Development and characterization of smart composites reinforced with fibrillated cellulose and nickel-titanium alloy.

The current study presents the synergistic effects of fibrillated cellulose (FC) and nickel-titanium (NiTi) alloy on the performance properties of smart composites. Epoxy resin was reinforced with loadings of 1 %, 3 %, and 5 % FC and 3 % NiTi. The composites were produced using the casting method. The morphological properties have been analyzed using scanning electron microscopy (SEM). For mechanical properties, yield strength, modulus of elasticity, hardness, and impact energy were determined. The corrosion rate was determined via electrochemical corrosion testing. The recovery test was used to measure the shape-memory of the composites. The self-healing of the artificial defect in the composites was observed using a thermal camera. The yield strength, modulus of elasticity, hardness, and impact energy of composites reinforced with 5 % FC and 3 % NiTi increased by 168.2 %, 290 %, 33.3 %, and 114.3 %, respectively, compared to pure epoxy resin. There has been a 56.3 % decrease in the corrosion rate. The percentage of composites that returned from the final state to the original state after a deformation was 4 %. Self-healing analysis revealed that the scratch defect in composites was healed after 24 h. It is concluded that smart composites can be used in the aviation and automotive industries.

Corrosion, ion release, and surface hardness of Ti-6Al-4V and cobalt-chromium alloys produced by CAD-CAM milling and laser sintering.

STATEMENT OF PROBLEM: How the corrosion properties of cobalt-chromium (Co-Cr) and Ti (Ti-6Al-4V) alloys, frequently used in dental prostheses, are affected by different production methods is unclear. PURPOSE: The purpose of this in vitro study was to compare Co-Cr and Ti-6Al-4V alloys produced by computer-aided design and computer-aided manufacturing (CAD-CAM) milling or laser sintering in terms of corrosion, ion release, and surface hardness. MATERIAL AND METHODS: Co-Cr and Ti-6Al-4V specimens were produced by CAD-CAM milling and direct metal laser sintering/selective laser sintering techniques. Testing included Vickers hardness and then open circuit potential (OCP), Tafel extrapolation, and static immersion to determine the corrosion behavior. The study used an inductively coupled plasma mass spectrometer to measure ion release. The data were analyzed by using the Kruskal-Wallis and Mann-Whitney U tests, with Bonferroni correction (α=.05). RESULTS: The Ti-6Al-4V laser-sintered group showed the highest Vickers hardness value (P<.008), the lowest OCP value (P<.008), and the lowest corrosion potential (Vcorr) value (P<.008). The corrosion current density (Icorr) level of the Co-Cr CAD-CAM milling group was statistically significantly lower than that of the Ti-6Al-4V CAD-CAM milling and the Ti-6Al-4V laser-sintered groups (P<.008). The highest weight change was observed in the Ti-6Al-4V laser-sintered group. The Co, Cr, and Ti ion emissions were higher in specimens produced by laser sintering (P<.05), and no statistically significant difference in terms of Al and V oscillations was found among the groups (P>.05). CONCLUSIONS: Ti-6Al-4V alloys may be a good alternative for patients with Co-Cr allergies, but as per the results of this study, Co-Cr still seems more suitable for clinical use.

Production and characterization of highly porous biodegradable Mg alloy scaffolds containing Ca, Zn and Co.

In this study, highly porous Mg-Ca-Zn-Co alloy scaffolds for tissue engineering applications were prepared by powder metallurgy based space holder method. Mg-Ca-Zn-Co alloy foam can be used as a scaffold material for hard tissue generation. Mechanical properties of the porous specimens are close to cancellous bone. Increasing Zn content in the alloy decreased the Mg grain size and enhanced the mechanical properties. Increasing Zn content of the alloy from 1.0 to 8.0 wt.% increased the Young's modulus from 12 GPa to 23 GPa. Ca addition prevented the oxidation of the specimens during sintering. Electrochemical corrosion behaviour of the specimens was examined in the simulated body fluid. Corrosion rate was decreased with Zn addition up to 3.0 wt.% and then increased. Increasing Co content increased the corrosion rate. Weight loss/gain and Mg ion release values were increased with increasing immersion time. Weight loss of the specimen was initially decreased with Zn addition up to about 3% and then increased.

