A method of permanently joining a first collagen-containing material to a second collagen-containing material, each material having free ends of collagen fibrils at a surface, by bringing the free ends of collagen fibrils at the surfaces of the first and second materials into contact, heating the first and second materials for a time and to a temperature sufficient to permanently join the first and second materials at an area of contact of the free ends, wherein the temperature is above a melting temperature of the collagen fibril free ends, and below a melting temperature of intact collagen fibrils, such that collagen fibrils in the first and second materials are not denatured except at their free ends, and optionally thereafter crosslinking the collagen along the area of contact.