Introduction: Neuroelectrodes are susceptible to deterioration via scar encapsulation following implantation. Biologically relevant nanosurfaces which mimic the biological length scale may prevent this deterioration via the modulation of protein adsorption and cell adhesion. Furthermore, nanotopography may significantly enhance electrode performance via enhanced charge transfer.
Here we describe a self-assembly process for the production of aligned and dense arrays of silicon nanopillars using block copolymers[1]. We discuss the effect of the surface modifications on cell-substrate interaction in vitro and how they may enhance electrode charge transfer and improve neuron/electrode integration.
Experimental Methods: Polystyrene-b-ethylene oxide (PS-b-PEO) diblock copolymer was dissolved in 1 wt% toluene. The thin film was formed by spin cast and annealed at 50°C exposed to toluene/water (1:1). The film was immersed at 40°C for 15h to obtain activated film. Different concentrations of iron (III) nitrate nonahydrate were dissolved and UV/Ozone treatment was used to oxidize the precursor and remove polymer. Surface morphologies were imaged by scanning probe microscopy in tapping mode and scanning electron microscopy. Electrochemical Impedance Spectroscopy was used to evaluate the charge transfer rate of the substrate. The effect of the surface modifications on cell-substrate interaction was investigated through a temporal study with primary rat mesencephalic neural cells which were analysed for phenotypic and genomic changes for 1, 7 and 14 days.
Results and Discussion:
Nanomodified Si surfaces possessed well-ordered nanoscale pillars across the entire substrate. The measured average centre-to-centre cylinder diameter was approx. 50 nm with pillar highs of 100 nm, 500 nm and 1 µm and diameters of approx. 20 nm.
Conclusion: We have fabricated sub-20 nm pillar features in silicon using a block copolymer mask technique. The impedance modulus of nanopillar silicon substrates was significantly reduced relative to planar control substrates in In addition, the adhesion and proliferation of primary rat mesencephalic neural cells on the substrates indicated the nanopillar substrates significantly modulated cell adhesion and function for up to 14 days in culture.
Acknowledgments: The authors would like to acknowledge CRANN and Science Foundation Ireland (SFI) for funding through SFI-CSET CRANN. Also Advance Microscopy Laboratory (AML) / CRANN for the collaborations. Bell Labs Ireland thanks the Industrial Development Agency (IDA) Ireland for their financial support. M.J. Biggs is an SFI SIRG fellow, grant no. 11/SIRG/B2135.
References:
[1] Ghoshal. et al., Adv.Mater. 24:2390-2397, 2012