Neurotrophin-Releasing Hydrogel-Electrospun Fiber Mat Composite Coatings for Neural Prostheses

In the US, thousands of people annually suffer from spinal cord injury (SCI), a condition for which there currently is no effective treatment. One promising strategy is to incorporate nerve regeneration approaches, such as utilization of physical scaffolds and eluted soluble factors, into neural prostheses. This combination has the potential to greatly improve device/tissue interaction by increasing device biocompatibility and stimulating nerve regeneration through controlled release. We present a novel composite electrode coating consisting of poly (ethylene glycol)-poly (ε-caprolactone) (PEGPCL) hydrogel, which can mimic the native brain structure and release soluble neurotrophins, combined with PCL electrospun fiber mats, which mimic native, fibrous, white matter tissue architecture. Composites were tested in vitro using retinal prosthesis electrodes and the PC12 cell line model system. Incorporation of PCL electrospun fiber mats with PEGPCL hydrogels provided three benefits in overall coating performance. First, the mats provided an additional hydrophobic diffusion barrier, dramatically reducing initial burst release and producing an extended, more linear drug release profile. Second, the PCL electrospun fiber mats also introduced a fibrous surface, which promoted cell adhesion and enhanced cell/electrode interface interaction, most likely as a result of the structural similarity to extracellular matrix (ECM). Moreover, PCL fiber mats significantly decreased the degradation rate of PEGPCL hydrogels, and thus composite coatings remained on electrode surfaces for over two months.