The Effect Of PEG In The Formation And Crystallization Of Amorphous Calcium Phosphate

Calcium phosphates are widely used as hard tissue substitute materials. Different biodegradation rates are needed in different biological processes and implant environments, so it is challenge to extend the dissolution range of calcium phosphates and develop calcium phosphate biomaterials with different biodegradation rates.The variations in dissolubility of monophasic calcium phosphates are limited. However, the dissolubility of α-TCP is ten times higher than that of β-TCP, so the combination of α-TCP and β-TCP can further widen the range of biodegradation rates of calcium phosphates. Our previous studies showed that the dissolubility rate of the biphasic calcium phosphates could be increased obviously with increasing of the β-TCP content. So the application of biomaterials can be extended by preparing α/β-TCP biphasic calcium phosphate with different two phase ratio.In order to increase the β-TCP content in α/β-TCP biphasic calcium phosphate, the high heating temperature was used in previous studies, which leaded to large size of the particles. Furthermore, different sintering temperature was indispensable for the different diphase powders, which would result in the difference of the powder particles size scale and asymmetric particles. All the above factors would make adverse effect to the dissolution performance of α/β-TCP biphasic calcium phosphate powders, which would restrict its applications.Prepared amorphous calcium phosphate (ACP) first and then heated it as a precursor. It was an easy and effective way to prepare the biphasic powders. But ACPs dissolved very fast in the water and its amorphous phase was very difficult to be contained.Poly(ethylene glycol) (PEG) is a non-ionic surface active agent, and it can be added to pack the particle in the precipitation preparation and solved the problem perfectly.PEG has the effects of packing and connecting the particles, which mean that PEG can limit the single particle growing and make the particles agglomerated. Different biphasic powders were obtained with the PEG content increasing because of delivering more energy during heating.In this work, The ACP powders were synthesized by reacting of Ca(NO₃)₂ with (NH₄)₂HPO₄ in aqueous solutions at 5℃ with presence of PEG polymer additive. It is found that the optimal condition to synthesize ACP is: starting PEG:Ca ratio equal or even bigger than 1:1.For the preparation of biphasic tricalcium phosphate, the ACPs were used as precursors. They were heated at 800℃ for 3h. As a result, the ACPs transformed to biphasic α/β-TCP powders before 800℃. More PEG content in ACP, higher β-TCP ratio is obtained in the biphasic powders. This research shows that α/β-TCP powders with different two phase ratio can be adjusted by controlling additive PEG content, and the content of α-TCP and β-TCP phase can vary between 0% and 100%.