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Cellulose nanofibers (CNFs) have received considerable attention as reinforcing fillers due to their excellent and versatile properties, including physical, morphological, and chemical features. Despite many advantages of CNFs, the hydrophilic nature of CNFs significantly limits their use as fillers. In this study, CNFs were modified by esterification with two kinds of carboxylic acids: valeric acid (VA) and hexanoic acid (HA). The degree of substitutions (DS) of VA-CNF and HA-CNF was 2.78 ± 0.04 and 2.61 ± 0.02, respectively. The dispersibility in an isopropanol solvent showed the controlled hydrophilicity of the modified CNFs. Moreover, the water contact angles of VA-CNF and HA-CNF were 79.2 ± 3.1° and 85.0 ± 1.7°, respectively, while the neat CNF was just 18.9 ± 1.6°. The thermogravimetric analysis (TGA) revealed that the modified CNFs have much better thermal stability than the neat CNFs. Also, the CNF films showed uniform-sized nano-porous structures after the modifications of CNFs. Combined with well-improved hydrophobicity, these multi-faceted results suggest that our esterification technique of CNFs can be applied in a wide range of eco-friendly materials applications.

A biosensor was prepared with natural melanin nanoparticles (MNP) decorated on a screen-printed carbon electrode (SPCE). Hexavalent chromium was selected as a well-known heavy metal ion to be detected for testing the performance of novel biosensor. Natural MNP was extracted from cuttlefish (Sepia officinalis) ink. Surface decoration of SPCEs with MNP was performed by two different methods. The first one was layer-by-layer assembly (LBL-A) for different cycle times(n). In the second one, plasma treatment of SPCE incorporated with evaporation-induced self-assembly (EI-SA) techniques including different incubation times in MNP solutions. The performance of both modified SPCEs were tested for amperometric detection of Cr(VI) in various water samples, and peak reduction of Cr(VI) was determined at 0.33 V. Amperometric results showed wide linear ranges of 0.1–2 ?M and 0.1–5 ?M of Cr(VI) for SPCEs modified with 14n-LBL-A and 12h-EI-SA, respectively. The sensitivities of SPCEs modified with 14n-LBL-A and 12h-EI-SA techniques were 0.27 ?A ?M?1 and 0.52 ?A ?M?1, respectively. In addition, both modified SPCEs selectively detected Cr(VI) in a model aqueous system composed of certain other heavy metals and minerals, and tap and lake water samples. The LOD and LOQ values for 12h-EI-SA were 0.03 ?M and 0.1 ?M, respectively. This showed that MNP-modified-SPCEs generated via EI-SA techniques have the potential to be an alternative to conventional detection methods such as ICP-MS.

Micro- and nanotextured surfaces with reconfigurable textures can enable advancements in the control of wetting and heat transfer, directed assembly of complex materials, and reconfigurable optics, among many applications. However, reliable and programmable directional shape in large scale is significant for prescribed applications. Herein, we demonstrate the self-directed fabrication and actuation of large-area elastomer micropillar arrays, using magnetic fields to both program a shape-directed actuation response and rapidly and reversibly actuate the arrays. Specifically, alignment of magnetic microparticles during casting of micropost arrays with hemicylindrical shapes imparts a deterministic anisotropy that can be exploited to achieve the prescribed, large-deformation bending or twisting of the pillars. The actuation coincides with the finite element method, and we demonstrate reversible, noncontact magnetic actuation of arrays of tens of thousands of pillars over hundreds of cycles, with the bending and twisting angles of up to 72 and 61°, respectively. Moreover, we demonstrate the use of the surfaces to control anisotropic liquid spreading and show that the capillary self-assembly of actuated micropost arrays enables highly complex architectures to be fabricated. The present technique could be scaled to indefinite areas using cost-effective materials and casting techniques, and the principle of shape-directed pillar actuation can be applied to other active material systems.

Conductive polymers (CPs) are gaining considerable attention as materials for implantable bioelectronics due to their unique features such as electronic-ionic hybrid conductivity, mechanical softness, ease of chemical modification, as well as moderate biocompatibility. CPs have been utilized for a wide range of applications including neural engineering, regenerative medicine, multi-functional sensors and actuators. This review focuses on CP materials design for use in bio-interfacing electronics including composites, conductive hydrogels, and electrochemical deposition. We start by elaborating on the fundamental materials characteristics of CPs, including bio-electrochemical charge-transfer mechanisms, and contrast them with naturally derived CPs. We then present recent critical examples of the bioelectronic and biomedical applications of CPs, including neural recording and stimulation, tissue regeneration, stretchable electronics, and mechanical actuation. We conclude with a perspective of the current material challenges of CPs in bio-interfacing electronics.

Achieving biological softness and flexibility has been a critical challenge for bio-electronic materials in areas of implantable bionic interfaces and wearable devices. Unlike inherently rigid electronic materials, bioengineered interfaces or scaffolds require stretchable softness as well as functional porosity for selective ionic transports. Toward this goal of providing electrically conducting biomaterials, we report ultrathin single-walled carbon nanotube (SWNT) layer coating on biodegradable polycaprolactone (PCL) membranes via layer-by-layer (LBL) assembly technique. The resulting membranes have unique, hierarchically structured 3D network of conductive paths around asymmetric nano-/micro-pores, providing softness as well as stretchable, anisotropic electrical conductivity. The strain sensors embedded on the membrane also demonstrate bending directional sensitivity as well as piezoresistivity with tunable Gauge Factor (GF) in the ranges of 5–13 with stretchability of up to 100%. Furthermore, these composite membranes are biocompatible as evident by neuronal cell attachment tests with in vitro PC12 cell lines. As follows, this newly developed implantable multifunctional membrane has considerable potential for applications in bioengineered devices such as mechano-sensitive artificial interfaces and skins.

