Synthesis and characterisation of multifunctional hydrogels for biomedical applications

The development of “smart” biomaterials for biomedical applications such as drug delivery systems, tissue engineering applications and neural prosthetics is a goal sought after by many researchers. Multifunctional and electroactive hydrogels as a class, possess inherent properties that can bring these goals to fruition. However, their practical applications are limited by the difficulties associated in synthesising hydrogels with properties which can be readily tuned and incorporating electroactive components into hydrogels without compromising the electrochemical properties of the overall structure. This work describes the synthesis and characterisation of hydrogels with easily tuneable mechanical and swelling properties, and the synthesis and characterisation of a novel electroactive hydrogel for potential applications in tissue engineering, drug delivery, and neural coatings respectively. An acrylate based copolymer, poly(acrylic acid)-cysteine-acrylic acid (PCA) was prepared and cross-linked via photo initiated thiol-acrylate chemistry. By using this Michael type addition chemistry, it was possible to synthesize a range of hydrogels and tune the mechanical and swelling properties of the formed hydrogels. The resulting hydrogels thus possessed mechanical and swelling properties which could be readily tuned by adjusting the ratio of thiol to acrylate concentration and changing the cross-linking time. Biocompatibility studies showed that the hydrogels exhibited excellent biocompatibility when tested against RPE1 cell line, and were observed to facilitate cell adhesion and proliferation without the need for further modification of the hydrogel with ECM proteins. These PCA hydrogels were used to further investigate the electrodeposition of electroactive polymers within hydrogels, and used to develop an electroactive hydrogel by electrochemically depositing PEDOT within the matrix of the hydrogels. In investigating the electrodeposition of electroactive polymers in hydrogels, PCA hydrogels were compared against pHEMA, one of the most widely used, commercially available, and biocompatible hydrogels. A sulfonated aniline polymer PMAS, was used as the electroactive component. Findings showed that the electrochemical growth and properties of PMAS was favoured in PCA hydrogels over pHEMA due to distinct chemical and physical properties present in the PCA hydrogels, but not in pHEMA. Moreover, during the electrochemical deposition of PEDOT, the PCA hydrogels proved to be chemically resistant and thus making it possible to carry out the electrochemical deposition in the three PCA hydrogels from an organic solution containing the monomer and electrolyte salt. Electrochemical characterisation of the three PCA-PEDOT hydrogels formed confirmed that all three hydrogels exhibited lowered impedance values at 1 kHz within the range applicable for in vivo applications. These findings, in addition to the biocompatibility studies carried on pristine PCA hydrogels, suggest that these hydrogels represent a class of multifunctional hydrogels which may be potentially used for a range of in vivo and in vitro biomedical applications.