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Acid solution on the structure and properties of chitosan / hydroxyapatite composite

Author: LiWeiYan
Tutor: ChenQingHua
School: Kunming University of Science and Technology
Course: Bio-engineering materials
Keywords: Chitosan Dissolution Hydroxyapatite Konjac glucomannan Tissue engineering scaffolds
CLC: R318.08
Type: Master's thesis
Year: 2011
Downloads: 8
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Abstract


Ideal bone-repaired materials should be of high bioactivity and good biocompatibility. And in addition, their mechanical properties should be equivalent to or better than those of natural bone. So, to design and prepare nano-hydroxyapatite with a composition closer to bone tissue engineering mineral and its composite scaffolds become a hot topic for bone tissue engineering repair materials research at present. Hydroxyapatite (HAP) and chitosan (CTS) which have good biocompatibility and Konjac glucomannan (KGM) which has excellent molding property were used in this work, in order to integrate the properties of these materials abone, to carry their good properties forward, design and prepare a three-dimensional porous scaffolds which can be used for bone tissue engineering repair.When the composite scaffolds based on CTS are prepared, CTS must firstly be dissolve in acid solution. Therefore, in the paper, the dissolving behavior of CTS were studied in citric acid(CA), L-malic acid (L-Mal) L-lactic acid (L-Lac) and phosphoric acid(H3PO4), by the method of viscosity analysis, potential analysis and conductivity analysis; n-HAP/CTS composite powder was prepared by co-titration method with acid and alkali, n-HAP/CTS/KGM porous scaffolds were prepared by sol-gel and freeze-drying method. Through the measurements and analysis about Materials and biology, the comprehensive performances of the scaffolds were researched. While some theoretical basises were provided to make it an ideal material for bone tissue engineering.The main conclusions of the work are as follows:(1). The dissolving behavior of CTS in CA, L-Mal, L-Lac and H3PO4 were separately studied, by the methods of potential analysis and conductivity analysis. The results showed that①The potential analysis indicated that, for different acid solvents, the greater the dissociation constant pk, the smaller the corresponding degree of proton while CTS dissolved completely; for the one acid solvent, the degree of proton of CTS that occurs completely dissolved mainly depends on the initial concentration of the acid solution, and if acid concentration in a certain range, the complete dissolution of CTS can be ensured;②The protonation process was obtained through the measurement of conductivity. With the increasing of the concentration, the proton degree firstly increased, got to a constant (α= 1.0) and gradually decreased③When the concentration of acid was in a certain range, there was a linear relationship between the intrinsic viscosity and acid concentration. Because CTS molecule was fully protonated at this time.(2) The n-HAP/CTS/CA, n-HAP/CTS/L-Mal, n-HAP/CTS/L-Lac and n-HAP/CTS/H3PO4 composite powders were prepared respectively by co-titration method with acid and alkali. The powders were characterized by X-ray diffraction (XRD), Fourier Transform-Infrared Spectroscopy (FT-IR), Transmission electron microscopy (TEM), TG/DTA and Scanning Electron Microscope (SEM), in order to research on the constituent parts, the structural feature and the ways of molecular interactions. The results showed that①In the n-HAP/CTS/CA composite powders, n-HAP with the shape of flakiness was coordinated on the molecular chain of CTS and CA played a role of chelating agent. In the n-HAP/CTS/L-Mal composite powders, n-HAP with the shape of ellipse was coordinated on the molecular chain of CTS. Due to L-Mal’s absorption of Ca2+, there were more calcium deficiency. In the n-HAP/CTS/L-Lac composite powders, n-HAP with the shape of an irregular polygon was coordinated on molecular chain of CTS.The growth of n-HAP in C-axis was particularly evident. In the n-HAP/CTS/H3PO4 composite powders, n-HAP with the shape of needle was coordinated on the molecular chain of CTS, being similar to the HAP in natural bone.②In the four n-HAP/CTS composite powders, there were strong chemical force between HAP and CTS, which was mainly reflected in the following:hydrogen bonding interaction between the-NH2 in CTS and-OH in HAP and strong chemical bonding between-NH2 in CTS and Ca2+ in HAP, the CTS substrate combined with n-HAP crystals more solid under these effectes, improving the comprehensive performance of materials.(3) From the point of view of bionics, the n-HAP/CTS/H3PO4 composite powder that was similar to the natural distribution of needle-like shape was selected, with the KGM as raw materials, to prepare composite porous scaffold, via sol-gel method and freeze-drying method. The composition, structure and performance of composite scaffold were characterized by orthogonal test analysis, Fourier Transform-Infrared Spectroscopy (FT-IR), Thermo Gravimetric Analysis(TG)/ Differential Thermal Analysis(DTA), Scanning Electron Microscope (SEM), experiment in vitro cell compatibility and vitro degradation. The results showed that①The n-HAP/CTS/KGM composite scaffolds prepared above were three-dimensional network-like structure of the sponge-like scaffold with the porosity between 84% and 94%. The central pore size of scaffolds situated between 85μm and 192μm, the compressive strength was found 0.98 MPa and 1.31 MPa, appropriate pore size and higher porosity structure were conducive to cell contact and adhesion with the hole wall, it was also beneficial to adherent cells exchange nutrients and gas with the surrounding environment, and excretion of waste;②Obtained by orthogonal experimental analysis of the composite scaffolds, the best preparation conditions and component were as follows:the amount of n-HAP/CTS/H3PO4 composite powder was 74%, the pre-frozen temperature during the preparation of the scaffolds was-25℃, pH= 10.2, so that the experimental 5 (corresponding to sample No.5#) was the optimal solution, the average central pore size of the 5# scaffold was 189.79μm and the pore ratio lied between 50μm and 250μm is 89%, the porosity was 92% and the compressive strength was 1.31 MPa, which basically meetted with the material science requirements of bone tissue engineering scaffolds;③The three-dimensional porous scaffolds were formed by the n-HAP/CTS/H3PO4 composite powder combined with KGM via hydrogen bond and/or physical reaction, the dispersive distribution of n-HAP/CTS/H3PO4 composite powder in the scaffolds played the role of enhancement of the KGM matrix, improving the mechanical properties of scaffolds;④The composite scaffolds in PBS solution had optimum vitro degradation rate, which situated between 49% and 69% in 12 weeks;⑤The composite scaffolds have good biocompatibility.

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