Protein adsorption under electrical stimulation of neural probe coated with polyaniline

A review of glycosaminoglycan-modified electrically conductive polymers for biomedical applications

The application areas of electrically conductive polymers have been steadily growing since their discovery in the late 1970s. Recently, electrically conductive polymers have found their way into biomedicine, allowing the realization of many relevant applications ranging from bioelectronics to scaffolds for tissue engineering. Extracellular matrix components, such as glycosaminoglycans, build an important class of biomaterials that are heavily researched for biomedical applications due to their favorable properties. Due to their highly anionic character and the presence of sulfate groups in glycosaminoglycans, these biomolecules can be employed to functionalize conductive polymers, which enables the tailorability and improvement of cell-material interactions of conductive polymers. This review paper gives an overview of recent research on glycosaminoglycan-modified conductive polymers intended for biomedical applications and discusses the effect of different biological dopants on material characteristics, such as surface roughness, stiffness, and electrochemical properties. Moreover, the key findings of the biological characterization in vitro and in vivo are summarized, and remaining challenges in the field, particularly related to the modification of electrically conductive polymers with glycosaminoglycans to achieve improved functional and biological outcomes, are discussed. STATEMENT OF SIGNIFICANCE: The development of functional biomaterials based on electrically conductive polymers (CPs) for various biomedical applications, such as neural regeneration, drug delivery, or bioelectronics, has been increasingly investigated over the last decades. Recent literature has shown that changes in the synthesis procedure or the chosen dopant could adjust the resulting material characteristics. Hence, an interesting approach lies in using natural biomolecules as dopants for CPs to tailor the biological outcome. This review comprehensively summarizes the state of the art in the field of glycosaminoglycan-modified electrically conductive polymers for the first time, particularly highlighting the effect of the chosen dopant on material characteristics, such as surface morphology or stiffness, electrochemical properties, and consequently, cell-material interactions.

Designing Electrical Stimulation Platforms for Neural Cell Cultivation Using Poly(aniline): Camphorsulfonic Acid

Electrical stimulation is a powerful strategy to improve the differentiation of neural stem cells into neurons. Such an approach can be implemented, in association with biomaterials and nanotechnology, for the development of new therapies for neurological diseases, including direct cell transplantation and the development of platforms for drug screening and disease progression evaluation. Poly(aniline):camphorsulfonic acid (PANI:CSA) is one of the most well-studied electroconductive polymers, capable of directing an externally applied electrical field to neural cells in culture. There are several examples in the literature on the development of PANI:CSA-based scaffolds and platforms for electrical stimulation, but no review has examined the fundamentals and physico-chemical determinants of PANI:CSA for the design of platforms for electrical stimulation. This review evaluates the current literature regarding the application of electrical stimulation to neural cells, specifically reviewing: (1) the fundamentals of bioelectricity and electrical stimulation; (2) the use of PANI:CSA-based systems for electrical stimulation of cell cultures; and (3) the development of scaffolds and setups to support the electrical stimulation of cells. Throughout this work, we critically evaluate the revised literature and provide a steppingstone for the clinical application of the electrical stimulation of cells using electroconductive PANI:CSA platforms/scaffolds.

Strategies for interface issues and challenges of neural electrodes

Neural electrodes, as a bridge for bidirectional communication between the body and external devices, are crucial means for detecting and controlling nerve activity. The electrodes play a vital role in monitoring the state of neural systems or influencing it to treat disease or restore functions. To achieve high-resolution, safe and long-term stable nerve recording and stimulation, a neural electrode with excellent electrochemical performance (e.g., impedance, charge storage capacity, charge injection limit), and good biocompatibility and stability is required. Here, the charge transfer process in the tissues, the electrode-tissue interfaces and the electrode materials are discussed respectively. Subsequently, the latest research methods and strategies for improving the electrochemical performance and biocompatibility of neural electrodes are reviewed. Finally, the challenges in the development of neural electrodes are proposed. It is expected that the development of neural electrodes will offer new opportunities for the evolution of neural prosthesis, bioelectronic medicine, brain science, and so on.

