Symposium F.SM04—Degradable and Self-Healing Electronic Materials for Biological Interfaces

Controlled jumping is a unique motion in nature and robotics to achieve rapid mobility and to avoid obstacles as well as rough terrains. One key challenge is the introduction of a remote powering system for untethered miniaturized robots as they have to work to overcome their own body mass without an internal power system. Toward light-fueled jumping, we synthesize photo-responsive polymer monoliths where spring-like molecular geometry is implemented via self-assembly of liquid crystalline polymer networks (LCNs). Upon light irradiation, the spring-like self-assembled photo-responsive molecules induce non-isometric structures providing unprecedented photomechanical jumping by an instantaneous energy release. The experimental jumping behavior is supported by a finite element method (FEM) simulation for quantitative analysis. The jumping capability of the soft robotic LCN reaches 15.5 body length (BL) height, and 880 BL/s take-off velocity. In addition, we demonstrate rotational axis- and angle-controlled jumping by programming the molecular alignment and macroscopic design. Finally, the controlled light irradiation provides continuous and directional jumping of soft robotic LCNs.

Human machine interfacing is a long challenge for researchers, in last few decades we have witnessed emerging of different materials and electrodes for the purpose. Successful interfacing of human body with machine involves coupling of ionic and electronic signal at the interface. In addition to the successful interfacing of the ionic and electronic signals, any conductive material for biological interfacing should be stretchable, flexible, stable in aqueous or humid environment, bio-compatible and bio-degradable. Developing a single material having all these properties is a challenge by itself. However, conductive polymers are one of the promising materials for this purpose due to their organic carbon-based nature. Over the years, many different types of conducting organic polymers have been emerged using different synthetic organic analogues, however, the development of a synthetic polymer that fits all the above-mentioned criteria is still consider a challenge for researchers. Inspired by natural electron and ion transfer processes mediated mainly by proteins, here we present a novel conductive polymer made out of 100% natural Bovine Serum Albumin (BSA) protein, which is a side product of bovine industry, cheap and available in large scale. The polymer film is free-standing, transparent, stretchable, and highly stable in aqueous environment. Moreover, it is bio-compatible and biodegradable due to its biological nature, the synthesis method is within one pot and energy-efficient process and there is no need for any post-synthetic purification. This polymer film can efficiently record brain (electroencephalogram) and heart signal (electroencephalogram) from the human body in a non-invasive way with several other potential applications. While considering its novelty, our polymer can be considered a new class of materials in the field of bioelectronics.
Keywords: Biological Interfacing, Conductive Polymers, Polymer Film, electroencephalogram, electroencephalogram.

Two-dimensional (2D) materials represented by graphene have been studied for biosensor applications owing to their excellent electronic properties and high specific surface areas. Lipid bilayer biosensors based on the 2D materials as supporting substrates have gained wide interest as a platform for highly-sensitive biosensing with inserted membrane proteins. For stable formation of a lipid film on the surface of 2D materials, it is essential to control the hydrophobicity of the surface which is correlated to the affinity of the surface with the lipid film. Moreover, it is important to control the lateral diffusivity of the lipid membrane for understanding interaction dynamics of biomolecules embedded into the membrane. In this study, to address this, we utilized self-assembled peptides as an adhesive layer for immobilization of planar lipid bilayer on h-BN, an insulative 2D material which is transparent in visible region. In our recent research, we developed a series of peptides which have an ability to form uniform monomolecular thick peptide thin film in a self-assembly manner [1]. More recently, peptides with a repeated amino acid sequence of glycine (G) and alanine (A) inspired by silk proteins have been demonstrated to form stable β-sheet structures on the surface of two-dimensional materials [2]. In this study, we utilized three types of peptides containing additional hydrophilic amino acids with the GA repeat sequence. These peptides formed self-assembled structures on h-BN surface and act as an adhesive layer to form a planar lipid bilayer. Self-assembled peptides were prepared by dropping an aqueous peptide solution onto the surface of transferred h-BN on a substrate of Si/SiO2 or cover glass, and it was incubated at room temperature for 1 hour. Then, planar lipid membranes were prepared by the rupture method, where DOPC vesicle suspension in 10 mM PB was placed on the sample with the self-assembled peptides,, and it was incubated at room temperature for 1 hour or more. The morphology of lipid membranes on the surface was observed by atomic force microscopy (AFM). Furthermore, to investigate the fluidity of lipid molecules in the membrane, DOPC was mixed with 1% 14:0 NBD PE (lipid molecule tagged with a fluorophore). The lateral diffusion constant of the lipid membrane was measured by the photobleaching after fluorescence recovery (FRAP) method. AFM observations showed that lipid bilayer can be formed on a h-BN surface with high coverage, indicating that self-assembled peptides support the lipid bilayer as a molecular scaffold with a controlled hydrophilicity. The FRAP results showed that the diffusion constants of lipid bilayers depend on peptide sequences. These results revealed the importance of the peptide design to control the physical properties of the planar lipid bilayer on 2D material, which could be essential to develop lipid-based biosensors with 2D materials.

Reference
[1] Y. Hayamizu, et al., Scientific rep 2016, 6:33778
[2] P. Li, et al., ACS Appl. Mater. Interfaces 2019, 11, 20670−20677

The fundamental biological process of electron transport (ET) takes place across proteins with common ET pathways of several nanometers. Recent discoveries from the bacterial world push this limit and show long-range extracellular ET over several micrometers. Here, we aim in deciphering how protein-bound intramolecular cofactors can facilitate such long-range ET. In contrast to natural systems, our protein-based platform enables us to modulate important factors associated with ET in a facile manner, such as the type of the cofactor and its quantity within the protein. We chose here the biologically-relevant porphyrin molecule as the electron mediator. We use electrochemical impedance measurements (EIS) as well as three-terminal field effect transistor (FET) measurements to explore the role of the porphyrin variant in mediating ET. Using different porphyrins with different metal centers, or lacking a metal center, we show that the metal redox center has no role in ET, and that ET is mediated solely by the conjugated backbone of the molecule. We further support these results with advanced density functional theory (DFT) calculations of the variants. We discuss several mechanisms accounting to possible contribution of coherent processes during the ET. Our results suggest that our high measured ET efficiency is probably due to coherence-assisted ET mechanism. Our work can help understand the participation of heme molecules in common long-range biological ET and introduce the possibility of using the protein-based platform as a tool for the investigation of different systems.

Medical societies dedicated to treating musculoskeletal diseases are facing challenges due to an unprecedented increase in the aging population around the globe. As such, it is getting more important to develop novel class of materials that could assist the self-healing process of rigid body tissues. Hydroxyapatite (HAp, Ca₁₀(PO₄)₆(OH)₂), one of the most common form of naturally-occurring calcium orthophosphates, is actively investigated as a viable candidate as it integrates easily with the surrounding tissue, induced by its similarity with the main components and structure of human bones and teeth. To this end, it is most desirable that we fabricate HAp-based ceramic-polymer medical nanocomposites that significantly improves the unique mechanical and electrical properties of the host filler particles. However, the interface between the ceramic filler and the polymer matrix is very unstable due to the large discrepancy in their dielectric and bonding characteristics, which leads to the agglomeration of the ceramic particles inside the mixture. In order to resolve this issue, we sought to modify the HAp surface using mussel-inspired adhesive protein layer known as polydopamine (PDA) to reduce the interfacial energy between the two materials. Based on the result of our surface modification, we incorporated the PDA-coated HAp particles into a ferroelectric polymer membrane known as poly(vinylidenefluoride-co-trifluoroethylene) a.k.a. P(VDF-TrFE) to form a biocompatible nanocomposite that promotes electrochemical stimulus without any external bias. Our measurements suggests that the P(VDF-TrFE)/HAp nanocomposite has a high potential as a coating agent for a wide range of medical implants

Transparent conductive oxides (TCO) are a key component in many optoelectronic applications such as solar cells, flat panel displays, sensors, touch screens, light-emitting diodes, frost-resistant surfaces, and smart windows. The high electronic conductivity and high optical transmission are essential properties of TCOs for these applications. Owing to chemical inertness and high-temperature tolerance of F- doped tin oxide (FTO) films, they also have much demand in a variety of electrochemical devices. In this work, transparent and electrically conductive FTO thin films are prepared on soda-lime glass substrates. The films are fabricated by sequential nebulized spray pyrolysis with the help of a homemade low-cost spray gun. The surface morphology of the films is analyzed using scanning electron microscopy (SEM). It is found that surface is homogeneous and FTO crystallite sizes are in the order of ~10 nm. XRD pattern of the FTO films exhibits 2θ peaks for corresponding SnO₂ crystal planes at 26.64° (110), 33.90° (101), 37.95° (200), 51.87° (211), 56.17° (200), 60.05° (310), 61.89° (301). The crystallite sizes calculated from XRD data are in agreement with that of SEM. Optical transparency and bandgap energies are evaluated by UV visible spectroscopy. The FTO films with 15 Ω cm^-2 sheet resistance are used to prepare quasi-solid-state dye-sensitized solar cells with a TiO₂ photoelectrode. The solar cell showed a ~ 5% energy conversion efficiency with high short-term stability.

