Bone Morphogenic Protein-2(BMP-2) Loaded Plla Short Fibers Coating On Porous Hydroxyapatite Scaffolds

Since calcium phosphate-based bioceramics such as hydroxyapatite [Ca10(PO4)6(OH)2, HA] is known for its excellent biocompatibility due to its similarity in composition to the apatite found in natural bone. HA was popularly used for bone tissue engineering. Although pure HA is bioactive, it is very difficult to incorporate therapeutic agents within HA without destroying the biofunctionality of its surface. Therefore, after implantation of pure HA scaffold in vivo, it is prone to the have the problem of insufficient internal supply of nutrients during the growth process of tissue.To be the important ingredient of extracellular matrix (ECM), collagen mainly exists in the form of nanofiber and constitute the fibers-network, and may provide ideal micro-environment for in vitro growth of cells by building the biomimetic scaffold with structure similar to ECM.In this research, in the same time of constructing biomimetic scaffold with structure similar to ECM, in order to make porous HA scaffold to promote bone growth acceleration in the repair process of bone loss, we used polylactic acid staple fibers containing bone morphogenetic protein-2 (BMP-2) for modification of the surface of HA scaffold and forming a drug delivery system. Using emulsion electrospinning process, we prepared polylactic acid staple fibers containing BMP-2, after the fibers were chopped and dispersed in alginate solution, we applied the solution in the surface of porous HA scaffold to obtain staple fiber composite scaffold. Through characterization of microstructure, porosity, mechanical and other properties of composite scaffold, and further cell experiments and ectopic bone-formation experiments of composite scaffold, we got the following conclusions:(1) Using particle filtering method, HA porous scaffold with good penetration was prepared with compressive strength of 0.5MPa, which could be elevated to 1.18MPa after coated by staple fibers almost without any effect on the penetration and porosity of scaffolds.(2) The cooper slicing method was easy to perform in preparation of PLLA staple fibers, with single chopped fiber length of about 500p.m. And sodium alginate had the best dispersing effect for staple fibers, with which the fibers can be uniformly coated on the surface of scaffold.(3) In in vitro release experiments, the composite scaffold reduced early burst amount of protein, with a burst amount in 1 d to be merely 21.5%, and sustained release time is about 4 weeks.(4) From the cell experimental results, we found that staple fibers coating on surface of scaffold simulated ECM structure and facilitated cell adhesion and proliferation.(5) From in vivo ectopic implantation experimental results, we found that more tissue growth within the scaffold indicating good biocompatibility of scaffold; compared with HA scaffold, the fiber composite scaffold had more bone formation and vascular volume, indicating the ECM-like structure on surface of scaffold had significant impact on overall ectopic osteogenic inducing performance of scaffold; the most new bone and neovascularization were found in BMP-2 scaffold, indicating the drug delivery system within the scaffold has a good role in promoting bone formation.