Weir Biomechatronics Development Laboratory

Spiral Nerve Cuff for Systemic Inflammation

Vagus nerve stimulation (VNS) is a therapeutic technique clinically approved to treat depression, stroke recovery, migraines, and epilepsy. It is also being studied in the treatment of inflammatory diseases, such as Crohn’s and rheumatoid arthritis, as VNS has been shown to have anti-inflammatory effects.¹ VNS reduces the inflammatory response by acting through the cholinergic anti-inflammatory pathway to attenuate production of pro-inflammatory cytokines, such as TNF-⍺ and IL-6.^2,3 Current VNS methods utilize non-specific, electrode-based systems which can activate off-target pathways and lead to complications. Optogenetic methods can stimulate cells in a highly controlled manner with specific targeting. 

How do we target the nerves?

Utilizing optogenetic techniques, a spiral, silicone nerve cuff with an embedded µLED, like shown in Figure 1, is being  developed. Our device capitalizes on these optogenetic methods, applying them to VNS to provide specific, targeted stimulation of the vagus nerve for the study and regulation of VNS-mediated inflammatory diseases. The cuff is designed to “self-size” to the nerve, negate the need for sutures for securement, minimize nerve damage, and reduce off-target complications through optical stimulation. 

Nerve Cuff 1.0 was implanted on the cervical vagus nerve of a ChAT-Cre x ChR2 mouse. The nerve was stimulated with the embedded μLED: 5Hz, 10% duty cycle. As shown in Figure 2, when implanted, the device successfully stimulates the vagus nerve via optical stimulation, mirroring the effects of electrical VNS.

Nerve Cuff 1.0 was iterated and redesigned to give Nerve Cuff 2.0 which was used in the pilot experiments for this study, shown in Figure 3. Due to supply chain issues, the μLED was replaced with an optical fiber for the optical stimulation. This allowed for validation of the optical fiber with this cuff as well. 

How do we reduce systemic inflammation?

In the pilot experiments, we hypothesized that the stimulation of the cervical vagus nerve in ChAT-Cre x ChR2 mice with the Nerve Cuff 2.0 design would attenuate pro-inflammatory cytokines (IL-6, TNF-⍺, and IL-1β) and CRP. Previous literature has shown vagus nerve stimulation attenuates the production of these pro-inflammatory cytokines (IL-6, TNF-⍺, and IL-1β). CRP is commonly used as a clinical marker of inflammation with higher levels of the protein indicating higher severity of inflammation. The experiment was conducted as described in Figure 4. 

These pilot experiments were conducted on 4 mice, 2 controls and 2 experimental. With such a small sample size, the results are preliminary and incomplete. Our results, shown in Figure 5, indicate that TNF-⍺ and IL-1β attenuated with VNS. IL-6 levels were measured outside of the range of the assay, so the results of this marker are unclear. Finally, CRP resulted in increased levels with VNS, which contradicts the initial hypothesis.

What’s next in our research?

1. We will be continuing our experiments to determine the full effects of optical vagus nerve stimulation on inflammatory markers. 
2. We will be considering improvements that could be made to our experiment design:
   1. Optimizing the nerve cuff for easier implantation around the cervical vagus nerve
   2. Adjust the assay protocol to ensure all concentrations are within range of the assay
   3. Refinement of stimulation parameters