Synthesis, characterization and molecular architecture of electroactive and degradable polymers

Abstract: The third-generation biomaterials are designed to stimulate specific cellular responses at the molecular level. Recent studies have shown that electrical signals regulate cellular activities including cell adhesion, migration, proliferation and differentiation. One of the biggest limitations for conductive polymers in tissue engineering applications is their inherent inability to degrade, so the incorporation of conducting polymers into biodegradable polymers to obtain electroactive and biodegradable materials is still a challenge. Architecture plays an important role on the performance of polymers. To achieve the optimal mechanical, degradation, thermal and biological properties for each biomedical application, it is desirable to promote architectural diversity. To combine the electroactivity of conductive polymers and the degradability of aliphatic polyesters, linear, star-branched and hyperbranched copolymers based on Poly(L,L-lactide) (PLLA), Poly(?-caprolactone) (PCL), and aniline oligomers were synthesized by coupling reactions between the hydroxyl group at the chain end of the PLLAs or PCLs and the carboxyl group of the aniline oligomer, using the N, N’-dicyclohexyl carbodiimide / 4-dimethylaminopyridine (DCC/DMAP) catalytic system. The chemical structures of the polymers obtained were fully characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance, and size exclusion chromatography. The cyclic voltammetry and ultraviolet spectra of the copolymers demonstrated their good electroactive properties. Differential scanning calorimetry and thermogravimetric analysis studies showed the copolymers were more thermal stable than the corresponding PLLAs and PCLs. The wettability of the copolymer film increased sharply after doping with acid. The copolymers also exhibit much better processibility than conductive polymers because they are soluble in most organic solvents. Macromolecular architecture design as a useful tool to enhance the conductivity of degradable polymers has been presented. The hyperbranched copolymers showed a higher conductivity than that of the linear ones with the same content of conductive segments. It is proposed that the higher conductivity of the hyperbranched copolymers is due to the ordered distribution of peripheral emeraldine state of aniline pentamer (EMAP) segments. Thus, the conductivity of the polymers is controlled by the macromolecular design. In other words, the conductivity of the polymers was increased with the same content of aniline oligomer by macromolecular architecture.The copolymers with different architectures could be used to tailor the thermal properties, degradation properties and surface properties, to give materials that are favorable for the growth of electrically excitable cells in tissue engineering.