Formation of hydroxyapatite layer on bioactive Ti and Ti–6Al–4V by simple chemical technique

Bioactive coatings on cp-Ti and Ti–6Al–4V were prepared by a simple chemical technique. Specimens of cp-Ti and Ti–6Al–4V were initially immersed in a 5 M NaOH solution at 60 °C for 24 h which resulted in the formation of a porous network structure composed of Na₂Ti₅O₁₁ and TiO₂. The specimens were then immersed in a Ca-rich solution either at 60 °C or at 36.5 °C for 24 h. During this treatment Na⁺ was released and Ti–OH groups were formed. Subsequently, TiO₂ dissociated from the Ti–OH group and combined with calcium ions to form calcium titanate (CaTiO₃), which was embedded in a titania gel layer during the immersion period. The specimens were then immersed in r-SBF at 36.5 °C for 1–30 days. After immersion in r-SBF for 3 days, HAp (hydroxyapatite) spheroids began to deposit on the substrates, and within a week the surfaces were covered. The HAp spheroids were 5 μm in size with a Ca/P ratio of 1.68 which was close to bone-like apatite (1.67). The average thicknesses of HAp layer after immersion in r-SBF for 3 days, 1 week, and 2 weeks were 3.8, 5.6, and 6.4 μm, respectively. A scratch test, used to evaluate the adhesive strength of the HAp layer, showed that the HAp layer was not scraped off until the applied load reached 26 N.     

Nano-Structured Sorbent Injection Strategies for Heavy Metal Capture in Combustion Exhausts

Nano-structured sorbent injection is a promising technique for heavy metal capture in combustion systems. The importance of sorbent injection strategies, including the form of the sorbent and its injection location for metal capture and removal is investigated in this study. A multi-component tri-modal aerosol dynamic model was employed to understand the evolution of heavy metals and sorbents, as well as their interactions in the incineration system. Experiments were conducted to assess the performance of in-situ generated SiO₂, compared with bulk Ti-PICL sorbent, in capturing lead and cadmium from a demilitarization incineration system. Nano-structured SiO₂ generated in-situ was found to be more efficient than the bulk Ti-PICL sorbent because it offers a higher external surface area for condensation. The sorbent injection location is important as it affects the physical properties of the sorbent and the pathway for heavy metal capture. Extensive sintering and reduction in the surface area were observed when sorbent was injected into high temperature flue gas, i.e., directly into the combustor. However, when injected into much lower temperature flue gas, the pathway for heavy metal capture was altered from condensation to inter-particle coagulation due to the nucleation of heavy metal species. This study further revealed that new emission standards can be readily met with an optimal sorbent injection strategy.     

Isolation and characterisation of a novel Podoviridae-phage infecting Weissella cibaria N 22 from Nham, a Thai fermented pork sausage

A novel Podoviridae lactic acid bacteria (LAB) phage from Nham, a Thai fermented pork sausage, is reported. From a total of 36 samples, 41 isolates of LAB were obtained and employed as hosts for the isolation of phages. From these LAB, only one phage, designated Φ 22, was isolated. The lactic acid bacterial isolate named N 22, sensitive to phage Φ 22 infection was identified by an API 50 CHL kit and N 22’s complete sequence of the 16S rDNA sequence. BLASTN analysis of the 16S rDNA sequence revealed a 99% similarity to the 16S rDNA sequence of Weissella cibaria in the GenBank database. Electron micrographs indicated that the phage head was icosahedral with head size and tail length of 92 × 50 nm and 27 nm, respectively. On the basis of the morphology, this phage belongs to the family Podoviridae. Host-range determination revealed that the phage Φ 22 was not capable of infecting the other 40 isolates of LAB and referenced Weissella strains used. A one-step growth experiment showed that the latent period and burst size were estimated at 110 min and 55 phage particles/infected cell, respectively. Furthermore, the phage was infective over a wide range of pH (pH 5.0-8.0) and the D time of Φ 22 was calculated as 88 s at 70 °C and 15 s at 80 °C. Phage titers decreased below the detection limit (20 PFU/ml) after heating for more than 60 s at 80 °C, or 20 s at 90 °C or less than 10 s at 100 °C. The results from the study of Nham revealed that Φ 22 was active against the potential starter culture (W. cibaria N 22) for Nham fermentation. Phage infection could adversely affect the fermentation process of Nham by delaying acidification when using W. cibaria N 22 as a starter. However, the results from a sensory test revealed that the panelists did not detect any defects in the final products. This is the first report on the isolation of W. cibaria phage.     

