| On the basis of analysis and study of the quantities of the biology body structure, especially the structure of the nacre , bone, wood and bamboo stem et al, it's found that the layer structure plays an important role in their excellent mechanical propertities. To obtain the layer stucture mimicking the layer structure of wood, so-called annual ring structure, is the goal of the study. Chitosan(CS), abundant in nature derivated from chitin highly deacelylation, has excellent biocompatibility and bioactivities. While chitosan, insolubility and apt to oxidation, was limited as structure materials due to the difficulty of processing. Strong intro- and inter- molecular H-bond is responsible for its insoluble in water and active C2- NH2 is responsible for its instability at high temperature. In this study, in-situ precipitation method was developed to preparation chitosan rod by using chitosan membrane as template and NaOH as precipitant. The congealed chitosan rod was mildly auto-assembled into 3-D concentric layer by layer structure, similar to the annual ring structure of wood, when NaOH solution penetrated the chitosan membrane. The dried chitosan rod has excellent properties. Furthermore, hydroxyapatite(HA), a bioabsorble, biocompatible and osteoinductive materials, was introduced into the process of preparation and the congealed CS/HA rod was prepared via in-situ compositing route. The dried CS/HA nanocomposites has even better mechanical properties than pure chitosan rod. HA in chitosan matrix will also exert some sort of effct on the bioactivity and the bone-bonding ability of CS/HA composites when composits was implanted as bone substitute.1. Using chitosan membrane as template and NaOH as precipitant, in-situ precipitation method was developed to prepare chitosan rod. Molding mechanism of CS congealation rod and the effects of base concentration, CS concentration and temperature on the molding were studied. The results showed that in the process of in-situ precipitation CS was precipitated layer-by-layer in the template and then formed 3D layer CS congeal rod through acid-base neutralization of NaOH and the amino group of CS. The process conditions being well controlled, the congealed rod formed homogeneous structure.2. Molecular weight, crystallinity and water absorption of CS before and after process were studied. It was found that the preparation process had little influence on the CS molecular weight. The crystallization of the chitosan rod decreased but water absorption of CS rod wasstill large. Morphology investigations indicated that CS rod prepared by in-situ precipitation was bi-axis oriented with the property of anistropy.3. Mechanical strength of CS rod was tested and the effects of raw material and water content of CS rod were discussed. The results showed that mechanical strength of CS rod was improved as molecular weight increased with the same D.D. CS rod had good mechanical strength in dry state but mechanical strength decreased greatly as water content increased.4. The CS/HA nanocomposite with high performance were prepared via in-situ compositing route. The key of in-situ compositing is to pre-precipitate CS membrane which was used to obstruct the CS/HA precursor from NaOH aqueous solution. The CS membrane controlled the process of CS precipitation and transformation of HA from the precursor due to the change of pH simultaneously and tardily. XRD was carried out to determine the component of CS/HA composite. TEM and SEM were performed to investigate the morphology of HA granules and CS/HA composite. Results showed that the in-situ formed calcium phosphate in CS was exactly HA, and that nano-size HA granules (30-50nm width, l00nm length) were dispersed in CS matrix uniformly. The result of SEM showed that the structure of CS/HA composite prepared by in-situ compositing is layer-by-layer structure, which can further prove the mechanism of in-situ compositing. The mechanical properties of CS/HA were evaluated by the three point bending test. The bending strength and modulu...
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