The Effect of Adding V and Nb Microalloy Elements on the Bake Hardening Properties of ULC Steel before and after Annealing.

Bake hardening (BH) is a vital part of special steel production. Studies in this field have focused on steels under homogeneous yielding, but until now, none have been conducted on the phenomena that occur for steels under heterogeneous yielding. In the current study, the effect of adding Nb and V alloying elements on the strength of ultra-low carbon (ULC) steel after bake hardening was investigated. The effects of pre-strain, grain size, and recrystallization annealing temperature were analyzed, as well as the effect of Nb and V on the yield stress caused by the bake hardening process. For this purpose, five types of alloys with different V and Nb contents were melted, cast in an induction furnace, and subjected to hot hammering and hot rolling. Then, cold rolling was applied to the samples by ~80%. To eliminate the effects of cold working, tensile samples were subjected to recrystallization annealing at 750 and 800 °C for 30 min, and the samples were quickly quenched in a mixture of a NaCl solution and ice. The annealed samples were subjected to a pre-tensile strain in the range of 2-12% and then aged in a silicone oil bath at 180 °C for 30 min. Then they were subjected to a tensile test. The obtained results showed that with the increase of the pre-strain and the annealing temperature, the values of baking hardness increased. The presence of V in the composition of steel reduced the annealing temperature.

Hemocompatible and Bioactive Heparin-Loaded PCL-α-TCP Fibrous Membranes for Bone Tissue Engineering.

The combination of bioactive components such as calcium phosphates and fibrous structures are encouraging niche-mimetic keys for restoring bone defects. However, the importance of hemocompatibility of the membranes is widely ignored. Heparin-loaded nanocomposite poly(ε-caprolactone) (PCL)-α-tricalcium phosphate (α-TCP) fibrous membranes are developed to provide bioactive and hemocompatible constructs for bone tissue engineering. Nanocomposite membranes are optimized based on bioactivity, mechanical properties, and cell interaction. Consequently, various concentrations of heparin molecules are loaded within nanocomposite fibrous membranes. In vitro heparin release profiles reveal a sustained release of heparin over the period of 14 days without an initial burst. Moreover, heparin encapsulation enhances mesenchymal stem cell (MSC) attachment and proliferation, depending on the heparin content. It is concluded that the incorporation of heparin within TCP-PCL fibrous membranes provides the most effective cellular interactions through synergistic physical and chemical cues.

Preparation and biocompatibility evaluation of bioactive glass-forsterite nanocomposite powder for oral bone defects treatment applications.

Bone defects which emerge around dental implants are often seen when implants are placed in areas with insufficient alveolar bone, in extraction sockets, or around failing implants. Bone regeneration in above-mentioned defects using of bone grafts or bone substitutes may cure the long-term prognoses of dental implants. Biocompatibility, bioactivity and osteogenic properties are key factors affecting the applications of a bone substitute. This study was aimed at preparation, characterization, biocompatibility and bioactivity evaluation of the bioactive glass-forsterite nanocomposite powder as a desired candidate for oral bone defect treatments. Nanocomposite powders containing 58S bioactive glass and different amounts of forsterite nanopowder were synthesized in situ by sol-gel technique. Characterization of the prepared nanocomposite powders and their cytotoxicity assessment was performed via MTT test. Bioactivity assessment was done by immersing the prepared powder in the simulated body fluid (SBF). Results showed that nanocomposite powders containing forsterite with crystallite size of 20-50nm were successfully fabricated by calcination at 600°C. The prepared bioactive glass-forsterite nanocomposite powders revealed high in vitro biocompatibility; besides, the nanocomposite containing 20wt.% forsterite showed a substantial increase in the cell viability compared with control groups. During immersion in SBF, the formation of apatite layer confirmed the bioactivity of bioactive glass-forsterite nanocomposite powders. According to the results, the fabricated nanocomposite powders can be introduced as a promising candidate for oral bone imperfection treatments and hard tissue mend.

PCL-forsterite nanocomposite fibrous membranes for controlled release of dexamethasone.

The well-known treatment of the alveolar bone defects is guided tissue regeneration (GTR). Engineered membranes combined with osteo-differentiation factors have been offered a promising strategy for GTR application. Recently, poly(ε-caprolactone) (PCL)-forsterite (PCL-F) nanocomposite fibrous membranes have been developed. However, PCL-F membranes could not promote bone tissue regeneration. The aim of this research is to encapsulate an osteogenic factor [dexamethasone (DEX)] in PCL-F membranes and evaluate the effects of forsterite nanopowder (particle size = 25-45 nm) and fiber organization on DEX delivery for GTR application. The hypothesis is that the release kinetic and profile of DEX could be controlled through variation of forsterite content (0, 5 and 10 wt%) and fiber arrangement (aligned and random). Results demonstrated while DEX release was sustained over a period of 4 weeks, its kinetic was governed by the membrane architecture and composition. For example, aligned PCL-F nanocomposite fibrous membrane consisting of 10 %(w/v) forsterite nanopowder exhibited the least initial burst release (13 % release in the first 12 h) and allowed sustained release of DEX. Additionally, forsterite nanopowder inclusion changed the kinetic of DEX release from Fickian diffusion to an anomalous transport. The bioactivity of released DEX was estimated using culturing the stem cells from human exfoliated deciduous teeth (SHED) on the membranes. Results demonstrated that proliferation and osteogenic differentiation of SHED could be governed by DEX release process. While DEX release from the membranes decreased SHED proliferation, stimulated the matrix mineralization. Our finding indicated that aligned PCL-F/DEX membrane could be used as a carrier for the sustained release of drugs relevant for GTR trophy.

Fluoride release and bioactivity evaluation of glass ionomer: Forsterite nanocomposite.

BACKGROUND: The most important limitation of glass ionomer cements (GICs) is the weak mechanical properties. Our previous research showed that higher mechanical properties could be achieved by addition of forsterite (Mg2SiO4) nanoparticles to ceramic part of GIC. The objective of the present study was to fabricate a glass ionomer- Mg2SiO4 nanocomposite and to evaluate the effect of addition of Mg2SiO4 nanoparticles on bioactivity and fluoride release behavior of prepared nanocomposite. MATERIALS AND METHODS: Forsterite nanoparticles were made by sol-gel process. X-ray diffraction (XRD) technique was used in order to phase structure characterization and determination of grain size of Mg2SiO4 nanopowder. Nanocomposite was fabricated via adding 3wt.% of Mg2SiO4 nanoparticles to ceramic part of commercial GIC (Fuji II GC). Fluoride ion release and bioactivity of nanocomposite were measured using the artificial saliva and simulated body fluid (SBF), respectively. Bioactivity of specimens was investigated by Fourier transitioned-infrared spectroscopy (FTIR), scanning electronmicroscopy (SEM), Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and registration of the changes in pH of soaking solution at the soaking period. Statistical analysis was carried out by one Way analysis of variance and differences were considered significant if P < 0.05. RESULTS: The results of XRD analysis confirmed that nanocrystalline and pure Mg2SiO4 powder was obtained. Fluoride ion release evaluation showed that the values of released fluoride ions from nanocomposite are somewhat less than Fuji II GC. SEM images, pH changes of the SBF and results of the ICP-OES and FTIR tests confirmed the bioactivity of the nanocomposite. Statistical analysis showed that the differences between the results of all groups were significant (P < 0.05). CONCLUSION: Glass ionomer- Mg2SiO4 nanocomposite could be a good candidate for dentistry and orthopedic applications, through of desirable fluoride ion release and bioactivity.