-penetrating deep-red light is transduced into electrical signals. We therefore avoid faradaic reactions and the products thereof, and accomplish safe, non-invasive neuromodulation.

Understanding the functioning of the brain and the mechanisms involved in neuronal networks is one of the biggest scientific challenges yet to overcome. Within this field, remarkable advances were made, thanks to the development of a new generation of in-vitro micro-electrode arrays, in which the sensing elements are miniaturized and 3D-structured. Such devices, called Nanostructured Electrode Arrays (NEAs), offer real benefits, as they possess a high spatial resolution and an important surface-to-volume ratio leading to a higher affinity with cells. This technology enables to stimulate and record the neuronal activity at the single-cell level. However, reducing the size of the electrodes diminishes their effective area, which increases their impedance, leading to a loss in signal resolution. It also negatively affects the charge injection properties, a key parameter for stimulation processes.

Here, we demonstrate for the first time the ability to selectively deposit a nanolayer of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), a conductive polymer, on metal 3D nanoprobes through electrochemical deposition. These polymer-coated nanoelectrodes have been fully characterized, both electrochemically and morphologically, to establish a direct relationship between the synthesis conditions, the final morphology, and the conductive features

First, nanowires-based NEAs were fabricated at wafer scale using a cost-effective top-down approach, combining conventional lithography tools, plasma etching, sacrificial oxidation, metal deposition, and chemical etching steps. All sensing electrodes are formed by 7 connected vertical platinum-silicide nanowires. Each nanowire is 4µm high and has a diameter of 400nm. All the conductive access lines are insulated from the liquid media and only the nanowires are in contact with the solution. The nanoprobes were coated with PEDOT:PSS via electrochemical deposition. Different polymerization routes have been investigated, from galvanostatic to potentiodynamic, showing a large range of layer morphology. After optimizing the coating conditions, conformal and homogenous PEDOT:PSS layers were successfully deposited, down to 75nm thin. Indeed, Scanning Electron Microscopy demonstrated that the nanowires were wrapped tightly by the polymer coating, keeping the high aspect ratio of the nanoprobes.

The recording properties of the probes were evaluated, by performing Electrochemical Impedance Spectroscopy measurements in saline media. The impedance values (at 1kHz) of the coated nanoprobes decreased by 2 orders of magnitude compared to bare nano-electrodes. Cyclic voltammetry and voltage transients experiments have also been conducted, to estimate the charge injection capabilities of the polymer-coated NEAs. Results indicated an enhancement in delivering a higher charge at the 3D electrode-electrolyte interface. In fact, the charge storage capacity increased up to 10 times and the charge injection limit doubled compared to bare electrodes.

Thanks to their improved performances, PEDOT-coated 3D-nanostructured devices open new perspectives to stimulate and record the in-vitro neuronal activity with higher spatial and signal resolution.

Neural tissues are non-linearly elastic materials that display viscoelasticity and plasticity. They are extremely soft with elastic modulus in the 100 Pa to several kPa. Hydrogels are a unique class of materials that may be tuned to mimic the mechanical properties of neural tissues. Their high-water content and porous micro-structure greatly resemble the natural structure of the extracellular matrix. On the other end, the very same features impose many challenges e.g. swelling, electrical insulation or mechanical robustness for their integration into microfabricated devices. This talk will report on our efforts to integrate hydrogels as coating or structural materials to design, manufacture and test biomimetic neural interfaces.

In air, hydrogels dry progressively, leading to massive shrinkage of the organic network. Kept in water, they can swell up to more than ten times their initial volume. When used as a coating, re-swelling of the hydrogel film results in important shear stress at the interface with the encapsulated device. When used as the bulk carrier, the soft material in vivo may display stiffer properties than those in vitro. In both cases, this significant volume change is not compatible with the cohesion of a multilayer system and has irreversible impact on the structural and functional properties of the soft neural interface.

We are engineering and manipulating several hydrogels ranging from low swelling poly(2-hydroxyethyl methacrylate) [PHEMA] to anti-fouling zwitterionic hydrogels via ultra-soft polyacrylamide (PAAm) gels. Our observations are that hydrogels improve the biomimetic design of neural interfaces but their integration triggers additional challenges related to process compatibility and stability and in vivo use that call for further optimization.

Selective targeting and modulation of functionally distinct cell types and neuron subtypes is central to the bottom-up understanding of the complex neural circuitry. While the optogenetically engineered cells can express light-sensitive channelrhodopsins in a cell type-specific manner and enable targeted optical stimulation, such cell type specificity has not been demonstrated with implantable electronic probes. We address this challenge by modifying the surface of mesh electronics, an implantable neural probe that does not elicit chronic inflammatory immune response and allows for recording of neurons in deep brain structures for over one year. The device surface was functionalized with antibodies or aptamers capable of recognizing and targeting specific cell surface receptors for neurons, astrocytes, microglia, or dopaminergic neuron subtypes and was implanted in the hippocampus of mice. Time-dependent histology studies revealed the intimate association of the targeted cell types with the electronics, without affecting the distribution of other cell types. In vivo chronic electrophysiology showed that the identity of cells associated with the electronics had a significant influence on the properties of recordings. Recordings from electronics with modifications targeting dopaminergic neuron subtypes showed selective modulation under the influence of known dopamine receptor agonists and antagonists. These surface modifications may be extended to other neurotechnologies and could benefit the study of neural cells in model systems where genetic modifications are difficult or not possible.

Microelectrode arrays are widely adopted tools to investigate neuron-level and microscale circuit dynamics underlying brain function and disease. While standard microelectrodes enable detecting electrophysiological signaling, developing devices with optical stimulation, and recording capabilities, allows mapping neural dynamics at higher spatial and temporal resolution, and across multiple scales. Thus, there is a need of novel materials and processes to realize microelectrode arrays with tunable optical and impedance properties, while minimizing interference from photoelectric artifacts.
Here we demonstrate novel processing and fabrication approaches to develop low-impedance microelectrode arrays with tunable optical properties based on Ti₃C₂ MXene. Specifically, we explored several processing parameters and conditions, such as the concentration of the precursor solution as well as film thickness, to optimize sheet resistance, transparency, and electrochemical interface impedance of the Ti₃C₂ MXene films. The resulting films are ~20nm thick, have a 550 nm transmittance of 60% and sheet resistance of 60 Ω/�■. The corresponding figure of merit is 14, which is comparable to or higher than other optoelectronic transparent films used for neural interfacing. Then we fabricated parylene C-based 4 x 4 micro electrocorticography (µECoG) arrays using microfabrication techniques and solution processing of MXene. The arrays have 50 µm x 50 µm recording sites spaced 500 µm apart and an overall footprint of 2.75 mm x 2.75 mm. Electrochemical impedance spectroscopy measurements at 1kHz show a predominantly capacitive response and an average impedance modulus ranging from 143 kΩ ± 157 to 555 kΩ ± 103 (5 devices, 68 channels) which is 2 to 5 times lower than previously developed transparent graphene interfaces. To evaluate the feasibility of acquiring multimodal signals in vivo in a relevant disease model, signal recording ability and quality, we tested the devices in vivo in an epilepsy mouse model. We were able to successfully record epileptiform activity and simultaneous monitor calcium fluorescence fluctuations. Continued work with electrodes will involve dissecting recorded data and probing neural dynamics through concurrent optogenetic stimulation of neuronal activity to understand disordered mechanisms.

Complete recovery from volumetric muscle loss injuries requires adequate structural regeneration of the lost tissues with proper innervation. Although various tissue engineering strategies have been developed to facilitate regeneration, restoring adequate innervation remains an open challenge. Electrical stimulation has emerged as a promising intervention to enhance tissue innervation after trauma and restore motor control. This has been achieved via input/output (I/O) bioelectronics that interface engineered materials with biological entities. Recently, graphene and its composites have gained interest as building-blocks for bioelectronics due to their advantageous electrochemical properties and biocompatibility. However, graphene-based bioelectronics exhibit a two-dimensional (2D) topology resulting in limited electrochemical performance. Ideal bioelectronics need to leverage on three-dimensional (3D) topologies to maximize the exposed surface-area and enhance interaction with interfaced biological entities.
Here we report a breakthrough hybrid-nanomaterial based on nanowire-templated 3D fuzzy graphene (NT-3DFG) and poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS), for functional I/O bioelectronics. The hybrid-nanomaterial leverages on high surface-area of free-standing graphene flakes of NT-3DFG and the high charge storage capacity of PEDOT:PSS. The resultant hybrid-nanomaterial exhibits lower electrode impedance, cathodic charge storage capacity (CSC_C) up to 24.87 ± 5.40 mC/cm², and charge injection capacity (CIC) up to 13.21 ± 3.6 mC/cm² with footprint as small as 20 µm. We interface the developed hybrid-nanomaterial with in-vivo systems to effect cellular- and tissue-scale electrophysiology via electrical stimulation; and record the resultant electrical activity as electromyograms (EMG). Through our platform, we demonstrate the importance of extending the topology of nanomaterials to 3D to develop the next generation of functional I/O bioelectronics.

Living tissues are non-linearly elastic materials that exhibit viscoelasticity and plasticity. Man-made, implantable bioelectronic arrays mainly rely on rigid or elastic encapsulation materials and stiff films of ductile metals that can be manipulated with microscopic precision to offer reliable electrical properties. Here, we engineer a surface microelectrode array that replaces both the traditional encapsulation and conductive components with viscoelastic materials. Our entirely viscoelastic array overcomes previous limitations in matching the stiffness and relaxation behavior of soft biological tissues by using hydrogels as the outer layers. We introduce a novel hydrogel-based conductor made from an ionically conductive alginate matrix enhanced with carbon nanomaterials (e.g. graphene, carbon nanotubes). These high aspect ratio additives provide electrical percolation even at low loading fractions, and we fabricate ultra-soft viscoelastic conductive electrodes and electrical tracks that intimately conform to the convoluted surface of the heart or the brain cortex. Our combination of conducting and insulating viscoelastic materials, with top-down manufacturing, allows for the versatile fabrication of electrode arrays compatible with in vivo recording and stimulation.

Millimeter-sized bioelectronic implants can provide advanced therapies with minimal invasiveness providing a potential alternative to traditional pharmaceuticals. To create devices with millimeter-sized form factors we must overcome the challenges of sending data and power to miniature battery-free devices. This is particularly challenging for devices implanted deep within tissue because the body absorbs electromagnetic radiation at frequencies typically used for wireless data and power transmission. Here, we describe how magnetic materials like magnetoelectrics and superparamagnetic nanoparticles can enable precise control of neural circuits and millimeter-sized bioelectronic devices. Specifically, we show that these materials can improve the speed, reliability, and power densities possible with miniature bioelectronics

Understanding cellular electrical communications in both health and disease necessitates precise subcellular electrophysiological modulation. Nanomaterial-assisted photothermal stimulation was demonstrated to modulate cellular activity with high spatiotemporal resolution. Ideal candidates for such an application are expected to have high absorbance at the near-infrared (NIR) window, high photothermal conversion efficiency, and straightforward scale-up of production to allow future translation. Here, we demonstrate two-dimensional (2D) Ti₃C₂ (MXene) as an outstanding candidate for remote, nongenetic, optical modulation of neuronal electrical activity with high spatiotemporal resolution. Ti₃C₂ photothermal response measured for the first time at a single-flake level resulted in local temperature rises of 2.31 ± 0.03 K and 3.30 ± 0.02 K for 625 nm and 808 nm laser pulses (1 ms, 10 mW), respectively. Dorsal root ganglia (DRG) neurons incubated with MXene film (25 μg/cm²) or MXene flakes dispersion (100 μg/mL) for 24 h did not show a significant effect on cellular viability, indicating that MXene is non-cytotoxic. DRG neurons were photothermally stimulated using MXene films and flakes with as low as tens of micro-joule per pulse incident energy (635 nm, 2 μJ for film, 18 μJ for flake) with sub-cellular resolution. MXene’s straightforward and large-scale synthesis will allow translation of the reported photothermal stimulation approach in multiple scales, thus presenting a powerful tool for modulating electrophysiology from single cell to three-dimensional (3D) engineered tissues.

Bioelectronics devices have the potential for realizing personalized medicine and brain-machine interfaces. While significant progress has been made in this area, there is still room for improving the material designs to achieve better functionalities at the interfaces with cells and tissues. In particular, applying biomimetic design principles enables the development of new devices with improved properties in terms of their signal transduction efficiency and biocompatibility. In this talk, I will present a few latest processes in our lab, where new material building blocks have been identified for building bioelectronics systems. I will discuss a micelle-enabled self-assembly process to prepare a binder-free (i.e., monolithic), carbon-based, and flexible micro-supercapacitor-like system for various types of bioelectronic interfaces. The devices can operate under either micro-supercapacitor-like or a traditional monopolar electrode configuration under physiological conditions, yielding modulation of cardiomyocytes in vitro, excitation of isolated heart and retinal tissues ex vivo, stimulation of sciatic nerves in vivo, as well as bioelectronic cardiac recording. I will also present a newly developed nanoporous/non-porous heterojunction for improved biointerfaces. Without any interconnects or metal modifications, the heterojunction enables efficient non-genetic pulse stimulation of isolated rat hearts ex vivo and sciatic nerves in vivo with radiant exposure similar to that used in optogenetics. Finally, I will showcase a class of granules-enabled hydrogel composites, with multiple naturally occurring biopolymers and synthetic hydrogels as the key components. The composites have many tissue-like properties, such as strain-stiffening behaviors. The granules-enabled tissue-like materials have enabled the pneumatically actuated bioelectronic devices for applications such as recording the heart electrocardiogram signal ex vivo. At the end of my talk, I will present future material development in our lab.

In vitro models of biological systems are essential for our understanding of biological systems. In many cases where animal models have failed to translate to useful data for human diseases, physiologically relevant in vitro models can bridge the gap. Many difficulties exist in interfacing complex, 3D cell biology models with technology adapted for monitoring function. Polymeric electroactive materials and devices can bridge the gap between hard inflexible materials used for physical transducers and soft, compliant biological tissues. An additional advantage of these electronic materials is their flexibility for processing and fabrication in a wide range of formats. In this presentation, I will discuss our recent progress in pushing conducting polymer devices, to 3D, to simultaneously host and monitor complex multi-cellular models of tissues and organs. Building on our previous work that showcased a bioelectronic model of the human intestine, we are now incorporating elements of the microbiome and the immune system as well as the enteric nervous system. Coupling this model with our model of the neuro-vascular unit (including blood brain barrier) currently in progress, will bring us to our goal of a physiologically representative in vitro model of the gut-brain-microbiome axis.

Advances in three-dimensional (3D) cell culture modeling have extensively contributed to generate new sophisticated cell culture configurations broadening our understanding of cellular physiology and pathology for a wide range of biomedical applications (e.g., drug discovery, tissue engineering and regenerative medicine). Compared to two-dimensional (2D) cell culture, which is overall too simplistic and lacking most of the cell-cell and cell-environment interaction occurring in the in vivo milieu, such 3D formats are capable of resembling the tissue microenvironment in a more biomimetic manner ¹. Scaffold-based systems integrating natural and/or synthetic materials are extensively exploited in tissue engineering to develop tissue-specific microenvironments for better supporting cell survival and outgrowth, by providing the chemical and physical cues of the natural extracellular matrix (ECM) ². Using a freeze-drying technique, we engineered porous 3D composite scaffolds consisting of poly (3,4-ethylene-dioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS), containing ECM-derived proteins (i.e., Collagen, Hyaluronic Acid and Laminin) for hosting neural 3D cell culture. The highly porous microstructure of these scaffolds was characterised optically by scanning electron microscopy (SEM) along with confocal microscopy, and their conducting properties via electrochemical impedance spectroscopy (EIS). The resulting scaffolds exhibited remarkable mechanical stability and water uptake capacity, directly proportional to the increasing collagen/HA content. We further tested the cytocompatibility profile of these scaffolds and ultimately, their suitability for supporting neural differentiation of neuroblastoma-derived SH-SY5Y cells. We observed that the presence of ECM proteins within the scaffold backbone improves cell survival and proliferation rate compared to the pristine substrate, thus promoting cell propensity to differentiate into mature neurons and generate 3D neural networks. In conclusion, these conducting platforms used here for neuronal cell culture could be potentially amenable for regulating neuronal cell behaviour in a 3D configuration and customised for a variety of tissue engineering applications. Ultimately, to gain more insight into the effects of conducting polymers on neural firing, recording of electrophysiological activity of neurons cultured in 3D will be attempted via simultaneous EIS and MEA (microelectrode array).
References:
1. Moysidou CM, Barberio C, Owens RM. Advances in Engineering Human Tissue Models. Front Bioeng Biotechnol. 2021;8:620962. doi:10.3389/fbioe.2020.620962
2. Ullah S, Chen X. Fabrication, applications and challenges of natural biomaterials in tissue engineering. Appl Mater Today. 2020;20. doi:10.1016/j.apmt.2020.100656

Spinal cord injuries constitute an important clinical target. Emerging therapies to treat central nervous system (CNS) injuries seek to implant neural progenitor cells (NPCs) to promote repair of the neural network subsequent to neural injury. A debilitating aspect of this approach is the inability to non-invasively monitor NPCs during migration and differentiation at injured spots, which critically affects the therapeutic efficacy of neural repair.

Here we show that electrical impedance spectroscopy (EIS) can be used as a non-invasive and real time tool to probe cell adhesion and differentiation from midbrain floor plate progenitors into midbrain neurons, on Au electrodes coated with human laminin. The electrical data and equivalent circuit modelling are consistent with standard microscopy analysis and reveals that within the first 6 hours progenitor cells sediment, and attach to the electrode within 40 hours. Between 40 and 120 hours midbrain progenitor cells differentiate into midbrain neurons, followed by an electrochemically stable maturation phase. The ability to sense and characterize non-invasively and in real time cell differentiation opens up unprecedented avenues for implantable therapies and differentiation strategies.