Charged fraction and electrostatic collection of ultrafine and submicrometer particles formed during O2-CO2 coal combustion

The charged fraction of submicrometer and ultrafine particles generated during bench scale coal combustion and the subsequent penetration of particles through a cylindrical-wire electrostatic precipitator (ESP) in O₂-CO₂ and O₂-N₂ environments were measured. In all combustion environments, natural particle charging within the combustor was not adequate for high efficiency particle collection in the ESP; thus, corona generation was necessary for enhanced particle charging. With a positive applied potential, the corona inception voltage and voltage required to reach a given current level in the ESP in gas mixtures composed of O₂ and CO₂ were higher than those composed of O₂ and N₂, while similar voltages were needed for negative corona generation. In positive coronas, particle penetration through the ESP in O₂-CO₂ environments was 1-2 orders of magnitude higher than in O₂-N₂ environments. Little difference in particle penetration between O₂-N₂ and O₂-CO₂ was seen in negative coronas.     

Partial characterisation of bacteriocins produced by lactic acid bacteria isolated from Thai fermented meat and fish products

Lactic acid bacteria (LAB) from Thai fermented meat and fish products were isolated. From a total of 93 samples, 152 isolates of lactic acid bacteria were obtained. Antimicrobial activity screening was performed using the agar spot test and the agar well diffusion method. Of the six isolates which produced antimicrobial activities against Weissella confusa N31, only isolate N23 was identified as Weissella cibaria (GenBank accession number AB494716.1) with 99% similarity by 16S rDNA sequence analyses. Complete inactivation of antimicrobial activity produced by W. cibaria N23 was observed after treatment of the bacteriocins with trypsin, actinase, protease XIII, ficin, trypsin from porcine pancreas, α-chymotrypsin and pepsin. In addition, the inhibitory activities were not affected by the addition of catalase. Taken together, these results confirmed that the inhibitory compounds produced by this strain were proteinaceous in nature and possessed typical characteristics of bacteriocins. The highest yield of bacteriocin produced by W. cibaria N23 was recorded at 20 h. The bacteriocin N23 remained stable after 2 h of incubation at pH values between 2.0 and 8.0, and also for 15 min at 121 °C. The bacteriocin produced by W. cibaria N23 was found to have a narrow antibacterial spectrum, being able to inhibit only W. confusa N31. In addition, bacteriocin N23 did not adhere to the surface of the producer cells. The results produced from this study will contribute to the existing body of knowledge and enhance the databases of bacteriocin-producing Weissella.     

Electrochemical depositions of calcium phosphate film on commercial pure titanium and Ti–6Al–4V in two types of electrolyte at room temperature

Electrochemical depositions of calcium phosphate film on commercially pure titanium (cp-Ti) and Ti–6Al–4V in two types of electrolytes, mono-calcium phosphate monohydrate (MCPM) based aqueous solution and supersaturated calcium phosphate solution (SCPS), were carried out by the cathodic polarization. The calcium phosphate coating layer was successfully deposited on cp-Ti and Ti–6Al–4V under 3 mA/cm² current density for 45 min. The major phases that appeared in the film were DCPD (brushite) co-existed with octa-calcium phosphate (OCP). After soaking in revised simulated-body-fluid (r-SBF), the amorphous bone-like apatite became a single phase within a day for the specimen obtained from MCPM electrolyte. The specimens obtained from SCPS electrolyte took a week to complete the apatite precipitation in r-SBF. From the scratch test, the highest critical load of 87.2 N was obtained from the as-deposited rod-like DCPD on cp-Ti substrate. The critical load was decreasing almost 50% for all of the specimens after apatite precipitation in r-SBF. The decrease of critical load might result from loosening of the film structure during immersion of the specimens in r-SBF. The thickness of the films was 44–55 μm in average, which satisfied the qualification for using as an implant material.     

A novel sol–gel synthesis of mesoporous ZrO2–MoO3/WO3 mixed oxides

Mesoporous ZrO₂–MoO₃/WO₃ mixed oxides have been synthesized through a novel, convenient one step sol–gel technique. Water soluble molybdate/tungstate and zirconium (IV) carbonate complex have been employed in presence of cationic surfactant, tetradecyltrimethylammonium bromide under basic condition. The synthesized materials have shown high specific surface areas and narrow pore-size distributions which were achieved after optimization of the amount of surfactant. Mesoporous ZrO₂–MoO₃ and ZrO₂–WO₃ mixed oxides have shown specific surface areas of 228 and 275 m² g⁻¹ and pore sizes of 3.65 nm and 4.33 nm, respectively. FTIR and Raman studies prove the formation of hetero bonding in mixed oxides.