Theoretical Design And Application Research Of Titanium Implants And Bone Tissue Engineering Scaffolds

This Ph.D dissertation aimed at developing novel and effective bone substrates.Owing to the requirements of clinical practice,this dissertation managed to construct osteogenic factor delivery platform on the surface of titanium implants.In view of the intrinstic defects of metal implants,we tried to develop bone tissue scaffolds for bone repair.As the core element of bone tissue engineering,bone scaffold is of great significane.For an ideal bone scaffold,property requirements are diverse.Though researcher have done much work to optimize the properties of bone scaffolds,the currently available scaffolds are still faced with two challenges:(ⅰ)the inability to maintain high porosity and high mechanical strength for a scaffold;(ⅱ)the difficulty in maintaining the bioactivity of loaded osteogenic factors and controlling there release.We tried to solve the two problems and have done a series of pioneering work.The specific research contents are as follow:1.In this work,we constructed a stable,effective,and sustained dexamethasone delivery platform on titanium disc by immobilizing dexamethasone@zeolitic imidazolate framework-8 nanoparticles into the micrometer-scale artificial etch pits on titanium substrate using methanol-induced regenerated silk fibroin membrane encapsulation.In addition,the titanium substrate was aminated and covalent interactions were established between the titanium substrate and the silk fibroin membrane through genipin crosslinking.Briefly,owing to the synergistic barrier effect of the zeolitic imidazolate framework-8 shell and the silk fibroin membrane,the silk fibroin-dexamethasone@zeolitic imidazolate framework-8-titanium could release dexamethasone in a controlled manner over 30 days.Moreover,the pit walls together with the silk fibroin membrane protected the nanoparticles from detaching from the titanium substrate in the case of mechanical wear.The covalent interactions between the silk fibroin membrane and the titanium substrate prevented the silk fibroin membrane from selfpeeling from the titanium substrate in a moist environment.In vitro cell culture indicated that the as-prepared titanium disc had good cytocompatibility with MC3T3-E1 cells.Furthermore,the cells cultured on the titanium disc demonstrated higher differentiation,calcium deposition,and expression of osteogenic genes than the cells cultured on the silk fibroin-zeolitic imidazolate framework-8-titanium and pristine titanium.In this work,dexamethasone was utilized as a drug model and could be replaced by other osteogenic drugs or growth factors.Thus,we believed that our design philosophy could inspire future research work on the development of Ti implants.2.In this work,a chitosan-tussah silk fibroin/hydroxyapatite(CS-TSF/HAp)hydrogel was synthesized by using a novel in situ precipitation method.Through in situinducing the conformation transition of TSF in the CS-TSF/HAp hydrogel,which could be monitored byXRD,FT-IR,TGA,and DTA,the elastic modulus and fracture strength of the final CS-TSF/HAp compos-ite could be tailored in a wide range without changing its composition,morphology,roughness,andcrystal structures.The elastic modulus of the CS-TSF/HAp composite ranged from～250 to～400 MPawhile its fracture strength ranged from～45 to～100 MPa.In order to clarify the rationale behind thisprocess,a speculative explanation was provided.In vitro cell culture indicated that MC3T3-E1 cells cul-tured on the CS-TSF/HAp composite had positive adhesion,proliferation,and differentiation potential.We believed that the CS-TSF/HAp composite could be used as an ideal scaffold platform for cell cultureand implantation of bone reconstruction.3.In this work,a novelmulti-component organic/inorganic composite BC-GEL/HAp DN scaffold platform was prepared and systematically characterized for the first time.The wet BC-GEL/HAp hydrogel showed higher elastic modulus(0.27 MPa)than the BC/GEL hydrogel(0.12 MPa)and higher fracture stress(0.28 MPa)than the BC/HAp hydrogel(0.22 MPa).The dry BCGEL/HAp composite also demonstrated much higher strength and stiffness(177MPa in Young’smodulus and 12.95 in fracture stress)than the BC/HAp(48 MPa in Young’s modulus and 7.35 MPa in fracture stress),BC/GEL(127 MPa in Young’s modulus and 7.81 MPa in fracture stress),and BC(52 MPa in Young’s modulus and 4.22 MPa in fracture stress).In vitro cell culture demonstrated that the rBMSCs cultured on the BC-GEL/HAp composite showed better adhesion and higher proliferation and differentiation potential than the cells cultured on the BC/GEL composite.We hope the BC-GEL/HAp composite could be used as ideal bone scaffold platform or biomedical membrane in the future.4.In this work,a facile method termed "ammonia-induced method"(AIM)was proposed and applied to generate anisotropic pores in chitosan(CS)-based scaffolds.In addition,we investigated the rationale behind this process.The data indicated that scaffolds prepared by using this method demonstrated pores with diameter in the 100-400 range.In addition,its mechanical strength approximated that of human cancellous bone.5.In this work,we constructed an anisotropic triple-pass tubular framework within a lyophilized porous GEL scaffold using FP,which was prepared by coating DEX-covered Whatman paper(WP)using the silk fibroin(SF)membrane withβ-sheet conformation.This novel structural design endowed the functionalized paper frame(FPF)/scaffold implant high porosity,high mechanical strength,and sustained DEX delivery capability.Specifically,its porosity was as high as 88.2%,approximating that of human cancellous bone.The pore diameters of the implant ranged from 50 to 350 μm with an average pore diameter of 127.7 μm,indicating proper pore sizes for successful diffusion of essential nutrients/oxygen and bone tissue-ingrowth.Owing to the construction of double-network-like structure,the FPF/scaffold implant demonstrated excellent mechanical properties both in dry(174.7 MPa in elastic modulus and 14.9 MPa in compressive modulus)and wet states(59.0 MPa in elastic modulus and 3.3 MPa in compressive modulus),indicating its feasibility for in vivo implantation.Besides,the FPF/scaffold implant exhibited long-term DEX releasing behavior(over 50 days)with constant release rate in phosphate buffered saline(PBS).Murine osteoblasts MC3T3-E1 cultured in the porous FPF/scaffold implant had excellent viability.Furthermore,the cells cocultured with the FPF/scaffold implant showed positive proliferation,osteogenic differentiation,and calcium deposition.Twenty-eight days after implantation,extensive osteogenesis was observed in the rats treated with the FPF/scaffold implants.The anisotropic triple-pass tubular framework of the FPF/scaffold implant demonstrates structural similarities to the long bone.Therefore,this novel FPF/scaffold implant could be a better alternative for long bone defect repair.