Abstracts Book - IMRC 2018

• SB6-O002
SOFTENING SPINAL CORD STIMULATION ARRAYS FOR CHRONIC
TREATMENTS
Aldo Garcia Sandoval 1 , Ajay Pal 2 , Sydney Sherman 1 , Adriana Carolina Duran Martinez 1 ,
Alexandra Joshi Imre 3 , Jason Carmel 2 , Walter Voit 4
1 University of Texas at Dallas, Bioengineering, United States. 2 Cornell University, Burke Medical
Research Institute, United States. 3 University of Texas at Dallas, Center of engineering
innovation, United States. 4 University of Texas at Dallas, Materials Science and Engineering,
United States.
Cervical spinal cord stimulation (SCS) holds promise to improve arm and hand
function after brain or spinal cord injury, but today the approach is limited by
the devices used for stimulation. Chronic stimulation of the cervical spinal cord
has been difficult to achieve due to the large range of movement and rotation
of the neck. To study this approach, we need devices that can be used for rats
that are thin to fit in the narrow epidural space and to conform over the spinal
cord to prevent device migration. Current devices, made of parylene-C or
silicone, may not meet these demands and furthermore, the stiff polymer can
damage surrounding tissue. The mechanical mismatch between implants and
the spinal cord has been an issue for chronic devices as it leads to scar tissue
encapsulation of the electrodes.
We developed thiol-ene/acrylate based softening polymeric spinal cord
stimulation (SCS) arrays that are stiff, like parylene-C, at room temperature and
they soften when it’s exposed to physiological conditions. The mechanical
properties of the polymer were characterized at room temperature as well as in
physiological conditions by dynamic mechanical analysis and tensile tests.
Devices were fabricated by standard semiconductor processes using gold
interconnections and titanium nitride electrodes. In vitro electrochemical tests
were performed to determine the electrode impedance, charge storage
capacity, and charge injection capacity along with the softening encapsulation
layer properties.
Softening SCS arrays were implanted in rat models to test their in vivo behavior
and lifespan. SCS was performed using bi-polar current pulses while EMG and
visual motor response was recorded in addition to their stimulation threshold
current. Devices have been implanted for up to 29 weeks remaining functional.