Conducting polymers (CPs) possess unique electrical and electrochemical properties and hold great potential for a wide range of applications in the field of bioelectronics. However, the widespread implementation of CPs in this field has been critically hindered by their poor processibility. There are four key elements that determine the processibility of CPs, which are thermal tunability, chemical stability, solvent compatibility, and mechanical robustness.
This research aimed to create processible CP-based systems that were compatible with 3D printing techniques. It was hypothesised that by introducing a thiophene ring in the side group of polyoxazolines (POx) and polyoxazines (POzi), would produce a new class of polymers with the processability of POx and POzi, with the electrical functionality of CPs. For this purpose, eight monomers were first prepared by Seeliger and Wittig reactions. Here, the first crystal structures of Ox and Ozi were produced, as four of these monomers were present in solid phase at room temperature.
The polymerisation of these monomers followed a cationic ring-opening polymerisation (CROP). Poly(2-thiophene-3-oxazine) (P2Th3OZi) was obtained at high yield and efficiency. This polymer was further investigated as a feed for 3D printing. P2Th3Ozi was found to have good solubility in many organic solvents including chloroform and toluene. It possessed ideal thermal properties for melt-processing techniques such as melt electrospinning writing (MEW). Post-fabrication treatment of P2Th3Ozi scaffolds with water demonstrated swelling behaviour and amelioration of initially brittle mechanical properties. Since P2Th3Ozi was found to have low conductivity in its native state, further modification via intermolecular crosslinking with thiophene monomers in the presence of ferric chloride was explored, resulting in a 20-fold increase in conductivity.
Cytotoxicity studies demonstrated low toxicity of P2Th3OZi following adequate washing to remove solvents used for polymer synthesis. Printed scaffolds of P2Th3OZi were also found to promote cellular attachment and spreading along the scaffold structures. Future studies will focus on improving the electrical properties of the scaffolds. This new class of monomers have the potential to be a technology platform for the bespoke development of printable scaffolds in tissue regeneration.