Effect of sodium chloride as a porogen agent in mechanical properties of PLGA/HA nanocomposite scaffolds.

In this study, the novel poly (lactic-co-glycolic acid)-Hydroxyapatite nanoparticles (PLGA/HA) nanocomposite scaffolds were fabricated with solvent casting and particulate leaching (SCPL) method. The role of sodium chloride (NaCl) particles with diameters of 250-400 µm as porogen agent in the mechanical strength of the produced scaffolds was evaluated. The prepared scaffolds were characterized using Fourier transform infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal gravimetric analysis (TGA) and compressive tests. The results showed the high compressive strength and homogenous porous structures for PLGA/HA nanocomposite scaffolds compared to pure PLGA due to the presence of HA nanoparticles in nanocomposites. Furthermore, the compressive strength of nanocomposite scaffolds increased by varying the weight ratio of hydroxyapatite nanoparticles to polymer (0, 20, 40 wt%) at constant salt ratio and decreased by increasing the weight ratio of salt particles to polymer from 1 to 3 wt% due to more porosity in nanocomposite scaffolds. These results confirmed that not only the nanocomposite scaffolds exhibited high mechanical properties, homogenous structures, as well as good porosity but also, they could be useful for bone tissue application.

Evaluating morphology and mechanical properties of glass-reinforced natural hydroxyapatite composites.

Hydroxyapatite has been used in a wide variety of biomedical applications and it can be produced from natural resources such as bovine bone. This material does not have acceptable mechanical properties by itself. In the present work, hydroxyapatite composites with different weight percentages of sodalime glass were made and sintered at different temperatures (800-1200°C). Eventually the properties such as density, micro hardness, compressive strength and wear of specimens were evaluated. Specific percentages of glass additive increased the density and hardness of specimens due to increasing the sintering temperature. The hardness and density of specimens were decreased with higher percentage of glass additive. Moreover, the results of compressive test showed that increasing the glass addition increases the compressive performance. Furthermore, the SEM micrographs on worn specimens showed that the mechanism of wear was abrasive.

Development of wear resistant NFSS-HA novel biocomposites and study of their tribological properties for orthopaedic applications.

Implants made of nickel free austenitic stainless steel can reduce the toxic effect of released nickel ion and compounds from the conventional stainless steels. On the other hand, hydroxyapatite is a ceramic which has been used in orthopaedic applications due to its good osteoconductivity, biocompatibility and bioactivity. However, there is no evidence in the literature up to now on producing composites based on nickel free stainless steel and hydroxyapatite and study of their tribology. The aim of this work was to produce novel biocomposites made up of nickel free stainless steel with hydroxyapatite (prepared by heat treating bone ash) and studying their tribology under various loads in air and in Ringer's physiological solution. Different amounts of hydroxyapatite powder (10, 20, 30 and 40% Vol.) were added to this nickel free stainless steel powder to get the biocomposites. Variation of their density, hardness, wear resistance and friction with the ceramic (hydroxyapatite) content and wear load were investigated in air and in Ringer's solution. The density of the composites was decreased by increasing the volume percentage of the hydroxyapatite, while wear resistance of the composites was increased. The wear mechanism of these composites was changed by increasing the wear load and consequently the volume loss was enhanced dramatically. Furthermore, by increasing the sliding distance, the rate of volume loss was decreased slightly. The friction coefficient of the composites was also decreased by increasing the weight percentage of hydroxyapatite. Effect of the physiological Ringer's solution on wear resistance and friction coefficient of the composites was nearly negligible. The wear mechanisms of the samples were identified by studying the SEM images of the worn surfaces of the tested samples in different wear loads and HA contents.

Analysis of ligand binding to proteins using molecular dynamics simulations.

This work aims to explore theoretically the molecular mechanisms of ligand binding to proteins through the use of molecular dynamics simulations. The binding of sodium dodecyl sulfate (SDS) to cobra cardio toxin A3 (CTX A3) and thiourea (TOU) to lysozyme have been chosen as the two model systems. Data acquisitions were made by Gromacs software. To begin with, the collisions of ligand molecules with every residue of CTX A3 and lysozyme were evaluated. With this information in hand, the average numbers of collisions with each residue was defined and then assessed. Next, a measure of the affinity of a residue, P(i), referred to as conformational factor, toward a ligand molecule was established. Based on the results provided, all site-making residues for CTX A3 and lysozyme were identified. The results are in good agreement with the experimental data. Finally, based on this method, all site-making residues of bovine carbonic anhydrase (BCA) toward the SDS ligand were predicted.