Design of a Novel Electrically Conducting Biocompatible Polymer with Degradable Linkages for Biomedical Applications

Abstract

Upon the discovery of the first conducting polymer in 1976, the replacement of metal-based semiconductors in many applications with conducting polymers was inevitable. Perhaps more surprisingly these materials showed promise in many biomedical applications. The finding that electrical fields and charges modulate shape, size, and proliferation of a number of cell types including nerve and bone, has prompted biomedical engineers to focus on the development of conducting polymer scaffolds for tissue regeneration and neural probes. A number of polymers have been studied for these applications, including polypyrrole (PPy), polythiophene, and polyaniline. One serious limitation to the use of conducting polymers in biological systems is their inability to degrade. Therefore, it has been proposed to design and synthesize a biocompatible, biodegradable, semiconducting polymer, which could broaden the scope of applications for conducting polymers. For instance, these unique polymers could potentially be implemented in temporary tissue and neural scaffolds, drug delivery, short-term electrodes, and tethers between nanotubes. Therefore, the goal of this investigation is to synthesize a polymer that is degradable, while maintaining conductivity. Initially, the incorporation of pyrrole oligomers into a biodegradable polymer was attempted; however, to overcome difficulties associated with the instability of these oligopyrroles, a novel polymer design has been proposed which incorporates thiophene oligomers. Oligothiophenes (OTs) are apt to be more conductive than oligopyrroles due to a smaller band gap between the valence and conductance bands. Additionally, OTs share many of the advantageous properties of oligopyrroles, including cell compatibility, but are more stable. The proposed novel co-polymer consists of quaterthiophene oligomers tethered together by aliphatic ester linkages, which would potentially render the co-polymer conductive by means of inter and intra chain oligo overlap and degradable via cleavage of the ester bond by esterases in the body. The synthesis of the novel copolymer, poly-dialcohol dimethyl quaterthiophene-co-adipic acid (PAMQAA) has been completed successfully and corroborated by NMR and MALDI. Initial characterization indicates PAMQAA has the following properties: Mw = 11,240-64,080 g/mol, PI = 1.2-1.4, degradation temperature = ∼160°C. Currently PAMQAA is being characterized to assess its Tg, Tm, conductivity, degradability, and biocompatability. Polymer modifications could allow further optimization of properties, such as the rate of degradation and conductivity, to target better the application of interest.