Preparation And Properties Of Bone Tissue Engineering Scaffolds Based On Polysaccharide Nanofibers

Natural polysaccharides have good biocompatibility,potential bioactivity and biodegradability.The nanofibers prepared by electrospinning technology are similar to the natural extracellular matrix in structure.They have the characteristics of high porosity and good pore connectivity.Electrospun polysaccharides nanofibers have great application potential in bone tissue engineering fields because they combine the material characteristics of polysaccharides and the structural characteristics of nanofibers.The current reported polysaccharide nanofibers are mostly chitosan and alginate nanofibers,which have limited variety and function,and thus limited performance.Our group previously developped a new type of pectic polysaccharide nanofibers and a periodate oxidation-adapic acid dihydrazide crosslinking technique to prepare crosslinked polysaccharide nanofibers.This thesis is aimed to prepare new scaffolds for bone tissue engineering based on these previous work.Specific contents and results are as follows:In the first part,composite scaffolds of pectin nanofiber and hydroxyapatite nanocrystals with bone induction ability were developed by the technique of concentrated simulated body fluid culture.The bone cytocompatibility of nanofibers of high ester,low ester and low ester and amidated pectin was evaluated.The results showed that the three types of pectin nanofibers had no significant toxicity to bone cells and could support the adhesion and proliferation of bone cells.They are thus suitable for the deposition of hydroxyapatite nanocrystals.Pectin nanofiber and hydroxyapatite nanocrystal composite scaffolds were successfully prepared by concentrated simulated body fluid culture of low ester pectin nanofibers.The diameter of the composite fibers was between 1.8 and 15.7μm,and the area of hydroxyapatite crystals was between 0.3 and 4.2μm~2,and the thickness of the crystals was between 50 and 150 nm.With the increase of culture time of concentrated simulated body fluid,the fibers became thicker,the size and thickness of the crystal sheets increased,the crystallinity of the composite scaffolds increased,the Young’s modulus decreased,and the ultimate tensile strain increased.After immersion in simulated body fluid,the composite scaffolds could induce the deposition of new hydroxyapatite crystals on the surface of fibers as well as in the fiber gaps,and the fiber mass increased,indicating that the composite scaffolds could induce mineral deposition and is a potential scaffold material for bone tissue engineering.In the second part,novel crosslinked pullulan nanofiber scaffolds were successfully prepared by periodate oxidation–adapic acid dihydrazide crosslinking.Pullulan was oxidized with sodium periodate to oxidation degrees of 16%~50%.With the increase of sodium periodate usage,the oxidation degree of pullulan increased and the molecular weight of pullulan decreased.Adapic acid dihydrazide successfully crosslinked the oxidized pullulan nanofibers by forming hydrazone bonds between the molecular chains of pullulan.The mechanical strength of crosslinked pullulan nanofiber scaffolds was related to the oxidation degree of pullulan.With the increased of the oxidation degree of pullulan,the Young’s modulus of the fibers decreased first and then increased,and the ultimate tensile strain increased first and then decreased.The crosslinked pullulan nanofibers had good stability in simulated body fluid.After 4 weeks of culture,the quality remained above 63%,and the morphology of the fibers remained unchanged.Crosslinked pullulan nanofiber scaffolds showed no significant toxicity to MC3T3-E1 mouse preosteoblasts and supported their adhesion and proliferation.The crosslinked pullulan nanofibers are potential for applications in bone tissue engineering because of theirs adjustable mechanical strength,good stability and bone cell compatibility.In summary,this thesis on one hand developed pectin nanofiber and hydroxyapatite nanocrystal composite scaffolds with bone induction ability and on the other hand developed a new type of crosslinked pullulan nanofiber scaffolds with adjustable mechanical properties,good stability and bone cell compatibility.The work lay a foundation for the improvement of the application performance of polysaccharide nanofibers in bone tissue engineering.