On the Mechanics of Cell Adhesion and Proliferation on Fractal Surfaces

The effect of nano/micro-topography on cell adhesion, proliferation and differentiation is recognized as fundamental in the rational design of bio-inspired materials. Controversial is the literature on cell adhesion over randomly rough substrates: some studies documented a decrease in adhesion as the surface roughness (Ra) increased; others showed the opposite; few papers demonstrated a minor influence of Ra. More interestingly, it was also shown the existence of an ‘optimal’roughness for maximizing adhesion and proliferation. In this work, three cell lines of two different species were cultured over etched silicon substrates with Ra ranging from 2 to 100 nm. The rate of proliferation and surface density nd of adhering cells was monitored over three days using confocal and atomic force microscopy. Surface roughness was characterized within the realm of fractal surfaces. For all three cell lines, adhesion and proliferation were enhanced as D increased from a flat surface (D=2) to a Brownian surface (D=2.5). No correlation was observed with Ra. The observed behavior was interpreted within the theory of adhesion of soft solids on randomly rough substrates and the preferential formation of stable focal adhesions at the surface peaks.