Hydroxyapatite coating of AZ31 magnesium alloy by a solution treatment and its corrosion behavior in NaCl solution

Hydroxyapatite (HAp) coatings were formed directly on AZ31 magnesium alloy and pure Mg in a 250 mmol/L C₁₀H₁₂N₂O₈Na₂Ca aqueous solution of pH 8.9. Treatment time was varied from 2 h to 6 h. Crystal phase, morphology and composition of the coatings were investigated. Immersion and polarization tests in a 3.5 wt.% NaCl solution were performed to examine the corrosion behavior of the HAp-coated specimens. The HAp coating of AZ31 with short treatment time had defects which decreased with an increase in treatment time. The HAp coatings of AZ31 consisted of an inner dense layer and an outer coarse layer in the similar manner for pure Mg. The inner layer on AZ31 was composed of dome-shape precipitates densely packed. The outer layer was composed of rod-like crystals growing from each dome in the radial direction. The (002) plane of HAp of inner layer and rod-like crystals roughly oriented to the substrate. Magnesium ion-release and corrosion current density were remarkably reduced with HAp coatings. Each of these values was on the same order of magnitude between HAp-coated AZ31 and pure Mg. The ion release from AZ31 slightly decreased with an increase in treatment time. The original inner dense layer of AZ31 remained after the immersion. It is suggested that the protectiveness of HAp coating relays on the inner layer and does not significantly depend on the kind of Mg substrate.     

Morphology of hydroxyapatite coated nanotube surface of Ti-35Nb-xHf alloys for implant materials

The purpose of this research is to study the morphology of hydroxyapatite coated nanotube surface of Ti-35Nb-xHf for implant materials using various experiments. For this study, Ti-35Nb-xHf (x = 0, 3, 7 and 15 wt.%) alloys were prepared by arc melting and heat treated for 12 h at 1000 °C in an argon atmosphere and then water quenching. Nanotube formation on the Ti-35Nb-xHf alloys was achieved by anodizing in H₃PO₄ electrolytes containing 0.8 wt.% NaF at room temperature. Anodization was carried out using an electrochemical method and all experiments were conducted at room temperature. Hydroxyapatite (HA) was deposited on the nanotubular Ti-35Nb-xHf alloys surface for the biomaterials by radio-frequency (RF) magnetron sputtering method. The morphologies of nanotubular and HA coated surface were characterized by X-ray diffractometer (XRD), optical microscopy (OM), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM). The wettability of HA coated surface was measured by contact angle goniometer.The microstructure of Ti-35Nb-xHf alloys was transformed needle-like to equiaxed structure with Hf content and α″ phase decreased, whereas β phase increased as Hf content increased. HA coating surface was affected by microstructure of bulk and morphology of nanotube formation. In case of low Hf content, tip of nanotube formed at β phase was coated with HA film, whereas α″ phase was not coated with HA film. In case of high Hf content, nanotube surface was coated uniformly with HA film. The wettability of HA coated nanotubular surface was higher than that of non coated samples.     

Nanostructure effects on the bioactivity of forsterite bioceramic

Recently, forsterite (Mg₂SiO₄) has been introduced as a possible bioceramics due to its good biocompatibility. It has a better bending strength and fracture toughness than those of commercially available hydroxyapatite ceramics. In this study, nanostructure effects on the bioactivity of forsterite powder were investigated. For synthesizing forsterite powder, talc and magnesium carbonate powders were mechanically activated for various times. Then, the prepared powders were mixed with ammonium chloride (as a catalyst) and annealed at different temperatures. For bioactivity evaluation, the obtained forsterite powders were pressed in the form of tablets and then immersed in simulated body fluid (SBF). The results showed that nanostructure forsterite powder with crystallite size of about 31 nm, unlike micrometer-sized forsterite, possessed apatite formation ability and its bioactivity, biocompatibility, and good mechanical properties make it a suitable candidate for load bearing application in bone implant materials and open new horizons in tissue engineering.     

