Pravahan Salunke

In vivo monitoring the biodegradation of magnesium alloys with an electrochemical H2 sensor.

UNLABELLED Monitoring the biodegradation process of magnesium and its alloys in vivo is challenging. Currently, this process is monitored by micro-CT and X-ray imaging in vivo, which require large and costly instrumentation. Here we report a simple and effective methodology to monitor the biodegradation process in vivo by sensing H2 transdermally above a magnesium sample implanted subcutaneously in a mouse. An electrochemical H2 microsensor was used to measure the biodegradation product H2 at the surface of the skin for two magnesium alloys (ZK40 and AZ31) and one high purity magnesium single crystal (Mg8H). The sensor was able to easily detect low levels of H2 (30-400μM) permeating through the skin with a response time of about 30s. H2 levels were correlated with the biodegradation rate as determined from weight loss measurements of the implants. This new method is noninvasive, fast and requires no major equipment. STATEMENT OF SIGNIFICANCE Biomedical devices such as plates and screws used for broken bone repair are being developed out of biodegradable magnesium alloys that gradually dissolve when no longer needed. This avoids subsequent removal by surgery, which may be necessary if complications arise. A rapid, non-invasive means for monitoring the biodegradation process in vivo is needed for animal testing and point of care (POC) evaluation of patients. Here we report a novel, simple, fast, and noninvasive method to monitor the biodegradation of magnesium in vivo by measuring the biodegradation product H2 with an electrochemical H2 sensor. Since H2 rapidly permeates through biological tissue, measurements are made by simply pressing the sensor tip against the skin above the implant; the response is within 30s.

Magnesium single crystals for biomedical applications grown in vertical Bridgman apparatus

This paper describes successful efforts to design, build, test, and utilize a single crystal apparatus using the Bridgman approach for directional solidification. The created instrument has been successfully tested to grow magnesium single crystals from melt. Preliminary mechanical tests carried out on these single crystals indicate unique and promising properties, which can be harnessed for biomedical applications.

MODELING THE ELECTRICAL IMPEDANCE OF CARBON NANOTUBE RIBBON

Carbon Nanotube (CNT) ribbon is a thin layer of aligned, partially overlapping CNTs drawn from a forest of CNTs grown on a substrate. The electrical properties of the ribbon must be understood to put this material into multifunctional applications. Measurements show that CNT ribbon exhibits interesting characteristics including frequency-dependent electrical impedance. The impedance is mainly a combination of resistive and capacitive impedance. The magnitude of the impedance of ribbon increases moderately with increasing frequency then decreases significantly at higher frequency, MHz and above. An electrical model was developed to approximate the electrical impedance of the CNT ribbon. Based on this model, some important properties of the CNT ribbon can be understood. The ribbon capacitance, CNT–CNT contact resistance and resistivity can be approximated using the model. This information is useful in determining the suitability of ribbon for different applications. Methods to improve the electrical conduction of CNT ribbon are also discussed.

SUBSTRATE PREPARATION BY MAGNETRON SPUTTERING AND CVD GROWTH OF CARBON NANOTUBE ARRAYS

In this study we explored the use of magnetron sputtering as an alternative to e-beam deposition for preparation of the alumina intermediate layer and of the metal catalyst on an oxidized Si wafer. This approach offers large area deposition of the layered substrate including the intermediate alumina layer and the final catalyst film. The effects of the substrate design on the growth of long multi-wall carbon nanotube (MWCNT) arrays by CVD (Chemical Vapor Deposition) were also explored. The CNT synthesis was carried on in a hydrogen/ethylene/water/argon environment at 750 °C for different periods of deposition time. Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Thermal Gravimetric Analysis (TGA) and Transmission Electron Microscopy (TEM) were employed to characterize the substrates and the CNT arrays. The study showed that for specific processing conditions the length of highly oriented CNTs strongly depends on the thickness of Al2 O3 intermediate layer and on the catalyst film. The results obtained confirm that magnetron sputtering can be successfully employed as a tool for substrate preparation to grow 7 mm long CNT arrays with high purity. The aligned nanotubes do not suffer from limitations typical for powdered (spaghetti type) nanotubes which opens up new applications.Copyright