Thylakoids, on which complete sets of photosynthetic membrane proteins are contained, behave as soft nanoparticles of a few tens nm sizes. Thus, we separated the thylakoid extracts from spinach chloroplasts and densely organized them in a film with either insulating polyethyleneimine (PEI) or conducting polyaniline (PANI) by molecularly controlled layer-by-layer (LBL) assembly. The resulting nanostructured composite films demonstrated photoelectrochemical activities with thylakoids whose stabilities were significantly improved on the charge balanced LBL multilayers compared to one on a randomly deposited film or in solution. The thylakoid LBL films continuously generated photochemical electrons for longer than 130 h with the 2,6-dichlorophenolindophenol (DCPIP) mediated photosynthetic energy conversion cycle while photoactivities of thylakoid moiety slowly decreased in the open circuit potential measurements throughout which the photosynthetic redox cycles were incomplete. As the photofunctional groups of the thylakoid films originated from a biotic system and the photofuctional thylakoids were exceptionally well preserved on the charge-balanced artificial structures, the developed thylakoid LBL film have shown inherent biocompatibility upon PC12 neural cell attachment and differentiation tests, which are essential qualities for emerging human-friendly electronic applications such as disposable electronics, artificial retina, and implantable neural interfacing meditronics as well as cell-free photosynthetic production.

In advanced forms of diabetic retinopathy, retinal vascular occlusive disease and exudative age-related macular degeneration, vision loss is associated with elevated levels or extravasation of vascular endothelial-derived growth factor (VEGF) into the retina, vitreous, and anterior chamber of the eye. We hypothesize that point-of-care biosensors, capable of rapidly and precisely measuring VEGF levels within the eye will assist clinicians in assessing disease severity, and in establishing individualized dosing intervals for intraocular anti-VEGF injection therapy. An impedance biosensor based on a poly(3,4-ethylenedioxythiophene) (PEDOT)/gold nanoparticle (Au NP) composite was developed for detecting VEGF. PEDOT with Au NP was electrochemically deposited on three different medical electrode sensor designs: free-standing pads, screen printed dots, and interdigitated micro-strip electrodes. Anti-VEGF antibody was covalently immobilized on the surface of the polymer films through attachment to citrate-functionalized Au NPs, and the resulting composites were used to detect VEGF-165 by electrochemical impedance spectroscopy (EIS). The PEDOT-Au NP composite materials were characterized using optical microscopy, SEM/EDS, FIB, TEM, and STEM techniques. Among the different micro-electrodes, the interdigitated strip shape showed the best overall film stability and reproducibility. A linear relationship was established between the charge transfer resistance (R ct ) and VEGF concentration. The detection limit of VEGF was found to be 0.5 pg/mL, with a correlation coefficient of 0.99 ± 0.064%. These results indicate that the proposed PEDOT/Au NP composites can be used in designing low-cost and accurate VEGF biosensors for applications such as clinical diagnosis of VEGF-mediated eye disease.

The microporous layer (MPL) in proton exchange membrane fuel cells (PEMFCs) improves the fuel cell performance remarkably. However, PEMFCs suffer from local oxygen starvation at high current densities because of the accumulation of water at the cathode. This paper presents a novel water management technique that uses open furrows with serpentine patterns in the MPL. The laser ablation technique is used to carve open furrows in the MPL, and the various properties of the furrowed MPL are characterized. To examine the effects of the furrowed MPL on water management, the polarization behavior, impedance response, and potential variation under dynamic load tests are studied experimentally and theoretically for PEMFCs with three different gas diffusion layers. The results indicate that open furrows in the MPL reduce the water saturation in the catalyst layer and increase the water discharge to the gas flow channel, thereby promoting oxygen transport to the catalyst sites.

We describe the synthesis and characterization of hierarchically porous organic-inorganic hybrid silica with periodic 2-D hexagonal order and tunable location of secondary nanopores through co-condensation of tetraethylorthosilicate (TEOS) and a new type of amphiphilic organosilicate precursors. Our amphiphilic organosilicates offer unique tunability of secondary micropores by carefully controlled bond molecular structure and number of bonds between hydrophobic adamantylphenols pore-generating moieties and siloxane precursors. Small angle X-ray scattering (SAXS) and microscopy results show a good structural order of the organic-inorganic hybrid silica. In addition, 29Si CP-MAS NMR spectra confirm the successful incorporation of organosilicate precursors into a silica framework. The primary cylindrical mesopores (∼6.4 nm) were originated from the cooperative self-assembly of Pluronic P123 triblock copolymer templates while smaller meso-/micropores were derived from adamantylphenols groups. We have previously demonstrated that adam-graft SQ had an affinity for hydrophobic PO core blocks to be located close to PO segment, which resulted in small pores next to primary mesopores and the resultant increment of mesopore size as well as wrinkled silica walls. On the contrary, the secondary small pores were mainly generated within a silica network while the size of the primary mesopores unaffected with the addition of adam-bridge SQ due to its selective incorporation into a silica framework. Moreover, the organic-inorganic hybrid silica prepared with adam-bridge SQ showed higher thermal stability than that of adam-graft SQ and SBA-15 type mesoporous silica. It is attributed to more Si O Si bonds formed from the bridged structure as well as enhanced hydrogen-bonding interaction between adam-bridge SQ hybrid silica and P123 templates.

