Study On Silk Fibroin/Bioactive Glass Composite Porous Scaffolds

The phenomenon of bone tissue defects or organ defects caused by increasing trafficaccidents, the aging of the population and the increase of patients with various incurable diseaseshas become common in recent years. It is an important task of bone tissue engineering to prepareand search ideal alternative biological materials for bone repairing with the development of bonetissue engineering. Silk fibroin is a natural polymer fibrin which is widely used in the medicalfield especially in bone repair tissue engineering due to its good biological properties ofnon-toxic, non-polluting, non-stimulating effect, good biodegradability and superiorbiocompatibility. However, the bioactivity of silk fibroin is low, and silk fibroin cannot chemicalbond with bone tissue. On the other hand, the mechanical properties of silk fibroin is poor and itcannot meet to the request of bone tissue engineering, so these defects make silk fibroin notsuitable for bone tissue engineering field. Bioactive glass is CaO-SiO2based inorganic bioactivematerial with the properties of higher bioactivity, good biodegradability and biocompatibility andit is the only material which can be connect with hard tissue and soft tissue. Therefore, based onmedical applications, we tried to improve defects of silk fibroin through advantages of bioactiveglass, silk fibroin/bioactive glass composite porous scaffolds were prepared by freezing-dryingmethod and its structure and properties which was effected by incorporation of bioactive glasswas studied to make it have a better application in bone tissue engineering field in the text. Themain study contents and results were obtained as follows:1. Bioactive glass powder was prepared by sol-gel method and its properties werecharacterized by TEM and EDS. The results showed that the shape of bioactive glass wasspherical, the particle size was about30nm, and the composition element of bioactive glass wasthe same to58S bioactive glass.2. Silk fibroin/bioactive glass composite porous scaffolds were successfully prepared byfreezing-drying method and its surface morphology and porous structure were characterized bySEM, XRD and FTIR. The effect which was caused by incorporation of bioactive glass on theconformation change of silk fibroin was also studied. The results were described as follows: (1) The result of SEM and porosity surveying showed that the porous structures of silkfibroin/bioactive glass porous composite scaffold which was prepared by freezing-drying methodwas like porous sponge and they not only interconnected with each other better but alsodistributed uniformly. The porosity was between80.6%and90.3%, the pore size was about150um to300um. The quantity of the bioactive glass particles which were dispersed evenly inhole wall would become more and more with increasing of bioactive glass proportion, so thatsome bioactive glass particles agglomerated together, but the porous structures of silkfibroin/bioactive glass porous composite scaffold almost remained intact.(2) The analysis of XRD and FTIR indicated that the conformation of silk fibroin waspromoted to change from random coil to β-sheet structure with incorporation of bioactive glass.Side groups of the silk fibroin molecules and basic amino acids of Molecular terminal formedcoordination bonds with Ca2+of bioactive glass with bioactive glass added into it, so that theconformation of silk fibroin was promoted to change.3. The effect of adding bioactive glass on thermal property, the mechanical property andhydrophilic property of silk fibroin/bioactive glass porous composite scaffold was studiedthrough measuring these properties. The results were showed as follows：(1) TG and DTG thermal analysis showed that the thermal property of silkfibroin/bioactive glass porous composite scaffold was improved by adding bioactive glass into it.The reason was that crystallization and conformation transition of silk fibroin in a certain extentwas effected with incorporation of bioactive glass and lead to the thermal transition temperatureof porous composite scaffold increasing.(2) Mechanical property test showed that pure silk fibroin porous scaffold had poormechanical property. But the compressive modulus and compressive strength of silkfibroin/bioactive glass porous composite scaffold were both improved with incorporation ofbioactive glass compared to pure silk fibroin porous scaffold. And the more ratio of bioactiveglass increased, the more compressive modulus and compressive strength improved. Meanwhile,silk fibroin/bioactive glass porous composite scaffold gradually showed better mechanicalproperty.(3) Hydrophilic property test showed that pure silk fibroin porous scaffold showed poorhydrophilic property. But water contact angle of silk fibroin/bioactive glass porous composite scaffold continued to decrease with the ratio of bioactive glass increasing and silkfibroin/bioactive glass porous composite scaffold gradually showed better hydrophilic propertycompared to pure silk fibroin porous scaffold, so hydrophilic property of silk fibroin was greatlyimproved with incorporation of bioactive glass.4. The bioactivity in vitro and degradation in vitro of silk fibroin/bioactive glass porouscomposite scaffold were studied through immersion experiment in simulated body fluid and PBSbuffer. The results were showed as follows：(1) Immersion experiment by SBF showed that compared to pure silk fibroin porousscaffold, silk fibroin/bioactive glass porous composite scaffold was promoted to inducehydroxyapatite deposition and showed better bioactivity in vitro with incorporation of bioactiveglass.(2) Immersion experiment by PBS showed that compared to pure silk fibroin porousscaffold, silk fibroin/bioactive glass porous composite scaffold was promoted to be degradatedand showed better degradability in vitro with incorporation of bioactive glass.5. The cell culture experiment showed that silk fibroin/bioactive glass composite porousscaffolds which contained different ratio of bioactive glass not only were non-toxic for L929mouse fibroblast cells’growth but also could make L929mouse fibroblast cells have goodadhesion, proliferation and differentiation on silk fibroin/bioactive glass composite porousscaffolds, so silk fibroin/bioactive glass composite porous scaffolds had good biodegradability.And silk fibroin/bioactive glass composite porous scaffolds which contained higher ratio ofbioactive glass could provided better support for proliferation of mouse fibroblast cells and havebetter biodegradability compared to pure silk fibroin porous composite scaffold.From the above studies, silk fibroin/bioactive glass composite porous scaffolds which wereprepared by freezing-drying method in the text showed better comprehensive properties, so it isexpected to become a new scaffold material for using in bone tissue engineering field.