Mohammad Reza Abidian

Conducting-Polymer Nanotubes Improve Electrical Properties, Mechanical Adhesion, Neural Attachment, and Neurite Outgrowth of Neural Electrodes

An in vitro comparison of conducting-polymer nanotubes of poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(pyrrole) (PPy) and to their film counterparts is reported. Impedance, charge-capacity density (CCD), tendency towards delamination, and neurite outgrowth are compared. For the same deposition charge density, PPy films and nanotubes grow relatively faster vertically, while PEDOT films and nanotubes grow more laterally. For the same deposition charge density (1.44 C cm(-2)), PPy nanotubes and PEDOT nanotubes have lower impedance (19.5 +/- 2.1 kOmega for PPy nanotubes and 2.5 +/- 1.4 kOmega for PEDOT nanotubes at 1 kHz) and higher CCD (184 +/- 5.3 mC cm(-2) for PPy nanotubes and 392 +/- 6.2 mC cm(-2) for PEDOT nanotubes) compared to their film counterparts. However, PEDOT nanotubes decrease the impedance of neural-electrode sites by about two orders of magnitude (bare iridium 468.8 +/- 13.3 kOmega at 1 kHz) and increase capacity of charge density by about three orders of magnitude (bare iridium 0.1 +/- 0.5 mC cm(-2)). During cyclic voltammetry measurements, both PPy and PEDOT nanotubes remain adherent on the surface of the silicon dioxide while PPy and PEDOT films delaminate. In experiments of primary neurons with conducting-polymer nanotubes, cultured dorsal root ganglion explants remain more intact and exhibit longer neurites (1400 +/- 95 microm for PPy nanotubes and 2100 +/- 150 microm for PEDOT nanotubes) than their film counterparts. These findings suggest that conducting-polymer nanotubes may improve the long-term function of neural microelectrodes.

A Review of Organic and Inorganic Biomaterials for Neural Interfaces

Recent advances in nanotechnology have generated wide interest in applying nanomaterials for neural prostheses. An ideal neural interface should create seamless integration into the nervous system and performs reliably for long periods of time. As a result, many nanoscale materials not originally developed for neural interfaces become attractive candidates to detect neural signals and stimulate neurons. In this comprehensive review, an overview of state-of-the-art microelectrode technologies provided fi rst, with focus on the material properties of these microdevices. The advancements in electro active nanomaterials are then reviewed, including conducting polymers, carbon nanotubes, graphene, silicon nanowires, and hybrid organic-inorganic nanomaterials, for neural recording, stimulation, and growth. Finally, technical and scientific challenges are discussed regarding biocompatibility, mechanical mismatch, and electrical properties faced by these nanomaterials for the development of long-lasting functional neural interfaces.

Conducting Polymers for Neural Prosthetic and Neural Interface Applications

Neural-interfacing devices are an artificial mechanism for restoring or supplementing the function of the nervous system, lost as a result of injury or disease. Conducting polymers (CPs) are gaining significant attention due to their capacity to meet the performance criteria of a number of neuronal therapies including recording and stimulating neural activity, the regeneration of neural tissue and the delivery of bioactive molecules for mediating device-tissue interactions. CPs form a flexible platform technology that enables the development of tailored materials for a range of neuronal diagnostic and treatment therapies. In this review, the application of CPs for neural prostheses and other neural interfacing devices is discussed, with a specific focus on neural recording, neural stimulation, neural regeneration, and therapeutic drug delivery.

Hybrid Conducting Polymer–Hydrogel Conduits for Axonal Growth and Neural Tissue Engineering

Successfully and efficiently bridging peripheral nerve gaps without the use of autografts is a substantial clinical advance for peripheral nerve reconstructions. Novel templating methods for the fabrication of conductive hydrogel guidance channels for axonal regeneration are designed and developed. PEDOT is electrodeposited inside the lumen to create fully coated-PEDOT agarose conduits and partially coated-PEDOT agarose conduits.