Self-healing electronic materials are of primary interest for bioelectronics and sustainable electronics. In this work we report autonomic self-healing of films obtained from mixtures of the conducting polymer poly (3,4-ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS) and polyethylene glycol (PEG). The presence of PEG in PEDOT:PSS films decreases the elastic modulus and increases the elongation at break, thus leading to a softer material with enhanced self-healing characteristics. In situ imaging of the cutting/healing process shows that the healing mechanism is likely due to flowing back of the material to the damaged area right after the cutting.

Millions of people acquire spinal cord or traumatic brain injuries and over 5000 related deaths each year. There is currently no effective way to treat nervous system injuries. Besides, nerve cells do not regenerate in the body. Human dental pulp stem cells (hDPSCs) are important oral mesenchymal stem cells with strong proliferation and multidirectional differentiation functions. Due to their capability to differentiate into neurons, hDPSCs play an important role in dentin repair and regeneration, which provides a new approach for regeneration treatment of traumatic brain injuries in clinical applications. However, the specific mechanisms involved in the neurogenic differentiation process of hDPSCs are still unclear and require further research. To address the issue, hDPSCs were differentiated into neurons using two different polymers, PLA and P4VP. Using these two polymers, we cultured hDPSCs on substrates under eight different conditions, PLA, P4VP, flat flim, fiber, with Graphene and without Graphene. hDPSCs were cultured by neurobasal A media, consisting of 100 U/ml penicillin, 1 x B27 supplement, 100 µg/mL streptomycin, 20 ng/mL epidermal growth factor, and 40 ng/mL basic fibroblast growth factor (FGF) was used. After 7,14,21,28 days, we observed nerve cells numbers and differentiation by SEM and optical microscopy. For 28 days nerve cells, we used PCR technology to detect NES, TUBB3 and NEFM primer. Confocal Microscopy showed multiple layers on most substrates; more elongated cells directly on the substrate surface. SEM showed uniform fibers with no deformities, even with graphene. The results also show that greater elongation of DPSCs on PLA fibers, upregulation of neurogenic markers was slightly higher on flat surfaces than fibrous surfaces. Graphene was shown to be insignificant in neurogenic differentiation. Therefore, the substrates coated with PLA fibers with Graphene may help millions of people restore nerve cells injure cases annually.

Cellulose nanofibers have attracted great attention in recent years. Cellulose is an abundant biopolymer that combines not only structural functions with excellent mechanical properties and is also closely related to water transport functions in plants. Here, we show that aromatic polyamide reinforced with TEMPO-oxidized crystalline cellulose nanofibers shows better chlorine resistance, permeation, and antifouling as compared to plain polyamide membranes. Synthesis was carried out by interfacial polymerization over a supported polysulfone membrane. Membranes were conditioned and tested for desalination agains 3.5% sodium chloride salt solution. Fouling tests were carried out using bovine serum albumin as foulant model. Molecular dynamics studies show that cellulose nanofibers reduce the matrix mobility and improve the hydrophilicity without affecting the chemical composition of the surface layer of the membrane. Infrared and X-ray photoelectron spectroscopy results show a strong interaction between the carboxylic groups of the CNF surface and the m-phenylediamine monomer. Membrane morphology was studied by several microscopic techniques, such as SEM, TEM, AFM and laser confocal scanning microscopy. Molecular dynamics simulations show that m-phenylendiamine/cellulose nanofiber provides the matrix with higher water affinity improving the membrane permeation without affecting the salt rejection. CNF shows great potential as a novel nanoreinforcing material for the preparation of nanocomposite aromatic polyamide membranes with improved properties.

A new class of electronic devices based on stretchable materials can interact with the soft human body in an unprecedented manner. They are highly suitable for epidermal electronics because they can be designed to conform closely to and with the irregular shape of the skin, providing an improved functional interface even during motion, while being imperceptible to the user.^1,2
But does the stretchability also provide benefits for in vivo applications? This lecture will systematically discuss the challenges and possibilities for in vivo bioelectronics³:
The first part will discuss our progress on using metal nanowires embedded in PDMS that can be processed using regular photolithography or filtration to realize stretchable conductive leads down to 10 micrometer resolution. Stretchable and biocompatible transparent microelectrode arrays can thus be realized that enable stimulation and recording of brain activity directly from the cortex both electronically and optically. ^4,5
The technology also allows for creating strain sensors with up to 500% stretchability and Gauge factors of over 100 that can be used as smart and passive RFID tags to measure the filing level of the bladder in handicapped users, or to record the volume of the heart during operation.^6,7 Here, advanced imaging with coherent X-rays in combination with machine learning based data evaluation helped to provide a full theoretical understanding of the strain-response and to build a model with predictive value.⁸
The biggest challenge of in vivo bioelectronics remains the lack of understanding of the brain. Stretchable electronics can be used to create well-defined, in vitro neuron networks of human iPSC-derived neurons that can be stimulated and recorded in a closed-loop fashion enabling a new approach, i.e. bottom-up neuroscience.⁹


Trends in epidermal stretchable electronics for noninvasive long-term healthcare applications, H. Han, et al., Automation and Smart Technology, 2017.
Skin Conformal Polymer Electrodes for Clinical ECG and EEG Recordings; F. Stauffer, et al. Adv. H. Mat. 2018
A guide towards long-term functional electrodes interfacing neuronal tissue, A.F. Renz et al, J. Neur. Eng. 2018.
High-Density Stretchable Electrode Grids for Chronic Neural Recording; K. Tybrandt et al., Adv. Materials, 2018.
Opto-e-dura: a soft, stretchable ECoG array for multimodal, multi-scale neuroscience; A.F. Renz et al., Adv. H. Mat. 2020, submitted.
Soft Electronic Strain Sensor with Chipless Wireless Readout: Toward Real-Time Monitoring of Bladder Volume; F. Stauffer, et al.; Advanced Materials Technologies, 2018.
Continuous heart volume monitoring by fully implantable soft strain sensor; B.L. Zambrano et al., Adv. H. Mat. 2020, submitted.
Visualizing and Analyzing 3D Metal Nanowire Networks for Stretchable Electronics; C. Forró, et al., Adv. Theory and Simulations, 2020, in press.
Modular microstructure design to build neural structures with defined functional connectivity; C. Forró, et al.; Biosensors and Bioelectronics, 2018

