Materials for {grafts or} prostheses or for coating {grafts or} prostheses containing ingredients of undetermined constitution or reaction products thereof {, e.g. transplant tissue, natural bone, extracellular matrix subjected to a specific treatment prior to implantation, e.g. decellularising, demineralising, grinding, cellular disruption/non-collagenous protein removal, anti-calcification, crosslinking, supercritical fluid extraction, enzyme treatment}