Ultra-thin polymer coating for promoting neural cells integration with neural implants

Human neuroblastoma (SH-SY5Y) cells were used to demonstrate biocompatibility (including control over direction of neurites) for multilayer thin polymer coatings with neural cells. The ultra-thin (<20 nm) coatings were synthesised using plasma deposition process with (CH₄, C₂H₂ and O₂) gasses as precursors. The aim is to use these thin films to add bio-selectivity to orthopaedic and neurological implants such as cervical disc and interbody replacement, in addition to providing other qualities such as degradation resistance and permeation barrier. X-ray photo electron spectroscopy and contact angle measurements were used to provide surface molecular and surface energy information, respectively. The thin coatings’ functionality remained intact despite robust sterilisation process. The coatings showed no toxicity effects on neural cells growth and spreading after 6 days. Neural cells responded favourably (cell growth and spreading) to thinner (<6 nm) coatings that are rich in oxygen. Closer inspection revealed that neurites grow denser on surfaces with C[dbnd]O functional groups and reacted negatively to the increase in C–O functional groups on the surface. Best neurite-like differentiation towards neural-like cells was observed on surfaces that were plasma deposited using C₂H₂ gas (with or without oxygen). Plasma treatment using CH₄ produced thin coatings with lowest surface energy that repelled neurites cells (very low cell density). Hence, the latter treatment is useful for cases where cells/bio-coatings inhibition is desired.