Green and Heavy-Duty Anticorrosion Coatings: Waterborne Epoxy Thermoset Composites Modified through Variation of Zinc Dust Loading and Incorporation of Amine-Capped Aniline Trimer and Graphene Oxide

In this study, an array of environmentally friendly and heavy-duty anticorrosion composite coatings were prepared. The synthesis involved amine-capped aniline trimer (ACAT) produced by an oxidative coupling reaction and graphene oxide (GO) prepared based on Hummer's method, and later, the waterborne epoxy thermoset composite (WETC) coatings were prepared by thermal ring-opening polymerization of EP 147w, a commercial waterborne epoxy resin, in the presence of ACAT and/or GO with zinc dust (ZD). A synergistic effect was observed by replacing a significant amount of the ZD loading in the WETC by simultaneously incorporating a small amount of ACAT and GO. The electrochemical corrosion measurements of the as-prepared WETC coatings indicated that incorporating 5% w/w ACAT or 0.5% w/w GO separately replaced approximately 30% w/w or 15% w/w of the ZD, respectively. Moreover, the WETC coatings containing 5% w/w ACAT and 0.5% w/w GO simultaneously were found to replace 45% w/w of the ZD. A salt spray test based on ASTM B-117 also showed a consistent trend with the electrochemical results. Incorporating small amounts of ACAT and GO in WETC coatings instead of ZD not only maintains the anticorrosion performance but also enhances adhesion and abrasion resistance, as demonstrated by the adhesion and abrasion tests.

Emerging Trends of Nanofibrous Piezoelectric and Triboelectric Applications: Mechanisms, Electroactive Materials, and Designed Architectures

Over the past few decades, significant progress in piezo-/triboelectric nanogenerators (PTEGs) has led to the development of cutting-edge wearable technologies. Nanofibers with good designability, controllable morphologies, large specific areas, and unique physicochemical properties provide a promising platform for PTEGs for various advanced applications. However, the further development of nanofiber-based PTEGs is limited by technical difficulties, ranging from materials design to device integration. Herein, the current developments in PTEGs based on electrospun nanofibers are systematically reviewed. This review begins with the mechanisms of PTEGs and the advantages of nanofibers and nanodevices, including high breathability, waterproofness, scalability, and thermal-moisture comfort. In terms of materials and structural design, novel electroactive nanofibers and structure assemblies based on 1D micro/nanostructures, 2D bionic structures, and 3D multilayered structures are discussed. Subsequently, nanofibrous PTEGs in applications such as energy harvesters, personalized medicine, personal protective equipment, and human-machine interactions are summarized. Nanofiber-based PTEGs still face many challenges such as energy efficiency, material durability, device stability, and device integration. Finally, the research gap between research and practical applications of PTEGs is discussed, and emerging trends are proposed, providing some ideas for the development of intelligent wearables.

Oriented Graphene Oxide Scaffold Promotes Nerve Regeneration in vitro and in vivo

Background

Treating peripheral nerve injuries (PNI) with defects remains challenging in clinical practice. The commercial conduits have shown suboptimal nerve regeneration and functional recovery due to their basic tubular design without electroactive and oriented topographical cues.

Purpose

To develop a new scaffold with oriented microstructure and electroactive Graphene oxide (GO) and investigate its' therapeutic effect on nerve regeneration in vitro and in vivo.

Methods

This study employed a straightforward approach to co-spin PCL and GO, yielding an oriented hybrid nanofibrous scaffold known as the O-GO/PCL scaffold. The physical and chemical properties of nanofibrous scaffold were tested by scanning electron microscopy (SEM), transmission electron microscope (TEM), tensile test and so on. Primary Schwann cells (SCs) and dorsal root ganglia (DRG) were used to investigate the impact of the newly developed scaffolds on the biological behavior of neural cells in vitro. Transcriptome sequencing (mRNA-seq) was employed to probe the underlying mechanisms of the synergistic effect of electroactive GO and longitudinal topographic guidance on nerve regeneration. Furthermore, the developed O-GO/PCL scaffold was utilized to bridge a 10-mm sciatic nerve defect in rat, aiming to investigate its therapeutic potential for peripheral nerve regeneration in vivo.