Micropatterned conductive elastomer patch based on poly(glycerol sebacate)-graphene for cardiac tissue repair

Preparing a micropatterned elastomer film with characteristics that can simulate the mechanical properties, anisotropy, and electroactivity of natural myocardial tissues is crucial in cardiac tissue engineering after myocardial infarction (MI). Therefore, in this study, we developed several elastomeric films with a surface micropattern based on poly (glycerol sebacate) (PGS) and graphene (Gr). These films have sufficient mechanical strength (0.6 ± 0.1-3.2 ± 0.08 MPa) to withstand heartbeats, and the micropatterned structure also satisfies the natural myocardium anisotropy in the transverse and vertical. Moreover, Gr makes these films conductive (up to 5.80 × 10-7 S/m), which is necessary for the conduction of electrical signals between cardiomyocytes and the cardiac tissue. Furthermore, they have good cytocompatibility and can promote cell proliferation in H9c2 rat cardiomyocyte cell lines. In vivo test results indicate that these films have good biocompatibility. Notably, a film with 1 wt% Gr content (PGS-Gr1) significantly affects the recovery of myocardial function in rats after MI. This film effectively decreased the infarct size and degree of myocardial fibrosis and reduced collagen deposition. Echocardiographic evaluation showed that after treatment with this film, the left ventricular internal dimension in systole and left ventricular internal dimension in diastole of rats exhibited a significant downward trend, whereas the fractional shortening and ejection fraction were significantly increased compared with the control group. These data indicate that this electroactive micropatterned anisotropic elastomer film can be applied in cardiac tissue engineering.

Preparations, Properties, and Applications of Polyaniline and Polyaniline Thin Films-A Review

Polyaniline (PANI) is a famous conductive polymer, and it has received tremendous consideration from researchers in the field of nanotechnology for the improvement of sensors, optoelectronic devices, and photonic devices. PANI is doped easily by different acids and dopants because of its easy synthesis and remarkable environmental stability. This review focuses on different preparation processes of PANI thin film by chemical and physical methods. Several features of PANI thin films, such as their magnetic, redox, and antioxidant, anti-corrosion, and electrical and sensing properties, are discussed in this review. PANI is a highly conductive polymer. Given its unique properties, easy synthesis, low cost, and high environmental stability in various applications such as electronics, drugs, and anti-corrosion materials, it has attracted extensive attention. The most important PANI applications are briefly reviewed at the end of this review.

Multimaterial and multifunctional neural interfaces: from surface-type and implantable electrodes to fiber-based devices

Development of neural interfaces from surface electrodes to fibers with various type, functionality, and materials.

Direct grafting of tetraaniline via perfluorophenylazide photochemistry to create antifouling, low bio-adhesion surfaces

Conjugated polyaniline has shown anticorrosive, hydrophilic, antibacterial, pH-responsive, and pseudocapacitive properties making it of interest in many fields. However, in situ grafting of polyaniline without harsh chemical treatments is challenging. In this study, we report a simple, fast, and non-destructive surface modification method for grafting tetraaniline (TANI), the smallest conjugated repeat unit of polyaniline, onto several materials via perfluorophenylazide photochemistry. The new materials are characterized by nuclear magnetic resonance (NMR) and electrospray ionization (ESI) mass spectroscopy. TANI is shown to be covalently bonded to important carbon materials including graphite, carbon nanotubes (CNTs), and reduced graphene oxide (rGO), as confirmed by transmission electron microscopy (TEM). Furthermore, large area modifications on polyethylene terephthalate (PET) films through dip-coating or spray-coating demonstrate the potential applicability in biomedical applications where high transparency, patternability, and low bio-adhesion are needed. Another important application is preventing biofouling in membranes for water purification. Here we report the first oligoaniline grafted water filtration membranes by modifying commercially available polyethersulfone (PES) ultrafiltration (UF) membranes. The modified membranes are hydrophilic as demonstrated by captive bubble experiments and exhibit extraordinarily low bovine serum albumin (BSA) and Escherichia coli adhesions. Superior membrane performance in terms of flux, BSA rejection and flux recovery after biofouling are demonstrated using a cross-flow system and dead-end cells, showing excellent fouling resistance produced by the in situ modification.

