Projects:2020s1-2110 Radio-Wave Induced Neural-Plasticity

Abstract here

Project Members

Project students

• Luke Smith
• Jaedon Bem

Supervisors

• Dr. Giuseppe Tettamanzi
• Prof. Christophe Fumeaux
• Prof. Mark Hutchinson

Introduction

Radio-Wave Induced Neural Plasticity is a broad project aiming to investigate the effects of Electromagnetic stimulation of neural tissue. Specifically Transcranial Magnetic Stimulation on neural tissue regrowth in the presence of a graft antenna.

The graft antenna is a suture-less device that can be implanted in nerves using light (e.g. a low power laser) and is able to stimulate remotely action potentials in nerve and muscles, being powered by a Transcranial magnetic stimulation (TMS). The device has a simple design when compared to current stimulators because it does not include circuitry and it functions concurrently as a stimulator and biocompatible conduit for nerve repair (graft). Inside the conduit there is a small metallic loop antenna that stimulates tissue upon TMS irradiation. The graft antenna avoids the usage of separate stimulating electrodes and thus significant shortcomings such as electrode fracture or migration. No clear model explaining the causes of these effects has yet been developed. In this project we are aiming in developing a semi-empirical microscopic modelling that can be used to clarify the causes of the observed microscopic neural effects

Objectives

There are three primary objectives for this project.

1. Calculate the electromagnetic fields inside and around the neuron due to the interactions between the TMS coil and the graft antenna.
2. Determine and quantitatively measure the effect that changing stimulation parameters, such as orientation and type of TMS coil, has on the created electromagnetic fields.
3. Identify the neural response to these fields and identify if the response can be used as a method of determining how effective a given treatment is.

Significance

The ability to improve regeneration of neurons can lead to many medical techniques used to improve the quality of life of patients suffering neuropathologies. These would include treatments to muscular weakness, loss of feeling, and chronic pain. If it could be used as a treatment for pain, it could also help fight the opioid epidemic throughout America.

Background

In 2019, Sliow et al. [3] developed a graft-antenna: a metal ring which could be wrapped around a damaged nerve bundle using a bio-adhesive polymer. In vivo studies using rats showed that when this ring was stimulated by an external Transcranial Magnetic Stimulation device, nerve repair was improved uniformly.

Sliow et al. were unable to identify the mechanisms behind electrical stimulation, necessitating the creation of an electromagnetic model. One unexplained observation of interest was the ‘no-touch-no-response’ effect; if the ring was not in direct contact with the nerve bundle, then no stimulation would occur, regardless of how the stimulation was applied.

Method

The Sim4Life computational environment was used to replicate the physical devices used by Sliow et al., shown to the right. A Quasi Magneto-Static solver was used to calculate the generated fields.

The project was split into two streams: one which developed the electromagnetic stimulation methods, the other which created a tissue and nerve model to be stimulated. The main task of the electromagnetic stream was to accurately model the TMS device used by Sliow et al., understand its characteristics, and then incorporate its effects into the neural component.

The main task of the neural stream was to create a CAD model of the nerve, developed from cross-sectional slices of the original rat nerve, which could be electrically stimulated. Additionally, this stream developed a model for the graft antenna which could be stimulated, and examined the neural response.

Results

The magnetic fields generated by the TMS were found to circulate through the two loops. In a small region occupied by the graft antenna, the magnetic fields were found to be uniform and monodirectional. In other words, the TMS device acted only as a constant magnetic field source to the graft antenna.

The interactions with the graft antenna showed three phenomena, all of which contributed to the neural stimulation. First, the metal ring acted as a shield to electric fields within it. This generated electric field gradients across segments of the nerve with and without the ring present, and these gradients are capable of causing nerve stimulation. Secondly, the metal ring created high intensity electric fields pointing in all directions at its edges. These edge effects were able to penetrate a short distance into the neural tube and excite a small part of it.

Interestingly, the neural regrowth which was identified by Sliow et al occurred homogeneously throughout the nerve, but most of the electrical stimulation was located at the nerve's surface. This may imply that in the biological system, there is some linking effect between the neurons, allowing the repair of a single neuron within the bundle to trigger repair in nearby neurons.

Conclusion

Uniform nerve response from non-uniform stimulation is not explained with classical models. This suggests the existence of a quantum linking effect within the neuron, though this will need to be experimentally confirmed.

This research could be continued through two key pathways.

1. Optimise the ring design to improve electrical stimulation.
2. Examine non-electrical behaviours in this system (biological, thermal, etc.) to develop a better understanding of this technology and potentially increase its application.

References

[1] a, b, c, "Simple page", In Proceedings of the Conference of Simpleness, 2010.

[2] ...