Organic Electronics are essential components of bio-integrated electronics for wearable electronics, electronic skins and soft robotics. However, there are a variety of obstacles like mechanical properties similar to biological surface (skin, tissues and organs), reliability of electrical characteristics under deformations, biocompatibility, biodegradability and low-voltage operation of electronics to apply organic electronics to biomedical devices. One of the candidates to reduce the operating voltage is using electrolyte as dielectrics in organic transistors as known as electrolyte-gated transistors (EGTs). Electrolytes can dramatically reduce operating voltage of organic electronics due to high capacitance from the electrical double layers, but liquid electrolyte requires harsh passivation layer to prevent it from escaping from the devices in the biological environment. Also, ion gel based on synthetic organic compound and polymers has not been proved as being biocompatible and biodegradable. Here, we suggest solid-state electrolytes based on natural compound such as gelatin, levan polysaccharide for organic electronics. Gelatin is a semi-solid electrolyte and a sort of natural, protein-based hydrogel with great biocompatibility and biodegradability. Moreover, thermo-responsive behavior of gelatin hydrogels can realize fabrication of organic electronics with printing method by solution process. We fabricated organic electrochemical transistors (OECT) and simple logic circuits by all printing-process with gelatin hydrogels. We also utilized choline as the biocompatible and biodegradable ionic compound to cast solid electrolyte by coupling with levan polysaccharide (Levan-based Solid-state Electrolyte, LSE). This electrolyte is flexible and highly transparent, also can be served as substrate for organic electronics. Therefore, we fabricated organic transistor on free-standing LSE films directly and we also utilized LSE based organic transistors for biomedical device due to their flexibility, biocompatibility and biodegradability, especially recording electrocardiogram by attaching on biological surface.

Low power consumption devices and hygienic material are the heist concern in biomedical devices. Our innovative material amorphous tungsten nitride (WNx) is one of the optimal solutions for both demand characteristics. Fabricating amorphous WNx based nanoelectromechanical (NEM) switches that can be used to obtain power by reusing the stored potential energy in a bent NEM switch to power the next logic operation could solve the power consummation issue. we exhibit the power dissipated in silicon CMOS adiabatic circuit and compare it with the power dissipated in an energy reversible adiabatic NEM switch fabricated with amorphous metal. Besides, amorphous WNx can provide an effective solution to nano-scaled devices and systems, as the absence of significantly larger grains and associated boundaries during subtractive etching provides more uniform architecture. Therefore, we are reporting dissolution characteristics and biocompatibility of an amorphous WNx – which has a grain-less molecular structure. Tungsten nitride's structure contributes to corrosion resistance, high endurance, smooth surface, low contact wear, and exacerbation resistance. Here, we report its dissolution characteristics and mechanism in groundwater (GW), deionized (DI) water, and saline. Complete dissolution times were analyzed for different size features, between the nanoscale and macroscale. As an example, we have fabricated an amorphous WNx based nanoelectromechanical (NEMS) switch to demonstrate nanoscale structures. We also fabricated an accelerometer to show a microscale device and a temperature sensor to display a large surface area macroscopic dimensions. The dissolution rate for all devices is approximately 20-60 nm/hour, at room temperature, in groundwater. The successful and complete dissolution of WNx based devices highlights the versatile nature and simple chemistry of amorphous WNx film and its utility in transient electronic applications. Besides, we reported the material amorphous WNx based devices could be used in sub-dermal implants for biodegradable function. We aim to insulate transdermal wires connected to an externally mounted miniaturized wireless potentiostat for data transmission. This biodegradable function will prevent bacteria from forming biofilms along transdermal wires, or seeding haematogenously, with the potential to migrate within the body and to provoke immune-mediated pathological tissue reactions. Another application is to use the amorphous WNx as a stent or tubular support placed temporarily inside a blood vessel, canal, or duct to aid healing or relieve an obstruction which degrades gradually by the time with no need for extraction surgery.

Hunger and chronic undernourishment impact over 800 million people, which equals 10.7% of the world population. While countries are increasingly making efforts to reduce poverty and hunger by pursuing sustainable energy and agricultural practices, a third of the food produced around the globe still never consumed and thus wasted. Reducing food shortages is vital in this effort and is often addressed by the development of genetically modified produce or chemical additives and inedible coatings to extend freshness, which creates additional health and environmental concerns. Hence, a novel material needed to be developed that is both protective of fresh produce, biocompatible, and biodegradable while at the same time brings economical and environmental sustainability. Herein, a multifunctional bio-nanocomposite comprised largely of egg-derived polymers and cellulose nanomaterials as a conformal coating onto fresh produce that slows down food decay by retarding ripening, dehydration, and microbial invasion is reported. Chemical composition and morphology of the composite were characterized by Infrared Spectra, TEM, and AFM. Affinity to multiple fruit surfaces and hydrophilicity of the coating was measured by the sessile droplet test. The composite forms a uniform coating of approximately 18 μm thick on fruits, as measured through confocal microscopy. The coating's effectiveness against fruit ripening was tested on representative climacteric and non-climacteric fruits: strawberries, bananas, avocados, and papayas. Through time-elapse photos, fruit stiffness measurement, and weight loss measurement of bare and coated fruits over time, the coating showed an extension of fruit freshness by more than a week. The dried coating film showed comparably low water vapor transmission rate and oxygen permeability rate among common packaging materials, and thus these distinct barrier properties likely contributed to the retarding of fruit ripening. Moreover, the coating film eliminated the bacteria on top within 24 hrs, displaying excellent antimicrobial property and thus prevent the microbial attack on fruit surfaces. Additionally, the coating is edible, washable, and made from readily available inexpensive or waste materials, making it a promising economic alternative to commercially available fruit coatings. This green coating composite also provides a potential solution to combat food wastage that is rampant in the world.

The ability to seamlessly integrate a diversity of electronic and optical materials within the flexible thermally-drawn fibers has recently enabled their applications as biocompatible and multifunctional tools for neural recording, modulation, and tissue repair. In this talk, I will highlight the advances in multimaterial fiber-based interfaces with neural tissue and illustrate how integration of active electronics and elastomers may allow for expanding the application domain of these devices toward probing physiology of other electroactive organs deep within the body. Furthermore, this talk will discuss the materials innovation to permit combinatorial thermal drawing and lithographic patterning within fibers that will further expand the geometries of fiber-based bioelectronic interfaces.

The reaction center (RC) photoenzymefrom Rhodobacter sphaeroidesphotosynthetic bacterium is a membranespanning proteincapable to convert solar energy intocharge separated states with efficiency close to 100%.The photogenerated electron-hole pairs can beexploited to produce photocurrents and the suitability of RC for photoconversioonin electronic and electrochemical devices is well estabilished [1,2].
However, the electronic interface of RC with electrodes and the photoenzyme stability after integration in devices still require optimization to improve theefficiency of thephotocurrent production [3]. Enzyme stability can be improved by encapsulationin soft structures, such as vescicles [4] and polymersomes [5].Electron transfer between RC and electrode surface can occur either directly or through electrochemical mediators. In the first case a suitable immobilization strategy is required [6]. Although in the second case the RC can be dispersed in solution, higher photocurrents are produced if it is immobilized onto the electrode. To this aim,variousprotocols are reported in literature,and we have recently demonstrated thatmodification under mild temperature and pH condititons of RC with biomimetic and adhesive polymers, such as polydopamine,is a very promising method to improve the electrode/protein interface without altering the enzyme photoactivity [7].

[1] F. Milano, A. Punzi, R. Ragni, M. Trotta, G. M. Farinola, Adv. Funct. Mater.,29,1805521, (2019).
[2] A.J. McCormick, P. Bombelli, R. W. Bradley, R. Thorne, T. Wenzele , C. J. HoweEnergy Environ. Sci., 8, 1092-1109, (2015).
[3] H.Yuk, B. Lu, X. Zhao, Chem. Soc. Rev., 48, 1642-1667 (2019)
[4] E. Altamura, F. Milano, M. Trotta, P. Stano, F. Mavelli, Advances in Bionanomaterials, Lecture Notes in Bioengineering, Springer, 97-109 (2018).
[5] 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),1844-52 (2015).
[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. 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. TrottaAdv. Electron. Mater. 2000140, (2020)

Although many animals have evolved intrinsic transparency for the purpose of concealment, the development of dynamic, that is, controllable and reversible, transparency for living human cells and tissues has remained elusive to date. By drawing inspiration from the structures and functionalities of adaptive cephalopod skin cells, we have designed and engineer human cells that contain reconfigurable protein-based photonic architectures and, as a result, possess tunable transparency-changing and light-scattering capabilities. Our findings may lead to the development of unique biophotonic and bioelectronic tools for applications in materials science and bioengineering, as well as ultimately facilitate an improved understanding of various biological systems.

