Study On Regulated Synthesis Of Hydroxyapatite Crystal Growth

Hydroxyapatite,?HAP and HA?, is similarly to bone tissue and teeth in chemical composition and structure. HA has been widely used in biomedical materials due to their excellent biocompatibility, interface biological activity, osteoconductive properties, and non-toxic side effects. In other areas, hydroxyapatite was applied to adsorb excessive fluorine ions in drinking water and heavy metal ions in industrial wastewater, due to ion exchange and excellent adsorption capacity. Moreover, hydroxyapatite ceramics has been used as a new type of wet sensitive semiconductor ceramic material because of a wide range of heat resistant, resistant to wet, resistant to aging, etc. It is well known that the performance of HA in the above applications depend on morphology, struture and chemical composition. Hence, the researchers are attempting to prepare materials with specific morphologies and structures.In this paper, Self-assembly technique was applied to introduce functional groups and form hydroxyl-, amine-, and carboxylterminal self-assembled monolayers?SAMs?. The SAMs were grafted onto titanium substrates to obtain a molecularly growth formed homogeneous and crack-free crystalline hydroxyapatite coatings on these substrates. AFM and XPS were used to characterize the SAM surfaces, and XRD, SEM, and TEM were used to characterize the HA coatings. Results show that highly crystalline, dense, and oriented HA coatings can be formed on the OH–, NH2–, and COOH–SAM surfaces. The SAM surface with –COOH exhibited stronger nucleating ability than that with –OH and –NH2. The nucleation and growth processes of HA coatings were effectively controlled by varying reaction time, pH, and temperature. By using this method, highly crystalline, dense, and adherent HA coatings were obtained. In addition, in vitro cell evaluation demonstrated that HA coatings improved cell adhesion as compared with pristine titanium substrate.The effect of ethylene diamine tetraacetic acid disodium salt?Na₂EDTA? on hydroxyapatite crystal morphology was studied under high pH value, which included anhydrous calcium chloride and disodium hydrogen phosphate. The morphology of HA were studied at different content of Na₂ EDTA and pH. Results show that high pH values could promote the formation of microspheres. The structures were transformed from tight to estrange with decreasing pH. The Na₂EDTA/Ca ratio affected self-assembled, the ratio of Na₂EDTA/Ca at 2:2 resulted in the formation of a dense spherical structure. The reaction temperature affected the degree of the density of the microspheres. The mechanism underlying the formation of HA microspheres in the presence of Na₂ EDTA at high pH was studied.Hydroxyapatite microspheres with hierarchical porous structure were synthesized using a new method?which is ammonia diffusion method?. The morphology and structure of the as-synthesised products were characterised by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy and Brunauer–Emmett–Teller gas sorptometry analyses. Results showed that the change in pH resulting from ammonia diffusion provided the driving force for the formation of HA crystals. Under the cooperative influences of reaction time and reaction temperature, the nucleation and growth processes of HA nanocrystals were effectively controlled. Therefore, porous HA microspheres with large surface areas were produced at 60 °C for 24 h. On the basis of the time-dependent experiments, a possible formation mechanism of hierarchical porous HA microsphere was proposed. Moreover, hierarchical porous HA microspheres were investigated as adsorbent, and they exhibited a high adsorptive capacity for heavy metals Pb²⁺ and Cu²⁺ of approximately 213.58 ± 2.63 and 59.68 ± 3.44 mg/g, respectively.Hydroxyapatite microspheres with hierarchical porous and hollow structure were synthesized based on an easy gas-diffusion method that uses ethylene diamine tetraacetic acid disodium salt as chelating agent. Results show that during the formation of hollow HA microspheres, the capability of Na₂ EDTA to control Ca²⁺ release and distribution in synthesis solution contributed to hollow structure formation. The reaction time also affected hollow nanostructure formation. We studied the possible formation mechanism of the microspheres based on time-dependent experiments.