The present invention provides a method for producing an improved biomaterial comprising treating a collagen biomaterial with a transglutaminase under conditions which permit the formation of cross-links within the collagen. Preferably, the transglutaminase is a tissue transglutaminase, a plasma transglutaminase or a microbial transglutaminase. In a preferred embodiment, the collagen biomaterial further comprises a cell adhesion factor, such as fibronectin. The invention further provides biomaterials obtainable by the methods of the invention, and medical implants and wound dressings comprising the same.