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Calcium sulfate bone cement (CSC) is extensively used as a bone repair material due to its ability to self-solidify, degradability, and osteogenic ability. However, the fast degradation, low mechanical strength, and insufficient biological activity limit its application. This study used magnesium polyphosphate (MPP) and constructed a composite bone cement composed of calcium sulfate (CS), MPP, tricalcium silicate (C3S), and plasticizer hydroxypropyl methylcellulose (HPMC). The optimized CS/MPP/C3S composite bone cement has a suitable setting time of approximately 15.0 min, a compressive strength of 26.6 MPa, and an injectability of about 93%. The CS/MPP/C3S composite bone cement has excellent biocompatibility and osteogenic capabilities; our results showed that cell proliferation is up to 114% compared with the control after 5 days. After 14 days, the expression levels of osteogenic-related genes, including Runx2, BMP2, OCN, OPN, and COL-1, are about 1.8, 2.8, 2.5, 2.2, and 2.2 times higher than those of the control, respectively, while the alkaline phosphatase activity is about 1.7 times higher. Therefore, the CS/MPP/C3S composite bone cement overcomes the limitations of CSC and has more effective potential in bone repair. [ABSTRACT FROM AUTHOR]

Calcium sulfate bone cement (CSC) is extensively used as a bone repair material due to its ability to self-solidify, degradability, and osteogenic ability. However, the fast degradation, low mechanical strength, and insufficient biological activity limit its application. This study used magnesium polyphosphate (MPP) and constructed a composite bone cement composed of calcium sulfate (CS), MPP, tricalcium silicate (C3S), and plasticizer hydroxypropyl methylcellulose (HPMC). The optimized CS/MPP/C3S composite bone cement has a suitable setting time of approximately 15.0 min, a compressive strength of 26.6 MPa, and an injectability of about 93%. The CS/MPP/C3S composite bone cement has excellent biocompatibility and osteogenic capabilities; our results showed that cell proliferation is up to 114% compared with the control after 5 days. After 14 days, the expression levels of osteogenic-related genes, including Runx2, BMP2, OCN, OPN, and COL-1, are about 1.8, 2.8, 2.5, 2.2, and 2.2 times higher than those of the control, respectively, while the alkaline phosphatase activity is about 1.7 times higher. Therefore, the CS/MPP/C3S composite bone cement overcomes the limitations of CSC and has more effective potential in bone repair.

Here we show that inorganic polyphosphate (polyP), a polyanionic metabolic regulator consisting of multiple phosphate residues linked by energy-rich phosphoanhydride bonds, is present in the synovial fluid. In a biomimetic approach, to enhance cartilage synthesis and regeneration, we prepared amorphous polyP microparticles with Mg2+ as counterions. The particles were characterised by X-ray diffraction (XRD), energy-dispersive X-ray (EDX) and Fourier transformed infrared spectroscopic (FTIR) analyses. Similar particles were obtained after addition of Mg2+ ions to a solution containing hyaluronic acid, as a major component of the synovial fluid, and soluble Na-polyP. The viscous paste-like material formed, composed of globular microparticles with diameter of 400 nm, strongly promoted the adhesion of chondrocytes and caused a significant upregulation of the expression of the genes encoding collagen type 3A1, as a marker for chondrocyte differentiation, and SOX9, a transcription factor that regulates chondrocyte differentiation and proliferation. The expression level of the collagen type 3A1 gene was also enhanced by exposure of chondrocytes to synovial fluid that was found to contain polyP with a size of about 80 phosphate residues. This stimulatory effect was abolished after pre-incubation of the synovial fluid with the polyP degrading alkaline phosphatase. We propose a strategy for treatment of joint dysfunctions caused by osteoarthritis based on the application of amorphous Mg2+-polyP microparticles thatprevent calcium crystal formation in the synovial fluid using scavenging Ca2+ ions (Mg2+/Ca2+ exchange) and enhance chondrocyte function after binding of the Ca2+-polyP to hyaluronic acid at the cartilage surface.