Results and discussion

The SEM and TEM revealed that the newly developed O-GO/PCL scaffold showed longitudinally oriented microstructure and GO particles were homogenously and uniformly distributed inside the nanofibers. Primary SCs were utilized to assess the biocompatibility of the GO-based scaffold, revealing that negligible cytotoxicity when GO concentration does not exceed 0.5%. In vitro analysis of nerve regeneration demonstrated that axons in the O-GO/PCL group exhibited an average length of 1054.88 ± 161.32 µm, significant longer than those in the other groups (P < 0.05). Moreover, mRNA sequencing results suggested that the O-GO/PCL scaffold could enhance nerve regeneration by upregulating genes associated with neural regeneration, encompassing ion transport, axon guidance and cell-cell interactions. Most importantly, we employed the O-GO/PCL scaffold to repair a 10-mm sciatic nerve defect in rat, resulting in augmented nerve regeneration, myelination, and functional recovery.

Conclusion

The O-GO/PCL scaffold with oriented microstructure and electroactive GO represents a promising heral nerve reconstruction.

The Preparation, Structural Design, and Application of Electroactive Poly(vinylidene fluoride)-Based Materials for Wearable Sensors and Human Energy Harvesters

Owing to their biocompatibility, chemical stability, film-forming ability, cost-effectiveness, and excellent electroactive properties, poly(vinylidene fluoride) (PVDF) and PVDF-based polymers are widely used in sensors, actuators, energy harvesters, etc. In this review, the recent research progress on the PVDF phase structures and identification of different phases is outlined. Several approaches for obtaining the electroactive phase of PVDF and preparing PVDF-based nanocomposites are described. Furthermore, the potential applications of these materials in wearable sensors and human energy harvesters are discussed. Finally, some challenges and perspectives for improving the properties and boosting the applications of these materials are presented.

Triphenylamine-Containing Benzoic Acids: Synthesis, Liquid Crystalline and Redox Properties

The synthesis, characterization and liquid crystalline and electrochemical properties of novel triarylamines, in which the triphenylamine platform is non-symmetrically modified with a 4-(6-oxyhexyloxy)benzoic acid group, are reported. Compounds show columnar liquid crystalline behavior, as confirmed through the use of polarized optical microscopy, differential scanning calorimetry and X-ray diffraction. Electrochemical properties were measured using cyclic voltammperometry, obtaining low oxidation potentials and HOMO values that were optimum for consideration as organic semiconductors in hole transport layers. In addition, the photoredox activity of one of these derivatives in dichloromethane was studied under light irradiation. A photooxidation/assembly process under white light irradiation occurs without the assistance of hydrogen bonding amide functional groups.

3D-Printed Piezoelectric Porous Bioactive Scaffolds and Clinical Ultrasonic Stimulation Can Help in Enhanced Bone Regeneration

