Photonic crystals with dynamic switching properties have tremendous potential applications in tunable lasers, biological/chemical sensors, and optical devices. As a building block, poly(N-isopropylacrylamide)(pNiPAm) hydrogel nanoparticles are particularly interesting due to their tunability in volume and size with response to temperature change. However, the use of pNiPAm nanoparticles as a building block has been strictly limited because the crystalline structures are easily destroyed by enhanced thermal fluctuations around their volume phase transition temperature. To circumvent this problem, two stepwise approaches have been proposed in previous studies; polymerization of monomers that are infiltrated through colloidal crystal templates; chemical interlocking of residual surface monomers between colloidal building blocks in crystal lattices. Both methods require several templating techniques followed by post chemical treatments. In this presentation we propose a direct method to assemble thermosensitive pNiPAm nanoparticles into a robust thermoresponsive photonic crystal. We use depletion forces to assemble colloidal particles under high ionic strength condition. The crystals forms spontaneously in the presence of non-adsorbing polymers, which stabilize the crystals against dissociation above the lower critical solution temperature (LCST) of the pNiPAm building blocks. The resulting photonic crystal displays dynamic switching of structural colors across full visible spectrum with temperature change.

During the last decade, as nanotechnology has built up excessively, a branch of it have been investigating reasons behind the coloration effects in biological sources such as pigments and structural coloring both of which currently have equal importance for the production of colored structures. However, beyond essence of this coloration for livings, physical phenomena responsible for them have attracted greater attention. Comprehensively, while pigments function by absorption and emission of specific visible wavelengths, mechanisms accounted for structural coloring observed in nature are associated with optical effects such as interference, scattering and photonic crystals or their combinations. Especially photonic crystals in living systems generally exhibit iridescence and brilliant coloring features, which exist not only for aesthetic beauty but also for camouflage, communication, sensing, and reasons that may still remain unexplored. Biomimicking of these nanostructures provides unmatched opportunities in nano-optics area and promotes design of novel photonic configurations. However, current fabrication methods could not provide mimicking of architectural complexity together with control, ease and economy as observed in nature and required for bio-inspired nano-featured macro-devices. This also accounts for even though there are successful biomimicking examples of 1D and 3D photonic crystals obtained by self-assembly or deposition techniques, more intricate one, 2D photonic crystals observed in nature cannot be replicated yet.
Here we investigate and perform successful nanobiomimicry of rare 2D photonic scheme observed on neck feathers of mallard drake. Our imitation is not limited with optical properties only but material features and architectural complexity are also taken into account. Home-built top-down approach called “Iterative size reduction” [1] is used for biomimicking since it supplies great advantages in terms of fabrication cost, speed and permit to control of final nanofeatured structure fabrication from macroscale. This work also demonstrates first all-polymer 2D solid core photonic crystal works at optical frequencies. Further engineering of photonic crystal fibers result with band-gap tunable coloration which cover whole visible spectrum in single fabrication process. In addition, superhydrophobicity observed on mallard feather is also imitated regarding hierarchical structures made up of aligned photonic crystal fibers.
[1] M. Yaman, Mehmet Bayindir, et al., Nature Materials 10, 494 (2011).

We are working with polymer nanomaterial composites. The materials we work with are inspired by human skin to incorporate functionalities, such as stretchability and self-healing in addition to being mechanically flexible. These materials not only allow the fabrication and demonstration of new types of devices, but also enable more robust performance and durability. I will discuss about these materials and their applications.

Stretchable electronics is a burgeoning field due to potential impactful applications such as sensor skins for robotics and prosthetics and wearable electronics for health monitoring and diagnosis. Effective multiplexing of stretchable sensor arrays can be facilitated by transistor-based active matrices. We have developed stretchable transistors that accommodate large strains (>150%) and are based on elastic components such as carbon nanotube (CNT) electrodes, elastomeric dielectrics, and organic semiconductors. Cost-effective solution processing methods, such as spincoating and spraycoating, have been utilized to suggest the potential for large-scale implementation. Bottom contact electrodes are patterned by spraycoating CNTs through a shadow mask onto a Si substrate and subsequently embedded in an elastomer. The semiconductor is transferred onto the electrodes, followed by spincoating an elastomeric dielectric. Performance characteristics for devices based on poly(3-hexylthiophene) (P3HT) include mobilities above 0.03 cm^2/Vs and an on/off ratio ~10^3. The substrate viscoelastic properties play an important role in determining the time-dependent characteristics of the device, and changes in device performance with cycling is dominated by the viscous relaxation of the substrate. The influence of each component (substrate, electrodes, dielectric, and semiconductor) on the device performance will be discussed.

