Engineering stable topography in dense bio-mimetic 3D collagen scaffolds.

Topographic features are well known to influence cell behaviour and can provide a powerful tool for engineering complex, functional tissues. This study aimed to investigate the mechanisms of formation of a stable micro-topography on plastic compressed (PC) collagen gels. The uni-directional fluid flow that accompanies PC of collagen gels creates a fluid leaving surface (FLS) and a non-fluid leaving surface (non-FLS). Here we tested the hypothesis that the resulting anisotropy in collagen density and stiffness between FLS and non-FLS would influence the fidelity and stability of micro-grooves patterned on these surfaces. A pattern template of parallel-aligned glass fibres was introduced to the FLS or non-FLS either at the start of the compression or halfway through, when a dense FLS had already formed. Results showed that both early and late patterning of the FLS generated grooves that had depth (25 ±7 µm and 19 ±8 µm, respectively) and width (55 ±11 µm and 50 ±12 µm, respectively) which matched the glass fibre diameter (50 µm). In contrast, early and late patterning of the non-FLS gave much wider (151 ±50 µm and 89 ±14 µm, respectively) and shallower (10 ±2.7 µm and 13 ±3.5 µm, respectively) grooves than expected. The depth to width ratio of the grooves generated on the FLS remained unaltered under static culture conditions over 2 weeks, indicating that grooves were stable under long term active cell-mediated matrix remodelling. These results indicate that the FLS, characterised by a higher matrix collagen density and stiffness than the non-FLS, provides the most favourable mechanical surface for precise engineering of a stable micro-topography in 3D collagen hydrogel scaffolds.