This paper presents a comprehensive effort to develop and analyze first-of-its-kind design-specific and bioactive piezoelectric scaffolds for treating orthopedic defects. The study has three major highlights. First, this is one of the first studies that utilize extrusion-based 3D printing to develop design-specific macroporous piezoelectric scaffolds for treating bone defects. The scaffolds with controlled pore size and architecture were synthesized based on unique composite formulations containing polycaprolactone (PCL) and micron-sized barium titanate (BaTiO3) particles. Second, the bioactive PCL-BaTiO3 piezoelectric composite formulations were explicitly developed in the form of uniform diameter filaments, which served as feedstock material for the fused filament fabrication (FFF)-based 3D printing. A combined method comprising solvent casting and extrusion (melt-blending) was designed and deemed suitable to develop the high-quality PCL-BaTiO3 bioactive composite filaments for 3D printing. Third, clinical ultrasonic stimulation (US) was used to stimulate the piezoelectric effect, i.e., create stress on the PCL-BaTiO3 scaffolds to generate electrical fields. Subsequently, we analyzed the impact of scaffold-generated piezoelectric stimulation on MC3T3 pre-osteoblast behavior. Our results confirmed that FFF could form high-resolution, macroporous piezoelectric scaffolds, and the poled PCL-BaTiO3 composites resulted in the d33 coefficient in the range of 1.2-2.6 pC/N, which is proven suitable for osteogenesis. In vitro results revealed that the scaffolds with a mean pore size of 320 µm resulted in the highest pre-osteoblast growth kinetics. While 1 Hz US resulted in enhanced pre-osteoblast adhesion, proliferation, and spreading, 3 Hz US benefited osteoblast differentiation by upregulating important osteogenic markers. This study proves that 3D-printed bioactive piezoelectric scaffolds coupled with US are promising to expedite bone regeneration in orthopedic defects.

Comparative Studies on Carbon Paste Electrode Modified with Electroactive Polyamic Acid and Corresponding Polyimide without/with Attached Sulfonated Group for Electrochemical Sensing of Ascorbic Acid

In this study, electroactive poly (amic acid) (EPAA) and corresponding polyimide (EPI) without or with a sulfonated group (i.e., S-EPAA, and S-EPI) were prepared and applied in electrochemical sensing of ascorbic acid (AA). The electroactive polymers (EAPs) containing EPAA/EPI and S-EPAA/S-EPI were synthesized by using an amine-capped aniline trimer (ACAT) and sulfonated amine-capped aniline trimer (S-ACAT) as an electroactive segment that controlled the redox capability and influenced the degree of sensitivity of the EAPs towards AA. Characterization of the as-prepared EAPs was identified by FTIR spectra. The redox capability of the EAPs was investigated by electrochemical cyclic voltammetric studies. It should be noted that the redox capability of the EAPs was found to show the following trend: S-EPAA > S-EPI > EPAA > EPI. For the electrochemical sensing studies, a sensor constructed from an S-EPAA-modified carbon paste electrode (CPE) demonstrated 2-fold, 1.27-fold, and 1.35-fold higher electro-catalytic activity towards the oxidation of AA, compared to those constructed using a bare CPE, S-EPI-, and EPI/EPAA-modified CPE, respectively. The higher redox capability of S-EPAA-modified CPE exhibited a good electrochemical response towards AA at a low oxidative potential, with good stability and selectivity. Moreover, an electrochemical sensor constructed from S-EPAA-modified CPE was found to reveal better selectivity for a tertiary mixture of AA/DA/UA, as compared to that of EPI-modified, EPAA-modified and S-EPI-modified CPE, based on a series of differential pulse voltammograms.

An Electroconductive, Thermosensitive, and Injectable Chitosan/Pluronic/Gold-Decorated Cellulose Nanofiber Hydrogel as an Efficient Carrier for Regeneration of Cardiac Tissue

Myocardial infarction is a major cause of death worldwide and remains a social and healthcare burden. Injectable hydrogels with the ability to locally deliver drugs or cells to the damaged area can revolutionize the treatment of heart diseases. Herein, we formulate a thermo-responsive and injectable hydrogel based on conjugated chitosan/poloxamers for cardiac repair. To tailor the mechanical properties and electrical signal transmission, gold nanoparticles (AuNPs) with an average diameter of 50 nm were physically bonded to oxidized bacterial nanocellulose fibers (OBC) and added to the thermosensitive hydrogel at the ratio of 1% w/v. The prepared hydrogels have a porous structure with open pore channels in the range of 50−200 µm. Shear rate sweep measurements demonstrate a reversible phase transition from sol to gel with increasing temperature and a gelation time of 5 min. The hydrogels show a shear-thinning behavior with a shear modulus ranging from 1 to 12 kPa dependent on gold concentration. Electrical conductivity studies reveal that the conductance of the polymer matrix is 6 × 10−2 S/m at 75 mM Au. In vitro cytocompatibility assays by H9C2 cells show high biocompatibility (cell viability of >90% after 72 h incubation) with good cell adhesion. In conclusion, the developed nanocomposite hydrogel has great potential for use as an injectable biomaterial for cardiac tissue regeneration.