Cephalopods are known as the chameleons of the sea - they can alter their skin&’s coloration, pattern, texture, and reflectivity to blend into the surrounding environment. Despite much research effort, there are few known strategies (natural or artificial) for emulating the unique dynamic reflectivity and coloration of cephalopods. We have drawn inspiration from self-assembled structures found in cephalopods to fabricate tunable biomimetic camouflage coatings. The reflectance of these coatings can be dynamically modulated between the visible and infrared regions of the electromagnetic spectrum in situ. Our studies represent a crucial step towards reconfigurable and disposable infrared camouflage for stealth applications.

Carbon nanomaterials, such as carbon nanotubes and graphene, constitute a relatively new class of materials exhibiting exceptional mechanical and electronic properties, and are also promising candidates as innovative materials for composites, electronic, sensing, and biomedical applications.
In the last few years, we have been working on the functionalization of nanotubes and graphene, with the scope of making these materials more biocompatible and to make them dispersible in solvents, including physiological solutions, and easier to manipulate.
We will therefore discuss our most recent results on the interaction of carbon-modified surfaces with biological/nonbiological matters, in attempts to offer new solutions to old problems.

Transformative nanomanufacturing routes is used to create single layer crumpled graphene nanoparticles through innovative electrohydromechanical concepts that capitalize on the salient mechanical features, rich surface chemistry and compelling colloidal properties of graphene in a multiscale and synergistic fashion to transcend the boundary for achieving high power density electrochemical capacitive energy storage. The proposed experimental strategies conceptually mimic the nano-emulsions at interfaces to confine the dimensional transitions of 2-D planar graphene into 3-D crumpled nanoparticles and their assembly into unprecedented superstructures, establishing a paradigm shift in synthesis and processing of crumpled graphene structures at nanoscale. Specifically, the work presented here enables the experimental isolation of single-layer crumpled graphene nanoparticles that first and foremost yield access to fully explore of exceptional “intrinsic material properties”, especially those pertinent to energy applications such as specific surface area, packing density, intrinsic capacitance, porosity, and ionic permeability.

Conjugated polymers are widely used in organic photovoltaics, biomedical interfaces, and chemical sensors for their reasonably high conductivity and relatively “soft” mechanical properties. Here we examined several polythiophene systems, including poly(3-hexylthiophene-2,5-diyl) (P3HT) and side group functionalized poly(3,4-propylenedioxythiophene) (PProDOT) derivatives by fabricating them into highly ordered polymer nanofibers via electrospinning. To facilitate the solution processing of the otherwise dilute and low viscosity conducting polymers, another relatively easy-to-process supporting polymer was introduced into the fabrication by either blending together with conjugated polymers or using a coaxial electrospinning setup. Macroscopically-aligned fibers were collected on substrates with an air gap of controlled geometry. Morphological results from electron microscopy confirmed that conjugated polymer nanofibers were obtained after solvent removal of the supporting polymer. Molecular orientation studies revealed the existence of preferred orientation between molecular backbones and the nanofiber axes, depending on specific electrospinning system. The electrical and mechanical properties of the conjugated polymer nanofibers were also investigated both macroscopically and microscopically.

Nowadays, the printed circuit boards (PCBs) are widely used in every electronic device as numerous kinds of forms with variety in their shapes, sizes and materials. As the next-generation flexible electronic devices, the flexible PCB systems have been researched and developed in various ways by designing flexible PCB itself or having unibody structure composed of both flexible inter-connectors and PCBs. We present a cost-effective stretchable inter-connection that can be readily used for PCBs fabricated by existing manufacturing process. We introduce a stretchable PCB inter-connection allowed by highly flexible silver nanowires (AgNWs) electrode on polydopamine-treated PDMS substrate[1, 2]. Optimized meander structure keeps silver nanowire&’s percolation for maintaining high conductivity during stretching experiment. The application of inter-connection on PCBs do not require sophisticated methods but only the non-soldering simple attachment and the promising stretchable capability of the inter-connection will broaden the applications of inter-connection with PCBs such as wearable PCBs.


