Preparation And Properties Of A Hydrogel Drived From Decellularized Bone Matrix Retaining Natural Hydroxyapatite

The repair mechanism of injured bone tissue is very complicated.Conventional tissue engineering has great challenges to artificially simulate the natural microenvironment for bone regeneration by using artificially synthesized biomaterials in combination with various bioactive factors.The extracellular matrix(ECM)of natural tissues retains key components including collagen,proteoglycan,glycosaminoglycan,and complex growth factors.When a decellularized ECM(D-ECM)is applied as a tissue engineering scaffold material,it can provide a biomimetic microenvironment to promote tissue regeneration.D-ECM materials are of low immunogenicity after the decellularization treatment,while keep the majority of their bioactive components.Additionally,D-ECM materials can be further digested with proper enzymes,which allow the formation of D-ECM hydrogels due to the self-assembly capacity of collagen fibers.These hydrogels display advantages over conventional biomaterials as tissue engineering scaffolds,at the meantime,showing the possibilities as delivery carriers for growth factors and seed cells.Recent studies have suggested that D-ECM scaffolds can promote the repair and reconstruction of various tissues,particularly,when they are derived from homologous tissues at specific sites rather than from heterologous sources.Thereof,it is anticipated that the D-ECM material derived from natural bone tissue ECM will undoubtedly be a suitable choice for inducing bone regeneration.It is known that the natural bone ECM is mainly composed of collagen and hydroxyapatite(HA).At present,the D-ECM hydrogel derived from bone tissue is normally obtained by using decellularized bone matrix with the HA having been completely removed.In this study,however,a method is reported for the time in order to obtain decellularized bone matrix hydrogels with the original HA being retained.To verify the feasibility of the method,comprehensive characterizations have been conducted on the prepared materials.Briefly,the works have done in this study include:1)Decellularization was successfully conducted on sheep cortical bone tissue without decalcification;2)The optimized parameters for the enzyme digestion treatment were obtained by using decalcified bone matrix,and the formation of D-ECM hydrogels were explored;3)For the first time,a phosphate-phosphate saturated solution was used as an acidic medium for pepsin digestion of ECM.Based on the previous optimization,the enzyme digestion of HA-retained D-ECM hydrogels were further explored by using sheep cortical bone tissue without decalcification and put forward solutions to the problems of insufficient mechanical strength and immutable HA content in the initial preparation of BM hydrogels;4)These hydrogels were proved non-cytotoxic via in vitro culture of bone marrow mesenchymal stromal cells(BMSCs),after that,they were subcutaneously injected into the back of rats for 6 weeks.The results of histological staining revealed that the HA-retained D-ECM composite hydrogel derived from natural bone tissue did not cause significant immune rejection and inflammation,showing good biocompatibility.In addition,BM hydrogel showed the ability to promote ectopic osteogenesis at 6 weeks after implantation.In summary,the HA-retained D-ECM composite hydrogel derived from bone tissue is expected to serve as promising scaffold material for bone regeneration,thanks to its organic-inorganic nature and its highly retained bioactive components from the native ECM of natural bone tissue.