Design of an Electro-Stimulated Hydrogel Actuator System with Fast Flexible Folding Deformation under a Low Electric Field

Soft actuators have recently been widely studied due to their significant advantages including light weight, continuous deformability, high environment adaptability, and safe human-robot interactions. In this study, we designed electrically responsive poly(sodium 4-vinylbenzenesulfonate/2-hydroxyethylmethacrylate/acrylamide) (P(VBS/HEMA/AAm)) and poly(sodium 4-vinylbenzenesulfonate/2-hydroxyethyl methacrylate/acrylic acid) (P(VBS/HEMA/AAc)) hydrogels. A series of P(VBS/HEMA/AAm) and P(VBS/HEMA/AAc) hydrogels were prepared by adjusting the monomer composition and cross-linking density to systemically analyze various factors affecting the actuation of hydrogels under an electric field. All hydrogels exhibited more than 65% gel fraction and a high equilibrium water content (EWC) of more than 90%. The EWC of hydrogels gradually increased with decreasing cross-linker content and was also influenced by the monomer composition. The mechanical properties of hydrogels were proportional to the cross-linking density. Particularly, hydrogels showed bending deformation even at low voltages below 10 V, and the electrically responsive bending actuation of hydrogels can be modulated by cross-linking density, monomer composition, applied voltage, ion strength of the electrolyte solution, and geometrical parameters of the hydrogel. By controlling these factors, hydrogels showed a fast response with a bending of more than 100° within a minute. In addition, hydrogels did not show significant cytotoxicity in a biocompatibility test and exhibited more than 84% cell viability. These results indicate that P(VBS/HEMA/AAm) and P(VBS/HEMA/AAc) hydrogels with fast response properties even under a low electric field have the potential to be used in a wide range of soft actuator applications.

Comparative Studies of CPEs Modified with Distinctive Metal Nanoparticle-Decorated Electroactive Polyimide for the Detection of UA

In this present work, an electrochemical sensor was developed for the sensing of uric acid (UA). The sensor was based on a carbon paste electrode (CPE) modified with electroactive polyimide (EPI) synthesized using aniline tetramer (ACAT) decorated with reduced nanoparticles (NPs) of Au, Pt, and Ag. The initial step involved the preparation and characterization of ACAT. Subsequently, the ACAT-based EPI synthesis was performed by chemical imidization of its precursors 4,4′-(4.4′-isopropylidene-diphenoxy) bis (phthalic anhydride) BPADA and ACAT. Then, EPI was doped with distinctive particles of Ag, Pt and Au, and the doped EPIs were abbreviated as EPIS, EPIP and EPIG, respectively. Their structures were characterized by XRD, XPS, and TEM, and the electrochemical properties were determined by cyclic voltammetry and chronoamperometry. Among these evaluated sensors, EPI with Au NPs turned out the best with a sensitivity of 1.53 uA uM⁻¹ UA, a low limit of detection (LOD) of 0.78 uM, and a linear detection range (LDR) of 5–50 uM UA at a low potential value of 310 mV. Additionally, differential pulse voltammetric (DPV) analysis showed that the EPIG sensor showed the best selectivity for a tertiary mixture of UA, dopamine (DA), and ascorbic acid (AA) as compared to EPIP and EPIS.