[1] T. Rai, P. Dantes, B. Bahreyni and W.S. Kim*, “Stretchable RF Antenna with Silver Nanowires” IEEE Electron Device Letters 34, pp.544-546 (2013).
[2] T. Aktar, and W.S. Kim*, “Reversibly Stretchable Transparent Conductive Coatings of Spray-deposited Silver Nanowires” ACS Applied Materials & Interfaces, 4, pp.1855-1859 (2012).

Nature fascinates scientists with remarkable livings and creatures. Insect eyes, gecko foots, or lotus leaves inspire science with their multi-functional surfaces and a number of lithography techniques have been developed to fabricate these bio-inspired architecture; paraboloid, triangular, cylindrical, or conic structures on behalf of use in optical and electronic applications.
In this study, we produced biomimetic nanostructures. Proposed facile method for large-area production, utilizes reusable silicon molds and drop casting at ambient conditions to overcome complex environment requirements and multistep fabrication processes. Anodized aluminum oxide (AAO) membranes are used as mask during plasma etching and tapered nanopores are formed at desired lengths with high packing density on silicon molds. Polymer nanostructures are produced by drop casting of polymer solution directly on the silicon molds. Polycarbonate (PC) is chosen due to its high-transmittance, biocompatibility, durability, high impact resistance, and wide usage in electronic components. The fabricated polymer films demonstrate promising qualities in terms of antireflective, hydrophobic and surface enhanced Raman spectroscopy (SERS) features. In order to obtain maximum antireflection performance, design parameters of the 3D nanostructures are simulated using FDTD method prior to fabrication process. Inductively coupled plasma (ICP) etch conditions (i. e. process duration and pressure) are optimized for obtaining desired lengths and structure profile. We achieved up to 92% transmission from single-side nanostructured polymer films by implementing optimized nanostructure parameters. Besides the antireflection feature, produced tapered structures exhibit highly hydrophobic properties (145° water contact angle). We also demonstrated our nanostructured polymer surfaces as stand-free SERS substrate and observed 4.9 x 10⁶ enhancement factor in average SERS experiments.¹ A prominent feature of our facile fabrication method is its versatile nature that it can allow the production biomimetic nanostructures from different kinds of polymers and other moldable materials.
[1] J. Mater. Chem. C, 2013, DOI: 10.1039/C3TC31616E

Protein based polymers (PBPs) are valuable for biological research because of their intrinsic biocompatibility. Additionally, they can be designed and customized as needed to contain functional groups to interact with organic as well as inorganic materials. In this work, we utilize elastin-like polypeptides (ELPs) to create stimuli responsive hydrogels. ELPs, derived from natural elastin, are able to undergo coacervation based on conditions such as temperature, pH, and salt similar to tropoelastin in addition to being highly elastic. We also genetically engineered ELPs with an aromatic amino acid containing sequence, previously found in our lab to bind carbon nanotubes, to enable ELP to physically bind reduced graphene oxide (rGO) nanosheets. The rGO nanosheets act as photothermal heaters absorbing near infrared (nIR) light to produce heat. Using rGO nanosheets and ELP, we have designed fast and controllable light-responsive composite hydrogels.
These composite hydrogels heat up upon exposure to nIR light causing ELP chains to collapse. Anisotropic structure of the gels with porous and solid layers allows for different swelling/deswelling ratios for across the gel and causes them to ‘flex&’. The focus of our work has been to characterize the structure and function of these gels with varying compositions of rGO, ELP and the crosslinking agent. We use atomic force microscopy to observe the hydrogel micro-structure and characterize surface mechanics. Additionally, we characterize the bending of gels by measuring forces generated as the gels are stimulated by laser. Such hydrogel actuators have applications in drug delivery, biophysics, and soft robotics.

