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 "Bioelectronics"
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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 Effect of Annealing Atmosphere on IGZO Thin Film Transistors on a Deformable Softening Polymer Substrate(Institute of Physics Publishing) Gutierrez-Heredia, Gerado; Maeng, Jimin; Conde, J.; Rodriguez-Lopez, O.; Voit, Walter E.; 0000-0002-9198-1822 (Gutierrez-Heredia, G); 0000-0003-0135-0531 (Voit, WE); Gutierrez-Heredia, Gerado; Maeng, Jimin; Rodriguez-Lopez, O.; Voit, Walter E.The effect of annealing atmosphere on indium-gallium-zinc-oxide (IGZO) thin film transistors (TFTs) fabricated on a deformable softening polymer substrate is presented in this work. Different annealing conditions - ambient, oxygen, vacuum and forming gas - are employed in the fabrication of IGZO TFTs and the changes in electrical characteristics are examined. Fabricated devices exhibit shape memory properties due to thiol-ene/acrylate substrates allowing the softening of bioelectronics to demonstrate modulus changes in aqueous conditions at body temperature. Gold (Au) is used as the contact metal for the gate, drain and source for its good adherence and malleability required for this polymer. It is found that annealing treatments at 250 °C can improve the field effect mobility of the TFTs from 10⁻² up to 30 cm² V⁻¹ s⁻¹. These improvements are attributed to the reduction of oxygen concentration in the active film of the TFTs. The contact resistance is also reduced by the annealing treatments from approximately 1 MΩ to 20 kΩ, indicating improvement in physical contact at the IGZO-Au interface. In addition, the contributions of contact resistance and channel resistance to other electrical parameters are analyzed. This study will pave the way for the development and optimization of high-performance bioelectronic devices on smart polymers.