Phase transformations, microstructure formation and in vitro osteoblast response in calcium silicate/brushite cement composites

Hydrolysis, setting properties and in vitro characterization of wollastonite/newberyite bone cement mixtures

Bone cements based on magnesium phosphates such as newberyite (N; MgHPO₄.3H₂O) have been shown as potential bone substitutes due to their biocompatibility, biodegradability and ability to support osteoblast differentiation and proliferation. Newberyite can hydrolyze to hydrated magnesium phosphate compounds (e.g. bobierite (Mg₃(PO₄)₂.8H₂O)) at alkaline conditions. In this study, 25 and 50 wt% of crystalline β -wollastonite (woll; CaSiO₃) was admixed to newberyite powder in order to both enhance the acid-base hydrolysis of newberyite and to produce a functional bone cement. The setting process of wollastonite/newberyite cement mixtures started with the hydrolysis of the wollastonite with further transformation of newberyite into bobierite and the formation of magnesium silicate phase. The results demonstrated that 25 wollastonite/newberyite and 50 wollastonite/newberyite cement pastes at optimal powder/liquid ratios had final setting times of ∼34 and 25 min and compressive strength values of 18 and 32 MPa after seven days setting, respectively. The tests of cytotoxicity of cement extracts on osteoblastic cells and contact cytotoxicity of the cement substrates showed different results. The osteoblasts cultured in cement extracts readily proliferated which confirmed the non-cytotoxic concentration of ions released from both cements. On the other hand, a strong cytotoxic character of 25 wollastonite/newberyite sample surface in contrary to high (∼80%) proliferation activity of cells on the 50 wollastonite/newberyite cement substrate was observed. The differences in cell proliferation activity was attributed to different surface topographies of cement substrates, where needle-like precipitated microcrystals of magnesium phosphate phase (in 25 wollastonite/newberyite cement) prevented the adhesion and proliferation of osteoblasts contrary to the smoother surface covered by extremely fine nanoparticles in the 50 wollastonite/newberyite cement.

Laser Sintered Magnesium-Calcium Silicate/Poly-ε-Caprolactone Scaffold for Bone Tissue Engineering

In this study, we manufacture and analyze bioactive magnesium-calcium silicate/poly-ε-caprolactone (Mg-CS/PCL) 3D scaffolds for bone tissue engineering. Mg-CS powder was incorporated into PCL, and we fabricated the 3D scaffolds using laser sintering technology. These scaffolds had high porosity and interconnected-design macropores and structures. As compared to pure PCL scaffolds without an Mg-CS powder, the hydrophilic properties and degradation rate are also improved. For scaffolds with more than 20% Mg-CS content, the specimens become completely covered by a dense bone-like apatite layer after soaking in simulated body fluid for 1 day. In vitro analyses were directed using human mesenchymal stem cells (hMSCs) on all scaffolds that were shown to be biocompatible and supported cell adhesion and proliferation. Increased focal adhesion kinase and promoted cell adhesion behavior were observed after an increase in Mg-CS content. In addition, the results indicate that the Mg-CS quantity in the composite is higher than 10%, and the quantity of cells and osteogenesis-related protein of hMSCs is stimulated by the Si ions released from the Mg-CS/PCL scaffolds when compared to PCL scaffolds. Our results proved that 3D Mg-CS/PCL scaffolds with such a specific ionic release and good degradability possessed the ability to promote osteogenetic differentiation of hMSCs, indicating that they might be promising biomaterials with potential for next-generation bone tissue engineering scaffolds.