Preparation And Properties Of Biodegradable Calcium Phosphates And Their Composites

Calcium phosphates are widely used as hard tissue substitute materials because of their chemical composition and biological properties are similar to those of inorganic phase in bone. Their biodegradable application as tissue engineering scaffold and control released carriers has attached a lot of attention in the biomaterials field and becomes a hot research topic. Different biodegradation rates are needed in different application fields and implant environments, but the biodegradable variations of calcium phosphates are limited. So, it is new challenge to develop these biomaterials with different biodegradation rate.In the calcium phosphates family, hydroxyapatite (HA) has ability to form a chemical bonding with the living bone tissue (i.e. bioactivity) due to its chemical composition similar to that of mineral phase of bone and its excellent biocompatibility, but its can not be biodegradable as the biomedical devices. Tricalcium phosphates (TCP) have also similar Ca/P ratio to that of normal bone mineral, and good biocompatibility and great ability to chemically bond with bone tissue and no rejective reaction. And TCP can be biodegradable, which make them greatly different from HA. Further, the dissolubility of α-TCP is higher than that of P-TCP. Then it is an effective way to obtain calcium phosphates with the tailorable biodegradation if combination of several kinds of the phases mentioned above. The tailorable biodegradation of calcium phosphates composite powders can be effectively improved with the composite powders containing nanostructured clusters, in which the different phases exist in uniformly.Then, in this thesis, the continued adjustable biodegradation rates in a given range of calcium phosphates were designed by combination of different nanostructred calcium phosphates powders containing different phases or pure calcium phosphates phases. The calcium phosphates composed of nanostructured clusters of pure phase were prepared using amorphous calcium phosphates (ACP) through the change of their Ca/P rates and control of dynamics factors (such as heat treatment temperature).Formation mechanism of ACP, pure calcium phosphates and nanostructured calciumphosphates composite powders, in vitro biodegradation and surface modification of calcium phosphates, and calcium phosphates/polylactide dense or porous composites were investigated systemically, in mis thesis.1. Synthesis of amorphous calcium phosphates (ACP) and its formation mechanism.ACP with controllable Ca/P ratios was successfully synthesized by addition of synthetic polymer and using low reaction temperature through the dynamical control.The effects of polymer type and adding amount of polymer, starting Ca/P ratios, pH values, starting materials and adding amount of carbonates on the formation of ACP were studied. It is found that the optimal condition to synthesize ACP is: starting Ca/P ratio 1.50, the molecular weight of PEG 10000, PEG:Ca2+=l:l and pH 10. ACP can form with pH above 7, and starting Ca/P ratio and adding CO32- group can not affect ACP formation, primary particle sizes of ACP is about 40-100nm.Ca/P ratio of ACP can vary in the range of 1.34-1.50 with different pH and 1.50-1.67 with adding different amount of carbonates.The ACP formation mechanism is examined. At first, the Polymer-Ca2+ complex formed between the polymer and Ca2+, and then ACP was obtained after reaction the complex and phosphates in the solution. Some of the polymer substitute the coalescent water among Ca9(PO4)6 or Ca(9+x)(PO4)6(CO3)x clusters of ACP, which can retard efficiently the self-alignment of the atoms, transfer and exchange of ions in the clusters. As a result, the nucleation of apatite is prohibited in the mother solution; meanwhile, some of the polymer adsorb on the surface of fresh ACP particles, which reduce the dissolution of ACP to some extent. So ACP is stabilized by the synthetic polymer in the mother solution. [Ca(6-2r)/2(HPO)x(PO4)3-x]n,-(polymer)m-1(H2O) with lower Ca/P ratios forms during the lower pH due to protonization of PO43⁽HPO42- forms...