Masoud Hafezi

Polyurethane/58S bioglass nanofibers: synthesis, characterization, and in vitro evaluation

In this study, polyurethane nanofibers containing 5 and 10 wt% synthesized 58S bioglass were designed and fabricated by the electrospinning process. The physicochemical and mechanical properties and in vitro behavior of the scaffolds were evaluated by scanning electron microscopy (SEM), dynamic mechanical thermal analysis (DMTA), Fourier transform infrared spectroscopy (FTIR), contact angle, phosphate-buffered saline (PBS) uptake, in vitro bioactivity, MTT assay, and cellular response. The FTIR results showed an increase in the urethane bond between the OH (from BG) and NCO (from PU) groups with the increase in BG. When the BG amount increased from 5% to 10%, the contact angle decreased to approximately 20° and the PBS uptake of the scaffold increased because of the hydrophilic property of the BG particles. DMTA showed that the glass transition temperature started to shift slightly to higher temperatures from −17 °C to −15 °C. SEM and X-ray diffraction analysis depicted hydroxyapatite formation on the scaffolds upon immersion in SBF. Cell proliferation and viability also increased significantly with the increase in BG. It is concluded that this composition provides a novel alternative for bone tissue engineering.

Effect of adding nano-titanium dioxide on the microstructure, mechanical properties and in vitro bioactivity of a freeze cast merwinite scaffold.

In the present research, merwinite (M) scaffolds with and without nano‐titanium dioxide (titania) were synthesized by water‐based freeze casting method. Two different amounts (7.5 and 10 wt%) of n‐TiO2 were added to M scaffolds. They were sintered at temperature of 1573.15°K and at cooling rate of 4°K/min. The changes in physical and mechanical properties were investigated. The results showed that although M and M containing 7.5 wt% n‐TiO2 (MT7.5) scaffolds had approximately the same microstructures in terms of pore size and wall thickness, these factors were different for sample MT10. In overall, the porosity, volume and linear shrinkage were decreased by adding different weight ratios of n‐TiO2 into the M structure. According to the obtained mechanical results, the optimum mechanical performance was related to the sample MT7.5 (E = 51 MPa and σ = 2 MPa) with respect to the other samples, i.e.: M (E = 47 MPa and σ = 1.8 MPa) and MT10 (E = 32 MPa and σ = 1.4 MPa). The acellular in vitro bioactivity experiment confirmed apatite formation on the surfaces of all samples for various periods of soaking time. Based on cell study, the sample which possessed favorable mechanical behavior (MT7.5) supported attachment and proliferation of osteoblastic cells. These results revealed that the MT7.5 scaffold with improved mechanical and biological properties could have a potential to be used in bone substitute.

Effect of Tricalcium Magnesium Silicate Coating on the Electrochemical and Biological Behavior of Ti-6Al-4V Alloys

In the current study, a sol-gel-synthesized tricalcium magnesium silicate powder was coated on Ti-6Al-4V alloys using plasma spray method. Composition of feed powder was evaluated by X-ray diffraction technique before and after the coating process. Scanning electron microscopy and atomic force microscopy were used to study the morphology of coated substrates. The corrosion behaviors of bare and coated Ti-6Al-4V alloys were examined using potentiodynamic polarization test and electrochemical impedance spectroscopy in stimulated body fluids. Moreover, bare and coated Ti-6Al-4V alloys were characterized in vitro by culturing osteoblast and mesenchymal stem cells for several days. Results demonstrated a meaningful improvement in the corrosion resistance of Ti-6Al-4V alloys coated with tricalcium magnesium silicate compared with the bare counterparts, by showing a decrease in corrosion current density from 1.84 μA/cm2 to 0.31 μA/cm2. Furthermore, the coating substantially improved the bioactivity of Ti-6Al-4Valloys. Our study on corrosion behavior and biological response of Ti-6Al-4V alloy coated by tricalcium magnesium silicate proved that the coating has considerably enhanced safety and applicability of Ti-6Al-4V alloys, suggesting its potential use in permanent implants and artificial joints.

Effect of ball milling time on the synthesis of nanocrystalline merwinite via mechanical activation and heat treatment

Abstract Nanocrystalline merwinite was successfully synthesized by mechanical activation of a mixture of magnesium hydroxide, calcium oxide and silica gel powders followed by heat treatment. The phase development and various physical properties were investigated as a function of milling time using X-ray diffraction, scanning electron microscopy, simultaneous thermal analysis, particle size analysis and transmission electron microscopy. The results showed that formation of merwinite in annealed powders was enhanced by increasing the milling time. Nanocrystalline merwinite powder with an average crystallite size of about 36 nm was obtained after 30 hours of ball milling and subsequent annealing in 900 °C for 1 hour.