Biomedical devices typically accumulate fibrous tissue on their surfaces during the first several weeks after implantation, i.e. the foreign body response (FBR). This fibrosis is particularly problematic for neural prosthetics, such as the cochlear implant. When electrode arrays become encapsulated in the dense avascular fibrotic tissue, the applied current, which stimulates the spiral ganglion neurons (SGNs), or inner ear neurons, is attenuated, thereby causing significant broadening of the current and lower signal resolution. Nonspecific adsorption of proteins to device surfaces marks the implant as foreign and instigates scar tissue formation. Zwitterionic polymers, or materials with an equal number of positive- and negative-charged atoms on each repeat unit, are a new class of material that show great promise in resisting nonspecific protein adsorption to mitigate the FBR. In this work, photopolymerization was used to covalently graft sulfobetaine methacrylate (SBMA) and carboxybetaine methacrylate (CBMA), two zwitterionic monomers, to glass surfaces. X-ray photoelectron spectroscopy (XPS) was used to confirm the successful grafting of both zwitterionic polymers. The physicochemical properties of the surface respond to changes in aqueous solution concentration of the zwitterionic monomers. These surfaces show a strong resistance to protein adsorption which correlates to changes in contact angle while varying solution concentrations. Further, parallel line pattern surfaces were fabricated to evaluate the efficacy of these materials to spatially control cell adhesion and growth. Fibroblasts, oligodendrocytes, astrocytes, Schwann cell, and spiral ganglion neurons (SGNs) all exhibit a strong repulsion to zwitterion-coated regions on both patterned and unpatterned surfaces. Interestingly, zwitterionic micropatterns formed using photopolymerization direct the regrowth SGN neurites. Neurite extensions grow directly between zwitterion-coated bands avoiding interaction with the functionalized regions. While SGN neurites extend along SBMA stripes, CBMA patterns significantly improve alignment compared to SBMA patterns. These results lay the foundation for next generation cochlear implants and other neural prosthetics.

Engineering zwitterionic polymers that control cell adhesion and direct neurite growth to improve cochlear implants

253rd National Meeting (2017)

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