Melanin is a common name used for a certain type of natural dark pigments existing in living organisms, particularly in human hair, eyes, and skin. The unique free radical scavenging effect of melanine could help protecting cells and tissues from harmful UV light. While their exact molecular structures in nature are not still well defined, their multifunctional properties including electrical and ionic conductivities, antioxidation, wet adhesion, and metal ion chelation, are highlighted for the potential applications in bioorganic electronics including biomedical sensors and devices. In this mini-review, we will discuss sources, synthesis methods, structures and multifunctional properties of melanin materials in addition to current research directions on a wide range of applications.

Cellulose, the chain of glucose residues easily obtained from nature, is the most common natural polymer. Owing to its own unique material properties, compared to the conventional usage, nanocellulose (NC) with a crystalline structure can be considered to be used in various industrial applications. As a novel sustainable future material, we review the recent achievements of NC from the view point of material extraction and the composite processes to some extended important applications. While the mechanical properties of NCs and the energy consumption during their composite processing are the key considerations, their application potentials have never been limited to mechanical or commodity products as conventional celluloses. In the latter part of this review, emerging engineering applications of NCs such as energy storage, flexible electronics, and smart materials will be further discussed for readers searching future high-end eco-friendly functional materials. Also some suggestions for potential applications will be also discussed.

We describe the synthesis and characterization of bicontinuous cubic poly(3,4-ethylenedioxythiophene) (PEDOT) conducting polymer gels prepared within lyotropic cubic poly(oxyethylene)10 nonylphenol ether (NP-10) templates with Ia3[combining macron]d (gyroid, GYR) symmetry. The chemical polymerization of EDOT monomer in the hydrophobic channels of the NP-10 GYR phase was initiated by AgNO3, a mild oxidant that is activated when exposed to ultraviolet (UV) radiation. The morphology and physical properties of the resulting PEDOT gels were examined as a function of temperature and frequency using optical and electron microscopy, small-angle X-ray scattering (SAXS), dynamic mechanical spectroscopy, and electrochemical impedance spectroscopy (EIS). Microscopy and SAXS results showed that the PEDOT gels remained ordered and stable after the UV-initiated chemical polymerization, confirming the successful templated-synthesis of PEDOT in bicontinuous GYR nanostructures. In comparison to unpolymerized 3,4-ethylenedioxythiophene (EDOT) gel phases, the PEDOT structures had a higher storage modulus, presumably due to the formation of semi-rigid PEDOT-rich nanochannels. Additionally, the storage modulus (G') for PEDOT gels decreased only modestly with increasing temperature, from ∼1.2 × 10(5) Pa (10 °C) to ∼7 × 10(4) Pa (40 °C), whereas G' for the NP-10 and EDOT gels decreased dramatically, from ∼5.0 × 10(4) Pa (10 °C) to ∼1.5 × 10(2) Pa (40 °C). EIS revealed that the impedance of the PEDOT gels was smaller than the impedance of EDOT gels at both high frequencies (PEDOT ∼10(2) Ω and EDOT 2-3 × 10(4) Ω at 10(5) Hz) and low frequencies (PEDOT 10(3)-10(5) Ω and EDOT ∼5 × 10(5) Ω at 10(-1) Hz). These results indicated that PEDOT gels were highly ordered, mechanically stable and electrically conductive, and thus should be of interest for applications for which such properties are important, including low impedance and compliant coatings for biomedical electrodes.

The real-time temperature measurement of nanostructured materials is particularly attractive in view of increasing needs of local temperature probing with high sensitivity and resolution in nanoelectronics, integrated photonics, and biomedicine. Light-induced heating and Raman scattering of single-walled carbon nanotubes with adsorbed gold nanoparticles decorating silica microparticles are reported, by both green and near IR lasers. The plasmonic shell is used as nanoheater, while the single-walled carbon nanotubes are Raman active and serve as a thermometer. Stokes and Anti-Stokes Raman spectra of single-walled carbon nanotubes serve to estimate the effective light-induced temperature rise on the metal nanoparticles. The temperature rise is constant with time, indicating stability of the adsorption density. The effective temperatures derived from Stokes and Anti-Stokes intensities are correlated with those measured in a heating stage. The resolution of the thermal experiments in our study was found to be 5-40 K.

Graphene, a carbon crystal sheet of molecular thickness, shows diverse and exceptional properties ranging from electrical and thermal conductivities, to optical and mechanical qualities. Thus, its potential applications include not only physicochemical materials but also extends to biological uses. Here, we review recent experimental studies about graphene for such bioapplications. As a prerequisite to the search to determine the potential of gra- phene for bioapplications, the essential qualities of graphene that support biocompatibility, were briefly summarized. Then, direct examples of tissue regeneration and tissue engineer - ing utilizing graphenes, were discussed, including uses for cell scaffolds, cell modulating interfaces, drug delivery, and neural interfaces.

Gold nanoparticle aggregate carbone nanotube functionalized colloidal particles serve as probes for label-free stable detection of biomolecules inside living cells. The probes provide the means of effective localization of signal and produce significant enhancement of Raman scattering of molecules. The approach demonstrated in this work opens opportunities for detection and imaging of biomolecules in cell biology and molecular sensing.

SAN/ nanofibers were fabricated by an electrospinning process and used as chemiresistors for sensing alcohol vapours. A hydrophobic and air-stable ionic liquid, , was used to impart electrical conductivity to insulating SAN nanofibers. The effects of addition on the morphology of the nanofibers were explained in terms of surface tension, viscosity and conductivity. After exposing the SAN/ nanofibers collected on an interdigitated electrode to alcohol vapours (ethanol, 1-propanol and 1-butanol), the resistance of the nanofibers decreased due to adsorption of alcohol molecules. The electrospun SAN/ nanofibers sensor exhibited good sensitivity and reproducibility.