The mechanical properties of biomaterials at the micro-scale have become increasingly important in the investigation of cellular behavior at the cell-substrate interface [1]. At this interface, biomaterials exposed to physiological environments immediately adsorb protein before cellular adhesion can occur through a complex process in which cells exert force on the biomaterial to probe the surface [2,3]. This interaction is one of many reasons why understanding mechanical properties is important in the design of biomaterials. While the influence of the elastic component of mechanical properties on cells has been investigated previously, it has been difficult to detect the influence the viscous component of a biomaterial has on cellular activity.
Microgels are colloidally stable, hydrogel nano- or microparticles that have previously been used in biomaterial applications due to their tunable mechanical and chemical properties. In this work, we employ microgels composed of the monomer N-isopropylacrylamide, the co-monomer acrylic acid, and the cross-linker N,N&’-methylenebisacrylamide or poly(ethylene glycol) diacrylate. Microgel films have been constructed from anionic microgels and polycations such as poly(diallyldimethylammonium chloride) and polyethyleneimine, using a layer-by-layer method.
Using these microgel-based films, we demonstrate the ability to modulate the viscoelastic mechanical behavior of film assemblies by means of chemical cross-linking [4]. We have interrogated the films&’ macro-scale mechanical properties, such as self-healing, via the application of controlled, uniaxial stress and subsequent exposure to water. While uncross-linked films are able to self-heal, exhibiting plastic deformation, cross-linked films do not self-heal, exhibiting brittle cracking. We have also interrogated micro-scale mechanical properties of films via atomic force microscopy nano-indentation. Upon cross-linking, films exhibit an order of magnitude increase in Young&’s modulus.
Protein adsorption studies show that fibronectin adsorption increases with layer number and cross-linking; all films except for those made of poly(ethylene glycol) diacrylate exhibit relatively high protein adsorption. However, fibroblast adhesion studies reveal that cell number and cell spreading are not commensurate with protein adsorption. Monolayers and cross-linked films exhibit increased cell numbers and cell spreading in comparison to other films. These data indicate that the non-adherent properties of microgel films cannot be attributed to a typical non-fouling mechanism and we instead attribute these non-cell-adherent properties of microgel films to their viscoelastic behavior.
1. Bechtle, S. et al. Biomaterials, 2010, 31, 6378-6385.
2. Schakenraad, J. M. et al. Colloid Surface, 1989, 42, 331-343.
3. Rahmany, M. B. et al. Acta Biomater, 2013, 9, 5431-5437.
4. Saxena, S. et al. 2013. Manuscript submitted for publication.

Carbon nanotubes have unprecedented mechanical properties as defect-free nanoscale building blocks for high performance composites, but their potential has not been fully realized in composite materials due to weakness at the interfaces and the poor load-transfer efficiency. Here, we want to demonstrate that through load-transfer-favoring three-dimensional architecture and efficient nanotube interconnects, true potential of CNTs can be realized in composites as initially envisioned. Composite thin membranes with reticulate nanotube architectures show large improvement in strength compared to randomly dispersed short CNT reinforced composites reported before. By further increasing the number of nanotube-nanotube and nanotube-matrix interconnections through ion irradiation, very high mechanical strength (~900 MPa) and elasticity modulus (~25 GPa) were demonstrated in 300-nm thin film composites of in-plane randomly oriented CNTs.
This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

The controlled actuation of soft objects with functional nanocomponents in aqueous environments offers opportunities for stretchable electronics and complex assembled super-structures with unusual mechanical properties. We firstly demonstrate that the symmetry of the surface tension for a Galinstan liquid metal droplet can be broken by continuous electrowetting (CEW) effect when an external potential is applied to the surrounding solution, leading to high speed actuation of the liquid metal droplet in both basic and acidic electrolytes. Later, we coat liquid metal droplets with semiconducting nanoparticles to form so-called “liquid metal marbles”. These liquid metal marbles possess multi-facetted characteristics, as both liquid metal cores and nanoparticle coatings can be independently affected by an electric field. The nanoparticles can readily migrate along the surface of the liquid metal droplet when an external potential is applied; this allows us to study the change of surface tension on the surface of the marble. More importantly, we demonstrate that nanoparticle coating of these marbles offers an extra dimension for affecting the surface tension induced actuation. The coating alters the behaviour of the electrical double layer (EDL) on the surface of the marble, inducing surface tension in a highly asymmetric fashion, thus creating new avenues for inducing asymmetry and actuation behaviours. This significant novel phenomenon, combined with unique properties of liquid metal marbles, represents an exciting possibility for the assembly of multi-functional electro-mechanical superstructures.

