Localized Temperature Field Measurements in Brain via Thin-Film Vertically Integrated Vanadium Oxide Thermistor Arrays

Open Access
Billard, Myles William
Area of Honors:
Engineering Science
Bachelor of Science
Document Type:
Thesis Supervisors:
  • Bruce Gluckman, Thesis Supervisor
  • Bruce Gluckman, Honors Advisor
  • Mark William Horn, Faculty Reader
  • Vanadium Oxide
  • Thermistor
  • Thin-film
  • Sensor
  • TCR
  • Seizure
  • PSU-EEG 8
  • Epilepsy
  • Temperature
  • Brain
Temperature plays a significant role in neurological function in normal and pathological brain physiology. Examining how temperature fields change within and between different regions of brain, and on a scale relative to the vasculature and neuronal cells that make up brain tissue, could help better characterize and understand the subtleties of neural activity in various physiological conditions such as wake and sleep, and in pathologies such as epilepsy. A device that is capable of localized, chronic temperature field recordings must be sensitive, must not disrupt surrounding tissue with its mechanics or size, must be biocompatible, and must not influence tissue with local heat dissipation or thermal shunting. A novel vertically-integrated vanadium oxide (VOx) thermistor array deposited on flexible polyimide substrate has been developed for measuring local temperature field dynamics in capillary and neuronal networks for rats with a Tetnus Toxin model of epilepsy. Acquisition electronics were developed to interface an array of eight thermistors to Dr. Gluckman’s PSU EEG-8 biopotential recording system. Samples of VOx deposits on glass and polyimide substrates with an active temperature sensing area of 10 μm × 10 μm were tested in-vitro for thermal characteristics and ability of parylene-C passivated samples to record in saline solution. Results from two samples showed temperature coefficient of resistance (TCR) values of -4.04 %/‰C and -4.53 %/C‰ with nominal resistances for functioning thermistors of about 1.3 MW. Analysis of a working channel used in the bulk-heat temperature experimentation showed a real-time average TCR of -4.4%/‰C over a 5 C temperature change. Passivated polyimide samples were able to record for an hour in liquid ionic solution. Additionally, a method for surgical implantation of our device has been developed using polyethylene glycol (PEG) encapsulation and 25 μm thick (1 1 1) type silicon shuttles for insertion assistance. 20 μm thick polyimide strips taken from deposition samples were inserted into 0.6% agarose gel to simulate brain implantation. Additional in-vitro experiments must be performed to test the array’s ability to measure small, controlled temperature gradients. Future in-vivo experiments will be conducted to monitor real-time, localized temperature field dynamics in brain.