Preliminary Study On Neovascularization And Tissue Regeneration Of Porous Silk Fibroin Materials

Within the past decades, biomaterials have been evolved from inert materials to bioactive materials and tissue inducing biomaterials which may induce tissue regeneration in situ. Because of nice biocompatibility, processible attributes and biodegradability of silk fibroin, study on the biomaterials based on silk fibroin has attracted more and more intrest.Angiogenesis is a key step during wound healing in most tissues, so biomaterials aided wound healing requires rapid and effective neovascularization of biomaterials after implantation. Althogh lots of researches focus on the problem such as design and preparation of porous biomaterials, application of growth factors and (stem) cells and artificial blood vessels, little real success has been abtained and bad neovascularization of biomaterials has been the main obstacle in terms of clinical application.In addition, little knowledge of detailed neovascularization of biomaterials, effects of in vivo circumstance on biomaterials implanted, and how to evaluate the degradation rate of biomaterials and tissue regeneration rate is known.Thus, the purpose of this study is to explore and analyze the essence of neovascularization and inducibility in biomaterials through observation on the neovascularization process occurred in porous silk fibroin materials and polyvinyl alcohol (PVA) sponges.In this study, porous silk fibroin materials and PVA sponges were implanted in muscles of hind limb and back skin in rats, and the neovascularization process in both materials has been observed in detail via tissue sections. In addition, the biocompatibility of porous silk fibroin materials and PVA sponges has been semi-quantitively compared through histological scoring method. The results showed that identical neovascularization process occurred in both materials either implanted in the muscles or the back skin. The process mainly included four sequential steps as follows: adsorptioin, organization of extracellular matrix (ECM), rapid proliferation of tissues and remodeling of the tissues and blood vessels networks. This might be the implication of general mode of neovascularization process in porous biomaterials. Furthermore, the results showed that porous silk fibroin materials have better biocompatibility than PVA sponges.The in vivo decoration of porous silk fibroin materials and tissue regenration in porous silk fibroin materials have been further examined by combination with in vivo implantation and in vitro cell culture. The definition of in vivo decoration mainly indicates the protein adsorption and ECM organization in the materials in vivo. As for the results that porous silk fibroin materials have been more advantageous than PVA sponges to neovascularization and tissue regeneration, there might be 4 reasons as follows: (1) silk fibroin, as a natural protein, has better biocompatibility than polymers; (2) the surface texture of porous silk fibroin materials might be suitable for protein adsorption and ECM organization; (3) the porous structure of porous silk fibroin materials facilitates the ingrowth of endothelial cells and fibroblasts; (4) the biodegradation rate of porous silk fibroin materials accords with the tissue regeneration rate.In the last chapter, the degradation of biomaterials and tissue regeneration were quantified by definition of area percentage of residual biomaterials (Rirs(%)=Sis/S1s×100%) and area percentage of newly formed tissues (Rint(%)=Sit/Sg×100%) in histological sections. Besides, biodegradation rate of biomaterials and tissue regeneration rate were compared by comparison of growth time of newly formed tissues (tr) and biodegradation time (tm) of biomaterials. In brief, a semi-quantitive method has been established in this paper to evaluate the synchronization extent between the degradation rate of biomaterials and regeneration rate of tissues.Where Sis is the area of residual biomaterials i days after implantation, S1s is the area of biomaterials 1 day after implantation, Sit is the area of newly formed tissues i days after implantation, Sg is the area of full recovery tissues. And tr indicates the time (day) when a certain amount of tissues have been regenerated and thus they could continue growing without any stent. tm indicates the time (day) when a certain amount of biomaterials have been biodegraded and thus they lose their whole support.Through this method, the accordance between tissue regeneration and biodegradation of biomaterials could be evaluated semi-quantitatively. Moreover, the feasibility of this method was testified through in vivo experiments, and the results suggested that this method is rapid, feasible and easy to operate. This work might provide solid basis for further quantifying attributes of biomaterials.