Study On Factors Affecting Purity And Crystal Structure Of Surgical Grade Calcium Sulfate And Its Properties

OBJECTIVE: To choose the influence factors on preparation of surgical grade calcium sulfate hemihydrate,which would provide a theoretical basis for the development of surgical grade calcium sulfate with high purity and excellent crystal structure.In addition,to analyze the optimum particle size or formula ratio of surgical grade calcium sulfate for the purpose of producing a perfect CSH,which have appropriate compressive strength,setting time and vitro degradation rate which conformed to ASTM standard,and attempt to provide theoretical basis for the first research injectable surgical grade calcium sulfate hemihydrate in China.METHODS: 1.The crystal structure and purity of CSH were analyzed.The effects of five factors,such as autoclaving time,temperature,raw material diameter,drying time and type of transcrystallizer,on purity,aspect ratio,diameter and crystal structure of surgical grade calcium sulfate hemihydrate were clarified.2.Three types of calcium sulfate hemihydrate particles with diameters of 0-37.5 um,37.5-75 um and > 75 um were screened by using 100 mesh,200 mesh and 400 mesh screens.Based on formulation ratio of different particles,this topic is divided into ten groups by the unconstrained third-order simplex lattice mixing design scheme in formula design experiment.The cylindrical mould with diameter of 10 mm and height of 15 mm are used to measure compressive strength,and three test samples were prepared for each group and their average values were taken.The cylindrical mould with diameter of 20 mm and height of 40 mm are used to measure initial setting time and final setting time,and three samples were prepared in each group and their average values were taken.9 samples were made to analysis degradation rate in vitro by using semicircular mould with diameter of 6 mm,and the degradation rates of 5,10,15,20,25 and 30 samples were observed respectively.The optimum formulation ratio of particle diameter for compressive strength,solidification time and degradation rate in vitro was analyzed.Results: 1.There was no statistical difference between two measurement method based on crystal water and TGA(P=0.543),and there was a significant linear correlation between the two groups(R=0.927,P= < 0.001),which could be used as one of the methods for calculating the purity of surgical grade calcium sulfate hemihydrate.There was a significant difference between the two groups in the results of free water method and TGA method(P= < 0.001),crystalline water method and free water method(P= < 0.001).The main influencing factors of high purity surgical grade calcium sulfate hemihydrate were autoclaved temperature(F=21.75,P<0.000),but it has nothing to do with autoclaved time(F=1.22,P=0.321),drying time(F=2.04,P=0.164),type of crystallizer(F=1.11,P=0.353),diameter of raw materials(F=0.76,P=0.482).In addition,the main factors affecting the diameter of calcium sulfate hemihydrate include autoclave temperature(F = 18.35,P < 0.000),raw material diameter(F = 4.22,P = 0.034)and drying time(F = 8.39,P = 0.003);the factors affecting the morphology and structure development of hexaprism of calcium sulfate hemihydrate are only the types of crystallizers(F = 4.02,P = 0.033).The autoclaving time did not affect the purity,diameter,aspect ratio and morphology of calcium sulfate hemihydrate.2.When the percentage of the particle diameter of calcium sulfate with 0-37.5um,37.5-75 um and > 75 um are 55.0%,17.4% and 27.6% respectively,the compressive strength of the test sample is the highest,which is 14.16 MPa.When the percentage of the particle diameter with 0-37.5um,37.5-75 um and > 75 um are 0.00%,0.00% and 100.00%,the compressive strength of the sample obtained is the smallest,which is 6.60 MPa.3.When the percentage of the particle diameter of calcium sulfate with 0-37.5um,37.5-75 um and > 75 um are 0.00%,0.00% and 100.00% respectively,the initial setting time of the sample is the longest,which is 410.0 seconds.When the percentage of the particle diameter of calcium sulfate with 0-37.5um,37.5-75 um and > 75 um are 94.2%,0.00% and 5.8% respectively,the initial setting time of the sample is the smallest,which is 268.9 seconds.4.When the percentage of the particle diameter of calcium sulfate with 0-37.5um,37.5-75 um and > 75 um are 0.00%,0.00% and 100.00% respectively,the final setting time of the sample is the largest,and the final setting time of the sample is 460.00 seconds;while when the percentage of the particle diameter of calcium sulfate with 0-37.5um,37.5-75 um and > 75 um are 89.7%,10.3% and 0.00%,respectively,the final setting time of the sample is the smallest,and the time is 316.28 seconds.5.When the percentage of the particle diameter of calcium sulfate with 0-37.5um,37.5-75 um and > 75 um are 0.00%,0.00% and 100.00%,respectively,the degradation rate of the sample in vitro is the slowest,which is 18.8%.When the percentage of the particle diameter of calcium sulfate with 0-37.5um,37.5-75 um and > 75 um are 55.7%,44.3% and 0.00% respectively,the degradation rate of the sample in vitro is the fastest,which is 50.7%.CONCLUSION: Choosing suitable autoclaving time,temperature,types of transcrystallizers and diameter of calcium sulfate dihydrate is of great significance for the preparation of calcium sulfate hemihydrate with purity higher than 98% and excellent crystal structure.Surgical calcium sulphate was prepared base on different uses.For bone defect in the load-bearing parts,calcium sulphate with higher mechanical strength should be selected,which should have a higher proportion of small particles;for the non-load-bearing parts with slow absorption,large diameter particles should account for a higher proportion.