Patterned Piezoelectric Scaffolds for Osteogenic Differentiation

The morphological clues of scaffolds can determine cell behavior and, therefore, the patterning of electroactive polymers can be a suitable strategy for bone tissue engineering. In this way, this work reports on the influence of poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) electroactive micropatterned scaffolds on the proliferation and differentiation of bone cells. For that, micropatterned P(VDF-TrFE) scaffolds were produced by lithography in the form of arrays of lines and hexagons and then tested for cell proliferation and differentiation of pre-osteoblast cell line. Results show that more anisotropic surface microstructures promote bone differentiation without the need of further biochemical stimulation. Thus, the combination of specific patterns with the inherent electroactivity of materials provides a promising platform for bone regeneration.

A Novel Electroactive Imide Oligomer and Its Application in Anticorrosion Coating

A novel aniline tetramer (AT) capped electroactive imide oligomer (EIO) for metal corrosion protection was successfully synthesized in this study. The chemical structure of the EIO was characterized by liquid chromatography-mass spectrometry and Fourier-transform infrared spectroscopy. Furthermore, the redox behavior of EIO was identified using electrochemical cyclic voltammetry studies. An EIO coated on a cold-rolled steel (CRS) electrode was found to possess superior corrosion resistance to polyimide (PI) on a series of electrochemical corrosion measurements in 3.5 wt.% NaCl solution over an extended period (30 days). The mechanism for the advanced corrosion protection of the PI coating on the CRS electrode could be attributed to the redox catalytic capabilities of the AT units present in the EIO. These capabilities may induce the formation of passive metal oxide layers on the CRS electrode. Scanning electron microscopy and X-ray photoelectron spectroscopy were used to analyze the surface condition of the CRS after the corrosion test. EIO- and PI-coated electrodes were identified by a series of electrochemical measurements, including corrosion potential (E_corr), polarization resistance (R_p), and corrosion current (I_corr) measurements, along with electrochemical impedance spectroscopy (EIS).

Electroresponsive Ionic Liquid Crystal Elastomers

This paper describes the preparation, physical properties, and electric bending actuation of a new class of active materials-ionic liquid crystal elastomers (iLCEs). It is demonstrated that iLCEs can be actuated by low-frequency AC or DC voltages of less than 1 V. The bending strains of the unoptimized first iLCEs are already comparable to the well-developed ionic electroactive polymers. Additionally, iLCEs exhibit several novel and superior features, such as the alignment that increases the performance of actuation, the possibility of preprogrammed actuation patterns at the level of the cross-linking process, and dual (thermal and electric) actuations in hybrid samples. Since liquid crystal elastomers are also sensitive to magnetic fields and can also be light sensitive, iLCEs have far-reaching potentials toward multiresponsive actuations that may have so far unmatched properties in soft robotics, sensing, and biomedical applications.

Fluorinated Polymers as Smart Materials for Advanced Biomedical Applications

Fluorinated polymers constitute a unique class of materials that exhibit a combination of suitable properties for a wide range of applications, which mainly arise from their outstanding chemical resistance, thermal stability, low friction coefficients and electrical properties. Furthermore, those presenting stimuli-responsive properties have found widespread industrial and commercial applications, based on their ability to change in a controlled fashion one or more of their physicochemical properties, in response to single or multiple external stimuli such as light, temperature, electrical and magnetic fields, pH and/or biological signals. In particular, some fluorinated polymers have been intensively investigated and applied due to their piezoelectric, pyroelectric and ferroelectric properties in biomedical applications including controlled drug delivery systems, tissue engineering, microfluidic and artificial muscle actuators, among others. This review summarizes the main characteristics, microstructures and biomedical applications of electroactive fluorinated polymers.

On-Demand Modulation of Bacterial Cell Fates on Multifunctional Dynamic Substrates

This paper reports unprecedented dynamic surfaces based on zwitterionic low-density self-assembled monolayers (LDSAMs) of alkanethiolates on gold, which integrate three interconvertible states-bacteria-adherable, bactericidal, and nonfouling states-through electrical modulations. The conformations of alkanethiolates were electrically modulated to generate zwitterionic, anionic, and cationic surfaces, which responded differently to bacteria and determined the fate of bacteria. Furthermore, the reversible switching of multifunctions of the surface was realized for killing bacteria and subsequently releasing dead bacteria from the surface. For practical application of our strategy, we examined the selective antibacterial effect of our surface for eradication of mycoplasma contaminants in contaminated mammalian cell cultures.

