Neural recording and modulation technologies

Abstract

Within the mammalian nervous system, billions of neurons connected by quadrillions of synapses exchange electrical, chemical and mechanical signals. Disruptions to this network manifest as neurological or psychiatric conditions. Despite decades of neuroscience research, our ability to treat or even to understand these conditions is limited by the tools capable of probing the signalling complexity of the nervous system. Although orders of magnitude smaller and computationally faster than neurons, conventional substrate-bound electronics do not address the chemical and mechanical properties of neural tissue. This mismatch results in a foreign-body response and the encapsulation of devices by glial scars, suggesting that the design of an interface between the nervous system and a synthetic sensor requires additional materials innovation. Advances in genetic tools for manipulating neural activity have fuelled the demand for devices capable of simultaneous recording and controlling individual neurons at unprecedented scales. Recently, flexible organic electronics and bio- and nanomaterials have been developed for multifunctional and minimally invasive probes for long-term interaction with the nervous system. In this Review, we discuss the design lessons from the quarter-century-old field of neural engineering, highlight recent materials-driven progress in neural probes, and look at emergent directions inspired by the principles of neural transduction.

Tissue-like Neural Probes for Understanding and Modulating the Brain

“…Studies indicate that the deleterious chronic immune response is in part due to the mechanical mismatch between the neural tissue and the probe, and together these factors prohibit stable recording and tracking of electrophysiological activities from single neurons over extended time periods. 18,23,28,49–53 …”

“…17 The near universal chronic immune response is believed to be the main contributor to reported degradation of recording and stimulation capabilities over extended time periods with common probes. 18 …”

Flexible and Organic Neural Interfaces: A Review

“…As reported in Figure 2, many different mechanisms can cause the failure of the neural implant (for a good review see [45]) Indeed, such kind of sensors are required to operate in water environments with a high concentration of ions [46,47]. In these conditions, electrochemical reactions could take place causing the device failure [48].…”

“…Biological failure mechanisms include initial tissue damage during insertion; breach of the blood-brain barrier; elastic mismatch and tissue micromotion; disruption of glial networks; formation of a glial scar; and neuronal death associated with the above-mentioned factors, as well as with materials neurotoxicity and chemical mismatch. Reprinted by permission from Macmillan Publishers Ltd.: Nature Reviews Materials [45], copyright 2017.…”

Electrochemical Roughening of Thin-Film Platinum for Neural Probe Arrays and Biosensing Applications

“…1,2 These neural interfaces typically contain conductive metal electrodes that serve as the 'interface' between the device and the tissue. 3 When microfabricated, these electrodes are typically thin films of metal, a few hundred nanometers thick and recent advances show these interfaces to be constructed on thin flexible substrates, further improving the ability of electrodes to interface with tissue. [4][5][6][7] While these thin film electrodes generally act very similar to bulk metal found in non-microfabricated neural interfaces, they can be more delicate than bulk metal, 8 especially when fabricated on a flexible substrate.…”