Surface characteristics, biodegradability and biocompatibility of porous silicon for microfabricated neural electrode

Porous Si (PSi) used for microfabrication of a novel neural electrode was prepared on Si wafers by an anodization process. Surface morphology and porous structure of the PSi were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). 3D interconnected and nano sized pores were homogeneously formed across the surface. Wettability of the PSi was determined using a sessile drop method. Although Si-Hx functional groups on the PSi surface had negative effect on wettability, water contact angle of the PSi reduced to 34.5 ± 0.5 ° due to the enhanced surface roughness and the capillary force generated by nano sized pores. Moreover, in vitro biocompatibility of the PSi was assessed by seeding a breast cancer cell line (MCF-7). After 5 days of culture, cell morphology was observed using a fluorescence microscope. Although more than 99% of the cells under the microscope were living for both Si and PSi samples, morphology of the cells attached on their surfaces was different. MTT assay was also used to quantitatively evaluate in vitro biocompatibility, and revealed false positive results due to the spontaneous reduction of MTT on the PSi surface. Therefore, MTT assay was not suitable for in vitro quantitatively study of PSi.