Nanosized micelles self-assembled from amphihilic block copolymers are promising carriers for delivery of anticancer drugs. Most anti-cancer drugs have limited water solubility, and short blood circulation in the body systems, leading to frequent administrations. The core-shell nanostructure of micelles allows hydrophobic anti-cancer drugs to be encapsulated in the core, providing increased water solubility, prolonged blood circulation, reduced protein adsorption and recognition by the mononuclear phagocytic system. Nanosize gives rise to accumulation of micelles in tumor tissues based on the enhanced permeability and retention (EPR) effect.
In this study, biodegradable block copolymers of urea- and acid-functionalized aliphatic polycarbonate and polyethylene glycol (PEG) were synthesized and employed to encapsulate anticancer drugs into micelles. The non-covalent interactions formed between the urea/acid groups and drug molecules provided high drug loading levels, nanosize and excellent stability in the blood stream. The micelles were not toxic. They were observed to accumulate in tumor tissues in a mouse breast cancer model. As an example, thioridazine (THZ), which kills cancer stem cells responsible for tumor metastasis and relapse, and an anticancer drug (doxorubicin, DOX) were loaded into the micelles. The drug-loaded micelles were used to target both cancer cells and cancer stem cells via a co-delivery therapy. An increased cancer stem cell population in BT-474 human breast cancer cells was observed after treated with DOX-loaded micelles. However, the presence of THZ-loaded micelles reduced the cancer stem cell population, and enhanced anticancer efficacy of DOX-loaded micelles. In BT-474 xenografts in nude mice, the co-delivery of DOX-loaded micelles and THZ-loaded micelles produced significantly stronger antitumor efficacy than DOX-loaded micelles or THZ-loaded micelles alone. Importantly, the combination therapy reduced the number of cancer stem cells in the tumors. These functional micelles can be used to deliver a variety of anticancer drugs containing amine groups.

For quantified understanding of biological events at a single cell or subcellular level, direct insertion of a nano-scale probe has been attempted for electrical or electrochemical analysis. To minimize cell damage during probe insertion into cells, nanoprobes with high aspect ratio and ultra-sharp tip end is required. Although silicon or metal nanowires are widely used for cell insertion, their fabrication processes are expensive and time-consuming. In this study, we introduce a rapid prototyping method based on silk screen printing and thermal drawing to fabricate vertically-aligned polymer nanoprobe arrays. A parametric study was performed to understand the relationship between the nanoprobe shape and operation parameters such as drawing speed, temperatures, contact time, and dipping depth. Using silk screen printing, a fluorescent dye-mixed polymer nanoprobe array was fabricated on a transparent substrate. First, a 3x3 circular pattern was bored through a polyimide film with laser machining and used as a silk screening mask. After the polyimide film was fixed on a glass substrate, SU-8 2150 mixed with Rhodamine B was poured on the polyimide mask and doctor bladed with a razor blade. Afterwards, the polymer pattern array was soft baked for solvent removal and the film mask was detached. This created 3x3 array of circular patterns of SU-8 2150 on the glass substrate. Thereafter, a tungsten pillar was heated above the glass transition temperature (Tg) of SU-8 2150, and glass substrates were heated just below the Tg. The heated micro pillar was dipped in the heated SU-8 pattern and vertically drawn to desired height. Finally, through the breakage of liquid bridge between the pillar and substrate, polymer nanoprobe structure with high aspect-ratio was fabricated. This resulted in 3x3 array of vertically-alligned nanoprobes with 400 nm in diameter and 20 mu;m height. Multiple nanoprobe insertion into single cells was achieved using algal cells, Chlamydomonas reinhardtii, and their confocal fluorescent images confirmed the nanoprobe insertion into the cells.

