Enhancing the tissue-biomaterial interface: Tissue-initiated integration of biomaterials

Integration of biomaterials within the body is a longstanding problem in medicine. The lack of proper biomaterial integration within the body sacrifices artificial implant longevity and function. Materials such as hydrogels may be able to integrate with soft tissue; however, a challenge remains to improve tissue-biomaterial interaction for hard tissues such as cartilage and bone. Cartilage poses a particularly difficult challenge for biomaterial integration since it has a dense extracellular matrix that impedes cellular migration, additionally, it has a smooth, lubricating surface. Collagen fibers, are abundant in the cartilage matrix and throughout the body, provide structural integrity and were chosen as the target for polymerization initiation, anchoring, and integration of hydrogel biomaterials. Principles of protein biochemistry and polymer science were applied to formulate a novel strategy to initiate and directly polymerize biomaterials to collagen. Initially, proteoglycans were removed from the cartilage surface by enzymatic digestion, followed by treatment with a mild oxidative reagent to create tyrosyl radicals on collagen. Afterwards, polymers containing acrylate groups were added and tyrosyl radicals, confirmed by electron spin resonance (ESR) were used to initiate polymerization with light. Chemical (Fourier-transform infrared spectroscopy) and morphological (scanning electron microscopy (SEM)) analyses revealed the presence of polymer bound to the cartilage surface after tissue-initiated photopolymerization. Mechanical analysis by the application of torsional stress demonstrated enhanced functional tissue integration of the tissue-initiated polymerized material. Cells in the surrounding cartilage tissue and encapsulated in the hydrogel, remained viable during the bonding and polymerization processes.