Preparation And Characterization Of PLLA/HAP Whisker/Liquid Crystalline Collagen Composite Scaffold

In this study a series of composites with PLLA (Poly (L-lactic acid)) reinforced byhydroxyapatite (HAP) whisker and type-I collagen matrix was formed with different methods,based on the research of liquid crystalline properties of type-I collagen extracted from rat tendon.The study was mainly divided into four sections. The first section was the preparation of thePLLA scaffolds. The forming craft that combining the particle leaching method and foamingmethod was formulated according to the forming properties of PLLA. In the craft, the solventwas dichioromethane and the pore forming agent was sucrose particles with the diameter500μm.The PLLA dichioromethane solution with certain concentration and appropriate amount of poreforming agent were mixed and casting in the aluminum foll mould. First, the dichioromethanewas volatilized in vacuum at appropriate temperature. Then, the sucrose particles were dissolvedin pure water and the pores were formed. At last, a PLLA scaffold with pores was formed. In thissection, the concentration of PLLA solution and some other forming factors were discussed. Theporosity of the PLLA scaffold was determined by pycnometer method to be not less than95%.The pores were connected and the compressive modulus was0.5MPa. And a new formingmethod with microballoons made by calcium carbonate particle and sodium alginate wasformulated. The mechanical properties were considered to be better. All the details would beexpounded in the main body.The second section was about the characterization and preparation of HAP whiskers. Thematerials for HAP whiskers were a hydrated calcium carbonate and phosphate. The twosubstances were prepared to be20mL solution for one with different concentration or it can becalled the ratio of calcium to phosphorus. The40mL reactant that the mixture of the twosolutions was moved to a high pressure stainless steel container with the volume of50mL andthe reaction was proceeded at the temperature150℃and the internal pressure was about4MPa.After24h, the reaction was ended. It was turned out that the production was HAP whisker withthe draw ratio of not less than50. The situation how the concentration and pH influenced theproduction of the reaction was studied with the method as XRD, TEM, FTIR and opticalmicroscopy. It was known by the study that the high pH was fit for the formation of HAP crystal.The low pH was good for the HAP to form as whiskers. The ideal concentration of the substances of reaction was also discussed and the ideal concentration of calcium salt was0.1M~0.13M. All the analysis would be shown in the main body.The main content of section three was about the liquid crystalline properties of type Icollagen. The type I collagen was obtained from the tendon of while rat tail. The enzymatichydrolysis method was proceeded in this experiment. After freeze dry, the collagen was tested byCD, Inferred and UV spectrum, XRD, Gel electrophoresis, etc. It was proved that the extractedcollagen was pure and remaining the bioactivities. The collagen was dissolved with0.5M aceticacid to form the solutions with the concentration40mg/mL~120mg/mL according to the collagenwas solute liquid crystal. It was proved by the POM that to obtain obvious birefringence, theconcentration was not less than80mg/mL. The research was mainly about120mg/mL solutionwith the most obvious phenomenon. The solution was sheared to form a film. With the methodsas AFM, SEM, XRD, SAXS and rheological test, it was proved that the internal action incollagen liquid crystal was complicated. The transformation of liquid crystalline state and theself-assembly was proceeded during the films was air dried. Collagen fibrils can be detected inthe dry film. And because of the special rheological curves, the banded bumps can be observedon the surface of the film with AFM. The changing process was very complex with the complexstructure of protein. All of the phenomenon would be discussed in the main body.The fourth section was preparation of the PLLA/HAP whisker/collagen I ternary compositescaffold. In this section, the most important problem was the interface interaction between HAPand PLLA. The silane coupling agent, PEG and amino acid ester was applied to improve theinternal reaction. The mechanical properties wound be listed in the main body. The collagen waspressed into the pores of the HAP/PLLA scaffold by centrifugation. Two different ways, airdrying and freeze drying were compared in the microstructure of collagen. And the growthsituation of cells on the two different structure collagen was studied preliminary. It was turnedout that the collagen in air dried specimen was more regular than freeze dried one. The griwthsituation on liquid crystalline structure was better than that on normal collagen. The toughness ofscaffolds was improved by the collagen.