The Study On Preparation And Properties Of α-hemihydrate Calcium Sulfate

Calcium sulfate is a very important artificial bone graft material,since it has rapid coagulation performance,excellent biodegradability,good biocompatibility and bone guidance.It can be applied to the surgery and treatment of bone fractures,bone defects,bone tumors and other bone diseases.α-Hemihydrate calcium sulfate(α-CSH),as raw materials and the premise of preparation of calcium sulfate bone material,is of great importance to the study and development of medical bone repair implant material.However,at present,domestic research on α-CSH is still in the primary stage and most of the bone products need to be imported.So the related products are expensive and their clinical applications are greatly limited.Traditionally,α-CSH is prepared with hydrothermal method.The related equipments are complicated and costly.The as-prepared α-CSH has a low purity and appears whisker morphology with large particle size,high aspect ratio,and poor uniformity,resulting in not good application performances.Therefore,in this master thesis,a so-called two-step method was developed to prepare α-CSH with tunable size,controlled shape and good medical properties.Firstly,high gravity reactive precipitation method(HGRP)was adopted to prepare calcium sulfate dehydrate(CSD),and a-CSH was further obtained by removing 1.5 H20 from CSD with atmospheric pressure salt solution method.Furthermore,the related mechanical properties and injection properties of hardening materials were investigated.The main contents of this paper are as follows:(1)CSD precursors were prepared with ethanol as modifier by high gravity reactive precipitation method in a rotating packed bed(RPB)reactor.The effects of the concentration of raw material,rotating bed speed,reaction temperature,feed flow rate,and addition amount of ethanol(ethanol/water volume ratio)on the preparation of precursors were explored.The optimal preparation conditions were thus obtained:the concentration of calcium chloride and sodium sulfate solution of 1.25 mol·L-1,anhydrous ethanol as modifier,ethanol/water volume ratio of 1:3,rotating bed speed of 2500 rpm,feed flow rate of 0.5 mol·L-1,and reaction temperature of 40 ℃.Under the optimal conditions,rod-shaped CSD crystals with a diameter of 0.3～0.8μm and a length of 0.5～4μm were achieved.In addition,CSD precursors prepared by RPB have a better morphology,a smaller particle size and a narrower size distribution than those of commercial products,and the precursors prepared in flask and in RPB without ethanol.(2)Based on the CSD precursors prepared in the RPB,a-CSH was further prepared with citric acid as crystal modifier by atmospheric pressure salt solution method in a traditional stirred tank reactor.The effects of reaction temperature,reaction time,and concentration of calcium chloride solution,the morphology and size of precursor were investigated.The optimum conditions were as follows:calcium chloride aqueous solution with a concentration of 25%as reaction medium,the mass ratio of CSD to solution of 5%,the addtion amount(0.06%)of citric acid,initial pH value of 4.4,reaction temperature of 95 ℃,reaction time of 4 h.Under the optimal conditions,the a-CSH crystals were prism-shaped with a length of 1～6 μm,a width of 0.5～2 μm,and a low aspect ratio of 1～3.Compared to the long whiskers with an aspect ratio of 30 prepared by traditional hydrothermal method,an ideal morphology and a lower aspect ratio can be obtained by this method.(3)An injectable calcium sulfate bone material with high compressive strength was successfully obtained by mixing α-CSH powders and physiological saline in a certain proportion.And a preliminary study on the biological properties of a-CSH was carried out.The effects of liquid-solid ratio,the addtion amount of crystal modifier,and the morphology and crystal size of CSD and a-CSH on the performance of bone materials were studied.The results indicated that the white cylindrical materials with smooth surface,compact structure,and stable property were achieved after the pouring and shaping of the slurry.At a liquid-solid ratio of 0.6,the as-prepared material showed a better mechanical performance with a highest compressive strength of 18.37 Mpa.At a liquid-solid ratio of 1.2,it showed a good injection performance and a compressive strength of 9.28 Mpa.