Single-wall carbon nanotubes modifi ed by anionic polyelectrolyte molecules are embedded into the shells of microcapsules. Carbon nanotubes serve as rigid rods in a softer polymeric capsule, which forms a free-standing shell upon treatment with glutaraldehyde and subsequent drying. The embedded carbon nanotubes exhibit a broad absorption in the UV‐near-infrared part of the spectrum, and that allows point-wise activation and opening of the microcapsules by laser. Raman signal analysis shows changes of carbon-nanotube-specifi c lines after high-power laser irradiation, which is characteristic of the formation of disordered carbonlike structures. These polyelectrolyte/carbon nanotube composite capsules represent a novel light-addressable type of microcontainers.

We present a conformal and lightweight antenna technology based on E-textile conductors and polymer-ceramic composites. Unique advantages of the proposed technology are its structural integrity, light weight and conformity to the platform. E-textile conductors are fabricated with single wall carbon nanotube (SWNT) and Ag coated textiles. They demonstrate good structural integrity with polymer composites due to their mechanical compatibility. Similarly, polymer composites demonstrate superior RF performance with permittivity ranging from 3 to 13. Fabrication process for E-textile conductors and integration process with polymer composites is described in detail. We also demonstrated merit of the proposed technology with a simple patch antenna whose radiation performance is measured when it was flat and conformed onto a cylindrical surface. We compared its performance with that of an ideal patch. Experiments suggested that the sample patch antenna based on the proposed technique achieved 6 dB gain, which is 2 dB below a patch which has the same dimensions and made of ideal lossless materials. When it is conformed onto a cylindrical surface, we achieved 2.5 dB less gain than that of antenna realized with a PEC surface. This clearly validates the merit of the proposed conformal antenna technique based on non-traditional materials.

Exponentially growing layer-by-layer (e-LBL) assembled films attracts a lot of attention mostly due to multiple practical applications in biology and medicine. However, e-LBL was observed only for a very limited number of polymers. This fact inevitably limits the area of research and functionalities that one can obtain for them. Also, it is fundamentally important to gain better understanding of the effect and importance of molecular flexibility for e-LBL films. Here we report that dispersions of rod-like nanocolloids such as single walled carbon nanotubes (SWNTs) and nanowires (NWs) can spontaneously “bore into” and stay in the e-LBL matrix. Molecular rigidity and surface charge appear to be the key parameters determining the possibility of such a process and its extent. SWNT forms a thick 2−25 μm penetration layer, while insufficient flexibility leads to hedgehog structures in the case of CdTe and Te NWs. Electrical properties of the films obtained display fundamental differences with SWNT composites ma...

Efficient coupling of mechanical properties of SWNTs with the matrix leading to the transfer of unique mechanical properties of SWNTs to the macroscopic composites is a tremendous challenge of today's materials science. The typical mechanical properties of known SWNT composites, such as strength, stiffness, and toughness, are assessed in an introductory survey where we focused on concrete numerical parameters characterizing mechanical properties. Obtaining ideal stress transfer will require fine optimization of nanotube-polymer interface. SWNT nanocomposites were made here by layer-by-layer (LBL) assembly with poly(vinyl alcohol) (PVA), and the first example of optimization in respect to key parameters determining the connectivity at the graphene-polymer interface, namely, degree of SWNT oxidation and cross-linking chemistry, was demonstrated. The resulting SWNT-PVA composites demonstrated tensile strength (σ(ult)) = 504.5 ± 67.3 MPa, stiffness (E) = 15.6 ± 3.8 GPa, and toughness (K) = 121.2 ± 19.2 J/g with maximum values recorded at σ(ult) = 600.1 MPa, E = 20.6 GPa, and K = 152.1 J/g. This represents the strongest and stiffest nonfibrous SWNT composites made to date outperforming other bulk composites by 2-10 times. Its high performance is attributed to both high nanotube content and efficient stress transfer. The resulting LBL composite is also one of the toughest in this category of materials and exceeding the toughness of Kevlar by 3-fold. Our observation suggests that the strengthening and toughening mechanism originates from the synergistic combination of high degree of SWNT exfoliation, efficient SWNT-PVA binding, crack surface roughening, and fairly efficient distribution of local stress over the SWNT network. The need for a multiscale approach in designing SWNT composites is advocated.

In this study the strong effect of surface density of stabilizers on the outcome of the typical cation replacement reaction in nanoparticles is demonstrated. The density of 2-aminoethanethiol coating determines the growth mode and morphology of the transformation products of CdTe nanoparticles induced by Ag cations. Using quantitative measurements of the stabilizer's surface density, it is demonstrated that CdTe nanoparticles produce Ag2Te nanowire networks upon partial removal of the stabilizer. This process follows the kinetically controlled growth mode but the mechanism changes drastically once stabilizer density is increased. The formation of spherical Ag2Te nanoparticles was observed when CdTe retained the original density of 2-aminoethanethiol. This study provides better understanding of (1) non-classical growth mechanisms of crystals at the nanoscale, (2) effect of stabilizer density on chemical transformations of nanoparticles, and (3) new routes for preparation of nanomaterials.

