Studies On Preparation Of Hydroxyapatite And Property Of Hydroxyapatite/Chitosan Composite

As a major inorganic component of natural bone, hydroxyapatite (HA, Ca10(PO4)6(OH)2) has been used for orthopedic/dental implants with good biocompatibility and bioactivity in bone tissue engineering. But, due to its low fracture toughness, hardness and brittleness, though, HA cannot serve as a bulk implant material under the high physiological loading conditions traditionally associated with orthopedic implants. In order to increase the mechanical property of HA, n-HA was made into a biocompatible composite with chitosan which could be made into any desirable form. Thus, significant interest has been generated in hydroxyapatite /chitosan(HA/CS) composite. Preparation of HA and the property of HA/CS composite were studied in this paper.1.Studies on preparation of HA by electrodeposition. The electrochemical quartz crystal microbalance (EQCM) was used to monitor the electrodeposition process. The result indicated the quantity of coating on the chip surface was influenced by the current density, and the optimal current density was confirmed as 0.6mA/cm2. Subsequently, the alkaline treatment process of calcium phosphate film in 0.1mol/l NaOH solution was monitored real-time by the piezoelectric quartz crystal impedance (PQCI) technique. The change of equivalent circuit parameters with immersion time could be used to characterize the dynamic variations of calcium phosphate, which showed that the structure forming process of HA was comprised of three stages: (1) Acid calcium phosphate dissolution; (2) Phase transformation; (3) HA formation. The correlative kinetic equations and parameters were obtained by fitting the static capacitance (Cs) versus time curves. Finally, the variation of morphology and composition for the corresponding stages were characterized by Scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) and X-ray diffraction (XRD), respectively.2.Studies on the biomineralization process of HA/CS. The biomineralization process of HA/CS in a simulated body fluid was studied by using PQCI. It can be found the frequency (f) decreased obviously due to the biomineralization process of hydroxyapatite/chitosan composite. The results indicate the optimal mass proportion of HA and CS is 6:4. Several parameters (f, Rm, Lm, Cm, Cs) were simultaneously obtained from the PQCI on-line measuring and applied to investigate the change of HA/CS during the biomineralization. It shows the mineralization process of HA/CS can be divided into three steps according to the slope ofΔf vs.ΔRm. The correlative kinetic equations and parameters are obtained from the frequency change. The proposed method may find wide applications in mineralization studies of materials for bone tissue engineering for its advantages in providing real - time multidimensional information.3. Studies on adsorption of human serum albumin (HSA) and ovalbumin (OVA) on HA/CS composite. In situ adsorption of HSA and OVA were real-time monitored by PQCI to fully understand the initial cellular response on HA/CS composite. The PQCI parameters, such as resonant frequency (f), static capacitance (Cs), and motional resistance (Rm) were measured for investigating the kinetic adsorption behaviors of both proteins. The change in frequency shifts (?f) depends on the amount of the adsorbed protein, and the change in motional resistance (?Rm) results from the microporosity variation of HA/CS coating. The results show that the amount of the absorbed HSA is much greater than that of OVA on HA/CS coating because of the unique construction of HSA as well as a flexible protein. Furthermore, ?f and ?Rm data were fitted according to the kinetic exponential decay equations. It can be seen that there is only one adsorption process for OVA, but the absorption process for HSA is followed by a rearrangement process, and the former process is faster than the rearrangement process. Subsequently, the composite binding with proteins were demonstrated by the Fourier transform infrared (FTIR), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS).