The past couple of decades have seen a spectacular amount of progress towards the development of a variety of probes, arrays, meshes, and fluidic channels for interacting with the brain. From recording electrical activity from individual neurons, to stimulating activity with electricity and light-activated biomolecules, to delivering drugs intracranially, the field of tools for interfacing with the brain has been progressively expanding. Despite this rapid growth of academic research on neuroimplantable devices, very few of these devices penetrate into the clinical and commercial worlds, where they could have significant impact towards diagnosis and treatment of many neurodegenerative disorders, such as Parkinson’s disease.
Reviews of the field often overlook the critical role that regulatory agencies play towards the clinical approval and eventual commercialization of neuroimplantable devices. In an effort to bridge the gap between research groups and regulatory agencies, we present a review paper that analyzes how early design decisions, such as materials choices, device structure, and implantation strategy, can affect the regulatory approval process downstream. We have also explored in detail the various biological and mechanical risk factors associated with implanting neural interfaces in various regions of the human brain. While neuroimplantable devices present biological challenges for long-term implantation, a review of the existing literature has shown a clear predominance of bacterial infections in the meningeal layers, comprising a majority fraction of biological device failures. The cortical and deep brain tissue encounter infections infrequently but are subject to scarring and inflammation as a result of probe placement. Still, it is important to note that most device recalls by the Food and Drug Administration (FDA) are caused by mechanical failures, especially those that occur during device implantation or removal. Accelerated approval through the FDA regulatory pathway, thus, necessitates more mechanically robust, commercializable designs that build on predicate device blueprints.
Based on the findings we report in our review paper, which was invited to contribute to a special issue of Advanced Materials on "Flexible Hybrid Electronics," we urge researchers to design neuroimplantable devices with commercializability in mind from an early stage. We also highlight the need for researchers to begin discussions with regulators from the FDA in the design phase, so as to receive early feedback on transitioning to the clinical and commercial phases. We additionally suggest fast-track paths to approval which incorporate existing predicate designs (501 (k)) or utilize accelerant options such as the humane device exemption (HDE).
Given the current state of the field, we conclude that shaping the next generation of neuroimplantable devices will be an evolutionary process which will involve utilizing predicate designs, engaging FDA regulators early in the clinical approval process, and innovating based on prior research. We hope that this, in turn, will spur greater innovation in bringing neuroimplantable devices to end users and facilitating novel treatments for complex brain disorders. As the focus of brain-machine interfaces may evolve beyond treating disabilities and chronic illness into the field of cognitive enhancement, it is possible that the regulatory environment will adapt as well to handle these radical new changes.