Biomedical Sensors and Subsystems
See project descriptions
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.