Hybrid bioelectronic systems offer a unique route toward achieving two-way electronic communication with living cells and tissues. In this talk, we will discuss recent advances in both devices and biomaterials that achieved stable and seamless interfaces with surrounding cells and tissues. We will first present an overview of our recent heart-on-a-chip platform which integrated both extra- and intracellular devices for monitoring cardiac electrophysiology during episodes of acute hypoxia. This system allowed us to monitor not only cell-cell communication (e.g., wavefront propagation) but also action potentials at several spatially-distinct regions simultaneously. Our platform provided a unique route toward undertraining the role of hypoxia on ion channel dynamics. For example, we found that APs shortnened during hypoxia, consistent with proposed mechanisms by which oxygen deficits activate ATP-dependent K⁺ channels that promote membrane repolarization. We will next discuss routes toward extending our bioelectronic platform to 3D, enabling new classes of hybrid, devices-embedded tissues. We developed a Photo-crosslinkable Silk Fibroin (PSF) derivative that was compatible with conventional photolithography processes and enabled flexible scaffolds with well-defined geometries and cm-scale uniformity. Our freestanding PSF-based scaffolds supported bioelectronic devices, provided excellent electrical passivation, and adhered both cardiac and neuron model cells, opening new avenues toward engineered brain hybrids. Finally, we will present a new class of electromagnetic stimulation elements which achieved highly-localized cellular activation. Taken together, these research directions open new avenues for engineered, bioelectronics-innervated cardiac and brain systems.

Bioresorbable electronic materials form the basis for broad classes of temporary implants with unique capabilities that address unmet clinical needs. Such types of devices can provide therapeutic functionality during the time course of a natural biological process such as healing, and then harmlessly disappear into the body, without a trace. Here, bioresorption eliminates unnecessary device load on the body in a way that bypasses the need for secondary surgical extraction. This talk describes the latest advances in the active and passive materials components of these systems, with examples in devices for (1) neural stimulation, (2) cardiac pacing and (3) programmable drug release.

Electroencephalography (EEG) is a widely used technique for clinical diagnostics and monitoring, for neuroscience research, as well as for non-invasive brain-computer interface (BCI) applications. Despite over 100 years of EEG research, the technology has benefitted from relatively few fundamental innovations in materials that enhance its resolution and form factor while maintaining high-quality signals. Today’s EEG technologies have limited spatial resolution because the sensors are relatively large (~1 cm diameter) and they typically require the use of conductive gels or pastes to achieve sufficiently low electrode-skin interface impedance. Such gelled or “wet” electrodes are prone to shorting via gel-bridging when they are placed close together for dense spatial sampling, which has made it challenging to push the spatial resolution limits of EEG technology. Gel-free or “dry” EEG electrode technologies offer an alternative solution to the limitations of wet EEG sensors. Existing dry EEG technologies, however, rely on large-area electrodes with poor spatial resolution in order to reduce contact impedance, and rigid, uncomfortable pillar structures to contact the scalp. Here, we present a novel gel-free EEG electrode technology based on the 2D nanomaterial Ti₃C₂ MXene which is capable of recording high-fidelity EEG signals from dry electrodes with high spatial resolution. The electrodes comprise a MXene composite aerogel which is compliant to enhance subject comfort, and can be molded into 3D “mini-pillar” geometries for contacting the scalp through hair. The high conductivity of Ti₃C₂ MXene, along with the porous structure of the composite foam, gives the electrodes low skin contact impedance, allowing high-fidelity EEG recording from mm-scale electrodes with signal quality comparable to standard gelled electrodes. To demonstrate the ability to map scalp EEG at high density, we fabricated 16-channel high-density EEG grids with 3 mm-diameter MXene contacts and 3 mm spacing, which offers higher spatial sampling than the densest EEG systems available today. We used these grids to record EEG signals on human subjects in frontal regions while they completed a battery of attention and working memory tasks shown to have frontal EEG signatures related to task performance. In these experiments, the MXene electrode grids were centered over F3 and F4 EEG coordinates (10-5 system) such that we obtained a total of 32 channels of high-density EEG signal across two frontal regions. Using this paradigm, we explore whether current source density transforms of the ultra high-density enabled by MXene reveal more detailed and localized correlates of frontal attentional function than previously observed. Furthermore, we demonstrate that the MXene electrodes are compatible with magnetic resonance imaging (MRI) and transcranial magnetic stimulation (TMS) due to the low magnetic susceptibility of Ti₃C₂ MXene. The magnetic compatibility of Ti₃C₂ MXene opens up the possibility of concurrent structural or functional MRI, TMS, and EEG recording.

Essential properties of the bioelectronic materials and interfaces, such and their abilities to exert effective stimulation or enable recording of biological signals, their interface electrochemistry and physiological stability, are widely studied and optimized from the individual perspective of the studied property. Lately, attention was focused on volume electrodes¹ and 3D structuring of bioelectronic devices² on all scales. We will demonstrate how optimizing the two-dimensional and three-dimensional structuring of the bioelectronic interfaces of a model device can amplify, suspend or channel the desired effects in comparison to trivial structures such as highly symmetric planar or rod-like electrodes. As a model device, we have used the organic electrolytic photocapacitor (OEPC), an organic semiconductor-based optoelectronic device capable of capacitive coupling with the excitable tissues. OEPCs have been shown to effectively modulate single cell membrane potentials³, to elicit action potentials in explanted retinal tissue⁴, and to chronically stimulate a peripheral nerve in a rodent model⁵.
We will discuss the basic principles guiding the active and return electrode spatial design for enhanced stimulation intensity and improved and controlled stimulation localization, demonstrated by the results of FEM numerical modelling, measurements of 3D transductive electric potential field maps in extracellular phantom, and in-vitro stimulation experiments. Multifold enhancement of the performance of the 3D micro-pyramid structured OEPC in comparison to the planar OEPC was observed, with the enhancement strongly depending on the micro-pyramid size and their density, while rationally designed 2D electrode shapes enabled localized and effective tissue stimulation, which would not be possible with the previously used simple designs. We will show how our optimization toolset can be extrapolated and applied to a more general class of bioelectronic interfaces.

[1] Pitsalidis, C. et al, Transistor in a tube: A route to three-dimensional bioelectronics, Science Advances, 4(10), p. eaat4253. doi: 10.1126/sciadv.aat4253 (2018)
[2] Pennacchio, F. A. et al. ‘Bioelectronics goes 3D: new trends in cell–chip interface engineering’, Journal of Materials Chemistry B, 6(44), pp. 7096–7101 (2018)
[3] M. Jakesova et al, Optoelectronic control of single cells using organic photocapacitors, Science advances, 5 (2019) eaav5265
[4] D. Rand et al, Direct Electrical Neurostimulation with Organic Pigment Photocapacitors, Adv. Mater. 30 (2018), 1707292
[5] M. Silvera-Ejneby et al, A chronic photocapacitor implant for noninvasive neurostimulation with deep red light, bioRxiv (DOI: 10.1101/2020.07.01.182113), accepted for publication (Nature Biomedical Engineering, June 2021)

To use the organic electrochemical transistor (OECT) as a biosensor is of great importance, as it is a state-of-the-art technique in the field of drug delivery.^[1] Allowing ion-to-electron conversion and having a high amplification of gating due to volumetric capacitance, enables the OECT to operate with aqueous electrolytes at low voltages.^[2] When utilizing the OECT as an inverter in a current-driven configuration, a constant current is applied at the channel by an external power supply. It was found that the OECT offers an enhanced sensitivity compared to standard transfer characteristics of an OECT.^[3] Even small variations in the ionic current can be detected with the OECT, which is required to study changes in the cell layer morphology, such as tight junction modulation.^[4] Tight junction barriers of epithelial cell layers impede the transcellular pathway of nutrients and drugs from organs into the blood.^[5,6] Hence, monitoring tight junction modulations is crucial for drug delivery.^[7] As a well-established model for oral drug delivery, the epithelial colon carcinoma (Caco-2) cell line,^[8] found in the small intestine, was used to evaluate reversible modulation of tight junctions over time. Recently, we showed the suitability of OECTs to in-situ monitor temporal barrier modulation and recovery, which can offer valuable information for drug delivery applications.^[9] Here, the origin of the enhanced sensitivity of OECTs with integrated barrier tissue in current-driven configuration is demonstrated. As next step, we have addressed both experimentally and theoretically the dynamics of OECTs operation. Understanding of the dynamics is a prerequisite to tune the sensitivity of the OECT in accordance with the resistance of the barrier under investigation. The quantitative agreement between experiment and modelling of the transient OECT characteristics allows us to directly translate the current-driven OECT characteristics into a resistance of the barrier tissue under investigation. ^[10]

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[3] M. Ghittorelli, L. Lingstedt, P. Romele, N. I. Craciun, Z.M. Kovács-Vajna, P.W.M. Blom, F. Torricelli, Nat. Commun. 2018, 1441;
[4] L. V. Lingstedt, M. Ghittorelli, M. Brückner, J. Reinholz, N. I. Craciun, F. Torricelli, V. Mailänder, P. Gkoupidenis, P. W. M. Blom, Adv. Healthcare Mater. 2019, 8, e1900128.
[5] M. Ramuz, A. Hama, M. Huerta, J. Rivnay, P. Leleux, R. M. Owens, Adv. Mater. 2014, 7083.
[6] L. H. Jimison, S. A. Tria, D. Khodagholy, Gurfinkel M., E. Lanzarini, A. Hama, G. G. Malliaras, R. M. Owens, Adv. Mater. 2012, 5919.
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[9] K. Lieberth, M. Brückner, F. Torricelli, V. Mailänder, P. Gkoupidenis, P.W.M. Blom, Adv. Mater. Tech. 2021 6, 2000940)
[10] K. Lieberth, D. Harig, P. Gkoupidenis, P.W.M. Blom, F. Torricelli (in progress)

Peripheral nerve interfaces are important for implementing neuromodulation strategies. For example, feedback loops can be employed to control the behavior of tissue by modulating the activity of the innervating input as a response to a biomarker. Cuff electrodes represent an important class of such nerve interfaces that are often used for applications in bioelectronic medicine. Large nerves, with diameters in the range of one mm or above, can be easily stimulated with appropriate cuff electrodes. However, the stimulation strategies often lack specificity as several fibers are typically addressed simultaneously. Stimulating small nerves, below 100 µm, can generate more specific responses but poses additional challenges for device development as well as handling during an operation. Here, we present a type of self-foldable cuff electrodes that can be readily applied in vivo for addressing small peripheral nerves. The devices are fabricated combining 3D printing and lithographic approaches employing strongly swelling materials. We demonstrate the usability of the nerve cuff electrodes after implantation on the extensor motor nerves by implementing a simple closed-loop strategy to control the angles of a locust’s legs in real time. Extensor motor nerves are stimulated using trains of stimulation pulses with a gradual response of the leg position determined by the applied stimulation frequencies. We monitor the leg’s angles using a flexible sensor and implement the feedback loop with a simple control algorithm on a microcontroller. The design of the cuff electrodes allows straightforward implantation and removal without impairment of the nerve functionality.

Bioelectronic devices are increasingly required to not only acquire biologic signals, but also to process them in real-time. For a subset of patients with epilepsy, responsive neurostimulation in the form of implanted devices are promising form of treatment. However, the only components capable of performing these functions at present are silicon-based, non-biocompatible, bulky, and need rigid encapsulation in physiologic environments. Here, we demonstrate an fully implantable, soft, biocompatible, neural acquisition and processing device based on complementary internal ion-gated organic electrochemical transistors (IGTs). A key function of these responsive neurostimulation devices is accurate detection of epileptic discharges. This detection can be challenging due to the variable amplitude of the neural potentials based on the location of the recording electrode with respect to local dipoles and the reference electrode. We combined a depletion and enhancement mode IGTs to create a non-linear rectification circuit that can be chronically implanted to recorded and detect epileptiform inter-ictal discharges (IEDs). This device was used to process signals acquired from the hippocampus of a freely moving epileptic rat. The IGT-based non-linear rectification circuit accurately detected epileptic discharges, with receiver operating characteristics that surpassed traditional filter thresholding methods. Therefore, IGTs and their ability to efficiently integrate enhancement and depletion mode devices within individual circuits can improve real-time processing of disease-relevant neurophysiological signals and have the potential to form fully implantable, conformable acquisition and processing units for bioelectronic devices. Overall, we have shown that e-IGTs can serve as reliable components for bioelectronic devices, with the potential to improve our ability to transduce and modulate physiologic signals. E-IGTs are also suitable for translation to use in humans, offering a safe, reliable, and high-performance building block for chronically implanted bioelectronics.

High-density neural interfaces are continuously progressing towards seamless integration of brain and electronics. As more effort has been dedicated to implantable devices, effective and non-invasive data communication between the implant and outside electronics becomes a critical unresolved issue, because biologic tissue absorbs most of the electromagnetic waves. Here we introduce the ionic communication (IC) that utilizes ions and water polarization for high-speed data communication. We describe the working principles of IC, and investigated the effect of material and geometrical properties such as area, material composition, ion type/concentration, and operating frequency and on the performance of the IC in the form of gain and spatial propagation. Based on these measurements, we developed a model to accurately estimate IC-based communication’s propagation depth in the body and established a multi-line implantable IC with several hundred MHz bandwidth. We chronically implanted conformable IC devices with no extruding elements and were able to acquire and transmit high-quality electrophysiological data at the level of signal neurons’ action potentials from freely moving rats. The IC and the resulting devices set the foundation for non-invasive, fully-implantable communication strategy for biomedical implantable systems, such as brain-computer interfaces, responsive neurostimulation devices, deep-brain-stimulators and cochlear implants that require a low consumption, high bandwidth wireless communication system.

Self-powered wearable systems relying on bioenergy harvesters commonly require excessive energy inputs from the human body and are highly inefficient when accounting for the overall energy expenses. A harvester independent from the external environment for sedentary states has yet to be developed. Herein, we present a touch-based lactate biofuel cell that leverages the high passive perspiration rate of fingertips for bioenergy harvesting. Powered by finger contact, such bioenergy harvesting process can continuously collect hundreds of mJ of energy during sleep without movements, representing the most efficient approach compared to any reported on-body harvesters. To maximize the energy harvesting, complementary piezoelectric generators were integrated under the biofuel cell to further scavenge mechanical energy from the finger presses. The harvesters can rapidly and efficiently power sensors and electrochromic displays to enable independent self-powered sensing. The passive perspiration-based harvester establishes a practical example of remarkably high energy return-on-investment for future self-sustainable electronic systems.

An implantable probe with an electrode array can precisely record brain signals from different groups of neurons simultaneously, yet maintaining high spatial resolution is still challenging. Each electrode of a dot matrix type needs an individual wire, and then, it is appropriate only for a few electrodes. A passive matrix design is better, since the total number of wires needed is C+R, where C is the number of columns and R is the number of rows in the passive array, respectively. However, the passive matrix design showed a cross talk issue among neighboring cells. In contrast, an active matrix design also needs C+R number of wires to fabricate C×R number of electrodes, but it can induce a good electrical isolation among cells. CMOS technology has been studied for high density electrodes. However, stiff silicon-based probes induce inflammation in the tissue. Therefore, flexible polymer-based probes can handle this problem by reducing mechanical mismatch between a probe and neural tissue and growth of the glial sheath. Here, we fabricated polyimide-based flexible neural probes with a 4×8 array of electrodes based on the active matrix design of a-IGZO thin-film transistors (TFTs) for neural signals recording. We measured electrical properties and conducted electrical signal recording tests. Our neural probe design has advantages in high spatial resolution, flexibility due to polyimide (PI) probe pattern, and high mobility of IGZO TFTs. We easily fabricated probes using photoresist PI (jsr-wpr 1201) by photolithography on a sacrificial layer. Then, back gate IGZO TFT was fabricated on the PI probe, followed by PI encapsulation layer photolithography. The sacrificial layer was wet etched, while the probe has 50μm spacing and 20μm diameter holes for large area undercut. Our 25μm thickness PI probe is flexible and can endure a-IGZO TFT annealing temperature. The cell size is 86μm×200μm and the electrode size is 40μm×80μm. To obtain a high signal-to-noise ratio (SNR), a high-performance transistor is studied. The width-length of the transistors is designed to 50μm/10μm, and the field-effect mobility is 20 cm² /V×s and on current is 7×10^-5A under a low driving voltage, 5V. The on-off ratio is 1.1×10⁷and the threshold voltage (V_th) is 2.7V. The passive matrix design consists of one transistor in a cell. A gate line turns on the TFT applying 5V which is higher than the V_th, and a drain line senses the signal. For amplifying signals, the active matrix design consisting of two transistors in a cell is also fabricated. By applying 5V, the switching TFT is turned on, and the sensed signal can be measured on the drain line. One transistor works as a switch and another works as an amplifier. The shank, a sensing area of the probe, was placed in the PBS solution, and we recorded electrical signals using a function generator, an oscilloscope, and a power supply. Signals were recorded and compared to the dot matrix design. Our active matrix design probes successfully amplified the amplitude value of electrical signals. Therefore, our active matrix design TFT electrode array probe can be used for accurate neural recordings with high SNR and would open a new generation of flexible neural probes with high spatial resolution.

The interface of excitable cells and stimulation or recording electrodes is essential for bioelectronic applications. Parameters such as the electrode impedance and capacitance, interface electrochemistry, surface structuring and long term in vivo stability have been thoroughly studied. However, in many applications, especially clinical ones, only trivial electrode geometries are used, resulting in increased charge density thresholds. Using optimized electrode geometries and stimulation protocols may overall be more effective, especially in the case of implanted bioelectronic devices with limited current generation capabilities.
For highly localized target specific electrostimulation, electrode design and stimulation protocol are crucial parameters to consider. We consider multiple planar and 3D electrode configurations for stimulating excitable cells and tissues, and different stimulation protocols using pulsed and modulated current. A comprehensive finite element method (FEM) model encompassing realistic capacitive photo-electrode (organic electrolytic photocapacitor – OEPC) and tissue model is made in COMSOL Multiphysics^® software. Electrodes are characterized by their contact electrical properties, contact capacitance and contact resistance, while the OEPC is characterized by its equivalent circuit model. Realistic cell membranes and action potential propagation are implemented using the Hodgkin–Huxley model which can be tailored to a specific cell type.
We show that using the optimized electrode configuration enables multifold current density enhancement at the targeted stimulation area which enables effective cell and tissue excitation while minimising the residual effect on the surrounding tissue. Our numerical findings are validated in vitro using cortical neuron cell cultures and mouse brain slices.

