Staining for endothelial marker CD31 confirms the presence of small capillaries within the granulation tissue of 60 and 100 μm porous hydrogel implants loaded with pVEGF (A, scale bar = 50 μm; PECAM positive staining (CD31+ endothelial cells) = red, cell nuclei = blue). 100 μm porous hydrogel implants loaded with pGFPluc are shown for comparison. Quantification of vessel density (n = 4 – 5) reveals a slight correlation to hydrogel porosity (B, black bars = pVEGF, grey bars = pGFPluc loaded hydrogels). Vessel diameters were also measured (C, solid bars = pVEGF, striped bars = pGFPluc loaded hydrogels). Approximately 40–50 % of vessels in all samples were less than 6 μm in diameter.