Photoinitiated Controlled Nitric Oxide Release Materials for Implanted Biomedical Devices

Friday, October 31, 2008 3:00 – 4:00 pm
Room 610, M&M Building

Dr. Megan C. Frost
Department of Biomedical Engineering
Michigan technological University

Abstract

The research in our laboratory is focused on the development of novel Snitrosothiol compounds (RSNOs) as nitric oxide (NO) donors that can use light ofdifferent wavelengths and intensities to trigger the release of NO. Preliminary datawill be presented for novel aromatic RSNOs that release NO in response to phototriggers. By altering the electronic properties of substituents on the aromatic ring,we are able to shift the specific wavelength of light needed to release NO. Work isunderway focused on developing the chemistries necessary to immobilize thesecompounds into polymeric materials so that they can be used in the fabrication ofimplantable biomedical devices such as fiber optic sensors and probes capable ofreleasing NO at continuously variable and controllable levels such that the devicesshow improved biocompatibility and enhanced performance.

Biography

Megan C. Frost joined the faculty of the Department of Biomedical Engineering asan assistant professor in August 2007. She comes to Michigan Tech from a postdoctoralposition at the University of Michigan. She holds a PhD in Analytical Chemistry from theUniversity of Michigan, an MS is Analytical Chemistry from Purdue University-Indianapolis and aBS in Biological Sciences from the University of Notre Dame. Her research interests involvedesigning nitric oxide releasing polymeric materials that exhibit reduced biological responsewhen implanted in the body and the development of intravascular and subcutaneous sensorswith these nitric oxide releasing materials that show improved in vivo performance.

Influence of the Starting Substrate Morphology on the Growth of Epitaxial (001)CeO2 Thin Films on r-Plane Al2O3 Substrates

Friday, October 24, 2008 3:30 – 3:55 pm
Room 610, M&M Building

Madhana Sunder
Graduate Student
Department of Materials Science and Engineering
Michigan Technological University
Houghton

Abstract

Epitaxial (001)-oriented cerium dioxide (CeO2) thin film is an essential buffer layer forsubsequent integration of functional single-crystal cubic perovskite films on the commerciallyavailable large area r-plane sapphire (Al2O3) substrates. We report on how modifying the startingsubstrate morphology can lead to growth of epitaxial (001)CeO2 films on r-plane Al2O3substrates. Films grown on as received substrates were primarily of mixed (001) and (111)orientations. In general, low film growth rates and higher substrate temperatures, lead to ahigher volume fraction of (001)CeO2. The highest volume fraction of (001)CeO2 achieved in thecase of films grown on as received substrates, using the highest growth temperature andslowest growth rate of 830°C and 0.05nm/min respectively, was 81%. However when thesubstrates were annealed prior to film deposition, 100% (001)CeO2 films was obtained. Theemergence of a regularly spaced atomic step terrace features on the annealed wafer surface isbelieved to be key in enabling growth of epitaxial (001)CeO2 films. Crystallographic relationshipsbetween the atomic step edges and (001)CeO2 unit cells were derived, to understand the role ofpre-growth substrate annealing in promoting nucleation of (001)CeO2 on r-plane Al2O3substrates. (001)CeO2 films with atomic terraces and improved crystallinity were grown on pregrowth annealed r-plane Al2O3 substrates.

Impact of Growth Surface on the Crystal Structure of PMN-30PT Thin Films

Friday, October 24, 2008 3:05 – 3:30 pm
Room 610, M&M Building

Lakshmi Krishna
Graduate Student
Department of Materials Science and Engineering
Michigan Technological University
Houghton

Abstract

The impact of the crystal structure on the dielectric properties of the PMN-30%PTthin films has not been investigated. This is due in part to a lack of knowledge onhow to promote one crystal structure by modifying the growth conditions. Bygrowing at low temperature (250ºC) and subsequently rapid thermal annealing at850 ºC, we have observed that PMN-30%PT thin films results in a single crystalperovskite phase. In contrast, a high temperature (900ºC) deposition ofPMN-30%PT on CeO2 buffered sapphire (Al2O3) results in a single crystalpyrochlore phase. X-ray diffraction scans were performed to investigate the phaseand degree of crystallinity of the PMN-PT thin films. These films will allow aninvestigation of how crystal structure impacts the dielectric properties of the singlecrystal PMN-PT thin films.