Polyaniline/Reduced Graphene Oxide Composite-Enhanced Visible-Light-Driven Photocatalytic Activity for the Degradation of Organic Dyes

Creation of an innovative composite photocatalyst, to advance its performance, has attracted researchers to the field of photocatalysis. In this article, a new photocatalyst based on polyaniline/reduced graphene oxide (PANI/RGO) composites has been prepared via the in situ oxidative polymerization method employing RGO as a template. For thermoelectric applications, though a higher percentage (50 wt %) of RGO has been used, for photocatalytic activity, lesser percentages (2, 5, and 8 wt %) of RGO in the composite have given a significant outcome. Furthermore, photoluminescence (PL) spectra, time-resolved fluorescence spectra, and Brunauer-Emmett-Teller surface area analyses confirmed the improved photocatalytic mechanism. PANI/RGO composites under visible light irradiation exhibit amazingly improved activity toward the degradation of cationic and anionic dyes in comparison with pristine PANI or RGO. Here, a PANI/RGO composite, with 5 wt % RGO(PG2), has emerged as the best combination with the degradation percentages of 99.68, 99.35, and 98.73 for malachite green, rhodamine B, and congo red within 15, 30, and 40 min, respectively. Experimental findings show that the introduction of RGO can relieve the agglomeration of PANI nanoparticles and enhance the light absorption of the materials due to an increased surface area. Moreover, the PG2 composite also showed excellent photocatalytic activity to reduce noxious Cr(VI). The effective removal of Cr(VI) up to 94.7% at pH 2 was observed within only 15 min. With the help of the active species trapping experiment, a plausible mechanism for the photocatalytic degradation has been proposed. The heightened activity of the as-synthesized composite compared to that of neat PANI or RGO was generally because of high concentrations of ^•OH radicals and partly of ^•O₂ ^- and holes (h⁺) as concluded from the nitroblue tetrazolium probe test and photoluminescence experiment. It is hoped that the exceptional photocatalytic performance of our work makes the conducting polymer-based composite an effective alternative in wastewater treatment for industrial applications.

Electroactive polymers for tissue regeneration: Developments and perspectives

Human body motion can generate a biological electric field and a current, creating a voltage gradient of -10 to -90 mV across cell membranes. In turn, this gradient triggers cells to transmit signals that alter cell proliferation and differentiation. Several cell types, counting osteoblasts, neurons and cardiomyocytes, are relatively sensitive to electrical signal stimulation. Employment of electrical signals in modulating cell proliferation and differentiation inspires us to use the electroactive polymers to achieve electrical stimulation for repairing impaired tissues. Electroactive polymers have found numerous applications in biomedicine due to their capability in effectively delivering electrical signals to the seeded cells, such as biosensing, tissue regeneration, drug delivery, and biomedical implants. Here we will summarize the electrical characteristics of electroactive polymers, which enables them to electrically influence cellular function and behavior, including conducting polymers, piezoelectric polymers, and polyelectrolyte gels. We will also discuss the biological response to these electroactive polymers under electrical stimulation. In particular, we focus this review on their applications in regenerating different tissues, including bone, nerve, heart muscle, cartilage and skin. Additionally, we discuss the challenges in tissue regeneration applications of electroactive polymers. We conclude that electroactive polymers have a great potential as regenerative biomaterials, due to their ability to stimulate desirable outcomes in various electrically responsive cells.

The Use of a β-lactamase-based Conductimetric Biosensor Assay to Detect Biomolecular Interactions

Biosensors are becoming increasingly important and implemented in various fields such as pathogen detection, molecular diagnosis, environmental monitoring, and food safety control. In this context, we used β-lactamases as efficient reporter enzymes in several protein-protein interaction studies. Furthermore, their ability to accept insertions of peptides or structured proteins/domains strongly encourages the use of these enzymes to generate chimeric proteins. In a recent study, we inserted a single-domain antibody fragment into the Bacillus licheniformis BlaP β-lactamase. These small domains, also called nanobodies, are defined as the antigen-binding domains of single chain antibodies from camelids. Like common double chain antibodies, they show high affinities and specificities for their targets. The resulting chimeric protein exhibited a high affinity against its target while retaining the β-lactamase activity. This suggests that the nanobody and β-lactamase moieties remain functional. In the present work, we report a detailed protocol that combines our hybrid β-lactamase system to the biosensor technology. The specific binding of the nanobody to its target can be detected thanks to a conductimetric measurement of the protons released by the catalytic activity of the enzyme.

