Physicochemical properties and cellular responses of strontium-doped gypsum biomaterials.

This paper describes some physical, structural, and biological properties of gypsum bioceramics doped with various amounts of strontium ions (0.19-2.23 wt%) and compares these properties with those of a pure gypsum as control. Strontium-doped gypsum (gypsum:Sr) was obtained by mixing calcium sulfate hemihydrate powder and solutions of strontium nitrate followed by washing the specimens with distilled water to remove residual salts. Gypsum was the only phase found in the composition of both pure and gypsum:Sr, meanwhile a shift into lower diffraction angles was observed in the X-ray diffraction patterns of doped specimens. Microstructure of all gypsum specimens consisted of many rod-like small crystals entangled to each other with more elongation and higher thickness in the case of gypsum:Sr. The Sr-doped sample exhibited higher compressive strength and lower solubility than pure gypsum. A continuous release of strontium ions was observed from the gypsum:Sr during soaking it in simulated body fluid for 14 days. Compared to pure gypsum, the osteoblasts cultured on strontium-doped samples showed better proliferation rate and higher alkaline phosphatase activity, depending on Sr concentration. These observations can predict better in vivo behavior of strontium-doped gypsum compared to pure one.

Physico-chemical and in vitro biological evaluation of strontium/calcium silicophosphate glass.

Strontium is known to reduce bone resorption and stimulate bone formation. Incorporation of strontium into calcium phosphate bioceramics has been widely reported. In this work, calcium and calcium/strontium silicophosphate glasses were synthesized from the sol-gel process and their rheological, thermal, and in vitro biological properties were studied and compared to each other. The results showed that the gel viscosity and thus the rate of gel formation increased by using strontium in glass composition and by increasing aging temperature. In strontium-containing glass, the crystallization temperature increased and the type of the crystallized phase was different to that of strontium-free glass. Both glasses favored precipitation of calcium phosphate layer when they were soaked in simulated body fluid; however strontium seemed to retard the rate of precipitation slightly. The in vitro biodegradation rate of the strontium/calcium silicophosphate glass was higher than that of strontium-free one. The cell culture experiments carried out using rat calvaria osteoblasts showed that the incorporation of strontium into the glass composition stimulated proliferation of the cells and enhanced their alkaline phosphatase activity, depending on cell culture period.

Effect of synthetic amorphous calcium phosphate nanoparticles on the physicochemical and biological properties of resin-modified glass ionomer cements.

The aim of this study was to find an optimum dose of the synthetic amorphous calcium phosphate (ACP) nanoparticles to be incorporated in resin-modified glass ionomer cements (RMGICs) for triggering the release of PO43-/Ca2+, alkaline phosphatase (ALP) activity and osteogenic differentiation of mesenchymal stem cells (hMSCs) without significantly affecting the essential properties of the cements. RMGICs were formulated from the powder composed of melt-derived strontium fluoro-aluminosilicate glass (SFAG) and synthetic ACP nanoparticles (0-20 wt%), as well as commercial polyalkenoic acid liquid. The effect of ACP incorporation on the workability, microstructure, Ca2+/PO43-/F- ion release and compressive strength was investigated. The response of hMSCs to the optimized cements was assessed by MTT cytotoxicity, ALP activity, and staining tests. The working time of the formulated RMGICs decreased significantly upon increase of ACP content from 5 to 20%. ACP (5%)-incorporated RMGICs showed improved photopolymerization and setting. An insignificant reduction was recorded in the compressive strength of RMGICs with addition of 1.5-5% ACP. The fluoride release didn't significantly decrease due to addition of 5% ACP. Upon incorporating 5% ACP, the biocompatibility of RMGICs rose to about 20%. In addition, ALP activity and osteogenic differentiation of hMSCs noticeably increased after exposure to ACP-incorporated RMGIC. ACP (5%)-incorporated RMGICs could be promising candidates for both restorative and regenerative dentistry owing to the optimum mechanical strength, prolonged ion release, and their effective role in the cell differentiation and biomineralization demanded for pulp regeneration.

Evaluation of Microstructure and Mechanical Properties of Al-TiC Metal Matrix Composite Prepared by Conventional, Microwave and Spark Plasma Sintering Methods.

In this research, the mechanical properties and microstructure of Al-15 wt % TiC composite samples prepared by spark plasma, microwave, and conventional sintering were investigated. The sintering process was performed by the speak plasma sintering (SPS) technique, microwave and conventional furnaces at 400 °C, 600 °C, and 700 °C, respectively. The results showed that sintered samples by SPS have the highest relative density (99% of theoretical density), bending strength (291 ± 12 MPa), and hardness (253 ± 23 HV). The X-ray diffraction (XRD) investigations showed the formation of TiO2 from the surface layer decomposition of TiC particles. Scanning electron microscopy (SEM) micrographs demonstrated uniform distribution of reinforcement particles in all sintered samples. The SEM/EDS analysis revealed the formation of TiO2 around the porous TiC particles.

Development of injectable biocomposites from hyaluronic acid and bioactive glass nano-particles obtained from different sol-gel routes.

Bioactive glass nano-powders with the same chemical composition and different particle characteristics were synthesized by acid-catalyzed (the glass is called BG1) and acid-base catalyzed (BG2) sol-gel processes. Morphological characteristics of powders were determined by TEM and BET methods. The powders were separately mixed with 3% hyaluronic acid solution to form a paste. In vitro reactivity of pastes was determined by soaking them in simulated body fluid. Rheological behaviors of paste in both rotation and oscillation modes were also measured. The results showed that BG1 particles was microporous with mean pore diameter of 1.6 nm and particle size of ~300 nm while BG2 was mesoporous with average pore diameter of 8 and 17 nm and particle size of 20-30 nm. The paste made of BG2 revealed better washout resistance and in vitro apatite formation ability than BG1. According to the rheological evaluations, both pastes exhibited shear thinning but non-thixotropic behavior, meanwhile paste of BG2 had higher viscosity than BG1. The oscillatory tests revealed that the pastes were viscoelastic materials with more viscous nature. Both pastes could be completely injected through standard syringe using low compressive load of 5-50 N. Overall, The biocomposites can potentially be used as bioactive paste for the treatment of hard and even soft tissues.

Polymerizable nanoparticulate silica-reinforced calcium phosphate bone cement.

Bone cements based on calcium phosphate powder and different concentrations of colloidal silica suspensions were developed. Setting time and washout behavior of the cements were recorded and compared with those of a control group prepared by the same powder phase and distilled water as liquid. The phase composition, compressive strength, and morphology of the cements were determined after incubation and soaking in simulated body fluid. Proliferation of osteoblasts seeded on samples was also determined as a function of time. The results showed that the long setting time, poor compressive strength, and undesirable washout behavior of the cement made with distilled water were considerably improved by adding colloidal silica in a dose-dependent manner. On the basis of XRD and SEM results, both control group and nanosilica-added cements composed of nanosized apatite flakes after 7 days soaking, in addition to tetracalcium phosphate residual for the latter. It was found that the rate of hydraulic reactions that are responsible for conversion of the cement reactants to nanostructured apatite was increased by the presence of colloidal silica. Furthermore, the osteoblasts exhibited better proliferation on nanosilica added cements compared to control one. This study suggests better applied properties for nanosilica-added calcium phosphate cement compared to traditional cements.