| The thrombogenecity of synthetic vascular grafts can be improved by applying a quiescent monolayer of endothelial cells on the graft surface. Whereas most investigations have focused on chemically modifying polymeric materials to promote endothelial cell adhesion, the approach in this thesis is to use micro-scale patterns of grooves, consisting of parallel ridges and channels, on a model silicone template to emulate the naturally aligned endothelium of the vascular vessels. Groove patterns are first prepared on silicon masters by photolithography, electron-beam lithography and reactive ion etching, and then replicated on the surface of silicone by film casting. Using fibronectin adsorption to promote initial cell attachment on silicone, the morphology, migration and proliferation of endothelial cells are then investigated. For groove widths ≤5 mum, a groove depth of 1 mum successfully induces the uniform alignment of endothelial cells, as well as actin microfilaments and focal adhesions, parallel to grooves within 1 h after seeding. Cell alignment and cell proliferation on grooved silicone remain unaltered until the culture reaches confluence. At a fixed groove depth of 1 mum, a variation in groove width, having ridge and channel dimensions (mum) of 5x5, 3x3, 2x2, and 4x2, is shown to modulate cell migration. The majority of cells, about 60%, migrate parallel to grooves, although cells migrating transverse to grooves increase as the channel width decreases to 2 mum, the length scale at which most focal adhesions form on the ridge edge. Under flow that applied parallel to grooves, a high shear stress, 58 dyne/cm 2, induces almost all the cells to migrate in the direction of both grooves and flow. When applied perpendicular to grooves, however, the same shear stress induces about 70% of cells to turn their migration direction transverse to grooves. While microgrooves on the substrate surface are found to strongly influence cell orientation and migration, the modulus of silicone from 0.063 to 2 MPa has a minor effect on cell spreading and proliferation. In summary, this thesis shows that the interactive polymeric graft displaying micro-scale patterns of grooves can mediate the alignment and directional migration of endothelial cells. |
