Medium and matrix for long-term proliferation of cells

The present invention provides a method of stimulating vascularization at a site in a mammal, said method comprising contacting said site with a matrix comprising gelatin and a nitric oxide inhibitor. The gelatin is preferably denatured collagen. The nitric oxide inhibitor may be a sulfonated moiety. The inhibitor may be an L-arginine analog, such as aminoguanidine, N-monoethyl L-arginine, N-nitro-L-arginine and D-arginine. The matrix may further comprise a nitric oxide scavenger, such as dextran, heparin, cysteine and cystine.