Abstract
Neural prostheses have already a long history and yet the cochlear implant remains the only success story about a longterm sensory function restoration. On the other hand, neural implants for deep brain stimulation are gaining acceptance for variety of disorders including Parkinsons disease and obsessive-compulsive disorder. It is anticipated that the progress in the field has been hampered by a combination of technological and biological factors, such as the limited understanding of the longterm behavior of implants, unreliability of devices, biocompatibility of the implants among others. While the field's understanding of the cell biology of interactions at the biotic-abiotic interface has improved, relatively little attention has been paid on the mechanical factors (stress, strain), and hence on the geometry that can modulate it. This focused review summarizes the recent progress in the understanding of the mechanisms of mechanical interaction between the implants and the brain. The review gives an overview of the factors by which the implants interact acutely and chronically with the tissue: blood-brain barrier (BBB) breach, vascular damage, micromotions, diffusion etc. We propose some design constraints to be considered in future studies. Aspects of the chronic cell-implant interaction will be discussed in view of the chronic local inflammation and the ways of modulating it.
Highlights
The therapeutic use of electrical stimulation of the nervous system is a rapidly growing field already distributed over a wide range of applications, such as Deep Brain Stimulation for Parkinson’s disease (Beitz, 2014), tremor, dystonia and obsessive-compulsive disorder (Greenberg et al, 2010); vagus nerve stimulation for epilepsy (Morris et al, 2013), respiratory pacing prostheses; the spinal cord stimulation to control chronic pain (Wolter, 2014) and the auditory neural prostheses, to name just the most broadly accepted treatments
There appears to be a spectrum of effects, related to the sterility of the implantation and environment; the acute brain inflammation with blood-brain barrier (BBB) breach, haematom resorption and perhaps infection linked to the implantation and environment sterility
BBB refers to the vascular segment of the capillaries that regulate diffusion of solutes, whereas in an inflammatory response, the term refers to the postcapillary venules, that is, the vessels from which leukocytes migrate into the CNS, which are distinct vascular segments (Owens et al, 2008)
Summary
The therapeutic use of electrical stimulation of the nervous system is a rapidly growing field already distributed over a wide range of applications, such as Deep Brain Stimulation for Parkinson’s disease (Beitz, 2014), tremor, dystonia and obsessive-compulsive disorder (Greenberg et al, 2010); vagus nerve stimulation for epilepsy (Morris et al, 2013), respiratory pacing prostheses; the spinal cord stimulation to control chronic pain (Wolter, 2014) and the auditory neural prostheses, to name just the most broadly accepted treatments Despite this acceptance there is still much space for progress, for example, by providing bi-directional (i.e., including sensing) interfaces, which would open the path for closed-loop approaches and titration of stimulation. We discuss the mechanisms of neuroinflammation in this perspective
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