Properties Of Calcium Phosphate Cement Modified By Incorporating Silicon Through Multiple Pathways

Calcium phosphate cement(CPC) is widely used as a bone-repair material because of its good plasticity, biocompatibility, bioactivity and self-setting characteristic. However, CPC possesses some shortcomings, such as long setting time, relatively low mechanical strength, poor anti-washout ability and lack of osteoinductivity, that restrict its application in clinic. Silicon(Si) plays an important role in physical development and bone formation, and participates in the process of bone calcification, especially the process of new bone formation. In order to overcome the weaknesses and improve the properties of CPC, in this study, Si has been introduced into CPC in different ways, and fabricated the Si-containing bone cements with excellent comprehensive performance. The study may develop a new approach to modify CPC.Amorphous calcium silicate(ACS) was added in CPC to obtain the ACS/CPC composite cement. The setting time of the composite cement was shortened and the compressive strength was improved by the addition of ACS. When the amount of ACS was 5 wt%, the setting time of ACS/CPC(29 min) was shorter for eleven minutes than that of pure CPC, and the compressive strength(35.7 ± 3.6 MPa) was increased by 35% while the injectability remained over 95%, which met the requirements of clinical operation. The speed of hydroxyapatite(HA) deposition on the surface of ACS/CPC was faster than pure CPC when soaked in the simulated body fluid(SBF), resulting in the lower degradation of ACS/CPC during the late immersion period. The results of cell experiment showed that, compared to pure CPC, ACS/CPC could significantly promote the adhesion and proliferation of mice bone marrow mesenchymal stem cells(mBMSCs) and human umbilical vein endothelial cells(HUVECs), and stimulate the differentiation of mBMSCs.Wollastonite(WS) was added into CPC to obtain the WS/CPC composite cement, and the effects of the particle size and content of WS on the physicochemical properties of the cement were systematically studied. The setting time of WS/CPC was prolonged and the compressive strength decreased with the increase in particle size of WS when the particle size of WS was greater than 106 μm. WS/CPC with the WS particles sized in 53-106 μm possessed better physicochemical properties than that with the WS particles smaller than 53 μm. Consequently, we chose the WS with the particle size ranged in 53-106 μm to modify CPC. The addition of WS promoted the hydration reaction without affecting the hydration product of CPC. The injectability of the WS/CPC composite cement declined with the incorporation of WS to a certain extent, particularly when the content of WS was higher than 20 wt%. By incorporating WS into CPC, the composite cement obtained feasible setting time, enhanced compressive strength, and the porosity and degradation decreased. It was shown that the cell responses of mBMSCs and HUVECs to WS/CPC were better than that to pure CPC if the amount of WS was appropriate.Si was doped in PCCP during the preparation process of PCCP by chemical precipitation. The analysis showed that Si had doped into the HA lattice, leading to the changes in the lattice parameters and the increase in unit cell volume. Si doped HA(Si-HA) crystals in PCCP were mainly need-like, but the crystallinity of HA became lower with excessive amount of Si. Si doped CPC(Si-CPC) was fabricated by mixing Si doped PCCP(Si-PCCP) with DCPA. Compared to pure CPC, Si-CPC performed shorter setting time, higher compressive strength, better bioactivity and cell responses(cell adhesion, proliferation and differentiation).According to the different solubility of the above-mentioned Si-containing compounds(ACS, WS and Si-PCCP), the composite cements with controlled release of Si were developed through collocation of these three compounds. The properties of the cement containing two or three of them, especially the cement containing all the three compounds(3SiCPC), were much better than those of the cement containing single compound. After soaking in SBF for 14 days, the concentration of Si released from 3SiCPC kept almost unchanged and maintained a high constant, namely reaching a sustained-release effect of Si. Within an appropriate range of concentration, CPC containing the two or more Si-containing compounds had better cell responses.Locust bean gum(LBG) and dopamine(DA) was used as the anti-washout agents and a good anti-washout and injectable CPC was prepared by incorporating the agents into 3SiCPC. The anti-washout performance of 3SiCPC was obviously improved by the addition of LBG or DA. Meanwhile, the setting time slightly increased and the injectability and compressive strength slightly decreased when the amount of LBG was no more than 1.0 wt%. Additionally, the 3SiCPC with 1.0 wt% LBG exhibited good cell compatibility of mBMSCs. When the amount of DA was no more than 0.4 wt%, the setting time of 3SiCPC was slightly prolonged and compressive strength slightly increased. The 3SiCPC containing 0.4 wt% DA was more favorable of protein adsorption and cell responses than 3SiCPC without anti-washout agent.