Synthesis and Characterization of Silver-containing Sol-gel Derived Bioactive Glass Coating

Silver doped-bioactive glass coatings offer the possibility of bioactivation, corrosion protection and infection prevention of metallic implants. A certain composition of glass (54SiO₂–36CaO–8P₂O₅–2Ag₂O (wt %)) was coated on titanium substrate using dip coating method by 1 cm/min withdrawal rate with controlling the effective factors like viscosity of sol, matching thermal expansion coefficient (a), heating rate and etc., then heated at 700°C for 1h at the rate of 3°C/min. Scanning electron microscopy (SEM) depicted a crack-free and homogeneous coating. The energy dispersive X-ray spectroscopy corresponding to the SEM image affirmed the presence of Si, P, Ca and Ag as main elements of Ag-BG coating. Contact angle measurement confirmed positive effect of silver on the wettability and adhesion of Ag-BG on the Ti surface. X-ray Diffraction analysis confirmed the amorphous nature of Ag-BG. Fourier transform infrared spectroscopy confirmed successful inclusion of silver in glass structure. X-ray Fluorescence Spectroscopy demonstrated that composition of Ag-BG was very close to the designed composition. Results of acellular in vitro bioactivity test showed formation of ball-like particles including a layer of entangled rough apatite crystals on the surface.     

Synthesis,characterization and biocompatibility evaluation of sol–gel derived bioactive glass scaffolds prepared by freeze casting method

In this study, a new class of bioactive glass scaffolds was prepared through freeze casting method for bone tissue engineering applications. After analyzing the structural characteristics of the scaffolds, in vitro biological evaluations were assessed through monitoring alkaline phosphatase (AP) activity of osteoblast cells and soaking in simulated body fluid (SBF) for different time intervals. It was shown that the scaffolds consisted of bioactive glass plates with interconnected pores between them, aligned along the ice growth direction. The ability of the scaffolds for supporting the growth of human fetal osteoblastic cells (hFOB 1.19) was approved. Moreover, inductively coupled plasma-atomic emission spectrometry (ICP-AES) showed meaningful compositional changes of calcium, phosphorus and silicon in SBF solution, indicating the apatite forming ability of the scaffolds. The present investigation revealed that freeze casting could be an effective method for the preparation of highly bioactive scaffolds. In addition, the scaffolds proved to be highly compatible for the proposed works in vivo.     

Synthesis of silicon-substituted hydroxyapatite by a hydrothermal method with two different phosphorous sources

Silicon-substituted hydroxyapatite (Si-HA) with up to 1.8 wt% Si content was prepared successfully by a hydrothermal method, using Ca(NO₃)₂, (NH₄)₃PO₄ or (NH₄)₂HPO₄ and Si(OCH₂CH₃)₄ (TEOS) as starting materials. Silicon has been incorporated in hydroxyapatite (HA) lattice by partially replacing phosphate (PO₄³⁻) groups with silicate (SiO₄⁴⁻) groups resulting in Si-HA described as Ca₁₀(PO₄)_6−x(SiO₄)_x(OH)_2−x. X-ray diffraction (XRD), Fourier transform IR spectroscopy (FTIR), inductively coupled plasma AES (ICP-AES) and scanning electron microscopy (SEM) techniques reveal that the substitution of phosphate groups by silicate groups causes some OH⁻ loss to maintain the charge balance and changes the lattice parameters of HA. The crystal shape of Si-HA has not altered compared to silicon-free reference hydroxyapatite but Si-incorporation reduces the size of Si-HA crystallites. Based on in vitro tests, soaking the specimens in simulated body fluid (SBF), and MTT assays by human osteoblast-like cells, Si-substituted hydroxyapatite is more bioactive than pure hydroxyapatite.     

Development of an electrochemical sulfite biosensor by immobilization of sulfite oxidase on conducting polyaniline film

In this work, a biosensor was developed for the determination of sulfite. The bioelectrochemical response of the enzyme-modified electrode based on electrochemical incorporation of sulfite oxidase into polyaniline aluminum modified electrode was investigated. Electropolymerization of polyaniline and simultaneous immobilization of sulfite oxidase on the aluminum were performed in an aqueous solution containing sulfite oxidase. The sulfite biosensor constructed by cycling the potential scan between +1.2 and ?0.5 V vs. saturated calomel electrode (SCE) that showed a sensitive response to sulfite with a linear calibration graph in the concentration ranges of 0.006–5 mM sulfite and detection limit 0.002 mM sulfite (S/N = 3). The obtained results from the stability tests of the biosensor show that the sulfite biosensor can be used for two different applications, for immediate usage and long term usage. Also, the bioelectrochemical response of the enzyme-modified electrode as a sulfite biosensor was evaluated at different experimental conditions. The optimum pH when using phosphate buffer and temperature were 8.5 and 35 °C, respectively. Finally, the apparent Michaelis–Menten constant was determined which has value of 0.365 mM which is really close to the magnitude of the Michaelis–Menten constant of free sulfite oxidase that shows the enzyme was not chemically modified and has its usual kinetic reaction.     

