Conductive hydrogels with tailored bioactivity for implantable electrode coatings

The development of high-resolution neuroprosthetics has driven the need for better electrode materials. Approaches to achieve both electrical and mechanical improvements have included the development of hydrogel and conducting polymer composites. However, these composites have limited biological interaction, as they are often composed of synthetic polymers or non-ideal biological polymers, which lack the required elements for biorecognition. This study explores the covalent incorporation of bioactive molecules within a conducting hydrogel (CH). The CH was formed from the biosynthetic co-hydrogel poly(vinyl alcohol)–heparin and the conductive polymer (CP), poly(3,4-ethylene dioxythiophene). Adhesive biomolecules sericin and gelatin were covalently incorporated via methacrylate crosslinking within the CH. Electrical properties of the bioactive CH were assessed, and it was shown that the polar biomolecules improved charge transfer. The bioactivity of heparin within the hybrid assessed by examining stimulation of B-lymphocyte (BaF3) proliferation showed that bioactivity was retained after electropolymerization of the CP through the hydrogel. Similarly, incorporation of sericin and gelatin in the CH promoted neural cell adhesion and proliferation, with only small percentages (⩽2 wt.%) required to achieve optimal results. Sericin provided the best support for the outgrowth of neural processes, and 1 wt.% was sufficient to facilitate adhesion and differentiation of neurons. The drug delivery capability of CH was shown through incorporation of nerve growth factor during polymer fabrication. NGF was delivered to the target cells, resulting in outgrowth of neural processes. The CH system is a flexible technology platform, which can be tailored to covalently incorporate bioactive protein sequences and deliver mobile water-soluble drug molecules.