1. Introduction Cell migration is critical in many biological processes including foetal development, wound healing and the immune response. However, occasionally it has an undesirable effect; for example in cancer growth and vascular (blood vessel) disease. Many surgical interventions used to treat vascular disease, such as the stent in the centre picture, are disrupted by the invasion of the surrounding tissue onto the implanted device. Proteins present in the blood can adsorb onto the surface of implanted materials and effect the way the tissue interacts with it. The aim of this work is to study how the interaction between human cells and implantable materials is affected by the nature of the material and the amount of protein adsorbed on it. Medical grade polyurethane of two different stiffnesses was used as the substrata. The protein investigated was fibronectin, an abundant protein in the blood and one which has a substantial effect on cell attachment. Cell Attachment Strength The adhesion of a cell to its substrate is central to its migration. A centrifugal detachment force was applied to the cells to determine the strength of attachment to the fibronectin-coated substrates. Cell Migration Rate A barrier migration assay (modified from the Teflon fence migration assay 1 ) was used: Vascular cells were grown on fibronectin-coated polymer membranes, restricted by a barrier. The barrier was then removed and the cells microscopically imaged as they populated the polymer surface. Cell Structure The mechanism by which a cell propels itself across a surface involves an internal framework, called the cytoskeleton, which attaches at numerous points to the substratum via the cell membrane. The cytoskeleton can provide traction forces to pull the cell along. Cells attached to the different stiffness polymers with various fibronectin coating densities were imaged using fluorescent microscopy to study the effect of the substrate on the cytoskeleton. Conclusions Many cell types have been found to have maximal migration rates on surfaces to which they adhere at intermediate adhesion strengths 2. Furthermore, both substrate stiffness and the density of surface-bound cell-adhesion sites have an effect with an increase in either producing an increase in the strength of cell attachment 3. An explanation for this maximal migration rate is that at lower cell- attachment strengths there is not enough traction to provide adequate propulsion at a cell’s leading end while with stronger adhesions a cell takes longer to detach from the substratum at its trailing end. The maximum migration rate occurs between the two. This study is the first to demonstrate that vascular cells have a maximal migration rate across medical grade polymers of various stiffnesses with a range of adsorbed fibronectin densities. These results have important implications for the design of implanted devices irrespective of whether or not migration of cells from the surrounding tissue is the desired outcome. 0hr 26hr 44hr 72hr Figure 2: Representative phase-contrast images of the migration of a cell population after the removal of the constraint at t=0 hours. Figure 1: Illustration of barrier migration assay. Figure 3: Graph showing migration rate of vascular cells over polymer surfaces of differing stiffnesses at various protein surface densities. The migration rate was maximal at intermediate protein coating densities on both polymer grades. The maxima occurred at lower densities on the stiffer substrate. The maximum migration rate was the same magnitude for both polymers. Andrew Whitton David J. Flint Richard A. Black Bioengineering Unit, University of Strathclyde Strathclyde Institute of Pharmacy and Biomedical Sciences Cell Invasion in Vascular Disease The attachment strength was found to increase with increasing fibronectin adsorption and was greater on the stiffer substrate. An increase in the substratum stiffness or adsorbed fibronectin density lead to a more pronounced cytoskeleton and an increase in the spread area of the attached cells. Figure 4: Graph showing median attachment strength of vascular cells on polymer surfaces of differing stiffnesses at various protein surface densities. Figure 5: Example fluorescent images of vascular cells attached to; A) soft substratum at low fibronectin densities and B) hard substratum at high fibronectin densities. Cell cytoskeleton is green, nuclei in blue. AB References 1 Pratt, B. M.; Harris, A. S.; Morrow, J. S. Am. J. Pathol., 1984, 117 (3), 349-354. 2 DiMilla, P, A, et al., J. Cell Biol., 1993, 122, 3, 729-737. 3 Peyton, S. R.; Putnam, A. J. J. Cell. Physiol., 2005, 204, 198–209