Nanostructured Conductive Polymers as Biomaterials

Abstract

Conductive polymers (CPs) are an emerging technology in the field of biomaterials. While CPs retain a predominantly investigative role in the field of medical implants, they have shown potential across a wide range of applications, including neural interfaces, biosensors, nerve grafts, and drug-delivery devices.CPs have been extensively explored for addressing the limitations of conventional neuroprosthetic implant devices which employ metallic electrodes to interface with neural tissue. In this application CPs have the potential to provide a conductive interface with properties more suited to soft-tissue integration. Unlike conventional conductive materials CPs are relatively soft, with a textured surface conducive to cell attachment. The high surface area relative to the geometric base area means these materials also have good charge-transfer properties, with low impedance and negligible bilayer capacitance, a substantial limitation of existing neural-stimulation electrode technologies. These types of properties have resulted in much investigation of conductive polymers for a range of other medical applications, including biosensors, nerve regeneration templates, and for drug-delivery applications.

CHAPTER 8. Bioactive Conducting Polymers for Optimising the Neural Interface

“…Electrical conduction not only occurs along the polymer backbone but also between neighbouring polymer strands. 3 Although not as well understood, conduction between polymer strands is critical to the observed macroscopic conduction within conducting polymers due to their highly disordered structure. The choice of dopant molecule plays a critical role in determining the properties of the resultant conducting polymer film.…”

“…5 Large, bulky, biological dopants may experience mass transport limitations during polymerisation resulting in a concentration deficit at the deposition interface, interfering with the electrodeposition process. 3,33 A critical aspect of creating bioactive conducting polymers is the retention of the dopants biofunctionality. In particular, biofunctionality may be compromised during electrodeposition due to chemical or electrical denaturation as a result of the organic solvents and electrical charge used during electrodeposition.…”

“…In chemical fabrication routes, the monomer is dissolved in an organic solvent and is added to a solution of mild Lewis-acid catalysts. 3 The catalyst enables oxidative coupling of monomer units to form polymer strands. Conducting polymer films can then be formed using solvent casting techniques.…”

“…Due to the thin film, substrate-dependent nature of conducting polymers many conventional techniques, such as tensile testing, do not apply. 3 Yang and Martin used nanoindentation to evaluate the mechanical properties of PEDOT/LiClO 4 . They found that films with higher surface area due to increased roughness, and hence lower impedances, were the most mechanically compliant films.…”

“…These are electrostatic incorporation of charged molecules as bioactive dopants, or through physical entrapment of neutral or weakly charged molecules as non-dopant inclusions. 3,27 Less commonly used methods of incorporation include physical adsorption and covalent attachment to the surface of conducting polymer films. The method of incorporation is typically determined by the properties of the bioactive molecule in question as well as the desired means of biological presentation.…”