| In this paper, some composite scaffolds consisted of nanometer scale hydroxyapatite (HA)and natural bioactive macromolecules such as chitosan and collagen for bone tissue engineeringwas fabricated in vitro via “bottom-up” strategy in Sol-Gel system.To mimic the components and structure of the natural bone, chitosan (CS) andhydroxyapatite (HA) were selected respectively as the macromolecule and the source of thecalcium phosphate. The raw materials were dissolved in a acid solvent to form homogeneoussolution, and then underwent Sol-Gel phase transition and aging procedure to preparenano-hydroxyapatite/chitosan porous composite scaffolds in situ. The effects of aging time andpH value on the composition, micromorphology and compressive strength of the HA/CScomposites were studied. The results show that the compressive strength and modulus of thescaffolds decrease obviously with the increase of the pH value, and the compressive strength ishigher than pure CS scaffolds when the pH is10and11. XRD indicates that the transition ofphosphorus calcium to HA can be impelled with aging treatment, and the growth of HAcrystallites orients along the c-axis in the crystal structure. SEM reveals that the scaffoldspossess inter-connected porous structure，and the rod-like or grainy nano-hydroxyapatite crystalparticles disperse uniformly in the scaffolds, which formed homogeneous denseorganic/inorganic composites. In vitro M-3T3cells culture found that the proliferation of M-3T3cells had been accelerated by the mineralized scaffolds remarkably. The result indicated that thecytocompatibility of the n-HA/CS composite scaffolds is more better than which of the pure CSscaffolds in terms of cell viability. This kind of fast and deep mineralization method forpreparation of bone scaffold provides a new way of thinking.The mineralization process of collagen is controlled through interactions between thecollagen matrix and non-collagenous extracellular proteins such as dentine matrix protein-1(DMP-1) in hard tissue. In this study, a low molecular weight polyacrylic acid was used toimitate the sequestration functional motif of the N-terminal fragment of DMP-1, and a smallinorganic polyphosphate-sodium tripolyphosphate (TPP) to replicate the templating functionalmotif of the C-terminal fragment of DMP-1. Both of them just like “soft templates” to regulatethe mineralization of collagen scaffolds, relativing to collagen as “hard templates”. And then the scaffolds were aged for0.5h,2h, and24h at37℃.The results of X-ray diffraction, FESEM, EDS,HRTEM and SAED demonstrated that in the presence of these dual biomimetic functionalanalogues in the mineralisation system, the intrafibrillar and extrafibrillar hydroxyapatite mineralwith collagen fibre via bottom-up nanoparticle assembly based on the non-classicalcrystallisation pathway could be identified.In vitro human umbilical cord mesenchymal stem cells(hUCMSCs) culture found that themineralized scaffolds have a certain the cytocompatibility in terms of cell viability，adhesion,proliferation and differentiation to osteoblasts. Furthermore,to confirm the bone regeneration andrepairing ability of n-HA/collagen composite scaffolds and the tissue-engineered boneconsisted of hUMSCs and the scaffolds, the rabbit femoral condyle defects model was fabricated.The images of gross anatomy, MRI, CT and histomorphology after surgery for6and12weeksshowed that the tissue-engineered bone and biomimetic mineralized collagen scaffolds canpromote the healing of bone defects distinctly in vivo, compared with bone defects in the controlgroup. As the formation of new bone tissue, the scaffolds were degradated and absorbedgradually. All these results demonstrated that both of them have nice histocompatibility. |
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