Preparation of 2-directional gradient surfaces for the analysis of cell-surface interactions

The ability to evaluate and control the cellular response to substrate materials is the key to a wide range of biomedical applications ranging from diagnostic tools to regenerative medicine. Gradient surfaces provide a simple and fast method for investigating optimal surface conditions for cellular responses such as attachment and growth. By using two orthogonal gradients on the same substrate, a large space of possible combinations can be screened simultaneously. Here, we have investigated the combination of a porous silicon (pSi) based topography gradient with a plasma polymer based thickness gradient. pSi was laterally anodised on a 1.5 × 2.5cm² silicon surface using hydrofluoric acid to form a pore size gradient along a single direction. The resulting pSi was characterised by SEM and AFM and pore sizes ranging from macro to mesoporous were found along the surface. Plasma polymerisation was used to form a thickness gradient orthogonal to the porous silicon gradient. Here, allylamine was chosen as the monomer and a mask placed over the substrate was used to achieve the thickness gradient. The analysis of this chemistry based gradient was carried out using profilometry and XPS. It is expected that orthogonal gradient substrates will be used increasingly for the in vitro screening of materials used in biomedical applications.