A Preliminary Study On Degradation Behaviors Of Silk Fibroin Scaffolds With Different Pore Sizes In Vivo

Objective:To study the morphological character of silk fibroin scaffolds with different pore sizes in the process of degradation in vivo preliminarily, and to find out the effect of the structure on degradable property of silk fibroin scaffolds in vivo.Materials and Methods:1. Three kinds of SF-1, SF-2, SF-3.Their average pore size is20±1.5μm,100±8μm and200±15μm, and their average porosity is86.8±0.2%、’92.4±0.1%and96.6±0.1%respectively. Then the surface and inside of the scaffolds were observed with SEM.2.18Sprague Dawley rats were selected for this experiment. Then, prepared three subcutaneous saclike lacuna with1.5cm×1.0cm at either side of the backbone by surgical operation.Three kinds of SF-1, SF-2, SF-3were implanted into the three subcutaneous saclike lacuna to observe their degradation rate in vivo.3. The SD rats in each group were sacrificed at postoperative weeks of2.6,12,18,24,30, then removed scrap material completely as specimens. The specimens were assessed by gross observation, scanning electron microscopic examination, histopathological HE staining and Masson staining.Results:1. The gross specimens showed:There was no infection and necrosis in each group. and the cut on SD rats’back is healing well. Thin connective tissue wrap could be found on the scaffold. SF-1had little degradation, SF-2had about40%degradation in30weeks after operation, while SF-3had complete degradation in24-30weeks.2. HE stained histopathological slice:SF-1:At2weeks after surgery, macrophage and neutrophil were observed in tissue section. At30weeks after surgery, fibroblasts and capillary vessels could not grow into the pore space. We did not find the border of the scaffolds break down at30weeks postoperatively.SF-2:At2weeks after surgery, fibroblast grew adherently on the surface of the material. The surrounding tissue hyperplasticly changes, inflammatory cell infiltrate is visible, most of which are lymphocytes and macrophages. No signs of tissue necrosis are found. From12weeks after operation.Some capillary vessels and histocytes gradually grew deep into the scaffold.SF-3:At2weeks after surgery.SF-3was dreadfully like SF-2at the same time.There were a few parts with eosinophilic staining inside the material disappears at6week postoperatively. and capillary vessels and histocytes gradually grew deep into the scaffold. At12weeks after surgery, histocytes grew more deeply into the scaffold, while new capillary vessel inside the material was obvious, while hyperblastosis was still obvious. At24weeks after surgery, The structure of the scaffold completely broke down, and no sign of tissue necrosis was found.3. Masson staining:SF-1:Fibrosis surrounding the tissue was obvious,while collagen fiber could not grow into the scaffold in the whole teaching experiment.SF-2:At18weeks after operation, collagen fiber grew into the scaffold. Residual material were partly surrounded by collagen fiber at30weeks postoperatively. SF-3:At2weeks after operation, we found the border of the scaffolds break down, and collagen fiber wrapped the scaffolds. At6weeks aftet operation, collagen fiber and some small blood vessels gradually grew deep into the scaffold. At24weeks after operation. Residual material were partly surrounded by collagen fiber.4. Scanning electron microscopic examination:SF-1:The surface structure of SF-1show disaggregation phenomenon at18weeks postoperatively, while its general structure remains. At the24weeks after operation, cross-section structure remained its original form.SF-2:At the2weeks after operation, histocytes grew along the surface of the scaffold or into the pores. The surface structure showed disaggregation phenomenon at12weeks postoperatively, At24weeks after operation, cross-section structure of residual material had complete disintegration.SF-3:At the2weeks after operation, we found some fragments on the surface of the scaffold, cross-section structure remains its general structure. At the12weeks after operation, the middle of cross-section structure remained its general structure, the structure of the whole material had complete disintegration.Conclusions:1. The degradation rate of silk fibroin scaffolds with different pore size or porosity is different in vivo.2. The degradation rate of three kinds of silk fibroin scaffolds is SF-3>SF-2>>F-1in vivo.3. At the beginning of experiment-inflammatory cells and fibroblasts were observed in tissue section, during the late experiment.inflammatory cells gradually decreased.fibroblasts and capillary vessels could grow into the pore spaces.and fibroblasts secreted large amounts of collagen fibers.