Increasing demand for personalized medicine has led to a surge of research into electronic biosensing approaches, particularly those involving the use of a field-effect transistor (FET) as the transduction element in ion-sensitive FET-like structures. While electrical biosensors adhere to many of the tenets of the so-called “ideal biosensor,” one limitation that could hinder their success in a solution-gated setup is gate leakage. As electrical devices become immersed in solution (such as physiological liquid), improper passivation of the components results in electrical current leaking between the BioFET and the solution, thus compromising the transduction signal and preventing sensitive biological detection. Focus in the field has been on singular demonstration of BioFET applications, yet there is no consensus on device design and passivation strategy, which leads to difficulty comparing results between reports that ostensibly investigate similar phenomena, particularly with regards to gate leakage.
In this work, we investigate various passivation strategies for printed, solution-gated carbon nanotube (CNT) BioFETs. Contact-only photoresist passivation is investigated alongside whole-device dielectric passivation, particularly in the context of gate leakage reduction, long-term device stability, and wafer-scale device yield. We find that while optimized photoresist-only and dielectric-only passivation both result in high-quality BioFETs, the combination of the two – coating the contacts with a photoresist then the entire device with a dielectric – results in highly consistent performance, with more than 90% of tested devices displaying nA-level gate leakage with on/off-current ratios greater than 10³ in solution. The photoresist+dielectric strategy also results in the best stability over 500 testing cycles, demonstrating robust performance on a timescale exceeding that required for most biomolecular binding reactions to occur. Finally, we show that the addition of a polyethylene glycol (PEG) polymer layer, which reduces non-specific protein adsorption and increases Debye length, has no significant impact on device performance both in initial device metrics and after long-term cycling when polymerized on these passivation structures. Ultimately, these results help pave the path toward the development of a truly high-yield, sensitive, stable, and robust electrical biosensing platform.

Heart failure affects over 6.4 million people in the United States alone, with over 550,000 new cases emerging annually. Ventricular assist devices (VADs) have become a popular means of long-term care; yet, due to their thrombogenic nature, patients are frequently prescribed anticoagulation medication (e.g., warfarin). To ensure dosages remain in the therapeutic window for this strong anticoagulation drug, periodic blood-based testing (every 1-4 weeks) is required to measure patients’ prothrombin time/international normalized ratio (PT/INR), which reflect the clotting tendency of blood and hence the extent of anticoagulation. This frequent, clinic-based monitoring of PT/INR is cumbersome and costly; thus, an at-home monitoring system to ensure adequate coagulation times would be transformative for those on warfarin therapy.
Although point-of-care (POC) coagulometers are commercially available and have been demonstrated to reduce the burden on both patients and the healthcare system, only a small percentage of VAD patients perform POC self-testing. Current POC coagulometers and reagent cartridges are high cost, which limits insurance coverage, and are inconsistent in device performance. Therefore, there is a need for an alternative device that offers an at-home and portable measurement of PT/INR that is low-cost, accurate, and user friendly. In this work, a fully printed POC PT/INR test using electrical transduction is demonstrated. In order to create a low-cost device, an inexpensive testing platform was designed, which consists of aerosol jet printed silver nanoparticle electrodes. The functionality of the device was demonstrated in whole blood derived from both animal and human subjects. Given the necessity of a robust sensor, identical clotting times were measured on both a ridged and a flexible substrate tested under bending strain. In addition, a handheld sensor with low-cost electronics was designed and shown to have a measurement accurate to within a standard deviation of the costly, stationary, computer-based testing system. Finally, to improve upon the accuracy of developed handheld devices, multiple sensing modalities were combined to incorporate on-chip calibration for the impedimetric coagulometer. Taken together, these results lay the groundwork for fully printed impedimetric sensors, which address the unmet need for a low-cost, robust, POC device, potentially improving outcomes for VAD patients by early detection of aberrations in PT/INR.

Cancer is one of the most frequent causes of death globally and kills more than 8 million people per year.¹ Early diagnosed cancers are relatively easier to treat and cure. Cancer biomarkers, such as circulating free tumor nucleic acids (ctNA), are promising for detecting cancers early.^2,3 There are various techniques to screen cancers and liquid biopsy is one of them.² This is a promising approach since it is used to diagnose tumor-specific biomarkers non-invasively.² Detecting ctNA in body fluids is challenging, because of the low ctNA concentration and the low frequency of mutations compared to wild-type sequences.² Nanotechnology bioelectronics methods can help to address this challenge. In particular, the Scanning Tunneling Microscopic (STM)-assisted break junctions method (STM-BJ)⁴ has recently allowed the first demonstration of detection and identification of RNA from E.Coli via single-molecule conductance.⁵ This is an ideal new method for liquid biopsy bioelectronics since it is non-invasive, highly sensitive, and specific.

This work focuses on characterizing ctNAs and investigating an effective method for their ultra-sensitive detection in complex samples using STM-BJ. The study’s main hypothesis is that the sequences of ctNAs can be used to detect cancers electrically, by finding their unique electronic fingerprints. We focus the study on KRAS, BRAF, and Nras as effective cancer biomarkers, in agreement with data from the Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium of the International Cancer Genome Consortium (ICGC) and The Cancer Genome Atlas (TCGA).^6,7 We already have obtained some preliminary data for RNA sequences for KRAS biomarker and we expect to understand the bioelectronics interface between genetic material(ctNA) and nanostructured electrodes. Our initial analysis and the results pave the way for the early detection of bioelectronic fingerprints from biomarkers, such as ctDNA and ctRNA, through liquid biopsy using nanotechnology. This new bioelectronics method may allow beginning treatments early, potentially saving many lives from cancer patients in the future.

References
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2. Das J, Kelley SO. High-Performance Nucleic Acid Sensors for Liquid Biopsy Applications. Angew Chemie - Int Ed. 2019. doi:10.1002/anie.201905005
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Organic electrochemical transistors (OECTs) leverage the volumetric capacitance of mixed conducting conjugated polymers to enable efficient signal transduction and amplification at the biotic/abiotic interface, which is advantageous for applications such as electrophysiology and biosensing. The specific properties of conducting polymer OECT channel materials can be synthetically tailored to meet a variety of application and device requirements, such as biocompatibility, high degree of amplification, fast switching times, processability, and more. However, issues of OECT stability must be addressed in order to realize long-term biological interfacing. First and foremost, the mechanisms of OECT degradation have yet to be directly assessed. Further, a common standard for quantifying OECT stability has yet to be adopted across the field, limiting the general utility of published OECT stability results. Without addressing the fundamental issues of OECT stability and degradation, the translational potential of OECTs is unlikely to be realized.

We therefore have quantified OECT degradation during cycling with a suite of electrical, electrochemical, and in situ spectroscopic measurements which enable the separate investigation of OECT channel degradation near the source and drain electrodes, and allow the deconvolution of bias and current stress effects. Employing a prototypical P-Type polythiophene based polymer with oligoethylene glycol side chains, we find OECT degradation to be a complex phenomenon, exacerbated by the coexistence of oxidating and reducing potential environments arising near the source and drain electrodes during device operation. These environments depend on both the mass transport of electrochemically produced reactive species and the residence time of electronic charge carriers in the channel. Interestingly, device implementations that avoid the coexistence of oxidating and reducing potential environments drastically improve device stability. To test the universality of these results we have extended our studies to N-type and other P-type conjugated polymers.

Our results identify clear material properties targets (highest occupied and lowest unoccupied molecular orbital level positions) for directing the rational design of next generation OECT channel materials to maximize device stability. Further, we elucidate the most stable OECT biasing schemes and circuit implementations to maximize device stability, particularly for long-term biological sensing. Finally, we present suggestions for straightforward and rigorous OECT stability evaluation and discuss key caveats to consider when interpreting OECT stability results in the literature.

Heme-based nanowires found in the pili of Geobacter sulfurreducens bacteria show great promise as a biomaterial for sensors and nanodevices. These nanowires, which consist of stacked cytochromes in a protein scaffold, have been shown to have high metallic-like conductivity. The structure was only recently determined using cryo-EM techniques, showing alternating perpendicular and parallel coordinated heme porphyrins with a repeating six heme subunit that forms a helical wire. Previous studies have modeled charge transport in cytochromes using Marcus theory, which combines modeling methods with a semi-classical electron hopping model that uses transition states to determine rate kinetics. While this has yielded models that match some cytochrome systems, the electronic behavior of the pili nanowires indicates that coherent and decoherent transport contribute significantly to overall conductivity.

The electronic properties of these nanowires were investigated using density functional theory (DFT) with a localized atomic orbital basis in Gaussian 16. Terminated sub-units of the nanowire structure were investigated, looking at the dependency of quantum transmission on spin states and iron oxidation states. The generated Hamiltonian was used with the non-equilibrium Green’s function method to calculate quantum transmission and determine the single molecule conductance. The results show that the Fe (II) neutral structure has a moderate band gap (2.3-2.7eV) that drops significantly with a single oxidized heme site, and further oxidation restoring the original band gap. The quantum transmission was similarly affected, with resulting conductances matching experimental results. This demonstrates the nanowire sensitivity to oxidation state, which can be modulated chemically to change conductivity.

Living electronics that converge the unique functioning modality of biological and electrical circuits has the potential to transform both fundamental biophysical/biochemical inquiries and translational biomedical/engineering applications. The intrinsic mismatches in physiochemical properties and signaling modality at biotic/abiotic interfaces, however, have made the seamless integration challenging. Here we demonstrate the effective hybridization of living and artificial components through a bottom-up approach, where electrochemically active bacteria (such as Shewanella) initiate the interaction and drive the assembly of electronic building blocks to design and formulate new functions across multiple length scales. In particular, by exploiting graphene oxide (GO) as the solid-state electron acceptors, the bacterial metabolism leads to the construction of fully integrated 3-D living hydrogel material with significantly reduced interfacial charge transfer barrier. Combining desirable material and signaling attributes from both biotic and abiotic components, as assembled biohybrids feature mechanical integrity, optimal mass/charge transport, and bioactive performance. In particular, the electrical conductivity and morphology/shape of the living hydrogel can be simply tunned by changing ratios of two precursor solutions: bacteria and GO and using culture reactors with different shapes, respectively. With minimized charge transfer barrier between biological and electrical centers in our living system, it also enables us to quantitatively “read” intrinsic biological functions/activities based on detected electrical signals. Here we proved this possibility by translating bacteria’s metabolism towards heavy metal ions into the measurable electrical signals with both shape and magnitude being linked to specific bio activities. Lastly, we also proved that our hydrogel system is compatible to be interfaced with other biological machineries and therefore, could introduce more advanced functions to our system, such as photosynthetic function. In summary, these works describe by forging the structural and functional synergy between biological and electrical circuits, the as-formed “living electronics” is expected to open-up new opportunities for many cross-disciplinary applications in biosynthesis, sensing, energy transduction, and hybrid information processing.

The field of organic bioelectronics has experienced a dramatic development in recent years and during its existence has shown a number of applications such as metabolite sensing, drug delivery, fabrication of neuromorphic devices, and many more.
The organic electrochemical transistor (OECT), which combines both a sensor and a signal amplifier in its structure, is an ideal tool for the interface between biological and artificial systems. Currently, the OECT research is dominated by commercial PEDOT:PSS, which, however, has a number of disadvantages, such as operation in depletion mode, the difficulty of its chemical modification, and very high acidity. Therefore, it is necessary to focus development on other materials as well to remedy these unwanted properties. Both ionic and electrical conductivity are required for OECTs to function properly. It is therefore beneficial to functionalize the OECT active materials with hydrophilic moieties (such as glycol chains), but also to pay attention to their position so that the resulting material can remain structurally organised in order to preserve its electrical conductivity.
In this study, a series of four p-type polymer materials with a high density of glycol side chains were designed, synthesized, and subsequently fully characterized. By choosing different comonomer units, both straight and bent polymer geometries were achieved, with each polymer having been synthesized in two regioisomeric variants depending on the exact positioning of the glycol side chains. All polymers were found to operate efficiently in OECT accumulation mode. Subsequent detailed research revealed that even a small positioning change of side chains can have a major effect on molecular packing and electrochemical properties and can lead to nearly 6-fold increasement of the OECT figure of merit.

Pyroelectricity is a physical phenomenon of polarization change under temperature fluctuation in the environment. Biological building blocks, such as amino acids, nucleic acids (DNA and RNA), proteins, and biomaterials such as soft and hard tissues with hierarchical structures are composed of polar molecules and are also known to induce pyroelectric properties. However, the understanding of the biological pyroelectric effect is still lacking due to the configurational complexity and few model system. Here, we present the M13 virus as a novel model system to demonstrate the structure-and-function relationship of biological pyroelectricity at the molecular level. M13 virus is a benign and non-harmful virus to infect only bacterial host cells. It has a filamentous shape with 880 nm in length and 6.6 nm in diameter. The M13 virus is assembled with 2700 copies of major pVIII coat protein hierarchically with spontaneous polarization. We observe that the pyroelectricity of the M13 is induced by the non-centrosymmetric structure and spontaneous polarization of the major coat protein (pVIII). With molecular dynamics simulations and circular dichroism spectroscopy, we demonstrate that the alpha-helical structure of pVIII changes to a random coil upon heating, resulting in the change in polar characteristics of M13. By fabricating unidirectionally polarized M13 film, we characterize the macroscopic pyroelectric potential of the M13 surface under various temperature fluctuations using Kelvin probe force microscopy. Further, we measure the pyroelectric voltage and current generated by pulse-modulated near-infrared laser under various frequencies and intensities. Our bioengineering approach shows how the hierarchical assembled polar molecules contribute to the pyroelectricity in a biological system and how we can develop novel virus-based self-powered systems and biomedical applications in the future.

Due to their low cost, wide band gap semiconducting nature, high chemical stability and admirable durability, nickel oxide (NiO) thin films were frequently utilized in electrochromic smart windows, p-type transparent conducting electrodes, photovoltaics (PVs), organic light-emitting diodes (OLEDs), gas sensors and functional layers for chemical sensors [1]. Chemical sensors used in healthcare have utmost importance, hydrogen peroxide (H₂O₂) and glucose being the two typical analytes. Excess H₂O₂ in the environment may lead to serious health problems as diabetes, cardiovascular disorders, cancer, and concerning neurodegenerative diseases so that an accurate, rapid and reliable method to detect H₂O₂ is of great importance [2]. Likewise, measurement of glucose concentration is also highly critical for clinical diagnosis of diabetes, fermentation and food quality control [3]. To date, many methods for determining H₂O₂ and glucose have been developed, but these methods are often time-consuming and expensive. On the other hand, electrochemical detection of H₂O₂ and glucose can be performed in a cost-effective manner, on-site with high sensitivity, using simple instrumentation. Electrochemical detection with enzyme-free electrodes has superior pH and temperature stability performance compared to that of enzyme-based sensors. Transition metals, metal oxides and their alloys are suitable candidates for the determination of H₂O₂ and glucose sensors owing to their electrocatalytic properties. And the sensor characteristics can simply be tuned via doping the electrochemically active thin films. In this work, NiO and doped NiO (cobalt, manganese and magnesium) thin films were deposited via ultrasonic spray deposition (USD) method. Then, deposited thin films were annealed to crystallize. The addition of different dopant atoms on the morphological, optical and electrochemical sensing properties of NiO thin films have been systematically investigated. Significant decrease in the crystallite sizes was observed upon doping NiO thin films. Likewise, the bandgap of doped NiO thin films decreased drastically compared to undoped NiO thin films (3.74 eV). Detection of H₂O₂ and glucose was performed using a 3-electrode setup where 0.1 M sodium hydroxide was used as an electrolyte, the fabricated thin film electrodes acted as working electrodes and Ag/AgCl and Pt wire were used as a reference and counter electrodes, respectively. The addition of interferences with different concentrations was monitored through the change in the current response at an applied potential of +0.65V (vs. Ag/AgCl). The NiO thin film H₂O₂ sensor showed a sensitivity of 1.5 µA/µM with a limit of detection of 3.8 µA. The response time was calculated as 5 seconds using 90% of initial step change in the current. These results showed the promise of ultrasonic spray deposited NiO thin films for amperometric detection of H₂O₂ and glucose.

Volumetric muscle loss (VML) injuries that result in fibrotic tissue formation and degradation of skeletomuscular function represent a significant hurdle for affected patients and clinicians. Upon wound formation, macrophages and neutrophils are recruited to the site to release cytokines and growth factors for proliferation and innervation. To understand the state of the wound and thus plot an optimal trajectory for rapid regeneration, one must track the wound healing process by spatially mapping key regulatory wound biomarkers, such as nitric oxide (NO). While single-point NO probes for acute measurements have been demonstrated, improvements in device stability and the number of sensing nodes are needed to achieve smart biointerfaces for in vivo applications. Here we leverage novel nanomaterials and their exceptional electrochemical properties to construct three-dimensional fuzzy graphene (3DFG) microelectrode arrays (MEAs) for the multiplexed electrochemical sensing of NO. We report in vitro results for 3DFG MEAs capable of detecting NO at physiological concentrations in the nanomolar regime. We investigate the effects of sensor size and semipermeable selective coatings to optimize the performance of our sensor arrays and benchmark performance against conventional Pt-based sensor arrays. Finally, we demonstrate our devices on a flexible platform for in vivo NO detection (rodent model) to aid in monitoring inflammatory wound states.

Conscious cultivation of plants has sustained human civilization for millennia. Maintaining optimal levels of macronutrients like potassium (K⁺) and calcium (Ca²⁺) is critical for promoting healthy plant growth and development. However, there remains no technical solution for monitoring these vital nutrients in plants in real-time. Existing nutrient detection methods typically require the excavation and transportation of plant samples to off-site laboratories for characterization, which is labor intensive and time consuming. Organic electrochemical transistors (OECTs) are devices that can monitor plant chemical levels in real-time due to their high sensitivity, low voltage and power requirements, and compatibility with living tissue. Additionally, OECTs can be fabricated using readily scalable additive manufacturing techniques (e.g., inkjet and screen printing) making them suitable for applications where many sensors are required under capital constraints.

This presentation will describe the development of fully printed, mechanically flexible, and ion selective OECTs that can accurately detect macronutrient concentrations in raw whole plant sap in real-time. The performance of these devices is drastically improved by doping PEDOT:PSS with common sugar alcohols to generate “internal ion reservoirs” within the OECT channel. The all-printed OECTs show maximum transconductances over 5 mS, which, as far as we are aware, is the highest reported for a fully printed OECT. By utilizing ion selective membranes (ISMs), OECT-based ion sensors are fabricated that show super-Nernstian sensitivity, selectivity to the target ion against similar ions over five orders of magnitude in concentration, and a limit of detection (LOD) as low as 10 µM. This work provides a potential path to high-throughput, low-cost, high spatiotemporal assessment of plant nutrition, enabling correlation of sap chemical composition to overall plant and soil health, and the potential for massive efficiency gains in agriculture.

