Corrosion Behavior of Nitrided Layer of Ti6Al4V Titanium Alloy by Hollow Cathodic Plasma Source Nitriding.

Ti6Al4V titanium alloys, with high specific strength and good biological compatibility with the human body, are ideal materials for medical surgical implants. However, Ti6Al4V titanium alloys are prone to corrosion in the human environment, which affects the service life of implants and harms human health. In this work, hollow cathode plasm source nitriding (HCPSN) was used to generate nitrided layers on the surfaces of Ti6Al4V titanium alloys to improve their corrosion resistance. Ti6Al4V titanium alloys were nitrided in NH3 at 510 °C for 0, 1, 2, and 4 h. The microstructure and phase composition of the Ti-N nitriding layer was characterized by high-resolution transmission electron microscopy, atomic force microscopy, scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. This modified layer was identified to be composed of TiN, Ti2N, and α-Ti (N) phase. To study the corrosion properties of different phases, the nitriding 4 h samples were mechanically ground and polished to obtain the various surfaces of Ti2N and α-Ti (N) phases. The potentiodynamic polarization and electrochemical impedance measurements were conducted in Hank's solution to characterize the corrosion resistance of Ti-N nitriding layers in the human environment. The relationship between corrosion resistance and the microstructure of the Ti-N nitriding layer was discussed. The new Ti-N nitriding layer that can improve corrosion resistance provides a broader prospect for applying Ti6Al4V titanium alloy in the medical field.

Protective effect of astrocyte-conditioned medium on neurons following hypoxia and mechanical injury.

OBJECTIVE: To investigate the protective effect of mouse astrocyte-conditioned medium (ACM) on hypoxic and mechanically injured neurons by a cell model in vitro, and to explore the possible mechanism. METHODS: The model of hypoxic neuronal injury was caused by 3% O2 in three-gas incubator. Neurons were cultured with ordinary medium or 20% ACM respectively and randomly divided into hypoxic group (hypoxia for 4, 8, 24 h and marked as H4R0, H8R0, H24R0) and hypoxia reoxygenation group (H4R24, H8R24, H24R24). Mechanical injury model was developed by scratching neurons cultured in 20% ACM or ordinary medium to different degrees. Neurons in both medium were divided into normal control group, mild, moderate and severe injury groups. The 20% ACM was added 24 h before hypoxia/reoxygenation or mechanical injury. The morphology and survival of neurons were observed and counted by trypan blue staining. The concentration of NO, lactic dehydrogenase (LDH) and membrane ATPase activity were detected by corresponding kits. RESULTS: It was showed that 20% ACM can obviously promote the survival rate of hypoxia/reoxygenated neurons and scratched neurons as well. The morphology and number of neurons exposed to hypoxia or scratch injury showed great difference between groups with or without ACM treatment. Compared with control group, the concentration of NO and LDH was much lower in hypoxic/reoxygenated neurons treated with 20% ACM, and the ATPase activity was higher. For the mechanical injury model, neurons with moderate injury also revealed a lower NO and LDH concentration than the control group. All the differences were statistically significant (P less than 0.05). CONCLUSION: ACM can promote the survival and functional recovery of neurons following hypoxia or scratching to a certain degree. The mechanism may be associated with reducing the synthesis and release of NO and LDH as well as increasing the activity of membrane ATPase.

A PbS quantum dots fiber amplifier excited by evanescent wave.

A PbS quantum dots (QDs) fiber amplifier was fabricated and characterized by using a standard single mode fiber (SMF) coupler. The fiber amplifier was fabricated by coating PbS QDs doped sol-gel films onto the tapered SMF coupler. Through the evanescent wave, the PbS quantum dots were excited. With a 980 nm wavelength laser diode (LD) as the pump, the fiber amplifier exhibited a wide band optical gain at 1310 nm with the largest gain as high as 10 dB. The amplified spontaneous emission (ASE) noise is very low resulted from the amplifier configuration of evanescent wave exciting, which is critical to improve the signal-to-noise ratio. Therefore the proposed fiber amplifier will find great potential in the fiber-optic communication systems.

Foodborne pathogens in retail oysters in south China.

OBJECTIVE: To investigate the occurrence of important foodborne pathogens in shellstock Pacific oysters in the food markets in South China. METHODS: From July 2007 to June 2008, retail oysters were collected in different seasons from South China and analyzed for the prevalence and levels of Listeria monocytogenes, Vibrio vulnificus and Vibrio parahaemolyticus. RESULTS: None of L. monocytogenes could be detected in any of the 202 oyster samples tested, while E vulnificus and V. parahaemolyticus could be detected in 67 (54.9%) and 109 (89.3%) of the 122 oyster samples analyzed, respectively, with an MPN (most probable number) value greater than or equal to 3. V. vulnificus and V. parahaemolyticus with a more than 102 MPN/g were found in 36 (29.5%) and 59 (48.4%) of the 122 oyster samples, respectively. The tdh and trh genes were detected in 4 (0.3%) and 8 (0.6%) of the 1 349 V parahaemolyticus isolates, respectively. Of the 122 samples, 4 (3.3%) was positive for either tdh or trh. The levels of V. vulnificus and total V. parahaemolyticus in oysters in South China varied in different seasons. CONCLUSION: V. vulnificus and pathogenic V. parahaemolyticus are frequently found in oysters in south China, which may pose a potential threat to public health. Data presented here will be useful for the microbiological risk assessment in oysters in China.

[Molecular typing of Listeria monocytogenes isolated from foodstuff in Guangdong province by pulsed-field gel electrophoresis].

OBJECTIVE: To establish molecular typing of Listeria monocytogenes isolates by pulsed-field gel electrophoresis (PFGE) for studying the epidemiologic characteristics of Listeria monocytogenes isolated from foodstuff in Guangdong province and to build up PFGE typing database of Listeria monocytogenes isolates for identifying the infectious resource of the outbreaks and other epidemiologic investigation. METHODS: "Standardized Protocol for Molecular Subtyping of Listeria monocytogenes by PFGE" was followed. BioNumerics software was applied on image analysis, database establishment, comparative and corresponding analysis. RESULTS: 107 Listeria monocytogenes isolates were typed by PFGE, 41 PFGE types were observed among the isolates. The PFGE types were dispersive among these isolates. Listeria monocytogenes isolates were most frequently isolated in raw chicken while the most PFGE types were found in this type of food. The positive rate was relatively high in cold and iced foods. Only 1-2 DNA fragment difference occurred in 26 Listeria monocytogenes isolates by PFGE, so high degree of relatedness remained among these isolates. There were unique PFGE patterns in the regions of Shaoguan and Huizhou. From time to time, a number of isolates remained close relationship. CONCLUSION: PFGE typing of the 107 Guangdong Listeria monocytogenes isolates demonstrated relative genetic diversity but a number of the isolates showed close relatedness.