Preparation, Characterization And Evaluation Of Bone-like Collagen Fibril Based Porous Tricalcium Phosphate/collagen Composites

The current biomaterials research focuses on creating capability of promoting and accelerating bone repair besides bioactivity and biodegradabillty.In this thesis, based on the compositional and microstructural characteristics of natural bones, bone-like collagen fibrils(collagen fibrils integrated with nano-tricalcium phosphate (TCP)particles)are proposed as units to construct porous TCP/collagen composites. Such microstructure is believed to make best use of both biological advantages of TCP and collagen in bioactivity,biodegradability,morphology control,carrier ability and cytocompatibility.The resulting composite is expected to become a novel bone repair/regeneration biomaterial.In this thesis,the researches include the preparation of various nano-TCP particles used as inorganic components,the preparation and characterization of the bone-like collagen fibril based porous TCP/collagen composite and preliminary study on biological evaluation of the resulting composites.These researches are summarized as:(1)An amorphous calcium phosphate(ACP)precursor was adopted to prepare nanosized TCP particles.PEG was used as an agent for stabilizing ACP.The nanosized TCP particles could be formed by crystallizing ACP at 800℃,the particle size ranged from 300 to 500nm.The crystalline phase of the TCP particles strongly depended on PEG content in ACE When the weight ratios of PEG/Ca during ACP formation were 4:1 and 16:1,the resulting TCP particles wereα-TCP andβ-TCP, respectively.When the ratios lied between 4:1 and 16:1,the resulting TCP particles were biphasicα/β-TCP and theβ-TCP content in the biphasic powders increased with increasing the ratio.The TEM and SEM results revealed that biphasicα/β-TCP powders consisted of 1μm aggregates in which nanosizedα-TCP andβ-TCP particles were well dispersed.The soaking results in phosphate buffer solution showed the biphasicα/β-TCP powders had a special behavior in reactions and surface morphology change.(2)Zinc incorporated nano-β-TCP(β-ZnTCP)particles were prepared through crystallizing zinc incorporated ACP.The structural analysis showed that zinc ions had entered calcium sites inβ-TCP lattice and formed zinc substitutedβ-TCP particles. The soaking results in phosphate buffer solution showed zinc release behavior ofβ-ZnTCP was slow and sustained.(3)Collagen fibers could be disassembled into fibrils in acidic solution.,When nano-β-TCP was added into the collagen fibril suspension,nano-β-TCP particles were integrated with fibrils to form bone-like collagen fibrils.After freeze-drying,bone-like collagen fibrils based porous TCP/collagen composites were obtained.And the pore walls in the porous composite showed to have mircopores The results showed that the optimized acidityof pH 2,the pore size of of～100μm,and porosity of 90%.In vitro and in vivo Evaluations demonstrated that the composites have good cytocompatibility and good ability of bone repair.(4)Collagen fibers could be disassembled into fibrils in alkali solution.When nano-β-TCP was added into the collagen fibril suspension,nano-β-TCP particles were integrated with fibrils to form bone-like collagen fibrils.After freeze-drying, bone-like collagen fibrils based porous TCP/collagen composites were obtained.And the pore walls in the porous composite showed dense.The results showed that the optimized alkalinity of pH 12,the pore size of of 100～300μm,and porosity of 90%. In vitro and in vivo Evaluations demonstrated that the composites have good cytocompatibility,the capability of accelerating osteoblast proliferation and differentiation,and good ability of bone repair.(5)In view of the influence of different collagen on the microstructure of the porous composite,enzyme-digestion collagen(e-collagen),other than above(salting-out collagen),was selected.The results showed bone-like collagen fibrils based porous TCP/collagen composites could be formed under alkali solution condition..However, the porousβ-TCP/e-collagen composite had a difference in microstructure withβ-TCP/s-collagen composite,the pore wall of the former had micropores,while that of the latter was dense.In vitro cell culture results showed the porousβ-TCP/e-collage composite had as good cytocompatibility asβ-TCP/s-collagen composite.(6)Considering favorable morphology changes ofα-TCP and Ca and phosphate ions release ofβ-TCP,the combination ofα-TCP andβ-TCP in the form of biphasic TCP powders is a good way to utilize the advantages of the two TCP phases.Bone-like collagen fibrils basedα/β-TCP/e-collagen composites were prepared in alkali condition.The pore sizes of composites ranged from 100μm to300μm and the porosity was about 90%.After soaked in phosphate buffer solution,α/β-TCP particles in the composites transformed to cluster shape in situ.Thus,surface morphology could be optimized by ratio ofα/β-TCP in biphasic TCP particles.In vitro cell culture results showed the composite had also good cytocompatibility.(7)Zinc has a positive effect on osteoblast activity during bone repair,as a result, bone regeneration can be accelerated.Ifβ-ZnTCP particles substitute forβ-TCP in theβ-TCP/collagen composite,the composite is believed to have a capability of releasing Zn ions.In alkali solution condition,bone-like collagen fibril based porousβ-ZnTCP/e-collagen composite could be formed.The pore size of composite was 300μm and the porosity was about 90%.The composite demonstrate a slow and sustained zinc release behavior.In vitro cell culture results showed the composite had good cytocompatibility.Based on above researches,bone-like collagen fibril based porous TCP/collagen composites can be constructed.Also,the composites show good cytocompatibility, and have positive effects on bone regeneration and accelerate bone repair.Hence,the porous TCP/Col composites could become a new bone repair material.