Examples of cross-linking agents that work with one or more proteins include but are not limited to condensing agents such as aldehydes e.g., glutaraldehyde, carbodiimide EDC (1-ethyl-3(3 dimethyl aminopropyl)), photosensitive materials that cross link upon exposure to specific wavelengths of light, osmium tetroxide, carbodiimide hydrochloride, and NHS (n-hydroxysuccinimide), and Factor XIIIa.