 After the initial discovery, further research led to the composition and fabrication of grafts that were evaluated in clinical trials.These grafts were synthesized as a graft copolymer of microfibrillar type I collagen and a glycosaminoglycan, chondroitin-6-sulfate, fabricated into porous sheets by freeze-drying, and then cross-linked by dehydrothermal treatment.Control of the structural features of the collagen scaffold (average pore size, degradation rate and surface chemistry) was eventually found to be a critical prerequisite for its unusual biological activity.