Exploration On The Mechanism Of The Angiogenesis Modes In Porous Silk Fibroin Materials

Because of excellent biological properties, silk materials receive much attention fromresearchers in the research area of biomedical materials in recent years. During the processof biomaterials repairing tissues, in order to make biomaterials scaffold form acircumstance that is suitable for tissue regeneration and cell survival, it requires rapid andeffective neovascularization of biomaterials after implantation, thus neovascularization ofbiomaterials is also the key subject of study on the biomaterials repairing tissues. However,in the field of biomedical materials, the problem about neovascularization of biomaterialsin vitro or in vivo is not fully settled, which is still a bottleneck problem of tissueengineering and biomaterial application. As an important step of realizing theneovascularization process, angiogenesis includes various modes that are predominantlysprouting angiogenesis and intussusceptive angiogenesis, and so far these kinds of modeshave been found under different physiological and pathological conditions, but problemson the mechanism of angiogenesis mode have not been completely clarified. The researchon the capillary angiogenesis mode is the front topic of angiogenesis, and related researchwork has received much concern from researchers in the last twenty years. With regard tothe angiogenesis mode in biomaterials, the past research reports are few. Based on thepresent situation, this paper aims at exploring the mechanism of angiogenesis modes inporous silk fibroin materials, and the angiogenesis courses under these two conditions ofbody growth process and porous silk fibroin materials repairing muscle were respectivelyinvestigated and studied.In this paper, the angiogenesis processes under these two conditions of both bodygrowth process and porous silk fibroin materials repairing muscle were observed andanalyzed by methods of HE staining and immunohistochemical assay. In addition, thequantity of the newly formed capillaries in the material was analyzed. Meanwhile, theangiogenesis mode was analyzed by TEM technology. Moreover, the expression degrees ofhypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) inthe each stage of body growth process and porous silk fibroin materials repairing musclewere calculated by semi-quantitive scoring method. The results showed that both sprouting and intussusception occurred at the early stage of tissue growth, but less sproutingphenomena were found; and with the increase of the age of the SD rat, intussusception isthe main angiogenesis mode at the middle and late stage of tissue growth. Correspondingly,there were strong expressions of both HIF-1α and VEGF at the early stage of growthprocess, while the expressions of both HIF-1α and VEGF weakened markedly at themiddle and late stage. On the other hand, according to the experiment that silk fibroinmaterials were implanted into the wound muscle of SD rats, it was found that capillarieswere mainly newly formed by sprouting before day13to supply oxygen for the cells,while by intussusception after day13to remodel and adjust the existing vascular network.Accordingly, at the early stage of implantation, there were strong expressions of bothHIF-1α and VEGF in the materials, while at the middle or latter stage of implantation, theexpressions of HIF-1α and VEGF gradually weakened. Therefore, it was speculated thatthere are close relations between the expressions of HIF-1α, VEGF and angiogenesismodes in materials. That is, when the expression levels of HIF-1α and VEGF during theangiogenesis process change from strong to weak, the main mode of capillariesangiogenesis also turn from sprouting to intussusception.In additon, by combining the literature reports and experimental results, this paperstretched from several aspects such as differences of hypoxia degree, growth factorexpression and endothelial cells in response to VEGF, and in accordance with thedifferences between the former stage and the late stage of the growth of newly formedcapillaries as well as the differences between sprouting angiogenesis and intussusceptiveangiogenesis, the mechanism of the angiogenesis modes was analyzed and explored underthe conditions of body growth process and porous silk fibroin materials repairing tissue,moreover, the angiogenesis process and capillary network construction mode in thematerials were thought and discussed after the implantation.This paper provided the basis for clarifying the neovascularization process andbiological mechanism of the materials as well as the theoretical basis and experimentalfoundation for the exploitation of biomedical materials with wider adaptability throughstudying on the angiogenesis mode and its mechanism in the porous silk fibroin materials.