Study On Crystal Habit And Dissolution Characteristic Of Hydroxyapatite

Hydroxyapatite (HA) is one of most important inorganic components. In recent 20 years, the study of biomaterials like natural bone is active. HA was believed to be the best materials for bone structure. Different kinds of HAP crystal morphology can be formed in terms of different growth conditions. As for the importance of crystal morphology, The crystal habit of HAP in vacuum condition and the effects of additives on crystal habits was studied theoretically.The equilibrium morphology of a crystal can be decided from a consideration of the surface free energies of the various crystallographic faces, but the growth morphology is decided by kinetic factors that are harder to predict. Considering the difficulty in predicting the practical crystal habit, the crystal habit of HAP in vacuum was studied first. Its morphology depends on the relative growth rates Rh rkell of crystal faces. Several theories, such as BFDH, PBC, AE, et al had been advanced to relate R_hkl^rel to geometric of energetic characteristics of the surfaces. The morphology of HAP predicted by BFDH model was different from the actual date, but the result of AE model was similar to the crystal morphology of HAP.Molecular modeling techniques are employed to investigate the adsorption of some environment factors such as citric acid, bacterial cellulose(BC) and hydrogen ion to a range of hydroxyapatite surfaces, and interactions between these factors and HAP surfaces was studied by energy calculations. The multiple interactions between the surfaces and the citric acid molecule and BC lead to large binding energies. Citric acid and BC would thus be good inhibitor for HAP. The binding energy on the HAP(100)surface is much more larger than other surfaces, which means that the citric acid and BC would more strongly inhibit growth of HAP(100) surface than other surfaces, leading to an elongated morphology in the c-direction of the HAP crystal. The adsorption of hydrogen ion changes the morphology importance of HAP, HAP(001) surface come to be more important on morphology, leading HAP crystal growing along the a-directon or b-direction.The dissolution chacracteristic of HAP was a key factor to affect its clinical performance. But the dissolution mechanics was not clear by now because of its complexity. Melocular dynamics method was used to research the dissolution behaviour of HAP under a hydrone layer, the results show that dissolution was initiated by hydroxyl and calcium dissolved from HAP surface. Besides, the dissolutioni process of Ca²⁺ for amorphous HAP and crystal HAP was studied by energy calculations, and the results shows amorphous HAP was more likely dissolved.