As the discovery of new drugs becomes slower and more expensive with time, there is an urgent need for a new approach to treating disease. Bioelectronic medicine, which uses electrical stimulation to influence neural behaviour, has emerged as a powerful technology to that end: Deep brain stimulation, for example, has shown exceptional promise in the treatment of neurological and neuropsychiatric disorders, while stimulation of peripheral nerves is being explored to treat autoimmune disorders. To bring these technologies to patients at scale, however, significant challenges remain to be addressed. Key among these is our ability to establish stable and efficient interfaces between electronics and the human body. I will show examples of how this can be achieved using new electronic materials and devices engineered to communicate with the body and evolve with it.

Recent progress in wearable devices provides new opportunities for precise, non-invasive, long-term recording of body mechanics. The soft device incorporating a single MEMS accelerometer captures subtle vibration of the skin with a resolution of 1×10^-4 g/sqrt(Hz) in frequency range 0 to 800 Hz. In this study, we introduce an on-body mechano-acoustic sensing technology based on a skin-mounted accelerometer array to assess the mechanical profiles of subdermal tissues in-vivo, similar to seismology. A system-level wearable device construction, optimized for a comfortable skin interface and high precision, incorporates a broadband dual-accelerometer sensor, an audio actuator, and a Bluetooth System-on-Chip and enables a wireless, automated operation. An automated algorithm, leveraging the spectral analysis of surface waves (SASW) methods, computes the depth-sensitive, elastic modulus information of the propagation media from the mechanical dispersion relationship. Comprehensive theoretical and experimental investigation verifies that the device, together with the automated data-processing platform, provides a precise, robust, and non-invasive evaluation of the elasticity with a resolution of ~5 kPa and depth information in the range of ~1-140 mm of various phantom materials (Young’s modulus E= ~10-1500 kPa). The device also identifies the softening of pork tissues with increasing injected water content and the changes of modulus of brachioradialis muscle under different levels of tension. The results are in agreement with the in-parallel Ultrasound Elastography measurements. A quantitative assessment of the stiffness profile of the rectus femoris muscle during leg-press exercise demonstrates the continuous monitoring capability in the ambulant environment that can support long-term clinical assessment of different tissues and disease states in a large population.

Intrinsically stretchable bioelectronic devices based on soft and conducting organic materials have been regarded as the ideal interface for seamless and biocompatible integration with the human body. However, the grand challenge remains for the conducting polymer to possess both high mechanical ductility and good electrical conduction at cellular level feature sizes. This longstanding material limitation in organic bioelectronics has impeded the full exploitation of its unique benefits.

Here, we introduce a new molecular engineering strategy based on rationally designed topological supramolecular networks, which allows effective decoupling of competing effects from multiple molecular building blocks to meet complex requirements. We achieve two orders of magnitude improvement in the conductivity under 100% strain in physiological environment, along with the capability for direct photopatterning down to 2 µm.

These unprecedented capabilities allow us to realize previously inaccessible bioelectronic applications including high-resolution monitoring of ‘soft and malleable’ creatures, e.g., octopus, and localized neuromodulation down to single nucleus precision for controlling organ-specific activities through delicate tissues, e.g., brainstem.

Smart contact lenses for continuous glucose monitoring (CGM) have great potential for huge clinical impact . To date, their development has been limited by challenges in rapid detection of glucose without hysteresis for tear glucose monitoring to track the blood glucose levels. Here, we demonstrate that bimetallic nanocatalysts immobilized in nanoporous hydrogels in smart contact lenses enable reliable CGM in diabetic rabbits. After redox reaction of glucose oxidase, the nanocatalysts facilitate rapid decomposition of hydrogen peroxide and nanoparticle-mediated charge transfer with drastically improved diffusion via rapid swelling of nanoporous hydrogels. The ocular glucose sensors result in high sensitivity, fast response time, low detection limit, low hysteresis, and rapid sensor warming-up time. In diabetic rabbits, smart contact lens can detect tear glucose levels consistent with blood glucose levels measured by a glucometer and a CGM device, reflecting rapid concentration changes without hysteresis. The CGM in a human demonstrates the feasibility of smart contact lenses for further clinical applications.

The development of bioelectronic devices for sensing or actuation requires materials that have properties similar to that of biological entities. In particular, a strong emphasis has recently been placed on minimizing the mechanical mismatch between ‘hard’ electronics and ‘soft’ biological tissues to reduce tissue scaring and increase device longevity. This mismatch can be partially addressed by using conductive polymers instead of inorganic materials. Not only do polymers have a lower Young’s modulus, but they can also behave as mixed ionic-electronic conductors. This mixed conduction is essential to transduce electronic to biological (ionic) signals (e.g., in neurological electrodes) and vice versa (e.g., in organic electrochemical transistors). Amongst organic mixed conductors, the polyelectrolyte complex poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is probably the most commonly used. While some properties of PEDOT:PSS are highly desirable for bioelectronics such as its high conductivity and biocompatibility, it remains difficult to access new functionality without using a composite approach. A major challenge stems from the lack of control over the molecular structure of PEDOT:PSS, which leads to a highly disordered morphology in the solid state. Instead of taking a blending approach toward functionalizing PEDOT:PSS, we have developed a method to direct its solid-state assembly using block copolymers. Our approach uses block copolymers of PSS with neutral polymers to drive the self-assembly of PEDOT particles in solution while imparting additional functionality. In this presentation, I will share some of our results showing the importance of controlling the molecular structure of PEDOT:PSS to access properties relevant to bioelectronics, such as volumetric capacitance and reversible self-assembly.

Organic Electrochemical Transistors (OECTs) offer transduction and high amplification of biological signals. Both p-type and n-type mixed ionic and electronic conductors and their corresponding OECT devices are gaining significant interest. Ambipolar OECTs, however, offer additional advantages including simplifying the design and fabrication of OECT-based complementary circuits, detecting biological multifunctional analytes, enabling versatile device architectures such as vertical OECTs, reducing device footprint and increasing the density of elements, etc. Still, ambipolar OECTs are scarce because it is difficult to balance the performance and stability of the device when operating under the negative and the positive conditions. Here we show that the bulk-heterojunction approach, borrowed from organic solar cells, can be harnessed to achieve ambipolarity in an OECT device. More specifically, a semiconducting polymer and small molecule are judiciously selected, blended at suitable ratios and annealed to yield the morphology optimal for mixed conductivity and ionic-electronic coupling. We demonstrate the approach using a common OECT p-type polymer and an n-type fullerene derivative and show, for the first time, a truly balanced ambipolar OECT device. Electrical and electrochemical techniques are used to follow the physical processes under bias, while the morphology is studied using Xray techniques and VPI. Device stability as a function of time and temperature are also investigated. Changes in the morphology induced by time and temperature are associated with device performance to realize structure-property relationships in bulk-heterojunction-based OECTs.

Organic electrochemical transistors (OECTs) are a novel device architecture, emerging as a potential platform for biosensors and neuromorphic computing. In an OECT, volumetric doping (gating) of the active semiconductor is achieved through ingress of electrolyte ions, under potential control. This opens unique transduction modalities, due to the mixed (ionic and electronic) modes of conduction. This also challenges established paradigms for the operation of traditional, organic field-effect transistors as operation involves the dynamic swelling of the active layer by both solvent and ion. Poly(3- (methoxyethoxyethoxymethyl)thiophene) (P3MEEMT) has emerged as an interesting, prototypical OECT material, differing from the classic OFET material, regioregular poly(3- hexyl)thiophene (P3HT), by the replacement of the non-polar alkyl side chains with oligoethylene glycol (OEG). In an early study of P3MEEMT,[1] is was observed to exhibit the counter-intuitive behavior of degraded charge transport upon thermal processing. We have conducted a detailed study of the variation of the structure and OECT performance of P3MEEMT with thermal processing. In the study we compare polymers with number average molecular mass, Mn, varying from (13 to 87) kg/mol. Using GIWAXS to characterize the degree of crystallinity and crystal orientation distribution, we find the OEG side chains introduce rich thermal processing behavior. All polymers exhibit only moderate and nearly isotropic order when coated from chlorobenzene. Low Mn material adopts an edge-on structure, with monotonically increasing degree of crystallinity with increasing anneal temperature. In contrast, high Mn material first adopts a face-on orientation when annealed at (115 to 125) ° C, and then a nearly isotropic crystal distribution when annealed above the last crystal melt transition near 145 ° C. Remarkably, the OECT device behavior (C*m) is nominally independent of the severe differences in orientation distribution across Mn at anneal temperatures below 120 ° C. Consistent with the earlier report,[1] 13 kg/mol Mn material exhibits a degradation in C*mu when melt-annealed (at T ≥145 ° C), in striking contrast to the higher Mn (≥ 23 kg/mol) material that exhibits anneal T independent performance. In accord with recent studies for the Mn dependence of transport in P3HT[2] we attribute the drop in performance of annealed, low Mn P3MEEMT to the phenomena of tie-chain-pullout and ripening of the crystalline domains.
[1] L.Q. Flagg, et al. J Am Chem Soc 2019, doi: 10.1021/jacs.8b12640
[2] K. Gu, et al. ACS Macro Lett 2018 doi: 10.1021/acsmacrolett.8b00626

The structure-based tuneability of the electronic and optical properties of conjugated polymers has enabled their application across a range of fields, including energy harvesting and optoelectronics. However, in the context of biological sensing, the use of conjugated polymers has thus far incorporated little specificity in terms of covalent modification.

Developing robust, highly selective, biologically compatible sensing platforms is of critical importance because the measurement of analyte concentrations in biological samples is crucial for the management or detection of many diseases. Currently, many devices which function for this purpose are complex, multi-component systems. However, directed synthetic strategy with conjugated polymers enables the fine-tuning of analyte specificity, electroactive or optical functionality, and physical and morphological properties, within a single multi-purpose material. In addition, these entirely organic systems offer affordability, biocompatibility, and simple design and fabrication.

I will present my work on a novel covalently-modified PEDOT polymer featuring a 15-crown-5 moiety. The introduction of such a group is shown to enhance a diverse range of characteristics in comparison to regular PEDOT, including: adhesion to ITO substrates, physical and electrochemical integrity, film uniformity, and spectroelectrochemical properties. Furthermore, we find that the long-term electrochromic behaviour of PEDOT-Crown is altered in the presence of its chelating ion, sodium, compared to unmodified and analyte-free controls, which may open the door to its application as a sensor material. The adaptable nature of the synthetic pathway also unlocks access to range of potential sensor materials, featuring differently modified PEDOTs specific to other biomarkers, a space we have begun to explore.

Organic mixed ionic-electronic conductors (OMIECs) are a class of materials that have recently drawn interest as materials for next generation biosensors. For these applications, cycling stability is an important parameter that is not yet well understood. Recent work has shown that redistributing the ethylene glycol side chain units along the backbone, while maintaining a constant number of ethylene glycol units, can be used to optimize the cyclability of polythiophenes. In this system the polymers with unevenly distributed sidechains showed a greatly suppressed active (in response to bias) swelling as measured by quartz crystal gravimetry. This reduced swelling in response to electrochemical bias correlated with increased cycling stability.¹ Here we investigate this side chain redistribution series using grazing incidence x-ray scattering (GIWAXS) with in-situ potential control to examine the passive and active swelling of the polymer crystallites in addition to the bulk film. We find that when the side chain is evenly distributed, the polymer crystallites swell minimally upon contact with electrolyte, implying that most of the swelling occurs in the amorphous regions of the film. However, in polymers with highly uneven side chain distribution, contact with electrolyte causes the formation of a hydrated crystal lattice that is ~ 50 percent expanded relative to the dry lattice. We hypothesize that this hydrated crystal lattice minimizes mechanical strain caused by cycling and helps explain the greater cycling stability of these polymers. Additionally, we examine the role of different anions in swelling both the hydrated state and the dry state of the polymer films to further understand electrochemically induced swelling of these films. Overall, this work provides insights into the synthetic design of highly cyclable OMIEC materials.

References
(1) Moser, M.; Hidalgo, T. C.; Surgailis, J.; Gladisch, J.; Ghosh, S.; Sheelamanthula, R.; Thiburce, Q.; Giovannitti, A.; Salleo, A.; Gasparini, N.; Wadsworth, A.; Zozoulenko, I.; Berggren, M.; Stavrinidou, E.; Inal, S.; McCulloch, I. Side Chain Redistribution as a Strategy to Boost Organic Electrochemical Transistor Performance and Stability. Adv. Mater. 2020, 32, 2002748. https://doi.org/10.1002/adma.202002748.

We previously proposed a one-step procedure for fabricating a solution-gated ultrathin channel indium tin oxide (ITO)-based field-effect transistor (FET) biosensor.¹ A thin-film sheet was placed on both ends of a metal shadow mask, which were contacted with a glass substrate. The bottom of the metal shadow mask corresponding to the channel was slightly raised from the substrate, resulting in the creeping of some particles into the gap during sputtering. Owing to this modified metal shadow mask, a thin ITO channel (< 30–40 nm) and thick ITO source/drain electrodes (ca. 100 nm) were simultaneously fabricated during the one-step sputtering. The thickness of ITO films was critical for them to be semiconductive, depending on the maximum depletion width, similarly to 2D materials. The ultrathin ITO channel worked as an ion-sensitive membrane as well, owing to the intrinsic oxidated surface directly contacting with an electrolyte solution. The solution-gated 20-nm-thick channel ITO-based FET, with a steep subthreshold slope (SS) of 55 mV per decade (pH 7.41) attributable to the electric double-layer capacitance at the electrolyte solution/channel interface and the absence of interfacial traps among electrodes formed in one step, demonstrated an ideal pH responsivity (~56 mV/pH). Therefore, the chemical modification of the ITO channel surface is expected to contribute to biomolecular recognition with ultrahigh sensitivity owing to the remarkably steep SS. In this study, we fabricate the solution-gated ultrathin channel ITO-based FET on glass substrate by one-step sputtering, then modify it with an aptamer, which binds to a specific target biomolecule (e.g., dopamine). Moreover, the fundamental electrical properties of the solution-gated ultrathin channel ITO-based FET with and without aptamer are investigated.
The ITO device was prepared on a glass substrate by sputtering. The ITO channel was immersed in 0.2% 3-aminopropyltrimethoxysilane (APTMS) solutions for 30 min. After the surface was washed by deionized (DI) water, the ITO transistor was heated for 10 min at 120°C. Then, the ITO channel was immersed in the mixed solution of 10% dimethyl sulfoxide (DMSO) and 90% phosphate buffered salts (PBS), containing 1 mM N-succinimidyl 3-maleimidobenzoate (MBS) for 1 h, and then the surface was washed with DI water. Finally, 5 mM dopamine aptamer solution (pH 7.4) was dropped on the ITO channel surface overnight. Using the prepared device, the fundamental electrical properties such as transfer characteristics (I_D-V_G), output characteristics (I_D-V_D), and real-time monitoring (I/V-t) were collected.
The solution-gated ultrathin channel ITO-based FET showed a good sensitivity near the Nernstian response to pH. Besides, by setting a gate potential in the subthreshold regime, the ITO device, which is modified by aptamer, should be capable of detecting dopamine with high sensitivity.
Reference
1. T. Sakata et al., ACS Appl. Mater. Interfaces, under revision (2021).

Nanosized bioelectronic detecting interfaces seem the privileged pathway to single-molecule detections. However, while giving access to rarer events, this near-field approach is unsuited to detect at concentrations lower than nanomolar because of the diffusion-barrier issue. Large-area (μm² - mm² wide) bioelectronic transistors are perceived as unsuited due to the irrelevant footprint of a single molecule on a much larger detecting interface. Indeed, detecting such an event would be like spotting the wave generated by a single droplet of water falling on a one-kilometer-wide pond. However, many field-effect large-area biosensors have been shown to detect at limit-of-detection below femtomolar, being also naturally suited for point-of-care applications. Here the field is reviewed, illustrating device architectures, materials used, and target analytes that can be selectively detected. The sensing mechanisms and the amplification effects enabling the large-area bioelectronic sensor to detect at the physical limit are also detailed

Electrolytes play a pivotal role in regulating cardiovascular functions, hydration, and muscle activation. The current standards for monitoring electrolytes involve periodic sampling of blood and measurements using laboratory techniques, which are often uncomfortable/inconvenient to the subjects and add considerable expense to the management of their conditions. The wide range of electrolytes in skin interstitial fluids (ISF) and their correlations with plasma create exciting opportunities for applications such as electrolyte and circadian metabolism monitoring. However, it has been challenging to monitor these electrolytes in the skin ISF. In this study, we report a minimally invasive microneedle-based potentiometric sensing system for multiplexed and continuous monitoring of Na⁺ and K⁺ in the skin ISF. The potentiometric sensing system consists of a miniaturized stainless-steel hollow-microneedle to prevent the sensor delamination and a set of modified microneedle electrodes for multiplex monitoring. We demonstrate the measurement of Na⁺ and K⁺ in artificial ISF with a fast response time, excellent reversibility and repeatability, adequate selectivity and negligible potential interferences upon the addition of physiologically relevant concentration of metabolites, dietary biomarker and nutrients. In addition, the sensor maintains the sensitivity after multiple insertions into the chicken skin model. Furthermore, the measurements in artificial ISF using calibrated sensors confirms the accurate measurements of physiological electrolytes in artificial ISF. Finally, the agarose gel model and chicken skin model experiments demonstrate sensor’s potential for minimally invasive monitoring of electrolytes in skin ISF. The developed sensor platform can be adapted for a wide range of other applications, including real-time monitoring of nutrients, metabolites and proteins.

When combined with oxidase enzymes, the NDI-T2 based electron transporting polymer led to high performance metabolite sensors, yet their working mechanism has been poorly understood.^1,2 Here using in-situ oxygen, hydrogen peroxide, and pH analysis during device operation, we shed light into the biocatalysis at the semiconducting polymer interface. We demonstrate the significant role that oxygen plays during the operation of glucose sensors made of n-type organic electrochemical transistors (OECTs). We show that the oxygen reduction capability of our polymer is mainly responsible for the observed sensing performance, where a strong correlation has been seen in the amount of solution oxygen and the charge carrier density of the n-type film in the OECT channel. Our results show the importance of in operando analysis for understanding polymer-catalytic enzyme activity, as well as the importance of ambient oxygen in the operation of n-type devices.