The idea of electronic yarns and textiles has appeared for quite some time, but their properties often do not meet practical expectations. In addition to chemicallmechanical durability and high electrical conductivity, important materials qualifications include weavablity, wearability, light weight, and "smart" functionalities. Here we demonstrate a simple process of transforming general commodity cotton threads into intelligent e-textiles using a polyelectrolyte-based coating with carbon nanotubes (CNTs). Efficient charge transport through the network of nanotubes (20 omega/cm) and the possibility to engineer tunneling junctions make them promising materials for many high-knowledge-content garments. Along with integrated humidity sensing, we demonstrate that CNT-cotton threads can be used to detect albumin, the key protein of blood, with high sensitivity and selectivity. Notwithstanding future challenges, these proof-of-concept demonstrations provide a direct pathway for the application of these materials as wearable biomonitoring and telemedicine sensors, which are simple, sensitive, selective, and versatile.

The preparation of a high-strength and highly transparent nacre-like nanocomposite via layer-by-layer assembly technique from poly(vinyl alcohol) (PVA) and Na+-montmorillonite clay nanosheets is reported in this article. We show that a high density of weak bonding interactions between the polymer and the clay particles: hydrogen, dipole-induced dipole, and van der Waals undergoing break-reform deformations, can lead to high strength nanocomposites: sigmaUTS approximately 150 MPa and E' approximately 13 GPa. Further introduction of ionic bonds into the polymeric matrix creates a double network of sacrificial bonds which dramatically increases the mechanical properties: sigmaUTS approximately 320 MPa and E' approximately 60 GPa.

Conductive organic and composite films represent the critical component of many areas of technology. This study demonstrates that highly conductive coatings can be made by layer-by-layer (LBL) assembly of single-walled carbon nanotubes (SWNTs). These films reveal electrical conductivities of 102 to ∼103 S/m at room temperature without doping with nanotube loading as low as ∼10%. This is indicative of efficient utilization of SWNT in percolation pathways. Low SWNT loading also makes the coatings quite transparent with transmission as high as 97% for visible light. Thicker delaminated LBL films displayed conductivities of 4.15 × 104 S/m. The free-standing films were highly flexible and possessed 160 MPa of tensile strength, which makes them the strongest organic conductor. The high strength and conductivities are attributed to the unique homogeneity of the LBL assembled composites, which opens the way to future optimization of electrical, mechanical, and optical properties and to fit the needs of specific a...

Molecular engineering of multilayered composites by layer-by-layer assembly (LBL) made possible easy replication of mechanical properties of nacre. Taking advantage of the ability of LBL to finely control the structure of the composite, one can further improve the mechanical properties of the multilayers, e.g., increase the strength and stiffness, and gain better understanding of the nanoscale and molecular scale mechanics of the materials critical for a variety of advanced technologies. In this study, we have replaced poly(diallyldimethylammonium chloride) (PDDA) (sigmaUTS approximately 12 MPa, E approximately 0.2 GPa) with a much stronger polysaccharide polycation, chitosan (CH, sigmaUTS approximately 108 MPa, E approximately 2 GPa), considering that its superior molecular strength will improve the macroscale mechanical properties of the nanocomposite: strength and stiffness. Free-standing films of the CH and montmorillonite (MTM) have been successfully made, and the resulting films revealed high uniformity with very high loading of MTM closely comparable to that in the natural nacre, approximately 80 wt %. Contrary to our expectations and theoretical predictions, the CH-MTM composite revealed lower strength and stiffness than those of PDDA-MTM and lower strength than CH polymer itself: sigmaUTS approximately 80 MPa and E approximately 6 GPa. Analysis of the morphology of adsorbing CH chains with atomic force microscopy revealed highly elongated molecules, which is opposite to the observations made for PDDA. Plane-to-plane adhesion showed a factor of approximately 4 lower strength when compared to PDDA-MTM nanocomposite. Altogether these facts support the conclusion that CH lacks flexibility necessary for strong adhesion and efficient load transfer between the organic matrix and MTM platelets. High rigidity of the CH chains does not allow them to acquire a conformation necessary for maximizing the interfacial attraction with nanoscale component of the composite. These observations create an important foundation in the experimental design of the high-performance nanocomposite materials.

electron displays and lighting elements. [13,14] We strongly believe that one of the most prolific areas of their applications will be in biomedicine, where compact, strong, and high-performance devices can be engineered. These devices will exploit the properties of SWNTs and will compete with existing products. The novel technologies of diagnostics and therapeutics can be based on SWNT composites and individual tubes. Along these lines, SWNTs have been demonstrated as potential sensing materials of biological systems, [15–19] which are typically considered for the use in ex vivo modality. The potential use of SWNT-based structures for the purpose of healing neurological and brain-related injuries represents one of the major scientific and practical interests. The high mechanical strength and electrical properties possessed by SWNTs makes these materials perfect candidates for various prosthetic devices, including bone and joint repair. It is important to realize, however, that successful utilization of SWNT-based devices in biomedicine is hinged on the ability of such materials to interface with living cells, support their growth, and at the same time preserve their viability. [20–24] These factors are not well understood for any SWNT structures, which limits the development of in vivo, that is, implantable devices from such materials. The actual processes and techniques used for the preparation of macroscopic objects from SWNTs will play a significant role in determining cellular effects of SWNT composites. Substrates prepared from multi-walled carbon nanotubes (MWNTs) as well as SWNTs have been reported to be biocompatible platforms for neuronal growth and differentiation. [25–27] The use of carbon nanofiber composites as devices for neural- and bone-tissue-implant integration has also been described. [28] Molecular engineering of any SWNT-based composite should have a great effect on how the material performs during long-term contact with tissue. The layer-by-layer (LBL) approach to prepare SWNT structures can be particularly useful in this respect because it allows one to exert control over the structure of the SWNT/polymer systems from angstrom to nanometer and micrometer scale, which is necessity for the engineering of the cell/SWNT interface. [29] Recently, we demonstrated that SWNT LBL films can support the growth, viability, and differentiation of neuronal NG10815 neuroblastoma/glioma hybrid cells. [30] The first example of free-standing SWNT/polymer thin-film membranes that can be mechanically compatible with tissues and can be used as implants and repair devices for neurological- or brain-related injuries has been demonstrated. [30] The free-standing SWNT/ polyelectrolyte multilayers can serve as a prototype for a variety of nanotube-based implants.

