Preparation And Evaluation Of Sulfonated Silk Fibroin/Hydroxyapatite Porous Scaffold

In recent years, with the acceleration of global aging society, osteoporosis and otherrelated diseases has more and more serious and affected people’s quality of life. Furthermore,autologous and allograft bone source is limited, which is a huge challenge to bone surgeryinduced by bone tissue injury. In order to treat the bone tissue disease through bone tissueengineering, preparing an ideal porous scaffold with a high biological activity is one of theprimary tasks of researchers.In this work, silk fibroin was used as the material for preparing sulfonated silk fibroin(SSF) throug diazonium salt coupling. the spectrum of SSF treated with different organicsolvents was obtained by attenuated total reflectance-fourier transformed infrared spectrum(ATR-FTIR), and proportional variation of secondary structures in SSF were assessedthrough Fourier self-deconvolution, second derivative and curve fitting. The results showedthat the proportion of β-sheet, random coil, α-type and turn in SSF were10.97%±1.32%,59.92%±2.72%,17.50%±2.13%, and11.61%±1.17%, respectively. After beingtreated with90%(v/v) of methanol, ethanol and isopropanol respectively, the changes ratesof secondary structure in SFF were showed a slow-down tendency with the prolong oftreatment time. After organic alcohol treatment, the random-coil was transformed intoα-form belonging to SilkⅠtype and then transformed into more stable β-sheet structure ofSilkⅡtype. Furthermore, random coil and α-form could be converted into each other indifferent solvents. In cellular level, the stimulatory reaction test in mouse spleen cells (T, Bcells) revealed that SSF has low immunogenicity.Hydroxyapatite was made by method of co-precipitation. The results showed that thehydroxyapatite, the particle size was100-500nm×20-50nm based on TEM photo. Theporous scaffold was prepared by the mix of hydroxyapatite and SSF, which was a betterperformance by lyophilization, and the results showed that the ideal ratio was as follows:SSF:SF was1:1-0:1, protein concentration was5-10%, and hydroxyapatite was5-10%.The results of degradation experiments in vitro showed that the degradation rate inthree kinds of degradation system was trypsin, α-chymotrypsin and PBS, and degradationrate increased with the increasing of enzyme concentration. The mechanism in PBS solutionwas that the porous scaffold is degraded through hydrolysis, and a synergy of enzymatic andhydrolysis in enzymatic solutions was taken place. The results of the mineralization insimulated body fluid and alternative soaking solutions showed that the porous scaffold has better biomimetic mineralization; however, there was a significant difference in the processand mechanism, Furthermore, he porous scaffold has good tissue compatibility insubcutaneous of SD rats.In repair experiment, the porous scaffold has better osteogenic induction for bonedefect modeled rabbits, and it was more obvious that more bone was formatted with theincreasing of incorporated BMP-2.In order to improve utilization efficiency of growth factors, the mesoporous silica withdifferent pore size (5-10nm,10-20nm,15-30nm) was added to the porous scaffold by amethod of polyurethane foam padded. The results showed that three kinds of mesoporoussilica were all extended the release time of a model drug fluorescein isothiocyanate (FITC),meanwhile, the smaller pore size was, and the more sustained-release effect was.Fluorescently labeled goat anti-mouse IgG antibody was also used as a model drug, theresult also showed that it has better slow-release effect.In conclusion, the porous scaffold prepared by freeze-drying has better pore size andporosity. It also has good biodegradability and biomimetic mineralization in vitro andsuperior tissue compatibility and osteogenic induction in vivo; the porous scaffold, as drugdelivery system, prepared by adding mesoporous silica has prolonged drug release time atcertain degree. The porous scaffold will promote the development of bone tissueengineering, and has a potential to develop an ideal scaffold materials for bone tissueengineering.