Vapor deposition of polyionic nanocoatings for reduction of microglia adhesion

Polyionics have great potential in improving the performance of neural probes by regulating microglial response. With the shrinkage of microelectrode size and increase in device complexity, challenges arise during liquid-based synthesis of polyionic compounds on neural probes. Nanocoatings of polyionics, with highly crosslinked bulk structure and abundant ionic functional groups on the surface, were synthesized using a process combining chemical vapor deposition and free radical polymerization. Both conformal surface engineering of neural microelectrodes and facile tailoring of surface ionic composition was achieved using this single-step vapor-based method. Adhesion of microglia was reduced on all the polyionic modified surfaces after a seven-day in vitro test, and polyionics with mixed charges presented much lower microglial adhesion than surfaces with single charges. Laminin adsorption on polyionics with mixed charges was significantly reduced due to the surface electrical neutrality and the enhanced wettability. These findings provide valuable information towards the development of neural probes with enhanced biocompatibility and signal stability.

A critical review on the prospect of polyaniline-grafted biodegradable nanocomposite

Among the various electrically conducting polymers, polyaniline (PANI) has gained attentions due to its unique properties and doping chemistry. A number of electrically conducting biodegradable polymers has been synthesized by incorporating a biodegradable content of cellulose, chitin, chitosan, etc. in the matrix of PANI. The hybrid materials are also employed as photocatalysts, antibacterial agents, sensors, fuel cells and as materials in biomedical applications. Furthermore, these biodegradable and biocompatible conducting polymers are employed in tissue engineering, dental implants and targeted drug delivery. This review presents state of the art of PANI based biodegradable polymers along with their synthesis routes and unique applications in diverse fields. In future, the synthesis of PANI-grafted biodegradable nanocomposite material is expected to open innovative ways for their outstanding applications.

Noncontact Electrical Permittivity Mapping and pH-Sensitive Films for Osseointegrated Prosthesis and Infection Monitoring

The objective of this paper is to develop a noncontact, noninvasive system for detecting and monitoring subcutaneous infection occurring at the tissue and osseointegrated prosthesis interface. It is known that the local pH of tissue can change due to infection. Therefore, the sensing system integrates two parts, namely, pH-sensitive thin films that can be coated onto prosthesis surfaces prior to them being implanted and an electrical capacitance tomography (ECT) algorithm that can reconstruct the spatial permittivity distribution of a region of space in a noncontact fashion. First, a thin film pH sensor was fabricated by spray coating, and tests confirmed that the film exhibited changes in its permittivity due to pH. Second, the ECT forward and inverse problems were implemented. Third, an aluminum rod was employed as a representative phantom of an osseointegrated prosthesis and then spray coated with the pH sensor. Finally, the film-coated phantom was immersed in different pH buffers, dried, and subjected to ECT interrogation and spatial permittivity reconstruction. The results validated that ECT was able to detect and localize permittivity variations correlated to pH changes.

Nanostructured Polyaniline Coating on ITO Glass Promotes the Neurite Outgrowth of PC 12 Cells by Electrical Stimulation

A conducting polymer polyaniline (PANI) with nanostructure was synthesized on indium tin oxide (ITO) glass. The effect of electrical stimulation on the proliferation and the length of neurites of PC 12 cells was investigated. The dynamic protein adsorption on PANI and ITO surfaces in a cell culture medium was also compared with and without electrical stimulation. The adsorbed proteins were characterized using SDS-PAGE. A PANI coating on ITO surface was shown with 30-50 nm spherical nanostructure. The number of PC 12 cells was significantly greater on the PANI/ITO surface than on ITO and plate surfaces after cell seeding for 24 and 36 h. This result confirmed that the PANI coating is nontoxic to PC 12 cells. The electrical stimulation for 1, 2, and 4 h significantly enhanced the cell numbers for both PANI and ITO conducting surfaces. Moreover, the application of electrical stimulation also improved the neurite outgrowth of PC 12 cells, and the number of PC 12 cells with longer neurite lengths increased obviously under electrical stimulation for the PANI surface. From the mechanism, the adsorption of DMEM proteins was found to be enhanced by electrical stimulation for both PANI/ITO and ITO surfaces. A new band 2 (around 37 kDa) was observed from the collected adsorbed proteins when PC 12 cells were cultured on these surfaces, and culturing PC 12 cells also seemed to increase the amount of band 1 (around 90 kDa). When immersing PANI/ITO and ITO surfaces in a DMEM medium without a cell culture, the number of band 3 (around 70 kDa) and band 4 (around 45 kDa) proteins decreased compared to that of PC 12 cell cultured surfaces. These results are valuable for the design and improvement of the material performance for neural regeneration.