Biological charge transfer processes are based on the controlled transport of charges (electrons, protons, ions) across specific pathways within proteins from the nm-scale up to the μm scale. With this biological inspiration, we report here on a new family of conductive and free-standing biological materials. We are using different types of proteins as building blocks to form various types of materials, which were later functionalized in a bioinspired fashion to exhibit efficient electron transport on the centimeter length scales. With this in mind, we focus only on proteins that can be produced in bulk quantities and in low cost from raw materials, in which most of our work to date has been focused on the bovine serum albumin protein. Following the formation of the biopolymer, we show that it can be functionalized in different ways for the formation of efficient ionomers with measured ionic conduction of >10 mS/cm at room temperature or for the formation of light responsive materials. Due to the protein-based nature of our materials, it enables us to explore the governing factors and mechanisms of long-range biological charge transport. Nonetheless, our new protein-based biopolymers have several attractive properties for their possible integration in various applications. Our materials are environmentally friendly, they possess inherent biodegradability and their formation obeys to most principals of green chemistry. In terms of their mechanical properties, they have high elastic modulus of ~160 MPa, but at the same time, they are highly stretchable, capable of stretching more than 4 times their length. They have high resistance to harsh organic solvents and acids, they are very easy to form, and have a very low price tag with materials cost of around $1/cm². Currently, our main targeted application for our new family of materials is for biological interfaces, while other lines of applications include the use of our biopolymers for biomedical application (tissue engineering) and for energy applications such as membranes for fuel cells.

Microbially produced electrically conductive protein nanowires (e-PNs) are a revolutionary ‘green’ electronic material with substantial sustainability and functional advantages over traditional materials such as silicon nanowires and carbon nanotubes. e-PNs are produced from renewable feedstocks, with 100-fold less energy demand than that required for producing silicon nanowires or carbon nanotubes. No toxic chemicals are required for e-PN fabrication and the final product is biocompatible, environmentally benign, and recyclable. Yet, e-PNs are remarkably robust, maintaining function even under harsh CMOS-compatible fabrication conditions. e-PNs can be processed into thin-film electronics, nanocables, and flexible conductive composites. However, development of applications has been slowed by the fact that bacteria and archaea known to naturally produce e-PNs are slow-growing anaerobes that are difficult to mass culture. We resolved this bottleneck by designing a nonpathogenic strain of E. coli (strain GPN) that expresses abundant e-PNs from synthetic variants of the e-PN monomer gene from Geobacter species (ACS Synthetic Biology 9:647-654 (2020)). Advantages of strain GPN for e-PN fabrication include: 1) rapid, and scalable mass-culture under aerobic conditions; 2) ‘plug and play’ simplicity for the design and expression of e-PNs with novel functionalities; and 3) a versatile E. coli genetic toolbox for the introduction of genetic circuits that control the expression of multiple monomer genes introduced into the same strain to fabricate e-PNs with advanced sensing and electronic features. When coupled with a newly developed, simplified filtration method for harvesting e-PNs, E. coli strain GPN ensures a ready supply of e-PNs for diverse electronics applications. Examples of recently developed novel applications for e-PNs include devices that generate electricity from the ambient humidity in air (Nature 578:550-554 (2020)); neuromorphic memory devices that operate at biological voltages (Nature Communications 11:1861 (2020)); and electronic sensors with high selectivity and sensitivity (Nano Research 13:1479-1484 (2020)). These and other applications are being further optimized by tailoring e-PN properties to specific applications. For example, e-PN conductivity has been tuned over a million-fold by designing genes for synthetic e-PNs with modified amino acid composition. Peptides can be displayed on the outer surface of e-PNs by expressing novel monomer genes designed to add the desired peptide to the carboxyl end of the e-PN monomer (ACS Synthetic Biology 8:1809-1817 (2019)). These peptide decorations can function as ligands to specifically bind analytes of interest for sensor applications or to enhance interactions of e-PNs with other materials. More than one ligand can be added to the same wire and the stoichiometry of the ligands on the wires can be controlled with genetic circuits. Newly designed e-PNs fabricated with E. coli strain GPN and their potential applications will be discussed.

About 466 million people are estimated to suffer from disabling hearing loss. When the transduction mechanism (i.e., sensory cells and/or neurons) is damaged, sensorineural hearing loss (SNHL) occurs. Up to now, severe SNHL is only possible using complex electronic implants, i.e., cochlear implants (CIs). Conventional CIs suffer from some important disadvantages impacting the quality of life and hearing after implantation and for such reasons a new class of CIs is desirable. The ear sensory cells, hair cells, act as biological transducers in the organ of Corti, where they convert the mechanical vibration of the basilar membrane into stimulation of the underlying spiral ganglion neurons. By exploiting the mechanical tonotopy still present in deaf cochleae, piezoelectric materials in contact with the basilar membrane could potentially enable a fine-tuning process of the sound vibrations, thus providing a better quality of hearing versus discretized electrodes in electronic CIs. Piezoelectric CIs would thus represent an innovative and smart solution: they work in a biomimetic fashion, are self-powered and fully implantable, less expensive (material-based) than bionic CIs and a-magnetic (i.e., MRI-compatible).
In our hypothesis, a tissue engineering-aided nanostructured piezoelectric device and its proper surgical implantation can promote direct contact with spiral ganglion neurons, thus reducing the necessary electric output for neural stimulation and finally achieving sufficient sensitivity. Specifically, we move forward the primitive concept of bulk-structured piezoelectric CIs by designing a new device based on ultrafine fibers produced via electrospinning to be precisely delivered and provided with a nano/microscale resolution to be intimately and efficiently integrated with the cochlear microenvironment.
Ceramic materials with a perovskite-like structure, possess higher piezoelectric properties than those of piezopolymers (e.g., polyvinylidene fluoride, PVDF), but are very rigid and difficult to process. To gain the multifunctionality of the nanofibrous device, we study the immunomodulatory and antibacterial properties of nanoceramics to be incorporated inside piezoelectric polymeric fibers. In fact, reducing the fibrotic tissue formation would allow the best electric delivery by the piezoelectric materials.
We investigate lithium niobate as a potential candidate material for next-generation CIs. Lithium niobate nanoparticles resulted otocompatible in vitro with OC-k3 cells, enhanced human beta-defensin (HBD-2) in HaCaT epithelial cells, and also showed direct antibacterial activity against P. aeruginosa. The LiNbO₃ ability of modulating the expression of IL-6 and IL-8 could play a beneficial role in vivo, by reducing the extent or duration of a post-implant inflammatory response. These nanoparticles were efficiently incorporated into PVDF-trifuoroethylene P(VDF-TrFE) fibers via electrospinning. Aligned composite fibers at 20% (w/w%) of lithium niobate showed an enhanced piezoelectric response, namely 90 ± 2 mV, with respect to their random counterparts, namely 40 ± 4 mV, under an applied load of 2.12 N. These composite fibrous structures supported SHSY-5Y neural-like cell growth in vitro.
Electroactive materials combining nanotechnology and tissue engineering show promise for cochlear stimulation and otoprotection.
This study was supported by MISTI funds 2016 (MIT-UNIPI project NANOSPARKS).