Versatile Fabrication Approach of Conductive Hydrogels via Copolymerization with Vinyl Monomers

Functionalized poly(ethylene dioxythiophene) (f-PEDOT) was copolymerized with two vinyl monomers of different hydrophilicity, acrylic acid and hydroxyethyl methacrylate, to produce electroconductive hydrogels with a range of physical and electronic properties. These hydrogels not only possessed tailored physical properties, such as swelling ratios and mechanical properties, but also displayed electroactivity dependent on the chemical composition of the network. Raman spectroscopy indicated that the functional PEDOT in the hydrogels is in an oxidized form, most likely accounting for the good electrochemical response of the hydrogels observed in physiological buffer. In vitro cell studies showed that cardiac cells respond differently when seeded on hydrogel substrates with different compositions. This study presents a facile approach for the fabrication of electroconductive hydrogels with a range of properties, paving the way for scaffolds that can meet the requirements of different electroresponsive tissues.

Fabrication of Biocompatible Potassium Sodium Niobate Piezoelectric Ceramic as an Electroactive Implant

The discovery of piezoelectricity in natural bone has attracted extensive research in emulating biological electricity for various tissue regeneration. Here, we carried out experiments to build biocompatible potassium sodium niobate (KNN) ceramics. Then, influence substrate surface charges on bovine serum albumin (BSA) protein adsorption and cell proliferation on KNN ceramics surfaces was investigated. KNN ceramics with piezoelectric constant of ~93 pC/N and relative density of ~93% were fabricated. The adsorption of protein on the positive surfaces (Ps) and negative surfaces (Ns) of KNN ceramics with piezoelectric constant of ~93 pC/N showed greater protein adsorption capacity than that on non-polarized surfaces (NPs). Biocompatibility of KNN ceramics was verified through cell culturing and live/dead cell staining of MC3T3. The cells experiment showed enhanced cell growth on the positive surfaces (Ps) and negative surfaces (Ns) compared to non-polarized surfaces (NPs). These results revealed that KNN ceramics had great potential to be used to understand the effect of surface potential on cells processes and would benefit future research in designing piezoelectric materials for tissue regeneration.

Electric Field Actuation of Tough Electroactive Hydrogels Cross-Linked by Functional Triblock Copolymer Micelles

Multiresponsive polyelectrolyte hydrogels with extraordinary toughness have great potential in soft device applications. Previously we have demonstrated a series of tough and multiresponsive hydrogels by using multifunctional triblock copolymer (Pluronic F127 diacrylate, F127DA) micelles to cross-link cationic polyelectrolyte chains into 3D network. Herein, we further synthesize negatively charged hydrogels comprising 2-acrylamido-2-methyl propylsulfonic acid (AMPS) monomers by using F127DA micelles as cross-linkers. Similar to the positive nanomicelle (NM) hydrogels, the negative NM hydrogels exhibited a compressive strength up to 59 MPa with a fracture strain up to 98%, and tensile fracture strain higher than 2000%. These charged hydrogels were actuated by electric field when immersed in salt solutions. The effects of electrolyte concentration, electric field strength, and ionic monomer content on the electric actuation behavior of these electroactive hydrogels (EAHs) have been systematically investigated. It is concluded that the electroactive hydrogels show a fast actuation rate with a bending angle up to 87° at 120 s and the bending angle was cyclically reversed upon changing bias direction without a large decrease. This study demonstrates that such tough and multiresponsive electroactive hydrogels may have great potential in sensors, actuators, switches, and artificial muscles.

