Study On The Distribution And Function Of Type H Vessels In The Bone Defect Repair Process And The Application Of Tissue-engineered Bone Implanted With Vascular Bundle And Sensory Nerve Tract In Repairing Large Segmental Bone Defect Of Sheep

Bone is a highly vascularized and innervated tissue.No matter in the process of bone injury repair or the application of tissue engineered bone to repair bone defects,timely and abundant vascular regeneration is the basis for normal repair process and the survival of tissue-engineered bone.Recently,it has been reported that there are two kinds of vascular endothelial cell subtypes,type H with high expression of CD31 and Emcn and type L with low expression of CD31 and Emcn.These two subtypes have different morphological,distribution and functional characteristics in mice.Type H endothelial cells play an important role in mediating angiogenesis and osteogenesis in bone development of mice.In the first part,the distribution and role of type H vessels in the bone of normal adult rats and in the repair process of bone injury in normal and osteoporotic rats were studied.The purpose of this study is to get a better understanding of the role and function of type H vessels in the bone injury repair process.We demonstrated that type H vessels were distributed in the metaphysis and endosteum and 3 days post-injury,type H vessels proliferated and were extensively distributed across the entire repair area.The abundance of type H vessels decreased at 7 and 14 days post-injury.However,these vessels were distributed specifically around the growing trabecular bones at the frontier growth area,indicating that these vessels guide and support new bone formation.The abundance of type H vessels,the number of osteoblasts,and the transcriptional levels of hypoxia-inducible factor-1?(Hif-1?),vascular endothelial growth factor A(VEGFA),bone morphogenetic protein 2(BMP2)and osterix decreased under osteoporosis conditions.Our data suggest that increasing the number and distribution of CD31 hiEmcnhi vessels via drug or physical therapy may constitute a novel treatment method for osteoporosis and bone non-union in the future.Insufficient vascularization and innervation of the tissue engineering bone are important factors that restrict the transformation of tissue engineering bone into clinical application.Some scholars have found that by implanting the arteriovenous loop or arteriovenous bundle into the tissue engineered bone can significantly promote the vascularization of tissue engineered bone and the repair of bone defect.Other scholars found that by implanting the sensory nerve tract into the tissue engineering bone could also promote osteogenesis as good as arteriovenous bundle implanting.The underlying reason were that,firstly,the sensory nerve tract had its own nourishing blood vessels.Secondly,the release of peptidergic neurotransmitters like CGRP,NPY and SP from sensory nerve tract could promote the survival and osteogenesis of the seeded cells.Accordingly,Professor Guoxian Pei firstly put forward the theory that it could be better to simultaneously construct a highly vascularization and innervation tissue engineering bone.In the second part,we implanted saphenous arteriovenous bundle and saphenous nerve tract simultaneously into the tissue-engineered bone to repair the large segmental tibia defects of sheep.The other two groups were saphenous arteriovenous bundle implanted group and pure tissue-engineered bone group.3 months later,the effect of bone defect repair were evaluated by X-ray plain film,three-dimensional reconstruction after micron-X-ray scan,biomechanical tests and VG staining.The results showed that both the bones mass and materials' degradation rate of Nerve+Vessel group were significantly higher than the other two groups.Furthermore,the bones of Nerve+Vessel group got a better biomechanical function recovery.The results suggest that simultaneously constructing a highly vascularization and innervation tissue-engineered bone could help promote bone defect repair and biomechanical function recovery.