Liposomes are tiny spherical capsules with a lipid bilayer shell and an aqueous core and have been used in many applications including gene and drug delivery. Liposomes can be prepared in the size scale of cells with lipid and protein compositions similar to that of natural cell membranes. These liposomes are referred to as giant proteoliposomes and closely mimic cellular membranes. They are, therefore, excellent model systems for studying complex cell surface processes such as the molecular events during the entry of pathogens and drugs into cells. Preparation of giant proteoliposomes with controlled size and composition is, however, challenging and typically requires rather sophisticated instruments.
Here we present a unique and versatile approach for the preparation of uniformly sized giant proteoliposomes without any specialized equipment. In this simple approach, hydrogel stamps first pattern lipids/proteins onto a conductive substrate. The patterned lipids/proteins are then applied for electroformation (hydration and exposure to an AC electric field) of giant (>10 µm) vesicles. Combining the commonly used technique of electroformation with the versatile technique of hydrogel stamping makes it possible to: (i) control the size of the resulting vesicles through adjusting the size of patterned lipid/protein patches, and (ii) incorporate functional membrane proteins in the membrane of giant vesicles.
We demonstrated the capability of the present method to produce vesicles populations with relatively narrow size distribution (38.8 ± 6.72 (mean ± S.D.) mu;m). We applied this technique to prepare giant liposomes from variety of lipid and protein compositions and further confirmed the bioactivity of the integral membrane proteins in these vesicles. The resulting liposomes are attached to the surface in an array format and can be used for the rapid and easy data collection for statistical analysis of membrane processes. Alternatively, these liposomes can be easily detached from the surface in order to produce a large number of giant vesicles with functional proteins. In the detached form, the liposomes can effectively encapsulate materials and provide an excellent tool for studying transport phenomenon across membranes. In addition, the use of adsorbent hydrogel stamps enables rapid production of multiple copies (>30) of a liposome array using minute amounts of lipids/proteins, making this technique attractive for high-throughput applications.
This approach may further be applicable to produce giant polymerosomes that offer increased stability compared to liposomes. This method of production of giant liposomes can, hence, be useful in biomaterials, biotechnology, and biosensing applications as well as in the biophysical fundamental studies.

The development of intelligent materials that can respond to the application of an external stimulus is of major interest for the fabrication of artificial sensing devices able to sense and transmit information about the physical, chemical and/or biological changes produced in our environment. Conducting crystalline organic solids exhibit a variety of interesting chemical and physical properties that could be used for developing such smart materials. However, these organic solids are generally obtained as small and fragile crystals precluding their use in practical devices. If these crystalline organic materials can be deposited or integrated on flexible and transparent substrates and processed employing low-cost techniques their appeal is greatly increased.[1]
Here, it will be shown that by using organic bi-layered thin films, composed of a polymeric matrix with a top-layer formed by a nanocrystalline network of a conducting crystalline molecular charge-transfer salt, is possible to translate the properties of single crystals onto the films yielding flexible, transparent, and thin materials with ultra sensitive piezoresistive properties showing durable, fast and completely reversible responses.[2] These bi-layered films can also be translated into different materials keeping their functionality intact. [3-4] In some cases the sensitivity (response) of such materials are one order of magnitude larger (faster) than most of commercial materials arising from the almost mass-less and composite nature of the thin film that combine the properties of the nanocrystals and the polymer. It is also possible to add to this kind of materials other properties like pyroresistivity and/or hygroresistivity making them real multifunctional materials.[5]
During this presentation a few proof-of-concept experiments with simple prototypes based on such soft nanocomposite polymeric materials will be discussed.
References
[1] M. Mas-Torrent et al., J. Mater. Chem. 2006, 16, 543
[2] R. Pfattner et al, Adv. Mater., 2010, 22 4198-4203
[3] L. Ferreras et al., J. Mater. Chem . 2011, 21, 637
[4] E. Steven et al, submitted, 2013
[5] V. Lebedev et al., J. Mater. Chem. C, DOI: 10.1039/C3TC31513D, 2013

