Calcium Phosphate/Silk Fibroin Composite For Vertebroplasty/Kyphoplasty And Osteochondral Tissue Engineering Scaffolds

Various orthopedic diseases caused great impact on the patients but also on theirfamilies and the whole society, and with regard to the treatment, kinds of biomaterialsplayed an important role. Calcium phosphate (CaP)can form synostosis with living tissuefor its material bioactivity, and thus usually used in artificial bone. Silk fibroin (SF), anatural protein with good degradability, easy modifiability, excellent biocompatibility andremarkable mechanical properties, is widely used in the field of biomedical materials inrecent years. This thesis aimed to enhance the calcium phosphate cement (CPC) with theaddition of SF, and then to expand its application in the treatment of bone defects. InMoreover, in the light of the proceeding study, we endeavored to fabricate a noveltri-layered osteochondral scaffold of CaP/SF assembly for articular cartilage repair.Firstly, we investigated the effect of degumming time on SF. Many fibroin fibrilswere observed by SEM due to over-dugmming. SDS-PAGE indicated thedugumming-induced breakage of SF molecular chains to various degrees, resulting insmaller particle size group of SF molecules and more transparent solution. On the contrast,SF with short degumming time has longer molecular chains. This SF solution can shortenthe setting time of CPC and improve its cohesion.Homogeneous hydroxyapatite-silk fibroin (HA-SF) complex were synthesized by theco-precipitation method and added to the CPC powder phase, while the silk fibroinsolution was used as liquid phase in order to reinforce the mechanical properties of CPC.With the increase of the HA-SF amount, the compressive strengths increased significantlyand then declined slightly. The characterizations, such as TGA, FTIR, XRD and SEM,were investigated to study the chemical bonding, crystal structure and microstructure of thecomplex and cements. Upon these characterizations, the reinforcement mechanism of CPCwith the addition of SF was supposed. Strong interactions between Ca2+and those negativecharged functional groups, existence of HA-SF complex as seeds, improvement of the interfacial integrity and the controlled growth of random plate structure by SFentanglement were conjectured to be in responsible for this enhancement. Moreover, thekey properties for clinical application, including setting time, injectability, washoutresistance, cytotoxicity and inflammatory responses were also evaluated, and the cementscomposed of SF show good handling properties and biocompatibility.On the basis of the above study, the CaP scaffolds were prepared using leachingmethod in the presence of sodium chloride (NaCl) particles as porogens, and SF solutionacted as cement liquid. SF solution with different concentrations were added layer by layeronto the CaP scaffold to fabricate the tri-layered CaP/SF scaffolds by the freeze dryingtechnique. The pore architecture of SF scaffolds is regulated by concentrations andfreezing conditions, with the pore sizes about100μm and25μm for chondral phase andinterface layer, respectively. The chondrocytes showed good adhesion and proliferationafter seeded in the top SF layer, and they were cultured to generate tissue-engineeredosteochondral composite. The composites were implanted into the cartilage defects, whichwere surgically created at the weightbearing surface of the bilateral femoral medialcondyles of mini-pigs. Six months after surgery, the tissue-engineered osteochondralcomposite group showed good results in the repair cartilage defects.