Interactions between chemical functionality and nanoscale surface topography impact fibronectin conformation and neuronal differentiation on model sol-gel silica substrates

Functional relationships between the biomaterial interface and extracellular matrix (ECM) proteins are intimately involved in cellular adhesion and function. Structural changes of ECM proteins upon adsorption to a surface alter the protein's biological activity by varying the availability of molecular binding sites. Recent work using native and organically modified sol-gel silica as a neuronal biointerface revealed that changes in surface nanotopography of bulk versus thin film materials result in dramatic differences in fibronectin structure, cell survival, and neuronal differentiation. In order to investigate interactions between chemical functionality and surface topography, we evaluated the global conformation of human fibronectin adsorbed to seven different organically modified silica gels and thin films. Chemical functional groups were introduced into the materials either by altering the starting precursor or by doping with poly-1-lysine or polyethylenimine. Surface topography measurements by atomic force microscopy show that films have surface features less than 25 nm while bulk materials of the same precursor chemistry have features ranging from 50 - 100 nm in size. Fluorescence resonance energy transfer spectroscopy (FRET) revealed a strong interaction between surface topography and chemical functionality. Fibronectin remain globular on all bulk materials regardless of chemical modification. The same changes in precursors or dopant chemistry, however, induced changes in the conformation of fibronectin on the thin films. The differentiation of PC12 cells on the surface indicated a strong impact of the surface features and suggest a possible optimal fibronectin folding state.