Material based technologies play an integral role in many medical treatment strategies, including joint replacements, vascular stents, drug delivery methods, contact lenses and medical sutures. The application of successful technologies continues to grow, with an estimated market size of $130 billion USD by 2020. Although successes are notable, a number of biomaterial-based devices are limited in application by non-specific material properties to tissue type and undesired inflammation at the device interface. In application, polyester materials have traditionally been an effective polymer strategy, with successes in tissue engineering scaffolds and a variety of biomedical devices. Leveraging advantageous polyester degradability and well understood chemical synthesis, these materials serve as a strong functional platform to further optimize material-cell microenvironments. In this talk, I will describe the development of polyesters that (a) exhibit controllable mechanical properties to mimic the elastic properties of cardiac tissue extracellular matrix (ECM) and (b) incorporate a biomimetic moiety of mammalian immunity to recapitulate mechanistic inflammation regulation at the material surface.
Development of engineered cardiac tissue requires material scaffolds that match the elastic behavior of cardiac ECM. Using polycondensation techniques to incorporate unsaturated carbonyl groups into elastic polyester material gels, we generated materials that can be molded into intricate designs with secondary crosslinking to generate constructs with highly tunable elasticity. By adapting material synthesis conditions (i.e. monomer ratios, reaction time), elastic mechanical behavior was highly tunable across a range of soft biomaterial applications. Material applicability was highlighted in a number of micro-designed elastomeric scaffold supports for engineered tissue, both for in vitro organ-on-a-chip and in vivo cardiac patch technologies, wherein the two-step synthesis process allowed for micro molding into intricate shapes prior to gelation.
With biomaterial application in vivo, inflammation at the biomaterial surface limits device application. To tackle this, we looked to itaconate, a powerful small molecule metabolite of innate immunity that has recently emerged as a regulator of innate immune inflammation. This molecule has been previously limited therapeutically by short circulation times. To circumvent this, itaconate was incorporated directly into material backbones to impart biomimetic small molecule modulation, with quantified hydrolytic degradation release from polyester chains. Harnessing hydrolytic degradation release from polyester backbones, itaconate polymers resulted in the mechanism specific immunoregulatory properties on macrophage polarization in vitro. In a functional assay, the polymer-released itaconate inhibited bacterial growth on acetate. Translation to an in vivo model of biomaterial associated inflammation, intraperitoneal injection of ITA polymers demonstrated a rapid resolution of inflammation in comparison to a control polymer silicone, demonstrating the value of sustained biomimetic presentation of itaconate. Using scalable polyester synthesis techniques, we have demonstrated the power of instructive biomaterial technologies as functional modulators of the cell microenvironment.

Self-assembling peptides that are inherently biodegradable and biocompatible are extremely suitable for use in devices that adhere on, or even implanted into, the human body in order to monitor and regulate biological functions. The challenge for incorporating these materials in bioelectronic devices is the optimization of their electronic properties for the desired application. In this talk I will present peptide design rules that can be used to prepare electron and/ or proton conducting peptide based materials. Specifically, I will discuss the influence of aromatic side chains (both natural and non-natural) on electron conductivity.^1,2 I will further present enhancement of proton conduction in these films by the incorporation of protonating side chains, which can lead to extremely high proton conductivity values in these materials.^3,4 I will finally discuss the control of conductivity, thermal stability and biodegradability of self-assembling peptide nanostructures by peptide backbone motifs. These studies demonstrate the great potential of using peptide building blocks for the fabrication of green electronic materials.

References
1. Ashkenasy, N.; Horne, W. S.; Ghadiri, M. R., Design of Self-Assembling Peptide Nanotubes with Delocalized Electronic States. Small 2006, 2, 99-102.
2. Ivnitski, D.; Amit, M.; Silberbush, O.; Atsmon-Raz, et al., The Strong Influence of Structure Polymorphism on the Conductivity of Peptide Fibrils. Angewandte Chemie-Int. Ed. 2016, 55, 9988-9992.
3. Amit, M.; Appel, S.; Cohen, R.; Cheng, G.; et al., Hybrid Proton and Electron Transport in Peptide Fibrils. Adv. Funct. Mater. 2014, 24, 5873-5880.
4. Silberbush, O.; Amit, M.; Roy, S.; Ashkenasy, N., Significant Enhancement of Proton Transport in Bioinspired Peptide Fibrils by Single Acidic or Basic Amino Acid Mutation. Adv. Funct. Mater. 2017, 27, 1604624.

The expanding use of electronics in all aspects of society broadens their use towards novel medical applications but also raises new environmental and health concerns. Medical electronic devices need to be able to store, harvest and transfer electric charges, while benefitting from physical properties harmonious with their biological interface, such as flexibility, stretchability and self-healing. One strategy to obtain both electrical and biocompatible properties is to use biological materials, which have the added benefit of being biodegradable, while having a much lower carbon footprint than other electronic materials like metals and organic polymers. Evolution has already generated biological materials, proteins, able to transfer electronic charges over long distances. Drawing inspiration from theoretical understanding of how electrons can be transferred in some native protein fibers through aromatic amino acids, fibrous proteins have been genetically engineered to exhibit conductivity. Curli fibers, which are grown naturally in the ubiquitous and very scalable Escherichia coli, are formed by the self-assembly of beta-helical CsgA monomers. Mutating a row of amino acids along the helix to aromatic residues confers conductivity to the dry amyloid film.
These proteins’ ability to self-assemble through non-covalent bonds and their dispersibility in water are good indicators for self-healing properties. Here, we tested the conductive and mechanical properties of genetically engineered conductive curli fiber films. Specifically, we evaluated whether they can regenerate from different tears and scratches, simply by rehydrating the film in water. We drop-cast conductive curli fibers between electrodes to form films of various thicknesses and cut at different sizes. We used SEM imaging to observe the mechanical healing of the drop-cast film. We further performed cycles of cuts and healing to observe longer-term reusability of the material. Next, to reveal the flexibility of a free-standing film, we performed tensile tests. We were able to reattach two pieces of film back together to determine the material’s resistance to breaks, and to quantify the regeneration of the electrical properties in doing so. We found that the material can recover almost entirely with micron-scale cut sizes, even for protein films as thin as 2 µm. These self-healing properties we defined show potential for use of conductive curli fibers as composites, or even pure materials, in wearable medical devices.

Solar energy transduction performed by photosynthetic organisms is the paramount process that ensures power to all metabolic activities on planet Earth[1]. Exploiting the highly efficient capability of the photosynthetic organisms to convert visible and near infrared radiations into energy forms viable to human beings is a dream that accompanies man-kind since the visionary and wishful speech by Giacomo Ciamician at the beginning of XX century[2].
In the last two decades, vast literature tackles the use of photosynthesis in energy conversion using several approaches ranging from the use of the isolated enzymatic machinery responsible of light photoconversion [3] to complex systems that exploit photosynthetic microorganisms[4].
The most recent advances regarding photovoltage generation and the subsequent current amplification in Light-modulated Electrolyte-gated organic transistors[5,6] will be presented. These hybrid systems, based on the unique coupling of photosynthetic materials or organisms with the peculiarities offered by the platform of organic electronics will be presented. The potential of these architectures will be discussed in view of the interaction of the photosynthetic apparatus employed in the voltage generation with the organic electronic device of choice.


[1] Nicola Armaroli, Vincenzo Balzani, Nick Serpone. Powering Planet Earth: Energy Solutions for the Future (2013) Wiley-VCH
[2] Giacomo Ciamician. The Photochemistry of the Future (1912) Science 36(926) 385-94
[3] Ravi, SK, Rawding, P, Elshahawy, AM, Huang, K, Sun, W, Zhao, F, Wang, J, Jones, MR & Tan, SC, Photosynthetic apparatus of Rhodobacter sphaeroides exhibits prolonged charge storage. (2019) Nature Comm. 10(902).
[4] F. Milano, A. Punzi, R. Ragni, M. Trotta, G.M. Farinola, Photonics and Optoelectronics with Bacteria: Making Materials from Photosynthetic Microorganisms (2018) Adv. Funct. Mat. 29(21) 1805521.
[5] 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 A Bacterial Photosynthetic Enzymatic Unit Modulating Organic Transistors with Light. Adv. Electr. Mat. 6(1) 1900888
[6] M. Di Lauro, G. Buscemi, M. Bianchi, A. De Salvo, M. Berto, S. Carli, G.M. Farinola, Luciano Fadiga, F. Biscarini, and M. Trotta. Photovoltage generation in enzymatic bio-hybrid architectures. (2020) MRS Advances 5(18-19), 985-990.