1: Pappa, A. M.; Ohayon, D.; Giovannitti, A.; Maria, I. P.; Savva, A.; Uguz, I.; Rivnay, J.; McCulloch, I.; Owens, R. M.; Inal, S., Direct metabolite detection with an n-type accumulation mode organic electrochemical transistor. Science advances 2018, 4 (6), eaat0911.

2: Ohayon, D.; Nikiforidis, G.; Savva, A.; Giugni, A.; Wustoni, S.; Palanisamy, T.; Chen, X.; Maria, I. P.; Di Fabrizio, E.; Costa, P. M., Biofuel powered glucose detection in bodily fluids with an n-type conjugated polymer. Nature materials 2020, 19 (4), 456-463.

Organic semiconductor devices are actively being applied to the next generation of wearable electronics, taking advantage of their lightweight, thinness, and flexibility. Flexible displays based on organic light-emitting diodes (LEDs) are being used in smartwatches and wristband applications to help reduce power consumption. Pulse oximetry has also been realized by combining organic LEDs with organic photodetectors. By making these organic optical sensors flexible, they can be attached directly to a human's skin with little discomfort and enable long-term health monitoring.
However, it is still difficult to integrate such thin organic optical sensors with power sources at the system level. In addition, ultra-thin organic LEDs are not stable enough to operate in air, which hinders long-term monitoring of biological signals.
Here, we present an ultra-thin, self-powered organic optical system for monitoring photoplethysmogram (PPG). The system consists of three ultra-thin electronic devices: a polymer LED (PLED), an organic solar cell, and an organic photodetector. By adopting an inverted structure and a polyethyleneimine ethoxylate (PEIE) layer doped with 8-quinolinolathritium (Liq) as the electron transport layer (ETL), organic light-emitting diodes exhibit improved operation stability under ambient air conditions. Because of the intrinsic air operational stability of inverted PLED with PEIE:Liq electron injection layers, the ultra-flexible OLED fabricated without passivation shows 70% of the initial brightness lifetime of 11.3 hours in air, which is more than three times the lifetime of conventional ultra-flexible OLEDs. In addition, the built-in light sensor showed high linearity with respect to the output of 0.98 of the PLED light sources. Such a self-powered ultra-flexible PPG sensor can stably monitor the blood flow pulse signal of human hands.

"A.I. Artificial Intelligence" (2001), Steven Spielberg's film, features a robot that tries to understand human emotions via communication. However, human sentiments, which are nonverbal communication tools, are very ambiguous in terms of interpretation and are difficult for machines or artificial intelligence (AI) to translate technically. If AI understands a user's mental state, AI will learn the right decisions from humans in unclear situations that have been difficult to judge. Here, we introduce a wirelessly operative, neuroadaptable (adaptable in relation to his/her mindset), communicable “Human-AI Collaborative System” (HACS) based on the earbud-like wireless EEG device (e-EEGd) composed of tattoo-like electrodes, connectors, and a wireless EEG earbud. The HACS can make up for AI-based machines’ incorrect decisions to revise and reinforce its decision accuracies according to P300 event-related potential (ERP) in volunteers’ brain signals. It is based on the P300 EEG signal, one of ERP components, positive rises around 300 msec after an unexpected external stimulus is applied due to the human decision-making process³⁷. In the case of the HACS, an unexpected behavior of the AI-based machine causes the P300. Since the intensity of P300 is small and the frequency range overlaps with the range of motion artifact, it is vital to measure high-quality EEG and accurately classify only P300 among various noises and components. We proposed an integration strategy based on gradually increasing thickness from ultra-thin electrodes (900 nm) to rigid earbud measurement system that enables lower motion artifacts. The e-EEGd conformally adheres to the skin on the head, minimizes volunteer motion artifacts, and continuously records EEG even while the volunteer is walking, driving, etc, which expands the variety of situations in which this technology can be used. The device weighs only 8.24 g, which is several times lighter than other available EEG devices, and generates 8.5-times less artifactual noise. The e-EEGd enables the achievement of high signal-to-noise ratio (SNR) EEG signals and transmits EEG signals wirelessly with minimal delay (up to 15 ms). We measured the P300 component with 12 subjects using e-EEGd by sensory stimulation and controlling the unexpected behavior of the autonomous machines. In addition, based on the measured P300, we conducted a signal processing and classifier optimizing study for efficient and fast real-time classification to be performed on an AI-based machine. The HACS can immediately correct unexpected working of AI-based machines or reinforce the system choices based on the presence/absence of the P300 in the user’s EEG. We demonstrated potential applications of the HACS and the e-EEGd with embedded real-time classification on AI-based machines, including virtual assistants, maze solvers, and autonomous remote-controlled (RC) cars.

Pre-diabetic patients with glucose levels between diabetes and normal can recover to normal levels without medication if their blood glucose management is well done. However, unlike diabetics who keep blood glucose levels with medication prescribed by doctors, pre-diabetes patients should make significant efforts to control blood glucose through diet and regular exercise. The basis of blood glucose management is blood glucose measurement. A commonly used blood glucometer is a one-time measurement through blood collection by a sharp needle, which is an invasive method. Hence, patients feel pain at each measurement. Recently, continuous blood glucometers using microneedles have been commercialized, allowing patients to continuously measure and manage blood glucose without pain. However, there are several drawbacks such as that medical staff has to help attach the blood glucose meter, and side effects such as inflammatory reactions can be caused by the use of metal needles. In this work, we present a painless, lightweight, and small patch-type wearable glucometer made of polydimethylsiloxane (PDMS) microneedle and a self-powered supercapacitor. The principle of self-powering of this patch-type glucose sensor is to charge the supercapacitor by generating a potential difference of the supercapacitor with electrons generated by the oxidation reaction of glucose. Due to this potential difference, ions present in the electrolyte are adsorbed on the surface of each electrode, and charging begins. Herein, the supercapacitor consists of polymeric thin films, which makes it mechanically flexible. We coated the electrode layer and enzyme layer by dip-coating method to form the glucose sensor on the uneven microneedle surface. The PDMS microneedle-type blood glucose sensor can penetrate the skin without pain and detect the blood glucose in the interstitial fluid (ISF). The experimental verification of the glucose-sensing by the microneedle-type sensor was done with an artificial skin immersed in the solution with glucose. The glucose concentration varies from the pre-diabetes level to diabetes, and the levels between the two. As glucose concentration increases, more electrons are produced by glucose oxidation. The potential difference between the supercapacitor electrodes increases, which gives the driving force for more electrolyte ions to move towards the electrodes. As a result, we confirmed that the supercapacitor was charged with more energy as the glucose concentration was increased through cyclic voltammetry. Finally, the self-powered patch-type glucose sensor is combined with a light-emitting diode (LED) on-off system to inform users of blood glucose levels easily and quickly. When the glucose concentration increased from the pre-diabetic to the diabetic level, the light turned on because enough energy was delivered to the connected LED.

Single-layer graphene (SLG) is an ideal material for neuronal interfaces such as electrodes and cell scaffolds thanks to its high biocompatibility, transparency, and electro-conductivity. Despite these useful properties, conventional SLG-based neuronal interfaces involve constrains related to a mismatch between the 2D SLG surface and the complex structure of 3D neuronal tissues. Self-folding with SLG-based film has recently emerged as a method to encapsulate cells for both constructing 3D-shaped tissues and sensing molecules from the encapsulated cells. This suggests it could be applied for electrophysiology from a 3D-shaped neuronal construct. The approach with a foldable electrode has recently attracted a great deal of interest in 3D-spatio electrophysiology of single neural spheroids. However, it is still challenging to investigate the firing dynamics exhibited by networks of interconnected neuronal constructs because the multiple neuronal constructs need to be in contact with each electrode. In this work, we propose a foldable SLG-based electrode array that allows for producing 3D-shaped neuronal constructs within the folded electrodes while recoding firing dynamics from neuronal constructs simultaneously.
To encapsulate cultured cells within an SLG surface, we modified our previous method to induce self-folding with SLG-based film. A previous report showed that this method causes a SLG/parylene-C bilayer to spontaneously roll up into a folded cylindrical structure (micro-roll), with the SLG formed on the outer face, so we need to modify it such that the SLG forms on the inner face. We transferred another SLG to the opposite side of the parylene-C layer, and the SLG-sandwiched parylene-C film formed a micro-roll that allowed us to encapsulate cells within the inner SLG surface. We applied the self-folding to an electrode array by incorporating the SLG-sandwiched parylene-C film as an electrode. To investigate whether the electrode allows for both creating cellular constructs and electrophysiology, dissociated hippocampal neurons were encapsulated by the self-folding electrodes. Immunocytochemical images indicated that the encapsulated neurons formed a neuronal construct within the folded SLG and interconnected between each neuronal construct via axons. Spontaneous activities of neurons were continuously recorded for 70 days from the folded electrodes, whereas the signals disappeared at 28 days in recordings of an aggregated culture by unfolded electrodes. These long-term recordings were possible because the confined structure provides a firm contact between the neuronal construct and the electrode. To take advantage of the long-term recording, we further investigated a development of functional networks in the interconnected neuronal constructs (clustered culture). The clustered culture exhibited synchronous bursting activities from nine days in culture, which is consistent with a homogenous culture. On the other hand, fewer electrodes participated in the synchronized activities in the clustered culture (40% of all electrodes) than in the homogenous culture (>90%), suggesting that the clustered culture contained the rich pattern repertories of smaller networks. These results demonstrate that our method for self-folding graphene-based electrode arrays allows us to characterize the firing dynamics exhibited by interconnected neuronal constructs for a long culture period.

Owing to outstanding electrical/electrochemical performance, device operational stability and solution processability, organic mixed ionic–electronic conductors (OMIECs) have been researched for their applications to flexible biosensors, bioelectronics interfaces, neuromorphic devices, etc. Considering essential device modalities in the modern electrical circuit architecture, not only transistors but also diodes are needed for many purposes such as signal processing and device protection. Herein, we report OMIEC-based electrochemical diodes operated with aqueous electrolytes. By designing an active layer asymmetrically patterned on source and drain electrodes, the channel could be electrochemically doped/dedoped under opposite bias polarity of the applied signal, and the unprecedented current density over 30 kAcm^-2 could be achieved by using high-transconductance OMIECs. The resultant device architecture was utilized to realize two-terminal rectifying electrochemical devices. Furthermore, not only analog signal rectification but also digital logic processing could be demonstrated by employing a simple circuitry based on the multiple number of organic electrochemical diodes.

Biopotential signals are extremely useful in assessing organ function and diagnosing diseases. In order to measure and record biopotentials, biopotential electrodes act as an interface between the biological tissue and the electronic circuit. The electrical and mechanical characteristics of the electrodes used for biopotential measurements significantly influence the measured signal quality.
This work proposes a highly flexible, conductive, antibacterial, and self-adhesive silver nanorods (AgNRs) embedded polydimethylsiloxane (PDMS) based dry electrode for biopotential measurements. We have used a unique glancing angle deposition method to fabricate aligned AgNRs and embedded them in a biocompatible PDMS matrix. These electrodes do not cause skin irritation even after several hours of use and work efficiently even without prior skin preparation. These AgNRs-PDMS electrodes have an electrical resistivity of 10⁻⁷ Ω-m and a skin contact impedance of 93.9 ± 0.7 kΩ to 6.2 ± 3.7 kΩ for frequencies ranging from 40 Hz to 1 kHz, which is comparable to the most conventional Ag/AgCl wet electrodes. Furthermore, it maintains its conductivity across various mechanical stress, including bending, twisting, and stretching, as illustrated by a light-emitting diode circuit. Nanoindentation was used to measure the mechanical properties of fabricated AgNRs-PDMS electrodes, which shows the elastic modulus and hardness of the AgNRs-PDMS are increased by 167.6 and 93.3 %, respectively, compared to PDMS film, due to the strong interfacial adhesion of AgNRs embedded in the PDMS matrix.
The proposed AgNRs-PDMS dry electrodes are expected to give greater comfort for use over time due to their flexible nature and a better match to the skin's modulus. Simultaneously, the antibacterial properties of silver make it an attractive candidate for wearable electronics. The fabrication method is simple, cost-effective, and scalable, thus permitting the production of arbitrary-shaped flexible electrodes for long-term biopotential monitoring.

Electrochemical biosensors directly detect electrical signals based on biomolecular charges or electrical changes in biomolecular recognition events, regardless of their molecular sizes; therefore, such electrochemical methods are suitable for the detection of small biomolecules. In general, carbon and metals such as gold and platinum are used for the electrodes of electrochemical biosensors. On the other hand, considering the development of a novel biosensor in the future, a conductive polymer, which shows a flexibility and then reduces the burden to a body, is a strong candidate for the electrode in an autonomous mobile biosensing system, whereby targeted biomolecules and ions are collected and detected all over in a biological fluid or a sample solution. However, the lack of mechanical strength for the conductive polymer prevents it from maintaining a free-standing state, even when it is coated on a supporting electrode, which is a concern of the conductive polymer for the practical use [1]. That is, the development of free-standing conductive polymer is expected for the autonomous mobile biosensor without the supporting electrode. In this study, we have developed the free-standing conductive hydrogel with a functional monomer that allows biomolecular recognition, and evaluated the electrical properties with the electrochemical setup. In particular, we would like to discuss about the possibility of the functionalized free-standing conductive hydrogel for its application to the autonomous mobile electrochemical biosensor.
As the conductive hydrogel used in this study, polyaniline (PAni) was prepared with self-oxidation of aniline (Ani) monomers in an ammonium persulfate solution. In particular, aminophenylboronic acid (APBA) was copolymerized to obtain the PAni-PBA hydrogel electrode; that is, diol compounds such as glucose bind to PBA on the basis of the equilibrium reaction, which allows the detection of glucose molecules. Furthermore, by adding polyvinyl alcohol (PVA) into the PAni-PBA polymer gel network, the obtained hydrogel showed the free-standing property [1]. This is because PVA also has diol groups and is cross-linked in the PAni-PBA polymer based on the diol binding. The PAni-PBA-PVA free-standing conductive hydrogel was connected to the gate electrode of field-effect transistor (FET) through a platinum wire, and then the change in the surface potential of the hydrogel was measured with varying the glucose concentrations.
As a result, the gate potential of the FET sensor with the PAni-PBA-PVA free-standing conductive hydrogel increased with increasing the glucose concentrations. Because the binding constant of PBA to glucose was higher than that to PVA, the binding of PBA to PVA was replaced by that to glucose in the hydrogel [2]. Therefore, the crosslink density based on PVA decreased with increasing the glucose concentrations in the hydrogel and then the negative charge of PBA was induced by the diol binding with glucose; as a result, the capacitance of the hydrogel increased, which contributed to the FET signals. In this study, we have found the electrical properties of the PAni-PBA-PVA free-standing conductive hydrogel for the glucose detection with the electrochemical setup. Moreover, we would like to discuss about the possibility of the fabricated free-standing conductive hydrogel for the autonomous mobile electrochemical biosensor.
References
[1] W. Li et. al., Angew. Chemie - Int. Ed., 55, 32, 9196–9201, (2016). [2] X. Zhang et.al., Biomacromolecules, 13, 1, 92–97, (2012).

Stem cell research has benefitted enormously from a variety of different materials used to create scaffolds to grow stem cells in 3D, however, only few studies report the development of structures that are able to recapitulate 3D tissue-like environments and exhibit multifunctional properties (i.e. electrical and optical). Three-dimensional organic bioelectronic devices proposed to bridge the dimensionality mismatch between 2D/static electronics and 3D/dynamic biology, comprising a versatile platform for hosting and monitoring cells. These devices take advantage of the mixed conduction properties of conjugated polymers (CPs) and enabled the realization of highly biomimetic, electro-active interfaces. Here we show the development of 3D, multifunctional polymer composite structures that exhibit good electrical and optical properties. Water-based solution mixtures of PEDOT:PSS, polythiophene and a polyethylene glycol-based crosslinker are freeze dried, and 3D scaffolds with an average pores size of 50 μm are realized. These structures exhibit lower Young’s modulus and higher water swelling capacity compared with pure PEDOT:PSS scaffolds cross-linked with GOPS. Scaffold slices with different thicknesses between 100 μm - 400 μm are attached on flat ITO substrates and their photo-electrochemical properties are measured with electrochemical impedance spectroscopy (EIS) and photo-amperometry. These multifunctional platforms are used to host human adipose derived stem cells (hADCs) and to monitor their proliferation in situ with both EIS and fluorescence microscopy.

Over the past decade, nanostructured materials have substantially improved the performance and the capabilities of in-vitro biosensors for cellular analyses. On the one hand, materials with ordered nanostructures or with randomly nanostructured morphology improve adhesion and coupling of cells. On the other hand, these materials enable new effects that are beyond the capabilities of planar interfaces, such as electrical and optical enhancements.
In this talk, I will focus on two recent nanotechnologies: (i) ultrashort pulsed lasers on nanostructured materials for enhancing detection capabilities of electrophysiological sensors, and (ii) novel strategies for electro-optical transduction of action potentials.
The key-enabling factor of ultrashort pulsed lasers in biosensing is the squeezing of high energy in short and sparsely distributed photon packages. Lasers with pulse duration in the picosecond range may reach extremely high peak powers for activating threshold phenomena while maintaining low average irradiation intensities and thus low photocytotoxicity. By proper irradiation with ultrashort pulsed lasers, nanostructured materials immersed in water can emit hot-electrons, which are highly energetic charges that can produce redox reactions and lead to useful effects on adhering cells. In particular, the emission of hot-charges from nanomaterials may result in the non-invasive poration of the cellular membrane or in the photostimulation of action potentials. I will show that such effects can be exploited for enabling intracellular recordings or stimulation of action potentials in electrogenic cells on microelectrode arrays (MEA) decorated with nanomaterials^1,2.
In the second part of the talk, I will describe the novel concept of “VIrtual mirror CEll” (VICE)³ for monitoring non-invasively the action potentials of electrogenic cells in-vitro with high spatial resolution. The approach relies on the “mirror charge” effect to transduce transmembrane ionic currents into the motion of fluorophores in a separated microfluidic compartment. The VICE biosensor consists in a thin silicon nitride (Si₃N₄) membrane (thickness 100 - 500 nm) decorated with pass-through gold nanoelectrodes in floating configuration. Electrogenic cells such as neurons or cardiomyocytes are cultivated on the Si₃N₄ membrane and adhere strongly on the gold nanoelectrodes. The other side of the Si₃N₄ membrane is in contact with a microfluidic chamber loaded with charged fluorescent dyes. When cells fire action potentials, the gold nanoelectrodes become polarized and the fluorescent dyes in the microfluidic compartment move according to the generated electric field. Thus, the fluorescent optical intensity under each gold nanoelectrode is directly proportional to variations of the membrane potential of the adhering cell above. By employing high resolution cameras to detect variations of fluorescence intensities under each gold nanoelectrode, the action potentials of thousands of cells can be monitored accurately and non-invasively. In fact, the key advantage of the VICE concept is that the fluorescence dyes are completely separated by the cells thanks to the Si₃N₄ membrane. Thus, cells remain in physiological conditions and can be measured in long-term experiments.

