Artificial neural stimulation uses electrical current to stimulate specific parts of the human nervous system. At present it is used to treat neurological conditions (e.g. Parkinson’s Disease), neural impairments or to enhance neural connectivity for prosthetics. Stimulation may be delivered by externally powered electrodes placed on the skin surface (transcutaneous) or under the skin (subcutaneous) in close proximity to muscles or nerves.
This research models the use of ultrasound as a method of wirelessly activating an implanted neural-stimulation device at a shallow depth of the tissue. The medical use of ultrasound for imaging is widespread, well understood and has recommended safety levels. Arrays of devices containing piezoelectric nanowires can convert incident ultrasound energy into electrical pulses. These pulses can stimulate nerve bundles (fascicles) to generate a stream of modulated signals along the nerve and deliver data packets to a more deeply embedded receiver. The maximum bit rate is 200 bit/s, limited by the rate at which nerves can generate electrical signals. The modulation is simple on-off keying (OOK) to create a stream of logic “ones” and “zeroes”.
The research also targets stimulus system on the vagus nerve in the neck sending modulated data pulses to an embedded multi-reservoir drug-delivery system in the brain. The drug-delivery system could use cerebrospinal glucose as a source for energy harvesting.
This strand also covers wireless optogenetic devices, where devices constructed from nanocomponents are assembled into devices that can be implanted into the brain to simulate engineered cells using light. The research has investigated techniques for charging the devices wirelessly using ultrasound, as well as modeling propagation of light through a group of neurons to understand how they are affected by the shapes of the neurons.
Research Objectives
- Modeling the input ultrasound energy (maximum 720 mW/cm2) and harvested power for single fixed-size nanowire-based nanodevices (1000µm2 with 20 nanowires per µm2) at different tissue depths and comparing these with the current and voltage levels required for peripheral neural stimulation.
- Modelling the dimensions of nanodevice arrays, embedded in biocompatible tissue patches, to meet neural stimulation requirements. The effect of degrees of tilt of the nanowire unit is also calculated.
- Using transmission theory to calculate the data capacity and transmission range of a stimulated nerve for different modulation techniques, subject to an overall limit of 200 bits/s.
- Modeling the propagation of light through neurons for stimulation, as well as group of neurons where multiple devices can use light to communicate and coordinate distributed stimulation.