The Study On Characteristics Of BCP/CSH/SF Cement

[Objective]This study is to evaluate the compressive strength and setting time of the biphasic calcium phosphate / calcium sulfate hemihydrate (BCP/CSH) complex with different mass fraction (wt%) of calcium sulfate hemihydrate (CSH) in a certain solid to liquid ratio and search for a complex with suitable such ratio, which is then mixed with different mass fraction of silk fibroin (SF) to form complexes, whose compressive strength and setting time are measured to search for a suitable ratio which can be used in the next step experiment to explore a suitable injectable complex that can be used in kyphoplasty.[Method]Preparation of soluble fibroin powder with raw silk: 60 wt% hydroxyapatite powder and 40 wt%β-tricalcium phosphate powder are mixed in dry state by planetary ball milling apparatus to prepare biphasic calcium phosphate powder; calcium sulfate hemihydrate powers are prepared by mixing calcium sulfate dihydrate powder and deionized water under appropriate temperature and pressure conditions. Under simulate body fluid (37±0.5℃, 100% humidity) environment, the compressive strength, initial setting time and final setting time of various BCP/CSH compounds are measured using biomechanical testing instrument and setting time analyzer (Vicat needle). These compounds contain 100 wt%, 90 wt%, 80 wt%, 70 wt%, 60 wt%, 50 wt%, 40 wt% and 30 wt%CSH, respectively, and are mixed with solidifying solution with liquid to solid ration of 0.600 ml/g. Five specimens are used for each compound and measurement. Based on the compressive strength data and the solidification time,the BCP / CSH compound with 50 wt% CSH is chosen for the next experiment. The compressive strength, initial setting time and final setting time of various BCP/CSH/SF compounds are measured and five specimens are used for each measurement. These compounds contain 0.5 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, and 3.0 wt% SF, respectively, and are mixed with solidifying solution with liquid to solid ratio of 0.600 ml/g. Based on the compressive strength of the materials and the solidification time, BCP / CSH / SF complex with 2.5 wt% SF is selected for next step study. The surface morphology and composition of the reaction product of BCP / CSH / SF compound containing 2.5 wt% SF are studied using scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively.[Results]With decreasing calcium sulfate hemihydrate content and increasing biphasic calcium phosphate content in the BCP / CSH composite, both initial setting time and final setting time gradually extended; and the interval between final setting time and initial setting time also accordingly increased. The compressive strength of composite materials decreased with decreasing calcium sulfate hemihydrate content and increasing biphasic calcium phosphate content. When compared to pure CSH control group, compound groups containing 70 wt% CSH, 60 wt% CSH, 50 wt% CSH, 40 wt% CSH, and 30 wt% CSH showed statistically significant difference (p <0.05) on initial setting time and compound groups containing 80 wt% CSH, 70 wt% CSH, 60 wt% CSH, 50 wt% CSH, 40 wt% CSH, and 30 wt% CSH showed statistically significant difference (p <0.05) on both final setting time and compressive strength. Based on the compressive strength and setting timing,BCP/CSH compound with 50 wt% CSH was selected for next experiment.With the addition of different percentage of SF, both the initial setting time and the final setting time of the BCP / CSH / SF composites extended. Based on the experimental results obtained, the less the added silk fibroin amount, the more apparent were the effects on the initial setting time and final setting time of the composite materials. Initial setting time and final setting time of compound groups containing 0.5 wt% SF, 1.0 wt% SF, 1.5 wt% SF, 2.0 wt% , 2.5 wt% SF, and 3.0 wt% SF showed statistically significant difference (p <0.05) when compared with the control group without SF. With increasing silk protein content, the compressive strength of the BCP / CSH / SF composites increased accordingly. The compressive strength of composite groups containing 1.0 wt% SF, 1.5 wt% SF, 2.0 wt% SF, 2.5 wt% SF, and 3.0 wt% SF showed statistically significant difference (p <0.05) when compared with the control group.Scanning electron microscope (SEM) observing results indicated that the BCP/CSH/SF2.5 composite product consists of amorphous granules and regular crystal structures which interweave with each. Uniform but irregular pores with size from 5– 10μm filled in the space between crystal structures and SF could be observed in some of the places.Characteristic peaks of calcium sulfate dihydrate, hydroxyapatite, and calcium phosphate can be seen on the X-ray diffraction (XRD) diagram of cured BCP/CSH/SF2.5 composite product powder, but no SF protein characteristic peak could be seen probably due to its very little amount in the composite.[Conclusions]Inorganic composite materials that have the potential to be used in kyphoplasty could be obtained by mixing biphasic calcium phosphate and calcium sulfate hemihydrate with appropriate composition. With addition of appropriate amount of silk fibroin, the inorganic composite materials could show improved property , appropriate setting time, and enhanced strength and toughness, leading to potential application in kyphoplasty.