- MSc, (2014-2017): Fabrication and Characterization of porous nanocomposite of calcium phosphate –forsterite modified with Strontium for filling bone defects
Calcium phosphate cement possesses wide application as degradable and injectable biomaterial. In spite of suitable biocompatibility of calcium phosphate bone cements, they have issues consisting of shortage of macropores and low mechanical strength leading to the restriction in their applications. The aim of present study was to fabricate and characterize porous nanocomposite cement of calcium phosphate–forsterite modified with Strontium(Sr). In this regard, forsterite nanopowder containing 0, 0.05, 0.1, 0.2 and 0.4 at.% Sr was firstly synthesized by sol-gel method and evaluated using X-ray diffraction, scanning electron microscope, transmission electron microscope and Fourier transform infrared spectroscopy. Moreover, bioactivity of Sr-modified forsterite was assessed using soaking in simulated body fluid (SBF). Furthermore, the effect of Sr content on the MG63 cells behavior was assessed. Then, calcium phosphate cement (CPC) based on nanometric α-TCP (98 wt.%) and hydroxyapatite (2 wt.%) as powder phase and 2.5 wt.% Na2HCO3 aqueous solution as liquid phase was prepared and characterized. In order to improve mechanical strength of calcium phosphate cement, various amounts of optimized Sr-modified forsterite (0.5, 1, 2 and 3 wt.%) were added to CPC and characterized. In this regard, the effect of Sr-modified forsterite nanopowder on mechanical strength, injectability, and setting time of nanocomposite cements were investigated. After optimization of Sr-modified forsterite content, porous nanocomposite CPC of was fabricated by using foaming agent and the effect of foaming agent on mechanical, structural and biological properties was evaluated. Results demonstrated that while forsterite was the main phase of Sr-modified forsterite nanopowder, the second phased could be detected when Sr content enhanced upon 0.2 at.%. Moreover, the presence of Sr atoms influenced the crystallite and particle size as well as lattice parameters of forsterite, while did not significantly change the morphology of powders. Noticeably, the incorporation of Sr element upon 0.2 at.% enhanced the average crystallite size of forsterite from 31± 3.9 nm to 62.9± 11.8 nm. In vitro bioactivity assessment in SBF revealed that while all Sr-modified forsterite powders revealed greater bioactivity than pure forsterite nanopowder, the incorporation of 0.1 at.% Sr revealed improved bioactivity compared to other Sr-modified samples. Moreover, while all forsterite based nanopowders did not revealed any cytotoxicity result, Sr-modified forsterite containing 0.05-0.1 at.% Sr revealed significantly promoted cell proliferation. Moreover, incorporation of 1 wt.% Sr-modified forsterite to CPC led to enhance in compression strength (1.45 times) and elastic modulus (2.87 times) in comparison with free-forsterite CPC. Additionally, the presence of Sr-modified forsterite nanoparticles resulted in decrease in initial setting time of cement from 23.8±5.49 min to 11.33±1.63 min. Since foaming agent was added to powder phase of cement containing 1wt.% Sr-modified forsterite nanoparticles, porous nanocomposite cement consisting of 77.98± 4.4 % macroporosity was fabricated. By introducing macroporosity in cement, compressive strength and elastic modulus were obtained 2.58±0.7 MPa and 0.33±0.08 GPa, respectively where were higher than those of in porous free-forsterite CPC with compression strength 1.3±0.2 MPa and elastic modulus 0.1±0.02 GPa. On the other hand, cell culture results confirmed that the proliferation and spreading of MG63 cells on nanocomposite and porous nanocomposite cements were improved compared to those in free-forsterite CPC. Based on the findings, it seems that porous nanocomposite of calcium phosphate –Sr-modified forsterite could be a suitable bone filler.