Production and Precipitation Hardening of Mg-Ca-Zn-Co Alloy for Tissue Engineering.

In this study, Mg-Ca-Zn-Co alloy specimens for biomedical applications were produced by the powder metallurgy method. The Mg-Ca-Zn-Co alloy could be used as a scaffold material in tissue engineering applications. Electrochemical corrosion behavior of the specimens was investigated in simulated body fluid environment. Electrochemical corrosion resistance of the specimens was increased with increasing Zn and Ca contents of the alloy up to an optimum composition and then decreased. Optimum values for Ca and Zn additions were about 0.7 wt.% and 3.0 wt.% respectively. Young's modulus values of the specimens were determined by nondestructive ultrasonic measurement. Alloying element addition increased the Young's modulus of the specimens. Precipitation hardening of the Mg-Ca-Zn-Co alloy increased the Young's modulus and the corrosion rate of the specimens.

Photocatalytical Antibacterial Activity of Mixed-Phase TiO2 Nanocomposite Thin Films against Aggregatibacter actinomycetemcomitans.

Mixed-phase TiO2 nanocomposite thin films consisting of anatase and rutile prepared on commercially pure Ti sheets via the electrochemical anodization and annealing treatments were investigated in terms of their photocatalytic activity for antibacterial use around dental implants. The resulting films were characterized by scanning electron microscopy (SEM), and X-ray diffraction (XRD). The topology was assessed by White Light Optical Profiling (WLOP) in the Vertical Scanning Interferometer (VSI) mode. Representative height descriptive parameters of roughness R a and R z were calculated. The photocatalytic activity of the resulting TiO2 films was evaluated by the photodegradation of Rhodamine B (RhB) dye solution. The antibacterial ability of the photocatalyst was examined by Aggregatibacter actinomycetemcomitans suspensions in a colony-forming assay. XRD showed that anatase/rutile mixed-phase TiO2 thin films were predominantly in anatase and rutile that were 54.6 wt% and 41.9 wt%, respectively. Craters (2-5 µm) and protruding hills (10-50 µm) on Ti substrates were produced after electrochemical anodization with higher R a and R z surface roughness values. Anatase/rutile mixed-phase TiO2 thin films showed 26% photocatalytic decolorization toward RhB dye solution. The number of colonizing bacteria on anatase/rutile mixed-phase TiO2 thin films was decreased significantly in vitro. The photocatalyst was effective against A. actinomycetemcomitans colonization.

Characterization of 17-4 PH stainless steel foam for biomedical applications in simulated body fluid and artificial saliva environments.

Highly porous 17-4 PH stainless steel foam for biomedical applications was produced by space holder technique. Metal release and weight loss from 17-4 PH stainless steel foams was investigated in simulated body fluid and artificial saliva environments by static immersion tests. Inductively coupled plasma-mass spectrometer was employed to measure the concentrations of various metal ions released from the 17-4 PH stainless steel foams into simulated body fluids and artificial saliva. Effect of immersion time and pH value on metal release and weight loss in simulated body fluid and artificial saliva were determined. Pore morphology, pore size and mechanical properties of the 17-4 PH stainless steel foams were close to human cancellous bone.

Biocompatibility of 17-4 PH stainless steel foam for implant applications.

In this study, biocompatibility of 17-4 PH stainless steel foam for biomedical implant applications was investigated. 17-4 PH stainless steel foams having porosities in the range of 40-82% with an average pore size of around 600 µm were produced by space holder-sintering technique. Sintered foams were precipitation hardened for times of 1-6 h at temperatures between 450-570 °C. Compressive yield strength and Young's modulus of aged stainless steel foams were observed to vary between 80-130 MPa and 0.73-1.54 GPa, respectively. Pore morphology, pore size and the mechanical properties of the 17-4 PH stainless steel foams were close to cancellous bone. In vitro evaluations of cytotoxicity of the foams were investigated by XTT and MTT assays and showed sufficient biocompatibility. Surface roughness parameters of the stainless steel foams were also determined to characterize the foams.