Browsing by Author "Frewin, Christopher L."
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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 Thinking Small: Progress on Microscale Neurostimulation Technology(Wiley, 2018-10-22) Pancrazio, Joseph J.; Deku, Felix; Ghazavi, Atefeh; Stiller, Allison M.; Rihani, Rashed; Frewin, Christopher L.; Varner, Victor D.; Gardner, Timothy J.; Cogan, Stuart F.; 0000 0000 2895 2047 (Cogan, SF); 43420545 (Cogan, SF); Pancrazio, Joseph J.; Deku, Felix; Ghazavi, Atefeh; Stiller, Allison M.; Rihani, Rashed; Frewin, Christopher L.; Varner, Victor D.; Gardner, Timothy J.; Cogan, Stuart F.Objectives: Neural stimulation is well-accepted as an effective therapy for a wide range of neurological disorders. While the scale of clinical devices is relatively large, translational, and pilot clinical applications are underway for microelectrode-based systems. Microelectrodes have the advantage of stimulating a relatively small tissue volume which may improve selectivity of therapeutic stimuli. Current microelectrode technology is associated with chronic tissue response which limits utility of these devices for neural recording and stimulation. One approach for addressing the tissue response problem may be to reduce physical dimensions of the device. "Thinking small" is a trend for the electronics industry, and for implantable neural interfaces, the result may be a device that can evade the foreign body response. Materials and Methods: This review paper surveys our current understanding pertaining to the relationship between implant size and tissue response and the state-of-the-art in ultrasmall microelectrodes. A comprehensive literature search was performed using PubMed, Web of Science (Clarivate Analytics), and Google Scholar. Results: The literature review shows recent efforts to create microelectrodes that are extremely thin appear to reduce or even eliminate the chronic tissue response. With high charge capacity coatings, ultramicroelectrodes fabricated from emerging polymers, and amorphous silicon carbide appear promising for neurostimulation applications. Conclusion: We envision the emergence of robust and manufacturable ultramicroelectrodes that leverage advanced materials where the small cross-sectional geometry enables compliance within tissue. Nevertheless, future testing under in vivo conditions is particularly important for assessing the stability of thin film devices under chronic stimulation.