Influence of aerogel mechanical properties on collagen micromorphology and its architecture

Previously, we demonstrated the promise of aerogels for the repair of nerve injuries as neural cells extend longer processes (neurites) when grown on aerogels compared to a control surface. We also reported that the aerogel surface topography influenced neurite length. Neurite extension may be boosted by depositing collagen on the aerogel prior to plating the cells. Indeed, collagen has many applications in biomaterials for nerve repair because it profoundly influences cellular properties such as shape and motility. Using collagen to enhance neurite extension requires knowing the effect of collagen deposition on the aerogel surface profile as well as how the aerogel's surface topography influences collagen organization into fibers or films. Herein, we have examined by SEM and profilometry the reciprocal relationship between collagen micromorphology and aerogel surface features including pore diameters, surface roughness, and Young's modulus (Y). Using 5 types of aerogels differing from each other by these parameters, we show that increasing the collagen surface concentration from 4 to 20 μg cm^-2 leads to a gradual transition in collagen architecture from discrete fibers to films where individual fibers were not discernible. The collagen surface concentration at which deposited collagen changes from filaments to films (transition point, T.P.) was strongly dependent on aerogel physical properties as it increased with increasing pore diameter and surface roughness, while Y had little effect. These results provide a practical framework to customize the organization of collagen fibers on scaffolds for biomedical applications.