Detecting a marker or a pathogen at the physical limit is the new frontier in medical analysis as it endows the clinicians with the attacker’s advantage over life-threatening diseases such as tumours and pandemics. It is also received that label-free and electronic transductions can be conveniently fast and wieldy. Within this field different transducing approaches are pursued. They involve a transducing interface functionalized with biological recognition elements, such as antibodies or DNA probes, that endow the device with recognition properties by selectively capturing the analyte e.g. an antigen or a genomic marker, respectively. One recently proposed approach involves a large interface hosting trillions of highly-packed bio-recognition elements. The challenge is indeed that of measuring one single molecule in a large volume such as for instance 100 ml. This means being able to deploy a technology that can detect 10 - 20 10^-21 mole l^-1 (zeptomolar).
Mimicking cell’s behaviour, ecently proposed approach involves a large interface hosting trillions of highly-packed bio-recognition elements. This is called, the “Single Molecule with a large Transistor (SiMoT)" technology that was proposed to sense a solution with markers present at extremely low concentrations. It is based on an Electrolyte Gated Organic filed-effect transistor operated in deionized water, with a gate that has an area of ca. 0.5 cm², hosting 10¹² antibodies or genomic probes. The SiMoT platform has been proven to perform label-free and selective detection at the physical limit in real biofluids of protein biomarkers such as: human Immunoglobulin G, Immunoglobulin M, C-reactive protein, MUC1 and HIV1 p24 antigen as well as genomic markers such as miR-182-5p and KRAS. Indeed, the widely applicable method used to conjugate the recognition elements to the gate electrode, makes the SiMoT platform suitable for the detection of different classes of markers and pathogens reaching world record detections limits for label-free protein detection.

In order for machines and electronics to interface with biological tissue, they should be soft and elastic – i.e. remain functional when stretched and then return to their natural length when unloaded. In recent years, there has been tremendous progress in creating conductive elastomers and gels that are capable of extreme stretchability and which have been successfully utilized as bioelectronic interfaces. These include material architectures that are self-healing and can restore electrical and/or mechanical functionality when torn or punctured.

In this talk, I will review recent efforts to create mechanically robust, stretchable electronics using a variety of soft material architectures. In particular, I will focus on the following approaches: (i) silver-hydrogel composites that exhibit an unprecedented combination of mechanical compliance and electrical conductivity; (ii) biphasic compositions of silver nanoparticles and eutectic gallium-indium (EGaIn) liquid metal alloy for ultrathin “epidermal" electronics; and (iii) EGaIn-polymer composites capable of high electrical conductivity, extreme stretchability, negligible electromechanical coupling, and a variety of self-healing properties. To demonstrate their potential role in future bioelectronic applications, I will present examples of how these soft material architectures are used as electrodes for physiological monitoring (e.g. EMG, ECG) and as electrical interconnects for highly stretchable digital circuits.

Transient electronics have gained attention in the recent years, showing great promise to reduce electronic waste, enabling devices that can disintegrate for data security purposes or novel biomedical implants which eliminate the need for re-operation. In this work, we focus on the latter, also called “bioresorbable electronics”, devices that will naturally dissolve or be degraded into benign byproducts in the body. Materials such as dissolvable metals, degradable semi-conductors, polymers and dielectrics have been proposed. However, due to their properties, these materials are often not compatible with processes that involve high temperature or harsh chemicals, making them challenging to pattern. Printing techniques show great promise to address this challenge and could pave the road to personalized implants based on digital additive manufacturing, but require joint optimization of the ink formulation, the printing conditions and the post-treatment. In this work, we leverage the potential of these techniques to deposit functional materials on bioresorbable elastomeric substrates, poly(glycerol sebacate) (PGS) and poly(octamethylene maleate (anhydride) citrate) (POMaC) as well as on a biopolymer derived from silkworms, silk fibroin. Bioresorbable elastomers are of particular interest, as they enable the development of low-profile transient bioelectronics, in that they can conform to the shape and curves of internal organs and minimize immune response. We focus on the manufacturing of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)-based organic electrochemical transistors (OECTs). OECTs, generally based on a conducting polymeric channel gated through an aqueous electrolyte, have generated a lot of attention recently for the detection of multiple biomolecules and ions and high signal-to-noise ratio electrophysiological recordings.
PGS and POMaC were synthetized as described in previous publications, spin-coated on silicon wafers onto sacrificial layers and formed into free-standing films after thermal curing. Silk fibroin was purified as described previously, blade-cast and treated with water vapor for 24h. The suitability of the transient polymers as substrates for printed electronics was assessed and compared with a conventional substrate, polyimide. Degradable inks based on respectively zinc and carbon pastes were developed and evaluated for the creation of contacts and interconnects and silk fibroin inks were formulated to be used as a dielectric layer. Various manufacturing methods such as screen printing and direct ink writing were investigated for the patterning of these inks, as well as post-treatments that are compatible with the relatively low thermal resistance of the bioresorbable substrates. The degradation behavior of the printed patterns was assessed in phosphate buffered saline (PBS). Inks based on aqueous dispersions of PEDOT:PSS were patterned using inkjet printing and the conductivity of the polymer was compared on the degradable substrates and polyimide. The behavior of the resulting OECTs on transient substrates was characterized in PBS and found to be in line with the state of the art considering channel dimensions. A preliminary test to demonstrate the ion sensing capabilities of the organic transistors was conducted with different concentrations of potassium chloride (KCl). The work presented here represents a step forward in the facile manufacturing of bioresorbable implantable sensors. The fabrication scheme used in this work leverages different methods of material deposition, and, while combining fabrication approaches may be advantageous in some cases, we aim to develop fully printed devices. This could allow to create personalizable implants made of bioresorbable materials, for example for regeneration or diagnosis applications, in a scalable and customized manner.

The immunotherapy market surpassed 75 billion USD in 2019, and many emerging drugs also leverage the body's immune system. Among these immunotherapies, many current and future cancer treatments utilize DNA damage. To follow these DNA damaging immunotherapies, we have applied bioinspired electrochemical devices for real-time measurements of DNA damaging drugs in cellular lysates. We have shown these devices to quantify concentration-dependent drug activity, identify therapeutic concentration windows of cancer-selective activity, and mechanistically correlate damage activity with cancer cell death. Recently, we have shown these devices to detect an onset of activity of a deoxyniboquinone derivative at 100 attomolar levels in approximately 100 microliters of cellular media. This device is ready to be implemented as a standard tool for analyzing the drug activity of cancer-selective treatments in the lab, enabling quantitative identification of effective drugs for patients while minimizing side effects.

The conventional bioelectronic interfaces have been based on either 2-D thin films or 1-D fibers/wires which limit 3-D scalability as well as volume-/mass-dependent performance. Moreover, biological tissues and organs typically exhibit 3D arbitrary curvatures with wet surface, which impeded the close physical contact between the target tissue/organ and bioelectronic interfaces, leading to the low efficiency in bioelectric signal recording and/or stimulation. In this research, we report on 3D monolithic architectures with arbitrary shapes by employing conducting polymer microstructures as building blocks. Such arbitrary 3D structures were constructed by performing the seamless fusion of separate conducting polymer microstructures without using binder or adhesive. The resultant 3D structures exhibited decent mechanical robustness, high water stability, and outstanding biocompatibility, while the sheet resistance was reduced below 1 Ohm/square and the gravimetric capacitance was increased up to 79 F/g by taking advantage of cumulative mass loading and structural fusion. Finally, we demonstrated that 3D conductive mesh electrodes could be attached to the wet surface of biological organs/tissues such as heart and sciatic nerves without glue or clamp and efficiently record/stimulate bioelectrical signals in vivo.

