Role of electrospun fibre diameter and corresponding specific surface area (SSA) on cell attachment

In order to develop scaffolds for tissue regeneration applications, it is important to develop an understanding of the kinetics of cell attachment as a function of scaffold geometry. In the present study, we investigated how the specific surface area of electrospun scaffolds affected cell attachment and spreading. Number of cells attached to the scaffold was measured by the relative intensity of a metabolic dye (MTS) and cell spreading was analysed for individual cells by measuring the area of projected F-actin cytoskeleton. We varied the fibre diameter to obtain a specific surface area distribution in the range 2.24-18.79 microm(-1). In addition, we had one case where the scaffolds had beads in them and therefore had non-uniform fibres. For each of these different geometries, we varied the cell-seeding density (0.5-1 x 10(5)) and the serum concentration (0-12%) over the first 8 h in an electrospun polycaprolactone NIH 3T3 fibroblast system. Cells on beaded scaffolds showed the lowest attachment and almost no F-actin spreading in all experiments indicating uniform fibre diameter is essential for electrospun scaffolds. For the uniform fibre scaffolds, cell attachment was a function of scaffold specific surface area (SSA) (18.79-2.24 microm(-1)) and followed two distinct trends: when scaffold SSA was < 7.13 microm(-1), cell adhesion rate remained largely unchanged; however, for SSA > 7.13 microm(-1) there was a significant increase in cellular attachment rate with increasing SSA. This indicated that nanofibrous scaffolds increased cellular adhesion compared to microfibrous scaffolds. This phenomenon is true for serum concentrations of 7.5% and higher. For 5% and lower serum concentration, cell attachment is low and higher SSA fails to make a significant improvement in cell attachment. When cell attachment was investigated at a single-cell level by measuring the projected actin area, a similar trend was noted where the effect of higher SSA led to higher projected area for cells at 8 h. These results indicate that uniform electrospun scaffolds with SSA provide a faster cell attachment compared to lower SSA and beaded scaffolds. These results indicate that continuous electrospun nanofibrous scaffolds may be a good substrate for rapid tissue regeneration.