1) M. Dipalo et al., Nature Nanotechnol., 2018
2) M. Dipalo et al., Science Advances, 2021
3) A. Barbaglia et al., Advanced Materials, 2021

Thin-film polymer microelectrode array (MEA) has emerged as an increasingly significant tool for neuroscience by enabling the measurement of neuronal activities through a more mechanically compliant substrate. The miniaturization of the MEA, which includes high electrode densities and thin encapsulation/substrate layers, is essential for achieving the desired spatial resolution and mechanical compliance. However, the miniaturized MEA sizes, along with the interest of recording neuronal signals in a wide frequency band, lead to the potential frequency-dependent crosstalk among the densely packed microelectrode and interconnects, which can cause severe interference in the signal recording, especially for polymer MEAs. To date, how device parameters affect this crosstalk in polymer MEAs remain poorly studies. In this work, the crosstalk between two adjacent microelectrodes in a thin Kapton thread is modelled using equivalent circuits, then validated with experimental results. Experimentally, crosstalks are measured between two microelectrodes distanced with a different gap, encapsulated by a SU8 layer of different thicknesses and fabricated when placed in different environments (dry, wet, vs. wet with different load resistances). Finite element analysis (FEA) simulation are then utilized to explore the crosstalk in more aggressively scaled polymer electrode threads. This study sheds light on the dependence of the crosstalk in polymer MEAs on a variety of important device parameters and provides the guidelines to the design of thin polymer MEAs for high-quality neural signal recording.

Over 200 million wearables were shipped in 2020 with the number of shipped devices likely to increase to over 700 million by 2026 [1]. Wearables are being used for a range of applications from human health monitoring, to lifestyle organizing. The rapidly increasing demand for wearable devices come at a time when environmental and interplanetary pollution are at an all-time high. It is becoming ever-more necessary to consider the sustainability and life-cycle of emerging wearables. To this end, the amount of electronic waste (e-waste) produced in 2020 was ~50 million tons with up to 80% of that waste expected to reach landfills [2]. Other devices such as medical implants remain in patients or require risky second surgeries to remove when their use is complete. The development and integration of degradable materials for wearables can facilitate the decomposition of electronic devices when they are no longer needed. This talk focuses on the use of bioresorbable materials to achieve transient flexible electronics for medical applications, including devices for use underwater and as implants. The talk will include a discussion about the use of natural materials, and resorbable conductive materials for transient electronics. An evaluation of their biocompatibility, moisture permeability, and biodegradation pathways will be presented.

[1] mordorintelligence.com
[2] thebalancemb.com

The COVID-19 pandemic has highlighted the need for rapid and sensitive protein detection and quantification in simple and robust formats for widespread point-of-care applications. We here introduce a modular nanobody-functionalized organic electrochemical transistors (OECT) architecture that enables rapid quantification of single-molecule-to-nanomolar levels of specific antigens in complex bodily fluids.¹ The sensors combine a new solution-processable organic semiconductor material in the transistor channel and the high-density and orientation-controlled bioconjugation of nanobody–SpyCatcher fusion proteins on disposable gate electrodes. They provide results after 10-min of exposure to 5 μL of unprocessed samples, maintain high specificity and single-molecule sensitivity in human saliva and serum, and can be reprogrammed to detect any protein antigen for which nanobodies exist. We demonstrate the use of this highly modular platform to detect green fluorescent protein (GFP), SARS-CoV-2 and MERS-CoV spike proteins, and for the COVID-19 screening of unprocessed clinical nasopharyngeal swab and saliva samples with a wide range of viral loads.

References
1. Guo, Keying, et al. Rapid single-molecule detection of COVID-19 and MERS antigens via nanobody-functionalized organic electrochemical transistors. Nature Biomedical Engineering (2021): 1-12.

S-layer proteins form the outermost cell envelope component in a wide range of bacteria and archaea [1]. They can be considered one of the most abundant biopolymers on Earth. In addition to the surface of bacterial cells, S-layer proteins have the natural ability to reassemble into crystalline monomolecular arrays on solid supports, at the air-water interface, on planar lipid films and liposomes. Recently, we have shown that the S-layer protein SbpA from Lysinibacillus sphaericus CCM2177 can be used to disperse and functionalize pristine or oxidized multi-walled carbon nanotubes (MWNTs) by fully coating them [2,3].
This presentation summarizes the covalent and non-covalent modification of MWNTs, characterizes the highly ordered helical arrangement of the S-layer proteins, but also lattice defects at kinks and describes the formation of caps on closed nanotubes. In addition, using the recombinant fusion protein rSbpA_31-1068GG (consisting of the SbpA S-layer protein and two copies of the IgG binding region of protein G) as a proof-of-concept, the introduced functionality could be confirmed by visualizing bound gold-labelled antibodies following a helical path around the nanotubes. Moreover, SbpA coated MWNTs were silicified with tetramethoxysilane (TMOS) in a mild biogenic approach. As expected, the thickness of the silica layer could be controlled by the reaction time. Since S-layer proteins have already demonstrated their capability to bind (bio)molecules in dense packing or to act as catalytic sites in biomineralization processes the successful coating of pristine or oxidized MWNTs has the potential for the development of new materials, such as biosensor surfaces. Key to such developments are S-layer fusion proteins, which - as shown here too - have retained the natural self-assembly properties of wild-type proteins, but are additionally equipped with specially tailored bio-reactive domains that enable a highly specific and sensitive functionalization of surfaces.

1. Sleytr, U.B.; Schuster, B.; Egelseer, E.M.; Pum, D. S-layers: principles and applications. FEMS Microbiol Rev 2014, 38, 823-864, doi:10.1111/1574-6976.12063.
2. Breitwieser, A.; Siedlaczek, P.; Lichtenegger, H.; Sleytr, B.U.; Pum, D. S-Layer Protein Coated Carbon Nanotubes. Coatings 2019, 9, 492, doi:10.3390/coatings9080492.
3. Breitwieser, A.; Sleytr, U.B.; Pum, D. A New Method for Dispersing Pristine Carbon Nanotubes Using Regularly Arranged S-Layer Proteins. Nanomaterials-Basel 2021, 11, doi:10.3390/nano11051346.

Organic electrochemical transistors (OECTs) based on the conducting polymer poly(3,4 ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS) allow for highly efficient bioelectronic interfaces which can transduce biological signals with high gain.¹ Due to their low operation voltage, high transconductance and biocompatibility, ² OECTs have been successfully employed for the detection of biochemical analytes and the impedance sensing of living tissue.³ Despite these promising applications, different studies demonstrate that the OECT gain is limited to the low frequency regime, ⁴ and a quantitative study on the transistor amplification in the frequency spectrum relevant for biosensing is still lacking.
To overcome the issue, we introduce a model experiment where we simulate the detection of a single cell by the impedance sensing of a dielectric microparticle. The microparticle is attached to an atomic force microscopy cantilever to have a refined control of its positioning on the device channel. Measurements are performed with both an OECT and a PEDOT:PSS microelectrode to study the impact of the transistor amplification on the device sensitivity. We interpret the experimental results with a mathematical model which relates the OECT gain to the applied frequency and the device geometry. We use this model as a guideline for the design of an optimized device, and we perform an in vitro experiment where we sense the impedance of a single cell with both an OECT and a PEDOT:PSS microelectrode.
By comparing the experimental sensitivities, we observe a significant gain for the transistor structure, thereby demonstrating the advantages arising from the OECT amplification in high precision bioelectronic impedance sensing.

References:
[1] Khodagholy, D. et al. High transconductance organic electrochemical transistors. Nat. Commun. (2013) doi:10.1038/ncomms3133.
[2] Bonafè, F. et al. Charge carrier mobility in organic mixed ionic-electronic conductors by the electrolyte gated van der Pauw method, accepted on Adv. Elect. Mat. (2021)
[3] Hempel, F. et al. PEDOT:PSS organic electrochemical transistors for electrical cell-substrate impedance sensing down to single cells. Biosens. Bioelectron. 180, 113101 (2021).
[4] Wang, N., Liu, Y., Fu, Y. & Yan, F. AC Measurements Using Organic Electrochemical Transistors for Accurate Sensing. ACS Appl. Mater. Interfaces 10, 25834–25840 (2018).

Electrolyte-gated organic field-Effect transistors (EGOFETs) are promising electronic devices for application as biosensors. Using organic semiconductors as active materials enables developing biocompatible, low-cost and highly sensitive devices for biorecognition events. Biosensing events modify the charge and/or specific capacitance of the biolayer/electrolyte interface at the gate electrode or semiconductor interfaces, resulting in the alteration of the semiconductor's conductivity, hence the electric current flowing through the device. EGOFETs can also be used to record the electrical activity of excitable cells since a slight potential variation at the gate electrode or semiconductor surface can lead to a shift into the current flowing through the transistor^1,2. Despite their wide use and potential, the theoretical modelling of the EGOFET biosensor still lacks a proper understanding of several of the experimental features observed. The main reason is the use of theoretical models borrowed from the analysis of solid-state devices like MOSFETs and TFTs, which lack the physics of liquid electrolytes present in EGOFETs.

In the current work, we present the theoretical modelling of EGOFET biosensors in the Nernst-Planck-Poisson and drift-diffusion framework. In the present approach, we offer a physical description of the coupling of the electrolyte and the semiconductor through its interface, retaining the entire physics of the formation and evolution of the electrical double layers. We analyze the voltage and charge distributions across the EGOFET devices and explore how the variations of the interfacial charge or the specific capacitances at the electrolyte interfaces during a biorecognition effect affect them. Moreover, we investigate the current-voltage characteristics of the devices predicted in this framework and propose a generalized phenomenological model for its description. Finally, and based on the phenomenological model proposed, we propose an interpretation technique of experimental biosensor data based on the analysis of the conductivity vs gate voltage function, which offer significant advantages with respect to the analysis of current-voltage transfer curves, common in the field at present.



¹E. Macchia, R. A. Picca, K. Manoli, C. Di Franco, D. Blasi, L. Sarcina, N. Ditaranto, N. Cioffi, R. Österbacka, G. Scamarcio, F. Torricelli and L. Torsi, "About the amplification factors in organic bioelectronic sensors," Mater. Horizons, vol. 7, p. 999–1013, 2020.
²A. Kyndiah, F. Leonardi, C. Tarantino, T. Cramer, R. Millan-Solsona, E. Garreta, N. Montserrat, M. Mas-Torrent and G. Gomila, "Bioelectronic Recordings of Cardiomyocytes with Accumulation Mode Electrolyte Gated Organic Field-Effect Transistors," Biosens. Bioelectron., vol. 150, p. 111844, 2020.

Wearable strain sensors have long been a prominent member of the biomedical sensing devices, however, their applications are mostly hindered by their low sensitivity (gauge factor of at most 32 at subtle strains as caused by most of the physiological motions), as well as insufficient stability. In order to overcome such shortcomings, we have focused on development of a nanoporous, highly stretchable styrene-butadiene-styrene (SBS) substrate via electrospinning, to provide nanofibrous, interconnected pathway for a conductive network. Further, a novel approach consisting of simultaneous ultrasonic-assisted atomization and vacuum-assisted filtration was taken to carefully deposit suspensions of two types of conductive 2D materials, graphene and MXene with varying ratios, onto the surface of each fiber within the interlocked network. Such approach managed to guarantee fiber decoration, instead of forming a blanket coating on the whole surface of electrospun membranes, and to preserve the nanofibrous network that contributes to both high sensitivity and ultra stretchability. Cellulose nanocrystals (CNC) were used both as a surfactant in the liquid phase to assist 2D materials dispersion and as a compatibilizer in solid phase to act as nano-stitches, consequently enhancing the interfacial bonding between the fillers and the SBS substrate, and providing long-term stability. In the meanwhile, in an optimal concentrations which includes equal contents of graphene and MXene, each of the conductive fillers play a vital role in formation of the conductive network and its ultimate reversible disconnection when exposed to subtle motions; graphene’s larger flakes provide mechanical strength by supporting the conductive framework, develop conductive interconnections for smaller MXene flakes, while they contribute to stability and easy slippage of the fillers over one another due to their inborn lubricity effect. On the other hand, smaller, yet metallic conductive MXene flakes form the conductive network at much lower filler contents (3.9 wt.% in total), while their irregular, more brittle nanoparticles with random morphologies contribute to the formation of small brittle structures that can respond to smallest of strains. The chemical, interfacial bonding between CNC, SBS and the conductive fillers were studied and verified by Fourier-transform infrared spectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) analyses, while the scanning electron microscopy (SEM) micrographs could prove the formation of a uniform, agglomerate-free, hybrid conductive network on each fiber of the interlocked network. Results of the tensile and dynamic mechanical analysis (DMA) tests, indicated the successful effect of both CNC and graphene in providing a mechanically robust conductive network with up to 171% and 167% increase in yield strength and elastic modulus, respectively. Moreover, the hybrid sensors, especially the one containing the optimal concentrations of fillers, showed the highest reported gauge factor of 68 for small strain regions, while the same factor went up to even 430 for higher strain regions, which is over 50% higher than the best value reported in the literature. Cyclic loading/unloading tests were carried out on the samples, the results of which indicated the effectiveness of CNC and graphene’s role in providing low hysteresis and stabilizing the conductive network over the long run. Results of the actual sensing performance of the samples indicated highly sensitive and repeatable detection of phonations, respiration patterns and muscle movement as physiological motions, thanks to the formation of the robust, reversibly disconnectable conductive network and the stabilization provided by the compatibilizer and the processing technique.

Because biosensors can be designed with a wide array of materials, device architectures, and used in a wide array of sensing environments, the rapid development and optimization of a biosensors is particularly amenable to automated high throughput testing. We have devised a screening system to rapidly perform electrochemical device testing in an array of sensing environments. Organic mixed electronic/ion conductors are emerging as an important material platform for applications diverse as energy storage, neuromorphic computing and organic electrochemical (OECT) biosensors. Unlike the related organic semiconductors, OECTs typically operate as bulk devices, in intimate contact with electrolyte. Therefore, their electronic and ionic conductivity is intimately linked to their swelling by both electrolyte and compensating ions. Insight into the impact of swelling on the fundamental operation of OECTs can be obtained by varying the polarity or dielectric constant of the solvent and by selecting a different ion from the Hofmeister series; however, these studies are rarely done due to their tedium. As a proof-of-concept we have deployed our automated measurement system to rapidly test OECT devices in multiple electrolytes. We compare the solvent and ion sensitivity of the prototypical PEDOT:PSS polymer semiconductor to a novel oligo(ether)-functionalized propylenedioxythiophene (ProDOT)-based copolymer[1] in a standard OECT architecture. When applied to complete sensors, the system enables testing against multiple analyte concentrations with varied interfering species. When combined with automated device fabrication, automated testing will enable machine-guided optimization of complete sensor architectures.
[1] Savagian et al. Adv Mater 2018, doi: 10.1002/adma.201804647

This research investigates the effects of Prednisone on the attachment of normal epithelial cells (HaCAT) and cancerous cells (A431) by electric impedance measurement. An alternating signal is applied to a series of electrodes on the bottom of cultureware on which cells were seeded. The impedance (resistance and capacitance) is recorded in real-time and corelated to cell spreading, cell-to-cell, and cell-to-substrate attachment. The real-time resistance and the capacitance were examined to infer the effects of prednisone on HaCAT and A431 cells. In harmony with prior work on these cells, it was observed the resistance increases with time and the capacitance decreases with time for both cell types. And consistently, a larger resistance and smaller capacitance were measured for A431 cell compared with HaCAT cells. The impedance data analysis indicates that Prednisone at applied doses does not have a significant effect on the impedance of HaCAT cells over a long time. The impedance data exhibits that Prednisone may result in partial detachment and reattachment of A431 cell-to-cell bonds, indicating cellular matrix restructuring.

Organic electrochemical transistors (OECTs) are promising devices for a wide variety of biological applications, as they exhibit a high transconductance at low operational regimes, and can mimic ion doping profiles of biochemical signals for artificial synapse applications. However, to our knowledge, the asymmetric nature of an OECTs transient drain current response to a uniform gate voltage pulse has not been addressed adequately, although it is apparent across devices shown in literature. In this work, we seek to analyze this asymmetric transient response, as well as hysteresis in the transistor’s characteristic curves, to gain a better understanding of the device physics of OECTs. We fabricated PEDOT:PSS-based OECTs with different configurations and dimensions, and took transfer and output characteristics, as well as tested the transient behavior of the device. The OECT under consideration showed a pinch off voltage of 0.54V, and a process transconductance parameter of 0.89 mA/V². A uniform pulse of 100mHz frequency, alternating between voltages -0.5V and +0.5V was applied to the gate terminal of the OECT with a source-drain voltage of 0.8V. The resulting drain current response was seen to have an asymmetric shape, i.e. for the falling edge of input gate voltage pulse, we witnessed a gradual increase in drain current magnitude (3.0 s), whereas we observed an abrupt decrease in drain current magnitude for the rising edge (0.4 s). This is a landmark observation in most OECTs published in literature, though not thoroughly explored.