The Regulation of Osteogenesis Using Electroactive Polypyrrole Films

To evaluate the effect of electrical conductivity of biomaterials on osteogenesis, polypyrrole (PPy) was fabricated by oxidative chemical polymerization as substrates for cell culture. Through adjusting the concentrations of monomer and initiator, polypyrrole films with different electrical conductivities were fabricated. These fabricated polypyrrole films are transparent enough for easy optical microscopy. Fourier transform infrared spectroscopy, X-ray spectroscopy and four-point probe were used to assess the microstructures, surface chemical compositions and electrical sheet resistance of films, respectively. Results indicate that higher monomer and initiator concentration leads to highly-branched PPy chains and thus promotes the electron mobility and electrical conductivity. Selected polypyrrole films then were applied for culturing rat bone marrow stromal cells. Cell viability and mineralization assays reveal that not only these films are biocompatible, but also capable of enhancing the calcium deposition into the extra cellular matrix by the differentiated cells.

Three-Dimensional BC/PEDOT Composite Nanofibers with High Performance for Electrode-Cell Interface

There is an increasing need to synthesize biocompatible nanofibers with excellent mechanical and electrical performance for electrochemical and biomedical applications. Here we report a facile approach to prepare electroactive and flexible 3D nanostructured biomaterials with high performance based on bacterial cellulose (BC) nanofibers. Our approach can coat BC nanofibers with poly(3,4-ethylenedioxythiophene) (PEDOT) by in situ interfacial polymerization in a controllable manner. The PEDOT coating thickness is adjustable by the monomer concentration or reaction time during polymerization, producing nanofibers with a total diameter ranging from 30 to 200 nm. This fabrication process also provides a convenient method to tune different parameters such as the average pore size and electrical conductivity on the demands of actual applications. Our experiments have demonstrated that the 3D BC/PEDOT nanofibers exhibit high specific surface area, excellent mechanical properties, electroactive stability, and low cell cytotoxicity. With electrical stimulation, calcium imaging of PC12 neural cells on BC/PEDOT nanofibers has revealed a significant increase in the percentage of cells with higher action potentials, suggesting an enhanced capacitance effect of charge injection. As an attractive solution to the challenge of designing better electrode-cell interfaces, 3D BC/PEDOT nanofibers promise many important applications such as biosensing devices, smart drug delivery systems, and implantable electrodes for tissue engineering.

Multifunctional Electroactive Nanocomposites Based on Piezoelectric Boron Nitride Nanotubes

Space exploration missions require sensors and devices capable of stable operation in harsh environments such as those that include high thermal fluctuation, atomic oxygen, and high-energy ionizing radiation. However, conventional or state-of-the-art electroactive materials like lead zirconate titanate, poly(vinylidene fluoride), and carbon nanotube (CNT)-doped polyimides have limitations on use in those extreme applications. Theoretical studies have shown that boron nitride nanotubes (BNNTs) have strength-to-weight ratios comparable to those of CNTs, excellent high-temperature stability (to 800 °C in air), large electroactive characteristics, and excellent neutron radiation shielding capability. In this study, we demonstrated the experimental electroactive characteristics of BNNTs in novel multifunctional electroactive nanocomposites. Upon application of an external electric field, the 2 wt % BNNT/polyimide composite was found to exhibit electroactive strain composed of a superposition of linear piezoelectric and nonlinear electrostrictive components. When the BNNTs were aligned by stretching the 2 wt % BNNT/polyimide composite, electroactive characteristics increased by about 460% compared to the nonstretched sample. An all-nanotube actuator consisting of a BNNT buckypaper layer between two single-walled carbon nanotube buckypaper electrode layers was found to have much larger electroactive properties. The additional neutron radiation shielding properties and ultraviolet/visible/near-infrared optical properties of the BNNT composites make them excellent candidates for use in the extreme environments of space missions.