Multifunctional surfaces that can conformally adhere to complex interfaces, degrade at a controllable rate and invoke minimal reaction within the body can be used for soft and implantable electronics, wound healing, tissue engineering, neural interfacing and in vivo disease diagnostics. Designing interfaces for applications at dynamic, non-planar biological environments is a problem of great interest. Recently, “kirigami”- the Japanese art of paper cutting has been proposed as a unique strategy to engineer flexibility and stretchabililty by introducing patterned defects or cuts.
We discuss how the concepts of kirigami can be applied to form photolithographically patterned cuts in flexible, mechanically robust silk proteins for the fabrication of biofunctional films.[1] These macroscale films are optically transparent and possess tuneable degradation and engineered flexibility with precisely defined microscale cuts. The kirigami cutting is formed using the technique of “protein photolithography” using silk fibroin as a route to multiscale fabrication.[2,3] Tensile tests performed on these films show a remarkable improvement in mechanical properties in comparison to pristine films. Using numerical modelling, the mechanical behavior of the silk kirigami films can be predicted as a function of different cut geometry. We show that these films can be used as multilayer, biodegradable cell culture substrates as a result of the biocompatibility of the substrate biomaterial. Finally, by incorporating the conducting polymer polyaniline (PANI) in the silk composite, we are able to make multifunctional conducting silk kirigami films. The films demonstrate excellent linear conductive behavior (µS range) over a voltage range of -0.5 to +0.5 V. The films are able to maintain their conductivity under severe mechanical flexure and deformations. These results indicate that silk kirigami can provide exceptional bioinspired and biodegradable structures towards flexible and stretchable biodevices.

References:

[1] S Pradhan, L Ventura, F Agostinacchio, M Xu, E Barbieri, A Motta, NM Pugno, VK Yadavalli. ACS Appl. Mater. Interfaces. 12(11),12436-44, 2020.
[2] NE Kurland, T Dey, C Wang, SC Kundu, VK Yadavalli, Adv. Mater. 26, 4431-4437, 2014.
[3] M Xu, S Pradhan, F. Agostinacchio, RK Pal, G Greco, B Mazzolai, NM Pugno, A Motta, VK Yadavalli, Adv. Mater. Interfaces, 6, 1801822, 2019

Healable and deformable conductive materials have received considerable attention for future electronics such as artificial human skin, internet of things, and bioelectronics. However, their practical applications are impeded by low electrical conductivity and irreversible conductivity degradation after breaking/healing cycles. Here we report a highly conductive completely reversible electron tunneling-assisted percolation network of silver nanosatellite particles for putty-like moldable and healable nanocomposites [1]. The hierarchically structured silver nanosatellite particles with a bimodal size (medium: 164 nm, small: 3.7 nm) distribution are generated by the radical and reactive oxygen species-mediated vigorous etching and reduction reaction of silver flakes using tetrahydrofuran peroxide in a healable silicone rubber matrix. The silver nanosatellite network dramatically increases electrical conductivity by ~5 orders of magnitude, achieving an unusually high conductivity (1020 S/cm) in putty-like nanocomposites with excellent moldability [1]. The silver nanosatellite particles are uniformly and densely distributed with an interparticle distance of 3.1 nm, and the close work function match between silver and silicone enables electron tunneling. This leads to a completely reversible reconstruction of the percolation network, achieving ~100% electrical healing efficiency after 1000 breaking/healing cycles [1]. Moreover, the conductivity is stable even after 1000 water immersion cycles and 6-month exposure to ambient air. An emergency electronics repair demonstration is also performed by a robot using the nanocomposites [1]. A recent progress in our laboratory will also be introduced. Reference: [1] Suh et al., Nature Communications 11, 2252 (2020). https: //doi.org/10.1038/s41467-020-15709-8

Production of repetitive polypeptides that comprise one or more tandem copies of a single unit with distinct amorphous and ordered regions have been an interest for the last couple of decades. The self-healing performance of tandem repeat polypeptides creates new opportunities for the design of bioinspired and biosynthetic materials that were not possible previously, and addresses current limitations in self-healing soft materials. In this talk, we review programmable design, structure, and properties of functional materials and composites from squid-inspired tandem repeat proteins, with applications in bioelectronics. Protein based self-healing materials provides a rich architecture that can micro-phase-separate to form periodic nanostructures with enhanced physicochemical properties via directed or natural evolution that often exceed those of conventional synthetic polymers. These materials show hydrogen-bonded nanostructure and network morphology, with programmable healing properties (2–23 MPa strength after 1 s of healing) that surpass by several orders of magnitude those of other natural and synthetic soft materials.

A new class of electronic devices based on stretchable materials can interact with the soft human body in an unprecedented manner. They are highly suitable for epidermal electronics because they can be designed to conform closely to and with the irregular shape of the skin, providing an improved functional interface even during motion, while being imperceptible to the user.^1,2
But does the stretchability also provide benefits for in vivo applications? This lecture will systematically discuss the challenges and possibilities for in vivo bioelectronics³:
The first part will discuss our progress on using metal nanowires embedded in PDMS that can be processed using regular photolithography or filtration to realize stretchable conductive leads down to 10 micrometer resolution. Stretchable and biocompatible transparent microelectrode arrays can thus be realized that enable stimulation and recording of brain activity directly from the cortex both electronically and optically. ^4,5
The technology also allows for creating strain sensors with up to 500% stretchability and Gauge factors of over 100 that can be used as smart and passive RFID tags to measure the filing level of the bladder in handicapped users, or to record the volume of the heart during operation.^6,7 Here, advanced imaging with coherent X-rays in combination with machine learning based data evaluation helped to provide a full theoretical understanding of the strain-response and to build a model with predictive value.⁸
The biggest challenge of in vivo bioelectronics remains the lack of understanding of the brain. Stretchable electronics can be used to create well-defined, in vitro neuron networks of human iPSC-derived neurons that can be stimulated and recorded in a closed-loop fashion enabling a new approach, i.e. bottom-up neuroscience.⁹


Trends in epidermal stretchable electronics for noninvasive long-term healthcare applications, H. Han, et al., Automation and Smart Technology, 2017.
Skin Conformal Polymer Electrodes for Clinical ECG and EEG Recordings; F. Stauffer, et al. Adv. H. Mat. 2018
A guide towards long-term functional electrodes interfacing neuronal tissue, A.F. Renz et al, J. Neur. Eng. 2018.
High-Density Stretchable Electrode Grids for Chronic Neural Recording; K. Tybrandt et al., Adv. Materials, 2018.
Opto-e-dura: a soft, stretchable ECoG array for multimodal, multi-scale neuroscience; A.F. Renz et al., Adv. H. Mat. 2020, submitted.
Soft Electronic Strain Sensor with Chipless Wireless Readout: Toward Real-Time Monitoring of Bladder Volume; F. Stauffer, et al.; Advanced Materials Technologies, 2018.
Continuous heart volume monitoring by fully implantable soft strain sensor; B.L. Zambrano et al., Adv. H. Mat. 2020, submitted.
Visualizing and Analyzing 3D Metal Nanowire Networks for Stretchable Electronics; C. Forró, et al., Adv. Theory and Simulations, 2020, in press.
Modular microstructure design to build neural structures with defined functional connectivity; C. Forró, et al.; Biosensors and Bioelectronics, 2018

Detecting a marker or a pathogen at the physical limit is the new frontier in medical analysis as it endows the clinicians with the attacker’s advantage over life-threatening diseases such as tumours and pandemics. It is also received that label-free and electronic transductions can be conveniently fast and wieldy. Within this field different transducing approaches are pursued. They involve a transducing interface functionalized with biological recognition elements, such as antibodies or DNA probes, that endow the device with recognition properties by selectively capturing the analyte e.g. an antigen or a genomic marker, respectively. One recently proposed approach involves a large interface hosting trillions of highly-packed bio-recognition elements. The challenge is indeed that of measuring one single molecule in a large volume such as for instance 100 ml. This means being able to deploy a technology that can detect 10 - 20 10^-21 mole l^-1 (zeptomolar).
Mimicking cell’s behaviour, ecently proposed approach involves a large interface hosting trillions of highly-packed bio-recognition elements. This is called, the “Single Molecule with a large Transistor (SiMoT)" technology that was proposed to sense a solution with markers present at extremely low concentrations. It is based on an Electrolyte Gated Organic filed-effect transistor operated in deionized water, with a gate that has an area of ca. 0.5 cm², hosting 10¹² antibodies or genomic probes. The SiMoT platform has been proven to perform label-free and selective detection at the physical limit in real biofluids of protein biomarkers such as: human Immunoglobulin G, Immunoglobulin M, C-reactive protein, MUC1 and HIV1 p24 antigen as well as genomic markers such as miR-182-5p and KRAS. Indeed, the widely applicable method used to conjugate the recognition elements to the gate electrode, makes the SiMoT platform suitable for the detection of different classes of markers and pathogens reaching world record detections limits for label-free protein detection.