High Resolution 2D and Tomographic X-Ray Microscopy in the SEM

Wednesday, October 22, 2008 2:00 – 3:00 pm
Room 610, M&M Building

Dr. Paul Mainwaring
Gatan Inc.
5794 West Las Positas Blvd.
Pleasanton, CA 9458

Abstract

The great advantage of X-ray microscopy is the ability to image the internal structure ofspecimens compared to the surface information obtained by SEM imaging. The two techniquescombine to deliver the maximum amount of structural information of the specimen. A SEMhosted X-ray ultra microscope consists of a metallic target material mounted on a high precisionsoftware-controlled positioning arm which is placed beneath the electron beam to produce apoint source of X-rays, a sample holder and a CCD camera for signal detection. Thesecomponents are fully compatible with the SEM working environment and allow switchingbetween SEM and X-ray imaging modes. The X-ray energy used can be “tuned” to increasevisibility of certain low contrast specimens. In general, spatial resolution of 200 – 400 nm can beachieved for 2D imaging.

X-ray microscopy allows the sample to be always in focus and the depth of focus enables stereo imaging and 3D micro-tomography to be carried out. Image contrast from the specimen is the result of both X-ray absorption and phase contrast mechanisms. Phase contrast arises from refraction and diffraction rather than absorption, and patented algorithms have been developed to extract this information. Variations in refractive index can occur in samples that present little variation in density and show little absorption contrast in the image. This allows fine detail,especially in low density materials which would be otherwise invisible, to be imaged using the phase contrast component of the total transmitted signal.

Recent improvements include custom built cameras for X-ray detection, robust phase contrast extraction algorithms, fast tomographic acquisition and very fast 3D reconstruction.Examples of the use of the X-ray microscope to image polymers, metal and graphite foams andbiological materials will be given.

Biography

Dr. Mainwaring received a Ph.D degree in geochemistry from the University of Toronto, Canada. In hisearly career, he joined the Canadian federal government Labs in the Department of Energy and built up a modernelectron beam and X-ray diffraction laboratory with SEMs, electron microprobe instruments and image analysissystems for materials characterization. Since 1995 he has been involved in the development of electronbackscattered diffraction systems with Oxford Instruments and EDAX/TSL. Dr. Mainwaring is now at Gatan Inc. asProduct Manager for Cathodoluminescence and X-ray Microscopy, both growing fields in the biological andmaterials research areas.

Inhibitory Effects of Copper-Vermiculite Against E. coli

Friday, October 10, 2008 3:00 – 3:30 pm
Room 610, M&M Building

Bowen Li
Graduate Student
Department of Materials Science and Engineering
Michigan Technological University

Abstract

Copper vermiculite (Cu-V) is new type of synthetic antimicrobial agent havingpotential as a functional additive in products such as plastics, paints, leathers, andwoods to reduce microbial persistence and biofilm formation. The Cu-V wasprepared by cation exchange reaction, and characterized by SEM and XRD; theCu atoms were homogeneously dispersed in the vermiculite structure. Theantibacterial efficiency of Cu-V was evaluated by determining its minimuminhibitory concentration (MIC) against Escherichia coli. In the control vermiculitesuspensions, E. coli densities remained constant during the 12 hour contact time;in contrast, bacteria levels with Cu-V significantly decreased. In the experimentwith 200 ppm Cu-V (5.10 ppm Cu), viable E. coli levels were reduced by 94.8% at1 hour, 99.6% at 2 hours, and >99.9% at 4 hours. The Cu-V MIC level against E.coli was10 ppm, while the untreated vermiculite had no antibacterial activity. Verylittle Cu was detected in the suspensions during the study, indicating that the CuV’s antimicrobial effect was due to surface interactions.