The Thermodynamic Properties Of Solid Dispersions Of Hydroxyapatite,Silybin With Polymers

Hydroxyapatite?HA?is a composite salt of calcium phosphate,where Ca/P has a molar ratio of 1.67.Among the CaP salts,HA is the most thermal stable crystalline phase in body,and the most similarity to the mineral part of bone.So it is to be considered as an artificial bone with its biocompatible,bioactive,osteoconductive,non-toxic,non-inflammatory,and non-immunogenic properties are better than other nonmetallic materials.However,pure HA is of brittleness and of lower strength,so it is still difficult to be used in bioapplication.Therefore,some researchers consider to prepare the solid dispersion of hydroxyapatite with polymers to fit the requirements in bio-application.Silybin is an active ingredient of silymarin,which can be used to protect the liver cells,and to cure the liver injury caused by different toxic liver.However,due to the poor water solubility,the bioavailability is poor.It was observed that the solid dispersions of some polymers have improved the solubility of silybin.So researches on the synthesis and properties of the solid dispersions are of significant interesting,and many reports have been published.In this paper,we focus on the preparation and thermodynamic properties of the solid dispersions of hydroxyapatite and silybin with some polymers.DSC technique has been used to measure the thermodynamic properties of the solid dispersions.So to evaluate the biomaterials performance of the solid dispersions.This paper includes three parts.1.The solid dispersion of HA-PVP?polyvinyl pyrrolidone?were prepared by a chemical precipitation method.The PVP acted as an dispersant for the HA-PVP solid dispersions.DSC was used to measured the heat capacity C_p of samples.By analyzing the data of C_p,we obtained some information about the changes of thermodynamic functions with the increasing in temperature and the mass fraction of PVP.Our result indicates that by increasing the mass of PVP,the C_p of samples increased,the enthalpy and entropy of HA-PVP were increased too,however the Gibbs free energy were decreased.This results indicates that the entropic effect of the system was increased with both increasing in temperature and the mass fraction of PVP,that is,the entropic effect plays a major role in the system.Our result indicates that,the HA-PVP has better thermal stability with the temperature increasing.These observation will provide important information that,the HA-PVP solid dispersions will have more biomedical application as an artificial bone materials.2.The solid dispersion of HA-PEG?polyethylene glycol?were prepared by a chemical precipitation method.The PEG acted as an dispersant in HA-PEG solid dispersions.The C_p of samples was measured by DSC.By analyzing the data of C_p,information about the changes of thermodynamic functions with temperature and the mass fraction of PEG were obtained.Similar to the system of HA-PVP,the entropic effect was more important with the increase in temperature and in the mass fraction of PEG.HA-PEG is of better thermal stability with the temperature increase.These results support the biomedical application of HA-PEG solid dispersion in artificial bone materials.3.The solid dispersion of silybin and?-cyclodextrin were prepared by a solvent dissolution method.?-Cyclodextrin acted as two roles,the inclusion and dispersion agent in the system.DSC was used to measured the C_p of the samples.By the analyzing the data of C_p,thermodynamic properties were obtained.With the increasing in temperature and the mass fraction of silybin,both enthalpy and entropy were increased,but the Gibbs free energy was decreased.The entropic effect become more important in higher temperature region,and in higher composition region of PEG.Entropic effect increase means the dispersion effect become more important than the inclusion effect.