Composite Calcium Phosphate Dissolved In Acetate Buffer Solution Behavior

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.The biomaterials applied in tissue engineering scaffold and repair needs a characteristic of biodegradability, as a result, the material biodegradibilty becomes a hot research topic.Different biodegradation rates are reqiured in various implant environments, but the biodegradability of single-phase calcium phosphates is limited. So, it is a challenge to develop calcium phosphates with a tailored biodegradation rate.In the calcium phosphates family, hydroxyapatite (HA) is unable to biodegradate. Tricalcium phosphates (TCP) is biodegradable. In TCP, there are two phases, a-TCP andP-TCP. The dissolubility of a-TCP is higher than that of P-TCP. Such, it could be an effective approach to obtaining calcium phosphates with a tailored biodegradation if the combination of different phases of TCP or HA becomes a multiphasic calcium phosphate. The tailored biodegradation of multiphasic calcium phosphate powders can be effectively improved to have nanostructured clusters, whithin which the different phase particles exist uniformly.In this thesis, the mulitphasic calcium phosphates were prepared using amorphous calcium phosphates (ACP) precursor through the change of their Ca/P rates and the control of dynamics factors (such as heat treatment temperature). The formation of single-phase and mulitphasic calcium phosphates, and in vitro biodegradation were investigated systemically1.Preparation of Pure or nanostructured calcium phosphatesSingle phase and mulitphasic calcium phosphates were obtained using ACP with different Ca/P ratios as precursors and the subsequent control of dynamics factors, the nanostructured calcium phosphate composite powders are ensured to be nanosized structure.Single phase a-TCP powders can be prepared by heated ACP with Ca/P =1.5 at 800℃ for lh, pure (3-TCP powders at 900℃ for lh and α/β-TCP nanostructured multiphasic calcium phosphate composite powders at 800-900℃ for lh,in which the content of β-TCP phase can vary from 0% to 100% by the heating temperature.α/β /HA nanostructured multiphasic calcium phosphate powders can be obtained by heated ACP with Ca/P> 1.5 due to adding carbonate. Only pure a-TCP or α/β-TCP powder appeared ifthe amount of carbonates added lower than 15 mol%; Only pure HA powder appeared if the amount of carbonates added higher than 60 mol%, however, a/(3/HA biphasic calcium phosphates powders can be obtained if carbonates added were between 15mol% and 60mol%, in which the content of HA phase can vary from 0% to 100% depending on the amount of carbonates added. It is testified that a/J3-TCP and a/p/HA nanostructured multiphasic calcium phosphate powders are constructional uniformity in a micrometer scale.Pure a-TCP, (5-TCP and HA, and their multiphasic calcium phosphate can be obained used ACP as precursor, which provides a novel way to prepare calcium phosphates materials with high performance.2. In vitro dissolution behaviors of calcium phosphate powders containing different phase or phase compositionIn vitro dissolution behaviors of pure and nanostructured multiphasic calcium phosphate powders were investigated by soaking in NaAc-HAc buffer solution (pH5.0) for different times and measuring the Ca2+ and PO43" concentration of the soaked solution.The result shows that the dissolution rate of calcium phosphates powders decreases in theorder: a-TCP > a/p-TCP > p-TCP > a/p7 HA > HA, This indicates that the dissolution rates of thecalcium phosphates prepared in this thesis can be tailored.Nanostructured multiphasic calcium phosphate powders are able to provide a spectrum of different dissolution rates, the calcium phosphates would act as biomedical devices with higher performance.