Incorporation of chitosan nanoparticles into silk fibroin-based porous scaffolds: Chondrogenic differentiation of stem cells

A silk fibroin-chondroitin sulfate-sodium alginate (SF-CHS-SA) porous scaffold containing chitosan nanoparticles (NPs) was investigated. The proliferation of adipose-derived stem cells (ASCs) was studied by SEM, fluorescent microscopy, alcian blue staining, dimethylmethylene blue assay, and real-time polymerization chain reaction. The results showed that incorporation of NPs into the scaffold improved compressive modulus (5.6 ± 0.15 MPa). The amount of glycosaminoglycan expression of the ASCs was reached to 8.9 ± 0.3 µg/mL. The gene expressions of aggrecan, collagen II, and SOX9 of the ASCs were significantly improved. This study revealed that the prepared scaffold can be used as a substrate for cartilage tissue engineering.     

Structure and properties of titania reinforced nano-hydroxyapatite/gelatin bio-composites for bone graft materials

This work deals with the preparation of ceramic composites to be employed for the development of load bearing bone substitutes, made of inorganic minerals of needle like nano hydroxyapatite [nHAp: Ca₁₀(PO₄)₆(OH)₂] with bioinert titania as a reinforcing phase and gelatin as protein that mimic the natural bone exhibiting improved biomechanical features. As a monolithic, use of nHAp is limited for biomedical applications because of its inherent low fracture toughness and lack of flexibility. Hence, the incorporation of ceramics such as alumina, zirconia and titania is considered necessary to boost its mechanical properties. The composites of nHAp/TiO₂/gelatin in different weight percentage were prepared by phase separation technique. The identification and morphology of chemically synthesized nHAp particles were determined by XRD, FTIR and SEM analyses. The porosity of scaffolds varied from 77% to 82%. FTIR and XRD analyses showed the presence of molecular interactions and chemical linkages between nHAp particles, titania and gelatin matrix. The compressive strength of titania reinforced nanocomposites scaffolds could be elevated up to 10.15 MPa while those of nHAp/gelatin were 4.87 MPa. These results show that newly developed nHAp/TiO₂/gelatin composites may be superior for bone tissue engineering.     

Preliminary experiments on metallisation of ceramic oxide superconductors

Abstract

The present paper briefly reports on preliminary experiments on two new methods for the metallisation of ceramic oxide high temperature superconductors )HTS compounds): sinter-permeate silver and chemically precipitated silver. By using well characterised HTS samples for the measurement of superconducting properties it is shown that successful metallisation and jointing were obtained. The two methods are considered to have potential for further development and application in this field.     

Synthesis and characterization of positively charged interpenetrating double-network hydrogel matrices for biomedical applications

In this study, positively charged interpenetrating double-network (DN) hydrogels of polyvinyl alcohol/polyacrylamide (PVA/PAm) were prepared using bifunctional cationic salt as a crosslinker. The cationic salts were synthesized by the Michael-addition of piperazine (PZ) with butanediol diacrylate (BDDA)/hexanediol diacrylate (HDDA) separately followed by the methylation of the products. The chemical characterization of the quaternary salts was performed using ATR-FTIR and NMR (¹H, ¹³C, DEPT) spectroscopy. The zeta potential of the cationic salts was found to be in the range of 17.6 ± 8.03–20.3 ± 10.1 mV for various monomers. Chemical crosslinking (free radical polymerization) and physical crosslinking (freeze–thaw) techniques were employed to crosslink PAm and PVA, respectively. The quaternized salt of BDDA and PZ was used to crosslink the PAm hydrogel network. The thermal stability and the compression modulus of the hydrogel increased, while the displacement value and the water absorption capacity decreased when crosslinker concentration was increased from 1.0 to 4.0 mol%. The excellent cell viability (?94%) and gel content (?92%) suggest that these matrices can be utilized as future biomaterials for biomedical applications.     

Biomass as Feedstock in the Chemical Industry – An Examination from an Exergetic Point of View

Crude oil is the most important raw material for the chemical industry. Due to the continually rising price of crude oil, alternative carbon sources are becoming increasingly important. Biomass is basically the only available renewable carbon source. Because the chemical composition of biomass differs from fossil raw materials, the raw‐material change also offers many chances for new product properties and applications. At the same time, the chemical processes have to be redesigned if the feedstock changes to biomass. Here, the effects of a raw‐material change are examined on a rather generic level. The study is based on exergy balances and indicates that it is exergetically advisable to reconsider the previously established system of platform and basic chemicals. In general, exergy losses can be minimized if the synthesis pathways leading to the final products are adapted to the chemical structure of biomass.