Patterning functional materials is a central challenge across many fields of science. Despite the fact that there are hundreds of commercially available photoresists, the functional diversity amongst these materials is severely limited. In most applications, the photoresist serves the sole purpose of a sacrificial mask or mold; very rarely is the resist material incorporated as a structural element or chemically functional interface. The ability to generate new kinds of chemically functional materials directly via photolithography would enable a host of new applications, for example in microelectromechanical systems (MEMS), microfluidics, patterned biomaterials and artificial optical materials. We recently reported a negative tone photoresist using a photoactivated olefin metathesis catalyst, which can be quickly prepared in a one-pot synthesis from commercially available starting materials.
Olefin metathesis is a robust synthetic methodology that has led to new polymeric materials with many applications, such as drug delivery, organic electronics, and photonic crystals. We recently developed a method of patterning using a ruthenium photocatalyst, PhotoLithographic Olefin Metathesis Polymerization (PLOMP). In this procedure, a latent metathesis catalyst is activated by light to react with the olefins in the surrounding environment. We demonstrate a negative tone resist by using the photocatalyst to crosslink a difunctional ROMP monomer within a matrix of linear polymer. The versatility of ruthenium-mediated olefin metathesis can now be utilized to photopattern a variety of functional materials via PLOMP, advancing the field of photoinitiated olefin metathesis from a curiosity to materials science applicable to mass microfabrication.
These olefin-rich solutions are competent UV photoresists, at both 254 nm and 352 nm. Under 254 nm irradiation, we were able to cure 1-2 micron thick films in 60 to 90 seconds using a benchtop 8-watt lamp. Functional diversity has been incorporated into PLOMP resists in a number of ways, including copolymerization of functional monomers into the linear polymer, and through the introduction of additives into the resist solution. We have successfully incorporated a variety of functional groups into the resist material, including esters, acids, ethers, amines and isocyanates. As well, we have demonstrated direct write lithography to generate 3D nanostructures with unique chemical functionality. We anticipate that PLOMP will enable the development of directly patterned micro- and nanostructures with chemical, mechanical and optical functionality not currently available with existing fabrication techniques.
1) Weitekamp, R.A., Atwater, H.A., Grubbs, R.H. JACS (ASAP) 2013

Recent research in flexible and stretchable electronics has shown remarkable advances along with their increasing applications in the wearable computer and bio-implantable electronics. Among various design strategies for stretchable electronics, positioning mechanical neutral plane and forming curved/serpentine interconnection enabled a stretching of the whole device over 50% via minimizing the strain applied to the active device area. In order to guarantee the mechanical stability, the whole device as well as the interconnections was additionally encapsulated with a thin polymer film.
In this work, we propose a novel design concept of stretchable devices with embedded interconnections in the soft elastomer substrate to reduce the local strain in the active device area. The new 3-dimensional (3D) stretchable substrate consists of relatively rigid island arrays (PDMS with young`s modulus of 615 kPa) for active devices on the both sides of the soft thin film (mixture of PDMS and Ecoflex with young`s modulus of 122 kPa), where the active devices are connected by 3D embedded liquid metal (EGaIn) interconnection. Such design of both-sided integration also increases the density of active devices by two.
Array of four different devices including CNT homo-junction diode, micro-supercapacitor, SnO2 nanowire UV sensor, and micro-LED array, was transferred onto the rigid islands via dry transfer process to form an integrated circuit on the newly fabricated 3D stretchable substrate. Upon stretching of the whole devices up-to 50%, the change of the individual device performance was not noticeable. It is attributed to the relatively small strain applied to the active device area: according to the finite element method (FEM), the local strain of less than 7% in the active device island was estimated while the whole 3D stretchable device was stretched to 50%. Furthermore, bending and twisting did not deteriorate the device performance.
This work demonstrates that our new 3D stretchable electronics design would contribute to the future wearable computer technology and the high density stretchable device application.

Availability of potable water in many parts of the world is becoming increasingly scarce due to many pollutants entering the water supply. The objective of this study was to prepare hybrid PVA-gluten hybrid nanofiber, which is a non-toxic and biodegradable for investigating the extractions of pollutants from water. Electrospinning was used to prepare the fiber mats and TEM, SEM, EDS and FTIR were used to investigate the morphology, elemental composition and functional groups on the surface. Influence of experimental pH, time and concentration of the nanoparticles towards extraction of nanoparticles from water were quantified using UV-Vis spectroscopy. The kinetic and equilibrium adsorption data were interpreted using Freundlich and Langmuir isotherms and adsorption mechanism was investigated to understand the adsorption process. Nanofiber mats with high surface area provided an efficient adsorption for nanoparticle removal from water. Nanofiber mats with 5wt% gluten exhibited a high extraction efficiency of 99% towards citrate capped silver (Ag) and gold (Au) nanoparticles with a maximum adsorptive capacity of 41.5 mg/g for citrate capped Ag nanoparticles and 23.3 mg/g for citrate capped Au nanoparticles. Our results indicate that the prepared PVA-Gluten nanofibers can be utilized as efficient low-cost nano-absorbents for removal and recovery of metal nanoparticles from aqueous environment.
Keywords: PVA, Gluten, Nanofiber, Nanoparticle, Environmental.
Acknowledgement: The authors acknowledge funding support from the National University of Singapore (NUS) and Singapore-Peking-Oxford Research Enterprise, COY-15-EWI-RCFSA/N197-1. Technical support from Department of Chemistry and NUS Environmental Research Institute is also acknowledged.