Effective and selective cell retention and recovery from whole blood by electroactive thin films

Hematogenous metastatic spread causes most cancer patient deaths. Because circulating tumor cells (CTCs) are highly relevant to early metastatic spread, the capture or detection of these cells provides a diagnostic tool for patients with metastatic conditions. Herein, we demonstrate a programmable electroactive multilayered material platform with a smart electrically induced "switch" that captures CTCs from biological plasma with high efficiency and releases the captured cells flexibly. The released cells are still viable and proliferative, which facilitates the detection of trace levels of CTCs by amplification. Furthermore, the inherent rough characteristics of the nanoparticle-composed interface can promote capture efficiency and cell purification by integration with a simple microfluidic device. This elegant, inexpensive, and versatile platform for cell sorting and enrichment makes subsequent molecular and cell biological analysis achievable. The strategy has broad implications for favoring fundamental cancer biology research, for the diagnosis and monitoring of cancer individually, and for advanced intervention based on blood purification.

Multiscale instabilities in soft heterogeneous dielectric elastomers

The development of instabilities in soft heterogeneous dielectric elastomers is investigated. Motivated by experiments and possible applications, we use in our analysis the physically relevant referential electric field instead of electric displacement. In terms of this variable, a closed form solution is derived for the class of layered neo-Hookean dielectrics. A criterion for the onset of electromechanical multiscale instabilities for the layered composites with anisotropic phases is formulated. A general condition for the onset of the macroscopic instability in soft multiphase dielectrics is introduced. In the example of the layered dielectrics, the essential influence of the microstructure on the onset of instabilities is revealed. We found that: (i) macroscopic instabilities dominate at moderate volume fractions of the stiffer phase, (ii) interface instabilities appear at small volume fractions of the stiffer phase and (iii) instabilities of a finite scale, comparable to the microstructure size, occur at large volume fractions of the stiffer phase. The latest new type of instabilities does not appear in the purely mechanical case and dominates in the region of large volume fractions of the stiff phase.

Targeted synthesis of electroactive porous organic frameworks containing triphenyl phosphine moieties

A novel electroactive porous aromatic framework (JUC-Z4-Cl) was designed and synthesized via Yamamoto-type Ullmann cross-coupling reaction with the monomer tris(4-chlorophenyl)phosphine. By simple redox chemical reactions, stable, reductive, porous polytri(p-phenyl)phosphine (JUC-Z4) and polytri(p-phenyl)phosphine oxide (JUC-Z5) could be obtained as off-white powders. The structures of JUC-Z4 and JUC-Z5 were confirmed using magic-angle spinning nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, etc. The microporous architectures exhibit high stability (471°C for JUC-Z4 and 484°C for JUC-Z5) and large surface area (793 and 648 m² g⁻¹ for JUC-Z4 and JUC-Z5, respectively). JUC-Z4 also exhibits efficient recognition ability of greenhouse gases from dry air.

Towards a Biocompatible, Biodegradable Copolymer Incorporating Electroactive Oligothiophene Units

As part of an ongoing effort to develop biocompatible, biodegradable conducting polymers, we report here the synthesis and characterization of a novel copolymer, 5,5"'bishydroxymethyl-3,3"'-dimethyl-2,2':5',2":5",2"'-quaterthiophene-co-adipic acid polyester (QAPE). This system was designed so as to incorporate alternating electroactive quaterthiophene units and biodegradable ester units into one macromolecular framework, while allowing for facile preparation of the polymer via a polycondensation reaction. In agreement with the design expectations, the ester groups were found to be incorporated into the polymer between the quaterthiophene subunits, as inferred from standard chemical and spectroscopic analyses. QAPE exhibited redox activity as detected by cyclic voltammetry and a new red-shifted absorption peak upon doping, providing support for the notion that the quaterthiophene units maintain electroactivity after incorporation into the QAPE polymer framework. The degradation, likely through surface erosion, of this polymer in the presence of cholesterol esterase was confirmed by the detection of a fluorescence signal at wavelengths corresponding to the quaterthiophene subunit and comparisons to appropriate controls. In vitro cytocompatability studies, carried out over 48 h, indicate that the QAPE polymer is nontoxic to Schwann cells.