Substrate porosity induces phenotypic alterations in retinal cells cultured on silicon nanowires
Arrays of silicon nanowires (Si NW) may be used in the development of implantable drug delivery systems. Here, we performed short- and long-term cultures of mouse retinal cells on substrates consisting of high aspect ratio Si NW, which confers high porosity to the surface. As controls, cells were grown on flat silicon substrates. The cell phenotype was assessed using immunocytochemistry, fluorescence microscopy and scanning electron microscopy. We observed that, despite good adhesion and long-term survival on Si NW (for at least 18 days in vitro), cells underwent striking phenotypic changes, characterized by the absence of neurites and an underexpression of most retinal cell markers. These alterations could, however, be prevented by functionalizing the surface using perfluorosilane molecules. The study also provides evidence that the altered cell behavior on Si NW can be attributed to contaminants entrapped in the nanowire array. Our data thus indicate that creating high aspect ratio pores, while increasing porosity in order to increase the loading capacity of the substrate, results in neurotoxicity. The functionalized substrates, while allowing for cell growth, would not be suitable for drug delivery. The findings are important for the design of porous silicon-based cell scaffolds and drug delivery systems, in particular when aimed at interfacing CNS cells.