We report novel cell co-culture platforms based on transparent, nanoporous, and transferable (TNT) polymeric membranes, allowing for controlling interaction types (i.e., paracrine or gap junction signaling) as well as the degree of signaling between co-cultivated cells. Since the TNT polymer membranes were prepared by the non-solvent induced phase separation of cellulose acetate (CA) solutions, pore size and film thickness of the TNT membranes can be easily adjusted, at the sub-micrometer scale, by controlling solvent type as well as solution concentration. The TNT membranes with controlled pore size and film thickness enable us to design precise in vitro analysis platforms to study different types of cell-cell communications. Based on the TNT membranes, we have investigated the behavior of metastatic cancer cells when they were subject to co-culture with three different stromal cell lines (i.e., fibroblasts, myoblasts, and human mesenchymal stem cells) by tracking cytokine-based paracrine signals with different stromal cell type. Furthermore, high flexibility in stacking and destacking of the TNT membranes allowed us to address many issues of conventional cell co-culture methods that lack in identifying the routes for efficient cell-cell signaling or to separate each cell line for further analysis and applications.

The diphenylalanine (FF) motif plays an important role in causing the Alzheimer&’s Aβ polypeptide to self-assemble into fibrils in vivo. These fibrils aggregate to become plaques, which are present in the brains of Alzheimer&’s patients. It is believed that the soluble pre-fibrillar aggregates are toxic rather than the final plaque products. Gazit et al. have shown that FF, when dissolved in water, will self-assemble into peptide nanotubes [1]. These nanotubes are attractive for applications in nanotechnology because they are inherently biocompatible, and have high chemical and thermal stability [2]. It is important to understand the FF self-assembly process in order to help inform strategies for treating Alzheimer&’s disease, and to obtain precise control over the assembly of these nanostructures.
The kinetics of the formation of these structures was studied experimentally while at the same time a multi-scale theoretical approach was followed to describe the assembly and growth of the nanotubes. To this aim, linear dichroism (LD) was used to produce time course data for the formation of these nanotubes. It was shown that 40 °C is a critical temperature in the onset of the assembly. Right-angle light scattering was used to confirm the LD results. Also, structural studies were done with scanning electron microscopy (SEM). These images clearly demonstrated the hexagonal, sometimes hollow nature of the fibres. SEM measurements also allowed us to quantify the fibre size distribution and to determine its dependence on different preparation methods. Finally, molecular dynamics (MD) simulations were employed to determine the origin of the very high aspect ratio of the fibres. The results showed that interactions within hexagonally ordered peptide planes are much less relevant than interactions perpendicular to these planes and thus parallel to the long axis of the fibres. The next step is to move from a thermodynamic explanation to a kinetic model which will be able to describe the experimentally observed growth curves.
References
[1] M. Reches and E. Gazit, (2006) &’Molecular Self-Assembly of Peptide Nanostructures: Mechanism of Association and Potential Uses&’, Current Nanoscience, vol. 2, pp. 105-111.
[2] N. Kol, D. Barlam, R.Z. Shneck, E. Gazit and I. Rousso, (2005) &’Self- Assembled Peptide Nanotubes Are Uniquely Rigid Bioinspired Supramolecular Structures&’, Nano Letters, vol. 5, pp. 1343-1346.

Self collapsing gels are a new type of gels that collapse due to formation of nanoparticles [1]. The formation of the gel is due to electrostatic attraction between Au(III) ions and chitosan. As the ions get reduced and become nanoparticles, the gels collapse due to breakage of bond between neighboring chitosan molecules. They have potential applications in drug delivery. In this research chitosan-gold self collapsing gels were made by adding HAuCl4.3H2O to 1 wt% chitosan solution containing 1.5 wt% acetic acid and then carbon nanotubes (CNTs) were added to the solution. It was observed that the stability of the gel depended upon the con