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Polymer-based biomedical electronics provide a tunable platform to interact with nervous tissue both in vitro and in vivo. Ultimately, the ability to control functional properties of neural interfaces may provide important advantages to study the nervous system or to restore function in patients with neurodegenerative disorders. Liquid crystal elastomers (LCEs) are a class of smart materials that reversibly change shape when exposed to a variety of stimuli. Our interest in LCEs is based on leveraging this shape change to deploy electrode sites beyond the tissue regions exhibiting inflammation associated with chronic implantation. As a first step, we demonstrate that LCEs are cellular compatible materials that can be used as substrates for fabricating microelectrode arrays (MEAs) capable of recording single unit activity in vitro. Extracts from LCEs are non-cytotoxic (>70% normalized percent viability), as determined in accordance to ISO protocol 10993-5 using fibroblasts and primary murine cortical neurons. LCEs are also not functionally neurotoxic as determined by exposing cortical neurons cultured on conventional microelectrode arrays to LCE extract for 48 h. Microelectrode arrays fabricated on LCEs are stable, as determined by electrochemical impedance spectroscopy. Examination of the impedance and phase at 1 kHz, a frequency associated with single unit recording, showed results well within range of electrophysiological recordings over 30 days of monitoring in phosphate-buffered saline (PBS). Moreover, the LCE arrays are shown to support viable cortical neuronal cultures over 27 days in vitro and to enable recording of prominent extracellular biopotentials comparable to those achieved with conventional commercially-available microelectrode arrays.
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Fully-Passive Wireless Implant for Neuropotential Acquisition: An In Vivo Validation
Implantable systems are often employed to perform continuous high-resolution recordings of neural activity. These systems frequently require invasive procedures when implanting and maintaining effective operation. This causes major interruptions to daily life. Previous work demonstrated an in vitro minimum detectable signal (MDS) of 15 μV in amplitude and RF sensitivity down to - 135 dBm. This suggests the possibility of detecting diminutive biopotentials in a wireless fully-passive manner. Here, for the first time, we validate this system through a series of in vivo electrophysiological recordings including both spontaneous cardiac activity and sensory evoked neural activity, with amplitudes ranging from a few microvolts to millivolts and across a spectrum of frequencies. We also present design considerations and the development of probes for neurosensing to accomplish detectability of biopotentials in the tens of microvolts in rats. The developed probes show improved impedance matching with the neurosensing system. Specifically, the new probes showed an impedance several orders of magnitude lower than those commercially available, thereby significantly improving signal detection. Notably, the presented in vivo validation of this technology has great future clinical implications in neuroscience as it offers a wireless and unobtrusive device for neurological research, monitoring, and therapeutic purposes.
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- Award ID(s):
- 1763350
- PAR ID:
- 10096588
- Date Published:
- Journal Name:
- IEEE Journal of Electromagnetics, RF and Microwaves in Medicine and Biology
- ISSN:
- 2469-7249
- Page Range / eLocation ID:
- 1 to 1
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1109/JERM.2019.2895657
