Electrochemistry-enabled fabrication of orthogonal nanotopography and surface chemistry gradients for high-throughput screening.

Gradient surfaces are emerging tools for investigating mammalian cell-surface interactions in high throughput. We demonstrate the electrochemical fabrication of an orthogonal gradient platform combining a porous silicon (pSi) pore size gradient with an orthogonal gradient of peptide ligand density. pSi gradients were fabricated via the anodic etching of a silicon wafer with pore sizes ranging from hundreds to tens of nanometers. A chemical gradient of ethyl-6-bromohexanoate was generated orthogonally to the pSi gradient via electrochemical attachment. Subsequent hydrolysis and activation of the chemical gradient allowed for the generation of a cyclic RGD gradient. Whilst mesenchymal stem cells (MSC) were shown to respond to both the topographical and chemical cues arising from the orthogonal gradient, the MSC's responded more strongly to changes in RGD density than to changes in pore size during short-term culture.