Self-assembling peptides that are inherently biodegradable and biocompatible are extremely suitable for use in devices that adhere on, or even implanted into, the human body in order to monitor and regulate biological functions. The challenge for incorporating these materials in bioelectronic devices is the optimization of their electronic properties for the desired application. In this talk I will present peptide design rules that can be used to prepare electron and/ or proton conducting peptide based materials. Specifically, I will discuss the influence of aromatic side chains (both natural and non-natural) on electron conductivity.^1,2 I will further present enhancement of proton conduction in these films by the incorporation of protonating side chains, which can lead to extremely high proton conductivity values in these materials.^3,4 I will finally discuss the control of conductivity, thermal stability and biodegradability of self-assembling peptide nanostructures by peptide backbone motifs. These studies demonstrate the great potential of using peptide building blocks for the fabrication of green electronic materials.

References
1. Ashkenasy, N.; Horne, W. S.; Ghadiri, M. R., Design of Self-Assembling Peptide Nanotubes with Delocalized Electronic States. Small 2006, 2, 99-102.
2. Ivnitski, D.; Amit, M.; Silberbush, O.; Atsmon-Raz, et al., The Strong Influence of Structure Polymorphism on the Conductivity of Peptide Fibrils. Angewandte Chemie-Int. Ed. 2016, 55, 9988-9992.
3. Amit, M.; Appel, S.; Cohen, R.; Cheng, G.; et al., Hybrid Proton and Electron Transport in Peptide Fibrils. Adv. Funct. Mater. 2014, 24, 5873-5880.
4. Silberbush, O.; Amit, M.; Roy, S.; Ashkenasy, N., Significant Enhancement of Proton Transport in Bioinspired Peptide Fibrils by Single Acidic or Basic Amino Acid Mutation. Adv. Funct. Mater. 2017, 27, 1604624.

The ability to seamlessly integrate a diversity of electronic and optical materials within the flexible thermally-drawn fibers has recently enabled their applications as biocompatible and multifunctional tools for neural recording, modulation, and tissue repair. In this talk, I will highlight the advances in multimaterial fiber-based interfaces with neural tissue and illustrate how integration of active electronics and elastomers may allow for expanding the application domain of these devices toward probing physiology of other electroactive organs deep within the body. Furthermore, this talk will discuss the materials innovation to permit combinatorial thermal drawing and lithographic patterning within fibers that will further expand the geometries of fiber-based bioelectronic interfaces.

Material based technologies play an integral role in many medical treatment strategies, including joint replacements, vascular stents, drug delivery methods, contact lenses and medical sutures. The application of successful technologies continues to grow, with an estimated market size of $130 billion USD by 2020. Although successes are notable, a number of biomaterial-based devices are limited in application by non-specific material properties to tissue type and undesired inflammation at the device interface. In application, polyester materials have traditionally been an effective polymer strategy, with successes in tissue engineering scaffolds and a variety of biomedical devices. Leveraging advantageous polyester degradability and well understood chemical synthesis, these materials serve as a strong functional platform to further optimize material-cell microenvironments. In this talk, I will describe the development of polyesters that (a) exhibit controllable mechanical properties to mimic the elastic properties of cardiac tissue extracellular matrix (ECM) and (b) incorporate a biomimetic moiety of mammalian immunity to recapitulate mechanistic inflammation regulation at the material surface.
Development of engineered cardiac tissue requires material scaffolds that match the elastic behavior of cardiac ECM. Using polycondensation techniques to incorporate unsaturated carbonyl groups into elastic polyester material gels, we generated materials that can be molded into intricate designs with secondary crosslinking to generate constructs with highly tunable elasticity. By adapting material synthesis conditions (i.e. monomer ratios, reaction time), elastic mechanical behavior was highly tunable across a range of soft biomaterial applications. Material applicability was highlighted in a number of micro-designed elastomeric scaffold supports for engineered tissue, both for in vitro organ-on-a-chip and in vivo cardiac patch technologies, wherein the two-step synthesis process allowed for micro molding into intricate shapes prior to gelation.
With biomaterial application in vivo, inflammation at the biomaterial surface limits device application. To tackle this, we looked to itaconate, a powerful small molecule metabolite of innate immunity that has recently emerged as a regulator of innate immune inflammation. This molecule has been previously limited therapeutically by short circulation times. To circumvent this, itaconate was incorporated directly into material backbones to impart biomimetic small molecule modulation, with quantified hydrolytic degradation release from polyester chains. Harnessing hydrolytic degradation release from polyester backbones, itaconate polymers resulted in the mechanism specific immunoregulatory properties on macrophage polarization in vitro. In a functional assay, the polymer-released itaconate inhibited bacterial growth on acetate. Translation to an in vivo model of biomaterial associated inflammation, intraperitoneal injection of ITA polymers demonstrated a rapid resolution of inflammation in comparison to a control polymer silicone, demonstrating the value of sustained biomimetic presentation of itaconate. Using scalable polyester synthesis techniques, we have demonstrated the power of instructive biomaterial technologies as functional modulators of the cell microenvironment.

In order for machines and electronics to interface with biological tissue, they should be soft and elastic – i.e. remain functional when stretched and then return to their natural length when unloaded. In recent years, there has been tremendous progress in creating conductive elastomers and gels that are capable of extreme stretchability and which have been successfully utilized as bioelectronic interfaces. These include material architectures that are self-healing and can restore electrical and/or mechanical functionality when torn or punctured.

In this talk, I will review recent efforts to create mechanically robust, stretchable electronics using a variety of soft material architectures. In particular, I will focus on the following approaches: (i) silver-hydrogel composites that exhibit an unprecedented combination of mechanical compliance and electrical conductivity; (ii) biphasic compositions of silver nanoparticles and eutectic gallium-indium (EGaIn) liquid metal alloy for ultrathin “epidermal" electronics; and (iii) EGaIn-polymer composites capable of high electrical conductivity, extreme stretchability, negligible electromechanical coupling, and a variety of self-healing properties. To demonstrate their potential role in future bioelectronic applications, I will present examples of how these soft material architectures are used as electrodes for physiological monitoring (e.g. EMG, ECG) and as electrical interconnects for highly stretchable digital circuits.

The conventional bioelectronic interfaces have been based on either 2-D thin films or 1-D fibers/wires which limit 3-D scalability as well as volume-/mass-dependent performance. Moreover, biological tissues and organs typically exhibit 3D arbitrary curvatures with wet surface, which impeded the close physical contact between the target tissue/organ and bioelectronic interfaces, leading to the low efficiency in bioelectric signal recording and/or stimulation. In this research, we report on 3D monolithic architectures with arbitrary shapes by employing conducting polymer microstructures as building blocks. Such arbitrary 3D structures were constructed by performing the seamless fusion of separate conducting polymer microstructures without using binder or adhesive. The resultant 3D structures exhibited decent mechanical robustness, high water stability, and outstanding biocompatibility, while the sheet resistance was reduced below 1 Ohm/square and the gravimetric capacitance was increased up to 79 F/g by taking advantage of cumulative mass loading and structural fusion. Finally, we demonstrated that 3D conductive mesh electrodes could be attached to the wet surface of biological organs/tissues such as heart and sciatic nerves without glue or clamp and efficiently record/stimulate bioelectrical signals in vivo.