We hypothesize that the interplay between concentration gradient (electrolyte to channel) and influence of applied voltage on the dedoping cations, alters the rate of cation movement in and out of the semiconductor channel. This consequently affects the rise and fall time in drain current response, ultimately giving rise to hysteresis in the characteristic curves and an asymmetric transient response. We model the components of the OECT, namely the gate electrolyte, its interface with the active channel (in this case, PEDOT:PSS), and the channel itself using resistances, capacitances, and a diode. Using device equations, characteristics, and dimensions of the devices, we can accurately predict the drain current response for any voltage input or shape (absolute error of 5.35% in simulated output characteristics). We argue this model can be applied to OECTs with different geometries and materials. Further, using discrete electrical elements in the model allows us to isolate how the OECT components affect the overall device performance. This can be a powerful tool for better design of future OECTs, and for more facile implementation of OECTs into more complex, higher order circuitry, which requires knowledge of device behavior at all points of operation.

An epoxy polymer, SU-8 shows important potential for fabrication of high aspect ratio of micro/nanostructures scaffolds for lab-on-a-chip devices. In particular, this polymer has been used as an impressive platform for the development of various smart biomedical devices owing to its excellent optical and mechanical properties, as well as chemical stability. Whilst SU-8 properties combined with its biocompatibility facilitate its application in bio-related material interfaces, still, how SU-8 physicochemical properties affect bacteria-surface interaction has not been properly evaluated so far.
In this work, we tailor SU-8 surface properties to investigate single cell motility and adhesion of Xylella fastidiosa bacteria. Different SU-8 samples have been prepared using UV illumination, thermal processing and oxygen plasma treatment. Atomic Force Microscopy and X-Ray Photoelectron Spectroscopy were used to determine nanoscale surface properties; in vitro studies at the level from single cell to biofilm formation were carried out with Confocal Laser Scanning Microscopy (CLSM). The mean velocity and displacement of single cells have been extracted from CLSM tracking information data and the architecture of biofilms as well as surface coverage are compared for different samples. We observed significant differences in bacterial cell motility, for both speed and direction, as well as adhesion and biofilm architecture on SU-8 as nanoscale surface property changes. Larger density of carboxyl groups in SU-8 plasma-treated surfaces provide enhanced cell motility, while denser biofilms are found in untreated SU-8. Our results can be interpreted based on how bacterial pili interaction with the surface takes place, therefore providing different bacterial motility and cluster assemby regimes.
These results advance our understanding of the role of surface functional groups and wettability on bacteria-surface interaction for biosensing and bioelectronics applications; additionally, they might indicate new strategies to prevent microbial adhesion and, consequently, biofilm development of pathogenic species.

Optogenetics is a powerful method to modulate neuronal activity with light¹. Currently used optogenetic light sources such as lasers, LEDs, and projectors are limited in spatial resolution and typically require sophisticated, bulky and expensive experimental setups. Here, we propose using smartphone displays as simple, low-cost light sources that provide high spatial resolution for optogenetic stimulation of larval and adult stages of Drosophila melanogaster (fruit fly)².
We developed a smartphone app that allows spectral, spatial, and temporal control over the light emitted by the display and used this to deliver light patterns to induce activation and inhibition of several sets of neurons, including motoneurons, muscles, all sensory and class IV multidendritic neurons using different light-sensitive proteins (UAS-CsChrimson, UAS-ChR2^XXL, UAS-GtACR1 and UAS-GtACR2). Using, e.g., the green/red light-sensitive CsChrimson expressed in the muscles of Drosophila larvae, we detected a strong muscle contraction in response to stimulation with green, red, and white light of around 2-6 μW/mm² intensity. We also used fine patterns of light to constrain larval movement within a maze pattern or guide larvae through a disk of light. We demonstrate the suitability of smartphones as a simple testbench for a wide range of standard optogenetic experiments in both flies and larvae. In order to precisely determine the optical power density of the display also for complex light patterns, we developed a routine to simulate the spatial light distribution. This tool improves our understanding of the larvae’s light-induced behaviour and leads to enhanced targeting of both individual and groups of larvae. We expect this low-cost test environment may be extended to other invertebrate species or adopted for use in teaching labs.
1. Deisseroth, K. Optogenetics: 10 years of microbial opsins in neuroscience. Nat. Neurosci. 18, 1213–1225 (2015).
2. Meloni, I., Sachidanandan, D., Thum, A. S., Kittel, R. J. & Murawski, C. Controlling the behaviour of Drosophila melanogaster via smartphone optogenetics. Sci. Rep. 10, 17614 (2020).

Recently, skin mountable wearable devices have gained much attention due to their non-invasive usage and wearer comfort for health care monitoring. These devices are generally used for applications such as pulse detection and e-skin application. For instance, monitoring pulse waveform detected from the wrist or neck artery can provide information on cardiovascular abnormalities such as arterial fibrosis or hypertension. The requirement for a high-performance flexible pressure sensor is good sensitivity, low power consumption, and instantaneous response for effective human-machine interfacing. In general, pressure sensors can be categorized by types of operations into piezoresistive, capacitive, piezoelectric, triboelectric, etc. Since all of these mechanisms require one flexible substrate, merging different sensing mechanisms into one multi-mechanism sensor can compound the advantages and minimize the shortcomings of these various modes of operation.
In this study, the design parameters were optimized to realize a breathable, multimodal pressure sensor consisting of piezoresistive, capacitive, and strain gauge sensing elements for precise monitoring of arterial pulse waveform. Using finite element analysis (commercial software COMSOL), simulation studies were carried out on micro-feature design parameters, such as pyramid angle, base size, and number density to find the design rules to achieve high sensitivity for the piezoresistive mode of the sensor. Also, based on finite element analysis of structural deformation, the rule for a micropatterned dielectric layer for the capacitive sensor has also been studied. These design rules yield a compact multi-mechanism sensing platform where each part has been fabricated separately. Moreover, fabrication of breathable polymeric substrate has been accomplished by methods such as electrospinning, sacrificial template, and electrostatic spray deposition to ensure long term comfortable wearability of the device. Finally, the conductive sensing material was realized via bi-polar electrochemistry to deposit porous graphene on the polymeric foundation for the piezoresistive sensor. The simulation results state that lower number density, smaller feature size, and an angle of about 50 degrees of microfeatures achieve the highest sensitivity. Furthermore, the fabrication of the multi-mechanism sensor followed the standard microfabrication techniques including photolithography and transfer printing method to integrate heterogeneous elements into the sensor. The detailed results will be discussed during the presentation.

Keywords: Wearable pressure sensor, pulse, simulation, bipolar electrochemistry, graphene, photolithography, transfer printing, finite element analysis, modeling.

Advanced brain imaging techniques are crucial in neuroscience research as well as in clinical diagnosis. Optical microscopy enables the targeting of specific molecules in the brain and provides a high spatial resolution. On the other hand, spectroscopic techniques like magnetic resonance imaging (MRI) can access deep regions of the brain over a large area and identify their functions. Additionally, electrical readout through neural electrodes is indispensable in measuring their activity. It is important in several applications, for example, in mapping different functions to different regions of the brain. Clinically, it is utilised in studying the initiation and spreading of seizure like activities. Unfortunately, simultaneous brain imaging and electrophysiology is challenging. Firstly, conventional electrodes are non-transparent, thus inhibiting optical imaging. In case of MRI, this is further compounded by the possibility of heating caused by eddy currents in metal electrodes. Mismatch between the magnetic susceptibilities of common electrode materials and the surrounding tissue also results in significant artefacts due to loss of signal. In this regard, conducting polymer electrodes are prospective alternatives since their compositions are closer to biological tissues. PEDOT:PSS, one of the most widely used conducting polymers, has been used in neural electrodes to improve their signal to noise ratio. This can be achieved by virtue of the volumetric capacitance effect in the conducting polymer which significantly reduces the electrode impedance. Here, we present PEDOT:PSS based versatile transparent microelectrode arrays (MEA). The glass substrate-based MEAs are immune to laser-induced artefacts and enable simultaneous Ca²⁺ imaging with electrophysiology in vitro. They are also compatible with the state-of-the-art optical imaging as well as super resolution microscopy techniques. Further, in the form of conformable electrocorticography arrays, the PEDOT:PSS electrodes can be coupled with optical brain imaging techniques. They allow MRI along with simultaneous electrical interrogation through stimulation and recording.

Miniaturization and minimization of mechanical mismatch in neural probes have been two well-proven directions in suppressing immune response and improving spatial resolution for neural stimulations and recordings. While the high impedance brought by the miniaturization of electrodes have been addressed by using conductive polymers (CPs) coatings in multiple reports, the stiffness of such coatings remains orders of magnitude from the brain tissue. In this study, we present a highly flexible microelectrode array neural probe of 8 gold electrodes with electrodeposited hydrogel coatings poly(2-hydroxyethyl methacrylate) (pHEMA) and conductive polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), with a cross-section area at only 300 μm x 2.5 μm. The porous and sponge-like pHEMA provided excellent cell adhesion properties and bridged the mechanical mismatch between the probe and the brain tissues. Besides, the PEDOT:PSS coating provides a low interfacial impedance that enhance the signal-to-noise ratio and allow the microelectrodes array to be engineered for both recording and stimulation purposes. The signal-to-noise ratio increases 70% while comparing with bare gold electrodes, and the charge injection capacity of the probe achieved 2.2 mC/cm². In vivo testing of microelectrode arrays implanted in rat hippocampus revealed that the microelectrodes show high signal-to-noise ratio and excellent charge injection capacity, providing a robust and low-cost solution in the brain interfaces problem.

A long-term, nondestructive monitoring of cells is significant for understanding different cellular processes and functions. However, traditional methods are limited to a certain range of testing conditions and may reduce cell viability. Furthermore, the ability to demonstrate cell recovery and pore resealing after electroporation for long periods remains elusive due to difficulties in cell maintenance. Here, we develop a small-size, multiple-pulse electroporation system for monitoring cell recovery for an extended period of time with the use of low bias voltage pulses. We demonstrate that our system is able to preserve cell viability during the electroporation of cells and achieve real-time cell monitoring during the recovery period. Theoretical studies elucidate the origin of the pulsing-facilitated change in recovery time. Additionally, our method does not require specialized equipment, which allows for easy access across laboratories and medical facilities.

In this research, we report ultra-thin gold-conducting polymer hybrid electrodes and their applications to flexible semi-transparent human skin interfaces. Ultra-thin hybrid electrodes were fabricated by thermal evaporation of a very thin gold layer on crystalline poly(3,4 ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) film, leading to low sheet resistance (39.13 Ω/sq) as well as substantial optical transparency (56%) at the visible light range. Subsequently, semi-transparent electrodes were realized on flexible top-contact OECT devices which exhibited decent optical transparency, high transconductance (1 mS), and operational stability even at the highly bent state. Finally, it was successfully demonstrated that these semi-transparent flexible OECTs were mounted on human skin for electromyography recording.

Smart Wound dressings with electrically controlled drug release and real-time monitoring can accelerate wound healing. Flexible electronics integrated with structurally and mechanically tissue-mimicked electrodes can not only provide high filling space for drug loading, but also can permit a seamless and biocompliant contact with skin to reduce the resistance for drug delivery and electrical signal transduction. Herein, an antibacterial hydrogel electrode is designed and integrated into a wireless system composed of a multimodality readout IC and an electrical current stimulator for electrically-controllable anti-inflammatroy drug release and uric acid (UA) detection. The doubly crosslinked microcapsules composed of carboxymethyl-hexanoyl chitosan-doped poly(3,4-ethylenedioxythiophene) and silk, called PEDOT:CHC/silk, are served as hydrogel electrodes to demonstrate tissue-like mechanical properties, electrochemical activity, and antibacterial ability. Active loading of ibuprofen (Ibu) in the PEDOT:CHC microgels allows large amount of drug loading, whereas the incorporation of silk leads to densely crosslinking of the microgels, in turns resulting in a precisely electrically-controlled release under the application of both DC (1-5V) and cyclic voltametric (CV) electrical stimulation. With the integration of hydrogel electrodes into a wireless multimodality chip fabricated in a 0.18um CMOS process, a repeated burst-to-zero-to-burst and UA detection through CA/CV is demonstrated. This smart wound dressing with highly biological and electrical compatibility is expected to provide more precise wound care.

Organic electrochemical transistors (OECTs) have attracted attention in recent years due to their high transconductance, low operating voltage, and compatibility with aqueous solutions for broad biosensing applications. Especially, OECT-based biocompatible electronic devices enable the monitoring of physiological signals on human skin. Poly-3,4-ethylenedioxythiophene:poly-4-styrenesulfonate (PEDOT:PSS) is a typical material acting as the active channel layer in OECTs. However, the poor electrical conductivity of pristine PEDOT:PSS diminish the lifetime and restrict the application scope of the electronic device systems. Although some additives in PEDOT:PSS have been proposed to enhance the conductivity, those additives are not proved to be non-toxic or biocompatible. Besides, 4-dodecylbenzenesulfonic acid (DBSA), glycerol, dimethyl sulfoxide (DMSO), and ethylene glycol (EG) have been claimed to be biocompatible and reported to obtain PEDOT:PSS based OECTs with higher performance, however, their contribution to the enhancement of OECT performance is limited. It is worth investigating whether there is any intrinsically biocompatible additive that is more effective. Herein, a biocompatible ionic liquid [MTEOA][MeOSO₃] is proposed as a biocompatible additive to enhance the performance of PEDOT:PSS based OECTs. The influence of [MTEOA][MeOSO₃] on the morphology, conductivity, and the redox process of PEDOT:PSS during electrochemical doping/de-doping processes are explored. The biocompatible P+[MTEOA][MeOSO₃] (PEDOT:PSS mixed with [MTEOA][MeOSO₃]) film as OECT channel layer exhibits enhanced transistor characteristics, including higher transconductance, excellent switching cycling stability, and low energy consumption. The electrophysiological (ECG) signals recording ability of the P+[MTEOA][MeOSO₃] based OECT is explored, ECG signals from the hand and heart of a volunteer are recorded successfully. Further, the P+[MTEOA][MeOSO₃] film is employed as the sensing component of a pressure sensor, and the integration of the pressure sensor with the OECT shows interesting tunable pressure sensitivity by gate bias and is demonstrated to monitor physiological signals on human skin as a wearable electronic device. In addition, the P+[MTEOA][MeOSO₃] film also shows robust resistance to physical deformation and desired compatibility with flexible substrates as the active channel layer of the flexible OECT.

Organic electrochemical transistors (OECTs) transduce ionic fluxes into electronic signals with exceptional performance.^[1] It has been shown that OECTs comprising channels made of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) show stable operation up to ~21 days.^[2] These transistors, however, operate in depletion mode, which show inferior ON/OFF ratios at low bias and are always ON, having adverse influence on power consumption. These are drawbacks hindering the practical use of these devices for long-term, biological sensing applications.
On the contrary, semiconducting polymers give rise to accumulation (enhancement) mode OECTs with inherently high ON/OFF ratios and low power consumption, and, as such, they are highly sought after. These polymers should however be stable at ambient and aqueous conditions, typical for biological sensing applications.

A good measure for OECT stability is switching the gate between ON and OFF states while biasing the drain electrode. As such, current degradation, and therefore transconductance loss, is probed. Nonetheless, longer term stability measurements, such as shelf-life stability, have often been overlooked. Recently, a p-type diketopyrrolopyrrole-based organic semiconducting polymer was reported to retain more than 85% its initial transconductance value over ~75 hours exposed to electrolyte.^[3] However, this value was reported for a large radius anion, which is not biologically relevant.
We show that by tuning the solvent mixture composition used to cast a thiophene-based p-type semiconducting polymer film, not only the OECT performance is enhanced but also the device shelf-life stability is significantly improved. The same effect is obtained by the use of a strong Lewis acid in the polymer solution. We find that the solvent additive and the acid both change the film morphology and microstructure, leading to such significant improvements in OECT performance and stability. As such, our work provides insights into structure-property relations of semiconducting polymers for applications in bioelectronics that require high performance alongside long shelf-life.

[1] Rivnay, J. et al. Organic electrochemical transistors. Nat. Rev. Mater. 3, 17086 (2018)
[2] Kim, S.-M. et al. Influence of PEDOT:PSS crystallinity and composition on electrochemical transistor performance and long-term stability. Nat. Commun. 9, 3858 (2018).
[3] Wu, X. et al. Enhancing the Electrochemical Doping Efficiency in Diketopyrrolopyrrole-Based Polymer for Organic Electrochemical Transistors. Adv. Electron. Mater. 7, 2000701 (2021).

In this talk, I will present recent development of materials and fabrication for sensors and electrode arrays for biointerfaces and their in vivo applications.

Deep brain stimulation (DBS) involves the delivery of electrical pulses to the brain via penetrating electrodes. While the mechanism is not well understood, DBS has proven to be a successful clinical approach to treat a variety of neurological disorders. Most recently, it has been shown that resident neural precursor cells in the brain are electrosensitive cells that expand in number, migrate and differentiate in response to stimulation. As such, the potential for electrical stimulation to promote brain repair by harnessing the regenerative properties of neural precursor cells (NPCs) is an exciting area of research. We have shown that metal-based electrodes with optimized electrical stimulation parameters can activate resident NPCs however, conventional rigid, metal-based materials are suboptimal for clinical application. This is due to the mechanical mismatch with brain tissue, poor biocompatibility and high electrode-tissue impedance that can cause damage to both electrodes and tissue during stimulation. Currently, there are numerous soft electrodes designs with good stimulating capacity and similar modulus with neural tissue in the kilopascal range but these are mostly surface electrodes that require sophisticated fabrication and additional implantation techniques due to low modulus. Here, we report a conductive and biocompatible cryogel electrode that has a simple modulus switching mechanism – high stiffness for penetration to brain tissue when dry, then softening to the kilopascal range in response to the wet environment of brain tissue. The material also exhibits high charge storage and injection capacities in brain electrolyte, reducing the interfacial impedance to deliver the required electrical field with ~7 times lower voltage under charge-balanced current controlled stimulation. We have demonstrated successful NPC stimulation using cryogel electrodes resulting in significant NPC expansion and migration of NPCs in ex-vivo brain tissue models. The cryogel material combined with optimized stimulation parameters is a promising approach to be used in DBS to promote endogenous neural repair.
Key words: deep brain stimulation, galvanotaxis, neural stem cells, conductive polymers, neuromodulation

Reliable recording and modulation of excitable tissue using implantable electronic devices have implications in diagnosing and treating many types of diseases. The advent of flexible electronics has enabled new concepts in interfacing devices with soft tissues. However, to date, most flexible electronics achieve mechanical compliance by using substrates composed of thin curable resins or elastomers. These materials are suboptimal for tissue interfacing because they: (1) exhibit Young’s moduli that are orders of magnitude larger than many excitable tissues, such as peripheral nerves and vascular structures; (2) are difficult to integrate with hydrated tissue in vivo. Here we present recent advances in materials and fabrication from our lab to address current limitations in flexible electronics. Specifically, the synthesis and formulation of flexible adhesive hydrogels and transfer printing to create ultracompliant devices to interface with peripheral nerves and cardiac tissues will be described. Details regarding the in vitro and in vivo performance of peripheral nerve interfaces and cardiac monitoring devices will be presented. Future prospective applications for this concept will also be highlighted, too.

