By Al Mashal, PhD and Ben Zwillinger, Cambridge Consultants
Though neurostimulation procedures have been performed for decades, recently, the improved understanding of neural circuitry has led to a desire for a new generation of neuromodulation devices. Even outside of traditional healthcare applications, moonshot ventures such as Bryan Johnson’s Kernel and Elon Musk’s Neural Lace are exploring enhanced cognitive functions.
Unfortunately, even as we continue to push the boundaries of what neuromodulation can do, implantable neurostimulation devices are seen as a last resort. Because they require invasive surgery by a skilled surgeon, they are a clinical solution that is offered sparingly when necessary, and not at all for minor conditions, let alone elective procedures.
It’s clear that mass market disruption will only happen if we can avoid the current bottlenecks of high costs and specialized surgeons through the development of point-of-care (POC) solutions, where the physician who diagnoses and recommends a patient for treatment can perform the procedure right then and there. Imagine having an appointment with your general practitioner and, instead of referring you to a specialist for a consultation, they pull out a neurostim kit and noninvasively insert an electrode the size of a grain of rice that can intelligently adapt to your specific condition and body morphology.
This vision does not require a radical shift in current procedure methods, but it will require intelligent tools and a greater understanding of doctor and patient considerations. While we can ponder and postulate all we want, the solutions will remain merely academic without consideration toward the practical aspects of developing a POC procedure.
In thinking about — and eventually developing — solutions, we need to integrate the technology with the workflow and user preference. This will not only ensure the procedure can be done in a safe, effective, and user-friendly way, but will guarantee the solution meets the needs of the patients and healthcare providers, leading to a commercially viable procedure.
In developing this framework, we identified three high-risk challenges that need to be overcome: electrode-tissue interface, electrode placement, and electrode anchoring. As a first step, we think these elements should be de-risked and addressed to ensure technological feasibility. Afterwards, the identified challenges and solutions will form the basis for a full-scale development plan.
Current electrode design and stimulation algorithms haven’t significantly changed over the past 20 years. This is rather unfortunate, as we now have more advanced materials and a better theoretical understanding of neuronal dynamics. For a new treatment, in which the electrode may have to be uniquely positioned (such as intravascularly), a complete new design is needed. Not only must the embodiment of the electrodes be different, but the device must address different neural interfaces, as the types of nerve fiber distributions are likely to vary by region.
From a purely electrical point of view, the electromagnetic properties of tissue change across different anatomical regions, which will impact the overall design of the system. In addition, less invasive POC procedures may result in less accurate electrode placement, which will require the electrode to provide greater stimulation coverage to compensate. The most efficient way to solve these challenges will be to conduct neuronal dynamics analysis to understand the parameter space, and help define the key technical requirements of the implant.
Electrode placement is perhaps the most challenging aspect of minimally invasive procedures. Right now, implant procedures are guided by complex imaging. For example, spinal cord electrode positioning require a multitude of C-arm images, while deep brain stimulation positioning relies on a combination of MRI and CT during planning, and O-arm images intra-operatively.
In a POC or outpatient setting, expensive imaging is not feasible, and often the capabilities are not even available. As such, a tool that has local imaging or sensing capabilities and aids with implanting the electrode is needed, though there is a limit on what is possible with current technology. For example, candidate imaging modalities such as ultrasound and optical coherence tomography have limited resolution and imaging depth, respectively. These technical limitations need to be addressed through unique designs, based on feedback from doctors who would be performing the procedure.
Additionally, the placement method will be critical in ensuring general practitioners and non-surgical specialists feel comfortable and confident administering the implant to patients. This includes making sure the procedure is possible given their skill set, and only requires tools that are accessible, and that they are comfortable using. Most importantly, the tool’s accuracy and feedback in alerting the user when the correct delivery location is reached and when to trigger the insertion mechanism will be critical to ensuring doctors are able to perform this procedure properly. Due to the precision required with this type of procedure, a user-centered approach to the technological development will be critical to ensure the product will be safe, usable, and viable as a POC procedure.
In current implant procedures, doctors spend a significant amount of time positioning the electrode in the target area and suturing the lead and electrodes in place. This is conducted under image guidance to confirm that movement did not occur during the anchoring process. Currently, the leads and electrodes are sutured to the fascia to prevent lead migration, because once an electrode migrates, the level of therapy is reduced, and a revision surgery is needed.
If future systems have no leads, there are two promising possibilities for anchoring the electrode in place. One potential solution could be to add a partial lead that acts as additional material to suture to the fascia, while also creating an additional area for harvesting external electromagnetic energy to power the device.
With this solution, similar to the electrode placement, doctor comfort and feedback will play a key role in acceptability of a POC procedure. Whatever tool and mechanism is used, the doctor will need to have feedback to know when the anchoring process is complete, if the connection between the electrode and the fascia is secure, and whether the electrode is in sufficient proximity to the nerve to provide therapy.
Another challenge is reducing electrode migration, which is the leading cause of long-term therapy reduction in current devices. In any nerve anatomy, migration would, at best, render the device non-efficacious and, at worst, lead to deleterious side-effects. Since the additional risk of a POC procedure will need to be balanced with the clinical benefits, doctors and patients will want to ensure prolonged benefits, and not a makeshift solution that will need regular revisions.
As such, it is important to consider ways to reduce migration or counteract the effect. Additionally, the possibility of removing the neurostimulator, if necessary, should be evaluated. Therefore, in order to have a commercially viable alternative to current methods, it is necessary to ensure that the device remains efficacious for as long, if not longer, than current implants.
The second solution would not require suturing at all, and instead is an intravascular implant, which would be held in place similar to how stents are currently deployed. While this solution can reduce migration challenges, it may require the patient to change health habits to mitigate against the potential risk of stent-like restenosis.
With both solutions, changes to lifestyle and body morphology must be taken into account. Unlike the traditional neurostimulator, where the reality is only patients with the most critical conditions are treated, a POC platform lends itself to a larger patient population. Moreover, if current moonshot projects focusing on cognitive enhancement materialize, the types of users will grow to include healthy individuals, who will need the implant to seamlessly fit into their lifestyle without adding unnecessary restrictions.
Where Do We Go From Here?
Only once these three critical elements are de-risked can a full development plan be considered. This would involve a series of proof-of-principle prototypes that get increasingly more realistic to ensure technological feasibility while satisfying user needs. As a part of this process, a number of technology deep-dives and fast-to-failure testing are needed to solidify and refine potential concepts.
The only way to achieve this vision is through a user-centered approach. The flexibility of an integrated product development plan allows for a give-and-take between technical requirements and user feedback, allowing for solutions to arise that may not have been possible if each workflow was conducted in isolation.
While it’s possible that the intersection between a device that fits within a POC framework and is technically feasible is currently not achievable, the technical advances may lead to procedures that are less dependent on highly-skilled surgeons and more reliant on advanced tools. This gets us one step closer to the vision of democratizing neurostimulation therapies.
About The Authors
Al Mashal, PhD is a Principal Engineer at Cambridge Consultants. He leads early-stage product development of surgical and interventional medical devices. He specializes in applied neurophysiology, energy-tissue interaction, and interventional oncology.
Ben Zwillinger is a Human Factors Engineer at Cambridge Consultants. He conducts human factors work on multi-disciplinary medical device development projects. His background includes human factors activities from concept development all the way through validation testing.