Layer-by-layer assembled (LBL) materials from single-wall carbon nanotubes and multiwall carbon nanotubes revealed promising mechanical properties attributed to the uniform distribution of inorganic filler in the organic polyelectrolyte matrix. In this paper, we extend the family of LBL layered nanocomposites to include another important building block i.e. vapor-grown carbon nanofibers (VGCFs). Besides the advantages of low cost, mass production, and relatively small amount of impurities, VGCFs have convenient tubular morphology. Using the LBL film deposition method free-standing polymer composite films with high loadings (>46%) of VGCFs were successfully prepared and examined by scanning electron microscopy, UV–visible spectroscopy and thermal gravimetric analysis. Combined with permeable nature of polyelectrolyte multilayers, these layered composites can be exceptionally useful for smart materials with release-on-command functionality, which requires considerable mechanical strength and thermal and/or electrical conductivity. Such applications may include biological implants, anticorrosion coatings, and thermal/electrical interface materials. Inherent versatility of LBL technology affords preparation of unique multifunctional materials by layering carbon nanofibers with other nanoscale building blocks, for instance, proteins, nanoparticles, clay sheets and others.

Cellulose nanocrystals are promising as a new class of reinforcing material for the preparation of nanostructured composites. We report here the preparation of cellulose nanocrystal multilayer composites with poly(diallyldimethylammonium chloride) using layer-by-layer assembly (LBL) technique. The LBL assembly was characterized with UV-Vis spectroscopy and ellipsometry. The average thickness of a single bilayer was found to be 11 nm. AFM and SEM characterization revealed uniform coverage and densely packed cellulose crystal surface.

Electrogenetic tissues in human body such as central and peripheral nerve systems, muscular and cardiomuscular systems are soft and stretchable materials. However, most of the artificial materials, interfacing with those conductive tissues, such as neural electrodes and cardiac pacemakers, have stiff mechanical properties. The rather contradictory properties between natural and artificial materials usually cause critical incompatibility problems in implanting bodymachine interfaces for wide ranges of biomedical devices. Thus, we developed a stretchable and electrically conductive material with complex hierarchical structures; multi-scale microstructures and nanostructural electrical pathways. For biomedical purposes, an implantable polycaprolactone (PCL) membrane was coated by molecularly controlled layer-bylayer (LBL) assembly of single-walled carbon nanotubes (SWNTs) or poly(3,4-ethylenedioxythiophene) (PEDOT). The soft PCL membrane with asymmetric micro- and nano-pores provides elastic properties, while conductive SWNT or PEDOT coating preserves stable electrical conductivity even in a fully stretched state. This electrical conductivity enhanced ionic cell transmission and cell-to-cell interactions as well as electrical cellular stimulation on the membrane. Our novel stretchable conducting materials will overcome long-lasting challenges for bioelectronic applications by significantly reducing mechanical property gaps between tissues and artificial materials and by providing 3D interconnected electro-active pathways which can be available even at a fully stretched state.

Conjugated polymers are attractive materials for interfacing electrically conducting devices with biological tissue. These polymers, which can be electrochemically polymerized on metal electrodes, are electrically and ionically conductive, mechanically softer than metals, and have low cytotoxicity. The surface area of conjugated polymers can be tailored to create films with low electrical impedance. In addition, through synthetic chemistry or electrochemical doping, biological molecules can be incorporated into conjugated polymer films. These properties enable conjugated polymers to effectively interface with ionically active tissues, most often nervous tissue. This chapter will focus on the conjugated polymers that have received the most attention for interfacing with tissue, polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene) (PEDOT). Derivatives of these polymers that can covalently bind to biological molecules, such as peptides, have been developed, along with composites of the polymers with hydrogels, which have greater tissue-like properties. Coatings of PPy and PEDOT have been put on devices, including neural probes, and made into fibers for neural regeneration. Many current research projects focus on addressing biological reactions that occur upon implantation of devices, such as inflammation and gliosis. Potential solutions to these problems include electrical actuation of conjugated polymers for drug delivery and in vivo electrochemical polymerization.

This chapter focuses on the preparation and applications of layer-by-layer (LBL) assembled organic/inorganic films. As model systems we use incorporation of two multifunctional nanomaterials in the LBL: the clay nanosheets and carbon nanotubes. All the aspects of the composite design starting with the structure of the individual nanoscale building blocks and their interactions with polymer matrix, orientation of the inorganic components in the multilayer, origin of record properties, and most likely applications of the resulting materials are given. Special attention is placed on the understanding of the control parameters for key functional properties such as mechanical strength/stiffness/toughness, electrical transport, transparency, and some properties relevant for biological applications. Keywords: layer-by-layer; clay nanoparticles; carbon nanotubes; multilayered assemblies

