Minimally Invasive & Long‐lasting Neural Probes from a Materials Perspective

Abstract

Neurological disorders in aging society have created the need to understand how the brain works. At present, there are limited engineered “non‐invasive” tools to study and characterize the brain activity. Advancement in neuroscience research is highly focused on the fabrication of implantable neural probes that can effectively integrate with the neural tissue. Challenges associated with the commercially available probes has driven the development of mechanically compliant and non‐invasive neural implants. Engineering the mechanical and electrical performance of these probes is necessary to obtain tremendous sensitivity and selectivity along with chronic functionality. Selection of proper materials and understanding their fundamentals plays an essential role in achieving the desired neural interface. In this review, we have highlighted the recent progress in the utilization of new materials to attain a neural probe with improved flexibility, biocompatibility and signal quality.

Advances in electrical impedance tomography-based brain imaging

“…Nevertheless, traditional electrode materials have high rigidity relative to the human skull. This mismatch in mechanical properties can result in brain damage [142], which limits the application of this technology for clinical diagnosis and treatment.…”

Soft Devices for High-Resolution Neuro-Stimulation: The Interplay Between Low-Rigidity and Resolution

“…One of the significant advantages of CNT electrodes is their electrical and mechanical interface with neurons. Their tridimensional structure and high surface area increases electrode capacitance, lowers the impedance, therefore enabling size reduction of the electrodes to achieve high density devices with high efficacy local stimulation, and reduces the tissue inflammatory response (240,242,(251)(252)(253). Vitale et al demonstrated neural recording and stimulation using CNT fiber electrodes, when neurons in vivo were activated as efficiently as metal electrodes with a 10 times larger surface area (254).…”

“…Nano electrodes with increased roughness, using nanowires, graphene, conductive polymers or carbon nanotube (CNT) coatings can resolve long-standing challenges ( 95 , 216 , 240 ). In particular, carbon nanotubes ( 241 , 242 ) which exhibit Young's Modulus as high as 1 TPa and tensile strength of 100 GPa, can bend and twist without breaking, and are therefore an appealing material for stable, thin and flexible electrodes ( 243 – 245 ). CNTs are known for their utility in recording neuronal signaling, demonstrating reduced impedance and much higher signal to noise ratio ( 156 , 217 , 246 – 248 ).…”

“…CNTs are known for their utility in recording neuronal signaling, demonstrating reduced impedance and much higher signal to noise ratio ( 156 , 217 , 246 – 248 ). The in vivo biocompatibility of CNTs and other carbon materials was addressed by Baldrihi and Veronica, concluding that it strongly depends on the administration site, dosage, purity, and agglomeration ( 241 , 242 , 245 ). In 2005, it was shown that CNTs can be used for neuronal signal improvement and enhanced dendrite elongation as well as cell adhesion and growth ( 217 , 249 , 250 ).…”

Ionic Hydrogel for Accelerated Dopamine Delivery via Retrodialysis

“…Likewise, new membrane materials that are compatible with microfabrication techniques could allow for adaptation of recently reported material/device architectures that mitigate the foreign body response. This is particularly important as the foreign body response is well-known to limit the long-term efficacy of medical implants for drug delivery and sensing. − …”