The applications of conductive nanomaterials in the biomedical field

As their name suggests, conductive nanomaterials (CNMs) are a type of functional materials, which not only have a high surface area to volume ratio, but also possess excellent conductivity. Thus far, CNMs have been widely used in biomedical applications, such as effectively transferring electrical signals, and providing a large surface area to adsorb proteins and induce cellular functions. Recent works propose further applications of CNMs in biosensors, tissue engineering, neural probes, and drug delivery. This review focuses on common types of CNMs and elaborates on their unique properties, which indicate that such CNMs have a potential to develop into a class of indispensable biomaterials for the diagnosis and therapy of human diseases.

Enhanced femoral nerve regeneration after tubulization with a tyrosine-derived polycarbonate terpolymer: effects of protein adsorption and independence of conduit porosity

Following complete nerve transection, entubulation of the nerve stumps helps guide axons to reconnect distally. In this study, a biodegradable and noncytotoxic tyrosine-derived polycarbonate terpolymer composed of 89.5 mol% desaminotyrosyl tyrosine ethyl ester (DTE), 10 mol% desaminotyrosyl tyrosine (DT), and 0.5 mol% poly(ethylene glycol) (PEG, molecular weight [Mw]=1 kDa) [designated as E10-0.5(1K)] was used to fabricate conduits for peripheral nerve regeneration. These conduits were evaluated against commercially available nonporous polyethylene (PE) tubes. The two materials are characterized in vitro for differences in surface properties, and the conduits are then evaluated in vivo in a critical-sized nerve defect in the mouse femoral nerve model. Conduits were fabricated from E10-0.5(1K) in both porous [P-E10-0.5(1K)] and nonporous [NP-E10-0.5(1K)] configurations. The results illustrate that adsorption of laminin, fibronectin, and collagen type I was enhanced on E10-0.5(1K) compared to PE. In addition, in vivo the E10-0.5(1K) conduits improved functional recovery over PE conduits, producing regenerated nerves with a fivefold increase in the number of axons, and an eightfold increase in the percentage of myelinated axons. These increases were observed for both P-E10-0.5(1K) and NP-E10-0.5(1K) after 15 weeks. When conduits were removed at 7 or 14 days following implantation, an increase in Schwann cell proteins and fibrin matrix formation was observed in E10-0.5(1K) conduits over PE conduits. These results indicate that E10-0.5(1K) is a pro-regenerative material for peripheral nerves and that the porosity of P-E10-0.5(1K) conduits was inconsequential in this model of nerve injury.

Protein adsorption and peroxidation of rat retinas under stimulation of a neural probe coated with polyaniline

For the purpose of investigating the potential use of conducting polymers, i.e. polyaniline (PANi), as electrode coating material for improving the function of neural probes, a PANi-coated platinum (Pt) electrode was prepared by the in situ polymerization method. Protein adsorption was observed by atomic force microscopy/scanning electron microscopy and sodium dodecyl sulfate polyacrylamide gel electrophoresis, as well as quantification. Peroxidation of rat retinas was evaluated by determination of conjugated dienes and PLOOH, which were quantified by UV-visible spectrophotometer and high-performance liquid chromatography. The stability of PANi coating for 6 months was also estimated with an in vitro electrical stimulation system. This revealed that: (1) PANi with regular and compact nanoparticles 20-40 nm in diameter was successfully polymerized on the uncoated platinum electrode surface; (2) the PANi-coated Pt electrode adsorbed fewer retinal fragments and induced less peroxidation than the uncoated platinum electrode; (3) in contrast to the uncoated platinum electrode, the PANi-coated Pt electrode surface tended to aggregate retinal fragments rather than spread them, which may help to reduce inflammation and scar formation in long-term implantation; (4) the PANi coating exhibited excellent properties in terms of the intactness and the stable nanoparticle morphology after 6 months' electrical stimulation, while corrosion occurred on the uncoated platinum electrode after 1 month.