New transparent conductors (TCs) capable of replacing traditional indium tin oxide (ITO) are much needed for displays, sensors, solar cells, smart energy-saving windows, and flexible electronics. Technical requirements of TCs include not only high electrical conductivity and transparency but also environmental stability and mechanical property which are often overlooked in the research environment. Single-walled carbon nanotube (SWNT) coatings have been suggested as alternative TC materials but typically lack sufficient wear resistance compared to ITO. Balancing conductance, transparency, durability, and flexibility is a formidable challenge, which leads us to the introduction of a new TC figure of merit, PiTC, incorporating all these qualities. Maximization of PiTC to that of ITO or better can be suggested as an initial research goal. Fine tuning of SWNT layer-by-layer (LBL) polymeric nanocomposite structures makes possible integration of all the necessary properties. The produced TC demonstrated resistivity of 86 Omega/sq with 80.2% optical transmittance combined with tensile modulus, strength, and toughness of the film of 12.3+/-3.4 GPa, 218+/-13 MPa, and 8+/-1.7 J/g, respectively. A new transparent capping layer to conserve these properties in the hostile environment with matching or better strength, toughness, and transparency parameters was also demonstrated. Due to application demands, bending performance of TC made by LBL was of special interest and exceeded that of ITO by at least 100 times. Cumulative figure of merit PiTC for the produced coatings was 0.15 Omega(-1), whereas the conventional ITO showed PiTC0.07 Omega(-1). With overall electrical and optical performance comparable to ITO and exceptional mechanical properties, the described coatings can provide an excellent alternative to ITO or other nanowire- and nanotube-based TC specifically in flexible electronics, displays, and sensors.

The purpose of this study is to optimize poly(3,4,- ethylenedioxythiophene) (PEDOT) polymerization into decellular nerve scaffolding for interfacing to peripheral nerves. Our ultimate aim is to permanently implant highly conductive peripheral nerve interfaces between amputee, stump, nerve fascicles and prosthetic electronics. Decellular nerve (DN) scaffolds are an FDA approved biomaterial (Axogen TM ) with the flexible tensile properties needed for successful permanent coaptation to peripheral nerves. Biocompatible, electroconductive, PEDOT facilitates electrical conduction through PEDOT coated acellular muscle. New electrochemical methods were used to polymerize various PEDOT concentrations into DN scaffolds without the need for a final dehydration step. DN scaffolds were then tested for electrical impedance and charge density. PEDOT coated DN scaffold materials were also implanted as 15-20mm peripheral nerve grafts. Measurement of in-situ nerve conduction immediately followed grafting. DN showed significant improvements in impedance for dehydrated and hydrated, DN, polymerized with moderate and low PEDOT concentrations when they were compared with DN alone (a≤ 0.05). These measurements were equivalent to those for DN with maximal PEDOT concentrations. In-situ, nerve conduction measurements demonstrated that DN alone is a poor electro-conductor while the addition of PEDOT allows DN scaffold grafts to compare favorably with the “gold standard”, autograft (Table 1). Surgical handling characteristics for conductive hydrated PEDOT DN scaffolds were rated 3 (pliable) while the dehydrated models were rated 1 (very stiff) when compared with autograft ratings of 4 (normal). Low concentrations of PEDOT on DN scaffolds provided significant increases in electro active properties which were comparable to the densest PEDOT coatings. DN pliability was closely maintained by continued hydration during PEDOT electrochemical polymerization without compromising electroconductivity.

Safety of water was for a long time and still is one of the most pressing needs for many countries and different communities. Despite the fact that there are potentially many methods to evaluate water safety, finding a simple, rapid, versatile, and inexpensive method for detection of toxins in everyday items is still a great challenge. In this study, we extend the concept of composites obtained impregnation of porous fibrous materials, such as fabrics and papers, by single walled carbon-nanotubes (SWNTs) toward very simple but high-performance biosensors. They utilize the strong dependence of electrical conductivity through nanotubes percolation network on the width of nanotubes-nanotube tunneling gap and can potentially satisfy all the requirements outlined above for the routine toxin monitoring. An antibody to the microcystin-LR (MC-LR), one of the common culprits in mass poisonings, was dispersed together with SWNTs. This dispersion was used to dip-coat the paper rendering it conductive. The change in conductivity of the paper was used to sense the MC-LR in the water rapidly and accurately. The method has the linear detection range up to 10 nmol/L and non-linear detection up to 40 nmol/L. The limit of detection was found to be 0.6 nmol/L (0.6 ng/mL), which satisfies the strictest World Health Organization standard for MC-LR content in drinking water (1 ng/mL), and is comparable to the detection limit of traditional ELISA method of MC-LR detection, while drastically reducing the time of analysis by more than an order of magnitude, which is one of the major hurdles in practical applications. Similar technology of sensor preparation can also be used for a variety of other rapid environmental sensors.

Composite nanocoating of poly(3,4-ethylenedioxythiophene)‐poly(styrenesulfonate) (PEDOT‐PSS) and aqueous dispersion of carbon nanotubes (CNT‐PSS) on lignocellulose wood microfibers has been developed to make conductive microfibers and paper sheets. To construct the multilayers on wood microfibers, cationic poly(ethyleneimine) (PEI) has been used in alternate deposition with anionic conductive PEDOT‐PSS and solubilized CNT‐PSS. Using a Keithley microprobe measurement system, current‐voltage measurements have been carried out on single composite microfibers after deposition of each layer to optimize the electrical properties of the coated microfibers. The conductivity of the resultant wood microfibers was in the range of 10 −2 ‐2 S cm −1 depending on the architecture of the coated layer. Further, the conductivity of the coated wood microfibers increased up to 20 S cm −1 by sandwiching multilayers of conductive co-polymer PEDOT‐PSS with CNT‐PSS through a polycation (PEI) interlayer. Moreover, paper hand sheets were manufactured from these coated wood microfibers with conductivity ranging from 1 to 20 S cm −1 . A paper composite structure consisting of conductive/dielectric/conductive layers that acts as a capacitor has also been fabricated and is reported. (Some figures in this article are in colour only in the electronic version)

