Voit, Walter E.
Permanent URI for this collectionhttps://hdl.handle.net/10735.1/4984
Walter Voit is an Associate Professor of Mecanical Engineering. He was a member of UTD's inaugural class of Eugene McDermott scholars in 2001 and finished his academic training with a PhD from Georgia Tech. He returned to UTD in 2010 as a member of the faculty. His research interests include:
- Shape memory polymers
- Polymer manufacturing
- Ionizing radiation
- Thermomechanical properties
- Biopolymer mechanics
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Browsing Voit, Walter E. by Subject "Flexible electronics"
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Item Chronic Softening Spinal Cord Stimulation Arrays(Institute of Physics Publishing) Garcia-Sandoval, Aldo; Pal, A.; Mishra, A. M.; Sherman, Sydney; Parikh, Ankit R.; Joshi-Imre, Alexandria; Arreaga-Salas, David; Gutierrez-Heredia, Gerardo; Duran-Martinez, Adriana C.; Nathan, J.; Hosseini, Seyed Mahmoud; Carmel, J. B.; Voit, Walter E.; 0000-0003-0135-0531 (Voit, WE); Garcia-Sandoval, Aldo; Sherman, Sydney; Parikh, Ankit R.; Joshi-Imre, Alexandria; Arreaga-Salas, David; Gutierrez-Heredia, Gerardo; Duran-Martinez, Adriana C.; Hosseini, Seyed Mahmoud; Voit, Walter E.Objective. We sought to develop a cervical spinal cord stimulator for the rat that is durable, stable, and does not perturb the underlying spinal cord. Approach. We created a softening spinal cord stimulation (SCS) array made from shape memory polymer (SMP)-based flexible electronics. We developed a new photolithographic process to pattern high surface area titanium nitride (TiN) electrodes onto gold (Au) interconnects. The thiol-ene acrylate polymers are stiff at room temperature and soften following implantation into the body. Durability was measured by the duration the devices produced effective stimulation and by accelerated aging in vitro. Stability was measured by the threshold to provoke an electromyogram (EMG) muscle response and by measuring impedance using electrochemical impedance spectroscopy (EIS). In addition, spinal cord modulation of motor cortex potentials was measured. The spinal column and implanted arrays were imaged with MRI ex vivo, and histology for astrogliosis and immune reaction was performed. Main results. For durability, the design of the arrays was modified over three generations to create an array that demonstrated activity up to 29 weeks. SCS arrays showed no significant degradation over a simulated 29 week period of accelerated aging. For stability, the threshold for provoking an EMG rose in the first few weeks and then remained stable out to 16 weeks; the impedance showed a similar rise early with stability thereafter. Spinal cord stimulation strongly enhanced motor cortex potentials throughout. Upon explantation, device performance returned to pre-implant levels, indicating that biotic rather than abiotic processes were the cause of changing metrics. MRI and histology showed that softening SCS produced less tissue deformation than Parylene-C arrays. There was no significant astrogliosis or immune reaction to either type of array. Significance. Softening SCS arrays meet the needs for research-grade devices in rats and could be developed into human devices in the future.Item Electrical Properties of Thiol-ene-Based Shape Memory Polymers Intended For Flexible Electronics(MDPI AG, 2019-05-17) Frewin, Christopher L.; Ecker, Melanie; Joshi-Imre, Alexandra; Kamgue, Jonathan; Waddell, Jeanneane; Danda, Vindhya Reddy; Stiller, Alison M.; Voit, Walter E.; Pancrazio, Joseph J.; 0000-0002-0603-6683 (Ecker, M); 0000-0002-4271-1623 (Joshi-Imre, A); 0000-0003-0135-0531 (Voit, WE); 0000-0001-8276-3690 (Pancrazio, JJ); Frewin, Christopher L.; Ecker, Melanie; Joshi-Imre, Alexandra; Kamgue, Jonathan; Waddell, Jeanneane; Danda, Vindhya Reddy; Stiller, Alison M.; Voit, Walter E.; Pancrazio, Joseph J.Thiol-ene/acrylate-based shape memory polymers (SMPs) with tunable mechanical and thermomechanical properties are promising substrate materials for flexible electronics applications. These UV-curable polymer compositions can easily be polymerized onto pre-fabricated electronic components and can be molded into desired geometries to provide a shape-changing behavior or a tunable softness. Alternatively, SMPs may be prepared as a flat substrate, and electronic circuitry may be built directly on top by thin film processing technologies. Whichever way the final structure is produced, the operation of electronic circuits will be influenced by the electrical and mechanical properties of the underlying (and sometimes also encapsulating) SMP substrate. Here, we present electronic properties, such as permittivity and resistivity of a typical SMP composition that has a low glass transition temperature (between 40 and 60 °C dependent on the curing process) in different thermomechanical states of polymer. We fabricated parallel plate capacitors from a previously reported SMP composition (fully softening (FS)-SMP) using two different curing processes, and then we determined the electrical properties of relative permittivity and resistivity below and above the glass transition temperature. Our data shows that the curing process influenced the electrical permittivity, but not the electrical resistivity. Corona-Kelvin metrology evaluated the quality of the surface of FS-SMP spun on the wafer. Overall, FS-SMP demonstrates resistivity appropriate for use as an insulating material. © 2019 by the authors.Item Solution-Processed Oxide Thin Film Transistors on Shape Memory Polymer Enabled by Photochemical Self-Patterning(Cambridge University Press) Daunis, Trey B.; Barrera, Diego; Gutierrez-Heredia, Gerado; Rodriguez-Lopez, Ovidio; Wang, Jian; Voit, Walter E.; Hsu, Julia W. P.; 0000-0003-0135-0531 (Voit, WE); 0000-0002-7821-3001 (Hsu, JWP); Hsu, Julia W. P.; Daunis, Trey B.; Barrera, Diego; Gutierrez-Heredia, Gerado; Rodriguez-Lopez, Ovidio; Wang, Jian; Voit, Walter E.Solution-processed metal oxide electronics on flexible substrates can enable applications from military to health care. Due to limited thermal budgets and mismatched coefficients of thermal expansion between oxides and substrates, achieving good performance in solution-processed oxide films remains a challenge. Additionally, the use of traditional photolithographic processes is incompatible with low-cost, high-throughput roll-to-roll processing. Here, we demonstrate solution-deposited oxide thin film transistors (TFTs) on a shape memory polymer substrate, which offers unique control of final device shape and modulus. The key enabling step is the exposure of the precursor film to UV-ozone through a shadow mask to perform patterning and photochemical conversion simultaneously. These TFTs exhibit mobility up to 160 cm2/(V s), subthreshold swing as low as 110 mV/dec, and threshold voltage between -2 and 0 V, while maintaining compatibility with a flexible form factor at processing temperatures below 250 °C. ©2018 Materials Research Society.