Synthesizing and Characterizing of Gelatin-Chitosan-Bioactive Glass (58s) Scaffolds for Bone Tissue Engineering

Nowadays repairing and regenerating of lost or damaged tissue still remain an important challenge in clinical techniques. Due to the variety of available bone grafts, different types of biodegradable materials are being utilized as a scaffold implant. The basic structure of the bone is an excellent natural composite which contains varieties of polymers and ceramics; therefore, it is important to manufacture a bone scaffold featuring sufficient mechanical strength, a good degree of biocompatibility, biodegradation and an increased rate of formation of new tissue. Bioactive glass has an appealing characteristic which can be utilized for repairing purposes as well as to cause a rapid response from the bone graft. In this study, a composite scaffold based on polymer matrix (gelatin-chitosan) and bioactive glass 58s was synthesized in the laboratory. Five samples of polymer scaffold with different proportions of bioactive glass were designed and investigated. The scaffolds were dried with freeze dryer, and a spongy structure was generated. The composite survey was carried out through FTIR technique to examine the crystallization of the structure, XRD to examine the morphology of the porosities, and SEM to examine the size of porosities and formation of apatite. This study reveals that the size of porosities is about 170–320 μm, which is suitable for angiogenesis and cell growth in the bone. The combination of enhanced properties and the formation of apatite on the surface of the scaffolds make them an ideal option as a bone substitute.     

In vitro biomimetic deposition of apatite on alkaline and heat treated Ti6A14V alloy surface

Titanium alloy (Ti6A14V) substrates, having the ability of biomimetic calcium phosphate-based materials, especially hydroxyapatite deposition in a simulated body fluid (SBF) means of chemical treatment (alkaline treatment) and subsequent heat treatment, was studied. The effects of alkaline treatment time, concentration and heat treatment temperature on the formation of calcium phosphate (carbonate-hydroxyapatite) on Ti6A14V surface were examined. For this purpose, the metallic substrates were treated in 0, 5 and 10 M NaOH solutions at a temperature of 60 or 80°C for 1 and 3 days. Subsequently the substrate was heat-treated at 500, 600 and 700°C for 1 h for consolidation of the sodium titanate hydrogel layer. Finally, they were soaked in SBF for 1 and 3 days. The substrate surfaces were characterized by the techniques commonly used for bulk material such as scanning electron microscopy (SEM) and thin film X-ray diffraction (TF-XRD). With regard to the SEM and TF-XRD results, the optimum process consists of 3 days soaking in 5 M NaOH in 80°C and subsequent heat treatment at 600°C for 1h. It is worth mentioning that the results showed that the apatite formed within 3 days on the specimen surfaces, however, there was no sign of apatite formation in the control samples (without alkaline and heat treatment) which was treated for up to 3 days immersion in SBF.     

Synthesis of Submicron Nanocrystalline Y<Subscript>2</Subscript>O<Subscript>3</Subscript>: Eu Particles via Solvothermal Approach Using Surface Modifiers

In this paper, solvothermal synthesis of submicron nanocrystalline Y₂O₃: Eu particles with and without surface modifier (β-alanine and Tween-80) is investigated. X-ray diffraction ananlysis confirms the one-step formation of Y₂(OH)₅NO₃H₂O phase during solvothermal process and its conversion to Y₂O₃: Eu after heat treatment at 600 °C. Fourier transformation infrared spectroscopy showed that C=C, C–C and C–H peaks are corresponded to the surface modifiers i.e. tween-80 and β-alanine. Scanning electron microscopy and transmission electron microscopy images also showed that the modifier results in the particle morphology improvement from sheet-like to submicron spherical particles. Photoluminescence experiments indicated that the emission intensity increases due to the morphology modification.     

Effects of GNP on the mechanical properties and sliding wear of WC-10wt%Co cemented carbide

WC-10Co cemented carbides reinforced with 0, 0.5, 1, and 2 wt% graphene nanoplatelet (GNP) were fabricated by ball milling and spark plasma sintering (SPS). The microstructure, structural and phase analysis, hardness, and fracture toughness of WC-10Co/GNP composites were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and Vickers indenter. Tribological behaviors of the fabricated composites against an alumina counterface were studied using a pin on disk configuration. It was found that GNP refined the microstructure, increased the fracture toughness, and postponed the stable-to-unstable friction transition. While transgranular fracture and crack deflection were observed in the base composite, crack bridging, micro-crack formation, and crack deflection were the major toughening mechanisms in GNP-reinforced cemented carbides. The addition of 1 wt% GNP resulted in the highest hardness and wear resistance. However, at higher GNP contents, both hardness and wear resistance decreased due to the agglomeration of GNPs. Widespread abrasive grooving and Co binder extrusion were characterized as the main controlling mechanisms of wear in GNP-free cemented carbides. The wear of GNP-reinforced cemented carbides was dominated by the formation of a lubricating surface layer and its cracking or fragmentation. Plastic flow is much less likely to occur in the presence of GNPs.     

Synthesis,Characterization and Biological Evaluation of a New Sol-Gel Derived B and Zn-Containing Bioactive Glass: <Emphasis Type="Italic">In Vitro</Emphasis> Study

In this study we employed the sol-gel method to synthesize new CaO–P₂O₅–SiO₂–ZnO–B₂O₃ bioactive glasses. Three samples with various B₂O₃ content (5, 10 and 15 mol %) was prepared and their bioactivity were evaluated by immersion in simulated body fluid (SBF) and the glasses were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) and scanning electron microscopy (SEM). The experimental results revealed that with increasing the amount of boron content, a more crystalline domain can be observed in their XRD patterns and consequently the formation of hydroxyapatite (HA) increased. FTIR spectra showed that the sample containing 10 mol% of boron had the sharpest peaks attributed to the formation of hydroxyapatite. Biocompatibility of the samples was examined by MTT assay and alkaline phosphatase activity. The result ascertained that the synthesized bioactive glass had good biocompatibility and can serve as a bone substitute in bone defects.