In recent years, carbon nanotubes have been utilized for a variety of applications, including nanoelectronics and various types of sensors. In particular, researchers have sought to take advantage of the superior electrical properties of carbon nanotubes for fabricating novel strain sensors. This article presents a single-walled carbon nanotube (SWNT)-polyelectrolyte (PE) composite thin film strain sensor fabricated with a layer-by-layer (LbL) process. Optimization of bulk SWNT-PE strain sensor properties is achieved by varying various LbL fabrication parameters, followed by characterization of strain-sensing electromechanical responses. A resistor and capacitor (RC)-circuit model is proposed and validated with electrical impedance spectroscopy to fit experimental results and to identify equivalent circuit element parameters sensitive to strain. Experimental results suggest consistent trends between SWNT and PE concentrations to strain sensor sensitivities. Simply by adjusting the weight fraction of SWNT solutions and film thickness, strain sensitivities between 0.1 and 1.8 have been achieved. While SWNT-PE strain sensitivity is lower than some metal-foil strain gauges ($2), the LbL method allows for precise tailoring of the properties (i.e., strain sensitivity, resistivity, among others) of a high-capacity (±10,000 μm m-1) homogeneous multilayer strain sensor.

We presented carbon nanotube coated conductive textiles and polymer-ceramic composites for novel load bearing antennas. We showed that the polymer-ceramic composite exhibits high permittivity with very low loss tangent depending on the ceramic-polymer mix ratio. We also discussed that conductive textile coated with carbon nanotubes and gold carry very promising features to achieve high conductivity and mechanical flexibility, which are critical for load bearing antennas. The strong adhesion between the conductive textile and the polymer-ceramic surface created a flexible, conformal, light-weight antenna. We specifically designed a patch antenna using a simple polymer-ceramic and textile mixing process. Quantitative RF and mechanical performance of the antenna will be presented at the conference.

Layer-by-layer (LBL) assembly is one of the most ubiquitous coating techniques today. It also offers a pathway for multifunctional/multicomponent materials with molecular-scale control of stratified structures. However, technological applications of LBL are impeded by laborious and fluid-demanding nature of the process. While vertical organization of LBL films is natural for this technique, the control of lateral organization of the films is fairly difficult. Using the deposition of carbon nanotubes (SWNTs) and other nanoscale colloids, we introduce here a new approach to LBL based on dewetting phenomena, d-LBL. Its strengths include: (1) elimination of rinsing steps, (2) significant acceleration of the process, (3) improvement of lateral organization of LBL films, and (4) ability to produce nanostructured coatings from colloids when classical LBL fails. The generality of d-LBL can compete with traditional LBL and is demonstrated for cellulose nanowires, polyelectrolyte pairs, and semiconductor nanoparticles, metal oxides, and Au nanorods.

Nanoscale building blocks are individually exceptionally strong because they are close to ideal, defect-free materials. It is, however, difficult to retain the ideal properties in macroscale composites. Bottom-up assembly of a clay/polymer nanocomposite allowed for the preparation of a homogeneous, optically transparent material with planar orientation of the alumosilicate nanosheets. The stiffness and tensile strength of these multilayer composites are one order of magnitude greater than those of analogous nanocomposites at a processing temperature that is much lower than those of ceramic or polymer materials with similar characteristics. A high level of ordering of the nanoscale building blocks, combined with dense covalent and hydrogen bonding and stiffening of the polymer chains, leads to highly effective load transfer between nanosheets and the polymer.

This paper demonstrated the physical properties of a layer-by-layer (LBL) assembled single-walled carbon nanotubes (SWNTs) – polymer composite thin film. The superior mechan ical and electrical properties that originate from SWNTs were successfully incorporated into a polymeric thin film by hydrogen bonding-directed LBL assemblies. The electrical conductivities and mechanical strength of a LBL composite are 8.5*10 3 S/m and 160 MPa with only 8±2wt% SWNT loading. The combination of high electrical and mechanical properties of SWNT-polymer LBL thin films makes this material unique, opening the way for a wide range of applications from flexible electronics to space telescopes and biomedical implantable devices. Keywords : SWNT, nanotube, multilayer assemblies, layer-by-layer assemblies, electrical properties, nanocomposites, composites 1. INTRODUCTION Layer-by-layer assembly (LBL) of nano-materials has been applauded as an alternative polymer nanocomposite fabrication technique which demonstrates a unique molecular-level structural control to optimize their physicochemical properties. The examples of nano-building blocks of LBL assemblies include single-walled carbon nanotubes (SWNTs)

Oriented SWNTs in polymer composites have shown dramatic improvements in the physical properties of a composite because of the anisotropic shape and properties of SWNTs. Controlled alignment of SWNTs during composite fabrication implies better material function performance. This letter reports a new fabrication technique whereby aligned SWNTs and robust SWNT-polymer composites can be made using a fusion method of SWNT combing and layer-by-layer (LBL) assembly. As we previously reported, LBL assembly demonstrated exceptional processing ability in constructing the uniform distribution of a SWNT-polymer composite. Combined with this uniformity, this SWNT combing technique endows controlled alignment of single-stranded SWNTs in a SWNT-polymer composite system. SWNT combing employs air-water interfacial forces to change the molecular topography from the random adsorption state to the stretched alignment of SWNTs. More specifically, air-water interfacial forces are associated with an excess viscous drag force and an intrinsic dewetting rate along SWNTs. Moreover, the alignment efficiency of SWNTs is high enough to construct a multilayered LBL film with horizontal-linear weaving structures. This simple method also can be applied for aligning other nanowire materials because it utilizes simple geometric features of SWNTs.