The interface between biological cells and non-biological materials has profound influences on cellular activities, chronic tissue responses, and ultimately the success of medical implants and bioelectronic devices. The optimal coupling between cells, i.e. neurons, and materials is mainly based on surface interaction, electrical communication and sensing.
In the last years, many efforts have been devoted to the engineering of materials to recapitulate both the environment (i.e. dimensionality, curvature, dynamicity)¹ and the functionalities (i.e. long and short term plasticity)² of the neuronal tissue to ensure a better integration of the bioelectronic platform and cells.
Here, we present how dendritic spine-like structures can be engineered by means of two-photon polymerization in 2.5 and 3D architectures³. In particular, these structures can be functionalized with ECM proteins and artificial lipid bilayers to emulate the composition of living spines in the neuronal tissue. Moreover, the topographical cues at the spine-neuron interface trigger different cell response in terms of neuronal polarization, network development and synaptic formation in primary and differentiated neuronal cultures.
In this way, both the topology and the material functionalities can be exploited for achieving in vitro biohybrid platforms for neuronal network interfacing.



References
(1) Pennacchio, F. A.; Garma, L. D.; Matino, L.; Santoro, F. Bioelectronics Goes 3D: New Trends in Cell–Chip Interface Engineering. J. Mater. Chem. B 2018, 6 (44), 7096–7101. https://doi.org/10.1039/C8TB01737A.
(2) Lubrano, C.; Matrone, G. M.; Forro, C.; Jahed, Z.; Offenhaeusser, A.; Salleo, A.; Cui, B.; Santoro, F. Towards Biomimetic Electronics That Emulate Cells. MRS Commun. 2020, 10 (3), 398–412. https://doi.org/10.1557/mrc.2020.56.
(3) Pennacchio, F. A.; Caliendo, F.; Iaccarino, G.; Langella, A.; Siciliano, V.; Santoro, F. Three-Dimensionally Patterned Scaffolds Modulate the Biointerface at the Nanoscale. Nano Lett. 2019, 19 (8), 5118–5123. https://doi.org/10.1021/acs.nanolett.9b01468.

Materials and fabrication concepts for the creation of soft electronics coupled with miniaturization of wireless energy harvesting schemes enable the construction of high-performance electronic and optoelectronic systems with sizes, shapes and physical properties matched its biological host^[1]. Applications range from continuous monitors for health diagnosis to minimally invasive exploratory tools for neuroscience^[2]. This talk presents science and engineering approaches for the creation of soft devices with near field power transfer and data communication capabilities^[3] and discusses application in devices for the stimulation of the brain and the peripherals in a range of complex 3D environments and contexts (e.g. social interactions) that cannot be explored with conventional technologies. We introduce a series of advances in subdermally implantable device technologies that follow from developments in materials, electronics and operational concepts that enable digitally controllable subdermal platforms with multimodal optogenetic and electrical stimulation capabilities^[4][5] with the ability to provide stimulus without the physical penetration of the blood brain barrier. Additional to these stimulation capabilities new developments in low power electronics allow for capabilities in recording genetically encoded calcium indicators and physiological states of organs to enable neuronal modulation with high precision and direct feedback in freely moving subjects.^[6] Because of the minimally invasive nature of these tools we show chronic neuromodulation capabilities over months in freely moving subjects. Combined these capabilities elevate device functionality substantially over current tethered platforms enabling fundamentally new approaches in experimental design to uncover the working principle of the central and peripheral nervous system and show promise to advance digital medicine approaches.
[1] P. Gutruf, J. A. Rogers, Curr. Opin. Neurobiol. 2018, 50, 42.
[2] P. Gutruf, C. H. Good, J. A. Rogers, APL Photonics 2018, 3, 120901.
[3] P. Gutruf, V. Krishnamurthi, A. Vázquez-Guardado, Z. Xie, A. Banks, C.-J. Su, Y. Xu, C. R. Haney, E. A. Waters, I. Kandela, Nat. Electron. 2018, 1, 652.
[4] P. Gutruf, R. T. Yin, K. B. Lee, J. Ausra, J. A. Brennan, Y. Qiao, Z. Xie, R. Peralta, O. Talarico, A. Murillo, S. W. Chen, J. P. Leshock, C. R. Haney, E. A. Waters, C. Zhang, H. Luan, Y. Huang, G. Trachiotis, I. R. Efimov, J. A. Rogers, Nat. Commun. 2019, 10, 5742.
[5] J. Ausra, S. J. Munger, A. Azami, A. Burton, R. Peralta, J. E. Miller, P. Gutruf, Nat. Commun. 2021, 12, 1968.
[6] A. Burton, S. N. Obaid, A. Vázquez-Guardado, M. B. Schmit, T. Stuart, L. Cai, Z. Chen, I. Kandela, C. R. Haney, E. A. Waters, H. Cai, J. A. Rogers, L. Lu, P. Gutruf, Proc. Natl. Acad. Sci. 2020, 201920073.

Developments in imaging techniques accounted for unravelling insights in plant signaling at the molecular level, elucidating the role of transporters, proteins and ions during plant growth, development and stress. However, the imaging technological improvements did not go hand in hand with stimulation approaches, as important molecular compounds are currently delivered through low resolution approaches, as foliar spraying or soaking. Therefore, the need of precise and controllable delivery techniques is evident. In this context, we have developed Organic Electronic Ion Pump (OEIP) that enables electrophoretic delivery of ions in a flow-free manner greatly reducing the imposed shear stress. The delivery channel is based on polyelectrolyte of high fixed charge concentration that prevents backflow of ions minimizing the disturbance of the ionic concentrations in the targeted tissue. Previously, we have demonstrated that miniaturized, capillary-based OEIP can be inserted in intact plant with low invasiveness allowing hormone ions delivery at cellular resolution, demonstrating local and precise electronic control of plant physiology. Here, we report the development of OEIP for implantation in hard tissue of plants, such as stem, hypocotyl or succulent leaves. The mechanical properties of the capillary-based OEIPs have been significantly enhanced thanks to the use of thin polyimide coating. These devices were applied in the model plant species Arabidopsis to deliver abscisic acid that controls plant response to environmental stresses. The device targeted the plant vascular tissue for systemic control of plant transpiration. Furthermore, OEIPs were used to gain insight on the high drought tolerance of the tropical plant Kalanchoe Blossfeldiana.

The development of bioelectronic technologies is driven by biomedical applications for new therapeutic and diagnostic tools. However, there are many important questions in plant biology that remain unanswered due to lack of sophisticate tools. Furthermore, the climate change and growing population calls for plants with increased tolerance to biotic and abiotic stress and plants with higher productivity. In my group we are developing organic bioelectronic technologies for sensing and actuation in plants that overcome limitations of conventional methods used in plant science. In my talk I will present our recent advancements of interfacing bioelectronic tools with plant model systems. We demonstrate enchanced plant resistance to drought via electronically controlled delivery of biomolecules with the organic electronic ion pump. Furthermore, with OECT implantable sensors we reveal previously uncharacterized sugars dynamics in trees and finally we present a novel bioelectronic platform for stimulation of plant growth. Our results highlight the potential of bioelectronics in elucidating and enhancing plant processes but also for their application in agriculture.

Sensors built on smart, functional materials pave the way for democratized health care by providing high quality personal health data at the point-of-care. In the aftermath of the novel coronavirus pandemic, the need for such technologies is salient. The required materials must be mediators of electronic and ionic transport, mechanically compliant and flexible, and crucially, chemically stable and biocompatible. Hydrogels of semiconducting conjugated polymers (CPs) fit this profile exceptionally well.
PEDOT:PSS (poly(3,4-ethylenedioxythiophene) polymerized with poly(styrene sulfonate)) may be readily gelated by various means [1]; however, so-called interpenetrating networks (IPNs), whereby separate conducting and structural polymers form a homogenous phase, are interesting because of the possibility for orthogonal design of electrical and mechanical properties. This allows for the use of optimized CP formulations with sensor functionality governed by the selection of hydrogel monomers, for instance, by including phenylboronic acid moieties to give selective binding towards diol-containing biomolecules [2].
In this study, we take a simple approach of polymerizing acrylamide monomers mixed with equal parts by weight of PEDOT:PSS from ready-made suspensions. Specifically, we took acrylamide (AAm) as the backbone, 2-acrylamido-2-methylpropanesulfonic acid (AMPS) as a polyelectrolytic mediator, 3-(acrylamido)phenylboronic acid (AAPBA) as a complexing site, and N-N’-methylenebisacrylamide (MBA) as cross-linker. The resulting PEDOT:PSS:P(AAm-co-AMPS-co-AAPBA) hydrogels, prepared as sheets tens of micrometers thick, (de)swelled reversibly in thickness by a factor of ~5 in phosphate-buffered saline (pH 7.4). Conductivities of ca. 50 (dry) and 10 S/cm (swelled, accumulating) were typical. These results indicate that the formation of IPN did not hinder electrical transport in the CP, and their high values compare favorably with previously reported pure PEDOT:PSS hydrogels [3] considering our CP loading.
Cyclic voltammetry revealed the effect of AAPBA as a secondary dopant, evidenced by the appearance of a redox peak that delayed the onset of PEDOT reduction and hastened its re-oxidation. This extended the range of pseudo-capacitance, giving a value of 2.2 F/cm³. Upon exposure to glucose, AAPBA redox activity is suppressed, suggesting that boronic acid is preferentially reduced to boronate by applied potentials, until the formation of boronate esters with addition of glucose shifts the equilibrium back towards boronic acid. Thanks to the high conductivity of our hydrogels, direct use as the channel of an organic electrochemical transistor is possible and an amplified signal from AAPBA-glucose binding was observed. These results indicate the possibility of using PEDOT:PSS:P(AAm-co-AMPS-co-AAPBA) hydrogels for the direct electrochemical detection of glucose concentration at physiologically-relevant levels.

[1] L. V. Kayser et al., Advanced Materials, vol. 31, no. 10, p. 1806133, 2019.
[2] G. Vancoillie et al., Polym. Chem., vol. 7, no. 35, pp. 5484–5495, Aug. 2016.
[3] B. Lu et al., Nat Commun, vol. 10, no. 1, p. 1043, Mar. 2019.

In developing an electrochemical biosensor, the design and fabrication of the bioelectrical interface is important for transducing the adsorption of a target biomolecule on an electrode to an electrical signal. Recently, a poly-dopamine (pDA) film has been attractive for the bioelectrical interface, because it can be easily synthesized with self-oxidation of DA monomers on an electrode;¹ thus, it has been used for many purposes.² Similarly to the pDA film, serotonin (ST) monomers are simply polymerized on the electrode with its self-oxidation in an alkaline solution; as a result, the pST film shows a good biocompatibility and adhesiveness.³ In particular, pST has been reported to be more slowly polymerized than pDA, which can expectedly lead to a smoother and thinner film formation on the electrode. On the other hand, the pDA film is utilized for a molecularly imprinted polymer (MIP)-based biosensor to detect biomarkers as one of the applications.² Also, considering our previous works,⁴ the MIP-based biosensor can detect target biomolecules with high binding affinities by measuring the change in the molecular charges. However, the surface roughness of pDA film may be too large to properly control the thickness and surface roughness of MIP films suitable for biomolecular sizes; therefore, the thin and smooth surface characteristics of pST film are expected as one of the bioelectrical interfaces for the MIP-based biosensor. In this paper, we show the fundamental surface and electrochemical characteristics of pST film for its application to the MIP-based electrochemical biosensor.
The pST film was coated on a gold electrode or a silicon substrate by the electrochemical deposition or the self-oxidation of ST monomers in the alkaline solution (pH 8.5). After that, the thickness and roughness of pST film were measured by atomic force microscopy (AFM), and cyclic voltammetry (CV) was performed to evaluate electrical properties in buffer solutions containing a redox couple. These fundamental characteristics of pST film were strictly controlled by the CV cycles for the electrochemical deposition or the polymerization time for the self-oxidation.
Not only was the thickness of pST film linearly controlled within 5 to 15 nm, according to the CV cycles or the polymerization time, but also the roughness of pST film was much smaller than that of pDA film. Moreover, the pST film was found to be insulative from the CV curve, the surface charge of which varied with the change in pH of the measurement solutions. The insulative film on the electrode was suitable for the bioelectrical interface to control the electrical conductivities, when including cavities like MIP films. Considering the above, the thinner and smoother pST insulative film, compared to the pDA film, is applied to the MIP-based electrochemical biosensor. In the conference we are going to introduce the results about the detection of biomarkers such as peptides with the pST-MIP-based electrochemical biosensor as well.
References
[1] S. Kim et al., Scientific Reports 2016, 6, 1–8. [2] P. Jolly et al., Biosensors and Bioelectronics 2016, 75, 188–195. [3] N. Nakatsuka et al., ACS Nano 2018, 12, 4761–4774. [4] T. Sakata et al., RSC Advances 2020, 10, 16999–17013.

By using flexible and lightweight electronics such as sensors and energy harvester fabricated on the µm-thick polymer film, developing the next-generation wearable electronics with the excellent conformability of human skin is expected¹. One of the important challenges for fabricating the practical electronics device is how to integrate each electronic such sensor, energy harvester, and control unit. Conductive adhesive such as anisotropic conductive film (ACF) is mainly used as a conventional conductive bonding method for the integration of each ultra-thin electronics now. However, such conventional conductive bonding lost flexibility at the bonding area because flexural rigidity gets large along with an increasing thickness.
This research shows the Au-Au direct bonding method by water vapor plasma activation. In this research, evaporated gold electrodes on 2 µm-thick of parylene substrate were used as a bonding target. A gold surface of a thin-film sample had a rough surface (root-mean roughness of 6.3 nm) compare with metal on a Si wafer. There is a simple bonding procedure: firstly, the gold surface was treated by water vapor plasma treatment. Secondly, treated gold surfaces contacted together, and keeping left several time. Then, we achieved direct bonding in the air at room temperature without any adhesive and post-treatment such as annealing and pressing.
The cross-sections of a bonded gold thin film were observed by scanning electron microscope. In the case of a sample bonded by using water vapor plasma, the bonding interface had disappeared and the gold deposited on the separate films had become one. On the other hand, thin-film samples bonded using conventional Ar plasma bonding^2,3, which is used to bond Si wafers, were clearly separated at the interface, and direct bonding of thin-film gold could not be achieved. Therefore, only water vapor plasma bonding achieved direct bonding of gold on thin film.
Moreover, the bonding area maintained excellent flexibility since there is no increase in thickness by the adhesive. In the flexibility test, two kinds of bonding samples were prepared, thin-film samples bonded by using the water vapor plasma and ACF tape. And each bonded sample placed on the plate having a bump of several bending radius. A bonded thin-film sample by water vapor plasma was exhibited excellent conformation even at a 0.5 mm radius, whereas bonded thin-film sample by ACF tape was not conformed at a less than 1 mm radius.
By using a new conductive bonding method using water vapor plasma, we have succeeded in flexibly bonding gold electrodes on a thin film without adhesives. It can be applied to fabricate the integration electronics using the ultra-thin sensor and energy harvester through investigation of the bonding of other metal materials by using water vapor plasma bonding.

1. Y khan, et al. Adv. Mater. 32. 1905279 (2020).
2. E. Higurashi, et al. IEICE Trans. Electron. E100.C, 156–160 (2017).
3. M. Yamamoto, et al. Micromachines, 11, 454 (2020).

Soft magnetic-elastomeric composites are a class of smart materials formed by embedding magnetic particles into non-magnetic elastomer matrix host materials and curing in the presence or absence of a magnetic field. When fabricated into films, magnetic-elastomeric composites can be readily integrated with micro-scale structures to achieve flexible and compact smart sensors. With respect to their magnetic/mechanical properties, magnetic-elastomeric composite films can exhibit rapid and robust mechanical responses to external magnetic fields, which are enabling for wide biomedical applications such as wireless soft robotics, remotely stimulated magnetic actuators, and medical localisation sensors.

One of the key technical challenges in the development of the magnetic-elastomeric materials is to achieve a strong and reversible magnetic response whilst maintaining high and long-lasting mechanical flexibility. The magnetic response is governed by intrinsic material properties, such as B-H behavior and the Young’s elastic modulus. Recent efforts have been centred on the fundamental mechanisms of magneto-mechanical coupling effects (dipole-dipole interactions of isolated magnetic particles) accounting for the static responses subject to external magnetic field, and magnetorheological effects that allow for dynamic changes to the elasticity of the composite material by applying an external magnetic field. It appears that multiple factors could all play vital but sometimes conflicting roles in the material performances, including: (i) the initial properties of magnetic particles and elastomers, (ii) the magnetic conditions for composite curing, (iii) the loading ratio of each component, and (iv) the film thickness. There is a significant need to understand and balance the trade-off effects of each factor to optimize the overall material properties.

Here, we report on the development of a simple, cost-effective, and scalable fabrication method to achieve centimetre-scale, highly flexible magnetic-elastomeric composite films with readily controllable magnetic particle loadings (0- 70 wt%) and film thickness (micron-scale). The composition-dependent magnetic and mechanical properties were explored by investigating a wide range of parameters including magnetic particle loading and film thickness. As a demonstration of their practical value in different applications, the magnetically induced mechanical deformations of the films with different particle loadings, field thickness and external magnetic field were simulated using a computational framework (Ansys Mechanical). Benefitting from their extremely high magnetization and maintained low Young’s moduli, magnetic-elastomeric composite films show large deformation and excellent stability in response to magnetic stimuli. We conclude that soft magnetic-elastomeric composites are very promising for a wide range of biomedical devices.