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Biomedical Sensors and Subsystems

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This Thrust is developing electronic interfaces to living systems for the gathering of diagnostic information and to provide treatment for various disorders. A wireless intraocular sensor is under development to gather pressure information at programmable intervals, store it, and read it out once per day when queried by an RF wand. This work explores a complete hermetic package with bio-compatible coating by integrating sub-10nW processors, microbatteries, energy scavenging, and the gathering of accurate data at very-low-power levels. A capacitive pressure sensor has been integrated on a silicon feedthrough glass substrate and various fixture shapes have been implemented to provide a stable anchor during implantation.

Two efforts are focused in interfacing with the nervous system. The first one is a thin-film cochlear electrode array having IrO sites on 250µm centers. The ultra-flexible array realized in parylene offers substantial challenges in interconnect, backing, and insertion so that the array can be positioned deeply in the scala tympani to achieve a broad frequency range and will hug the modiolar wall to minimize power. The multi-layered array body allows the entire structure to be pre-curled due to stress compensation and makes insertion more controllable with the aid of a multi-chamber pneumatic insertion tool. Monolithically-formed backing structures with a cavity formed by parylene provide the needed stiffness from the articulated insertion tools that can be easily shaped to curl.

The second work is to realize the penetrating electrodes for use in the central nervous system for capturing control signals from the motor cortex for use in overcoming paralysis. New high-yield structures for forming three-dimensional electrode arrays are being explored, and the effects of scaling probe width to cellular dimensions (<10µm) on probe encapsulation and far-field (50-100µm) cell loss are being studied. Extensive mapping algorithm will be realized in a custom ASIC front-end electronics to select the arbitrary combination of recording and stimulating sites based upon the command generated from a central processing unit. This bidirectional neural probe will have a total of 256 sites from which we can simultaneously access 32 recording sites and 16 stimulation sites. Cochlear nucleus mapping array has been fabricated to study signal transmission and frequency mapping in auditory nerve system. Five probes have been assembled in the two group of slots perpendicular to each other to position the probes for simultaneously access of dorsal cochlear nucleus and ventral nucleus. Peristimulus time histograms have been acquired for 64 electrodes sites for 70dB noise burst stimulation. Frequency mapping of ventral nucleus has been characterized in each electrode as a function of acoustic stimulus frequency and amplitude. Also, carbon nanotube (CNT) coating of electrode sites has been explored to reduce the impedance and enhance charge transfer. Optical stimulation capability has been added by integrating an optical waveguide on the probe shank to transmit a light at the probe tips for selective stimulation of specific neural cells which are genetically modified to express channelrhodopsin-2 (ChR2).

As an extension of cellular interface, in vitro cell interactions will be explored by realizing single-cell assay on a microfluidic array platform. This cell assay chip can load cells in each microwell at single-cell resolution and selectively inject reagents or drugs to monitor cell response. Single-cell clonal culture and chemodrug assay has been performed for prostate cancer cells in a continuous fluid flow without cross-migration of cells between neighbouring microwells. We successfully observed three subclones and their different drug responsiveness using PC3 cells.

Updated 09/01/2010

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