High-Performance Conducting Polymer Nanofiber Biosensors for Detection of Biomolecules

Sensitive detection and selective determination of the physiologically important chemicals involved in brain function have drawn much attention for the diagnosis and treatment of brain diseases and neurological disorders. This paper reports a novel method for fabrication of enzyme entrapped-conducting polymer nanofibers that offer higher sensitivity and increased lifetime compared to glucose sensors that are based on conducting polymer films.

A high performance hybrid asymmetric supercapacitor via nano-scale morphology control of graphene, conducting polymer, and carbon nanotube electrodes

An asymmetric supercapacitor, exploiting ultra-high density aligned activated graphene flakes as the positive electrode and nm-scale conformal coating of a conducting polymer poly(ethylenedioxythiophene) on aligned carbon nanotubes as the negative electrode, is introduced. By complementary tailoring of the asymmetric electrodes, the layered device exhibits a wide 4 V electrochemical window, with the highest power density (149 kW L−1) and energy density (113 Wh L−1) reported thus far for carbon-based supercapacitors.

Microencapsulation of Chemotherapeutics into Monodisperse and Tunable Biodegradable Polymers via Electrified Liquid Jets: Control of Size, Shape, and Drug Release

This paper describes microencapsulation of antitumor agent 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU, Carmustine) into biodegradable polymer poly(lactic-co-glycolic) acid (PLGA) using an electrojetting technique. The resulting BCNU-loaded PLGA microcapsules have significantly higher drug encapsulation efficiency, more tunable drug loading capacity, and (3) narrower size distribution than those generated using other encapsulation methods.

Cytotoxic analysis of the conducting polymer PEDOT using myocytes

Biosensors interact with biological systems at the surface of the sensor. Coating these sensors with electrically active polymers has been suggested to improve this interface. The electrically conducting polymer poly (3, 4 ethylenedioxythiophene) (PEDOT) enhances electrical recordings by improving conductivity while maintaining chemical stability. It also offers great flexibility in studying cell substrate interactions because of the variety of counter-ions that can be incorporated into the PEDOT matrix. To provide any true benefit in cell culture or in vivo experiments, the cytotoxicity of PEDOT must first be determined. This study evaluated the cytotoxicity of PEDOT doped with either polystyrene sulfonate (PSS) or phosphate buffered saline (PBS) ions and tested the efficacy of using the conductive PEDOT substrates for myoblast proliferation and differentiation. Results show that PEDOT/PBS and PEDOT/PSS are not cytotoxic to cells and successfully support cellular proliferation and differentiation. These results establish PEDOT as a material for cell-substrate interface studies. With biosensors being modified using the new polymer coating PEDOT, this cytotoxicity study provides evidence that PEDOT coatings will not induce a cytotoxic response when implanted in vivo.

Hydrogel‐Mediated Direct Patterning of Conducting Polymer Films with Multiple Surface Chemistries

A new methodology for selective electropolymerization of conducting polymer films using wet hydrogel stamps is presented. The ability of this simple method to generate patterned films of conducting polymers with multiple surface chemistries in a one-step process and to incorporate fragile biomolecules in these films is demonstrated.

In-vivo Evaluation of Chronically Implanted Neural Microelectrode Arrays Modified with Poly (3,4-ethylenedioxythiophene) Nanotubes

The interface between neural prostheses and neural tissue plays a significant role in the long term performance of these devices. Conducting polymers have been used to modify the electrical properties of neural microelectrodes. The objective of this study was to evaluate recording chronic neural activity of neural microelectrodes that were modified with nanofibers-templated of poly (3,4-ethylenedioxythiophene) (PEDOT) nanotubes over seven week periods using impedance spectroscopy and signal-to-noise ratio measurements. PEDOT nanotubes-coated sites were found to have lower impedance and higher signal-to-noise ratio than control site.