A guide towards long-term functional electrodes interfacing neuronal tissue

Abstract

Implantable electronics address therapeutical needs of patients with electrical signaling dysfunctions such as heart problems, neurological disorders or hearing impairments. While standard electronics are rigid, planar and made of hard materials, their surrounding biological tissues are soft, wet and constantly in motion. These intrinsic differences in mechanical and chemical properties cause physiological responses that constitute a fundamental challenge to create functional long-term interfaces. Using soft and stretchable materials for electronic implants decreases the mechanical mismatch between implant and biological tissues. As a result, tissue damage during and after implantation is reduced, leading not only to an attenuated foreign body response, but also enabling completely novel applications. However, but for a few exceptions, soft materials are not sufficient to create long-term stable functional implants. In this work, we review recent progress in interfacing both the central (CNS) and peripheral nervous system (PNS) for long-term functional devices. The basics of soft and stretchable devices are introduced by highlighting the importance of minimizing physical as well as mechanical mismatch between tissue and implant in the CNS and emphasizing the relevance of an appropriate surface chemistry for implants in the PNS. Finally, we report on the latest materials and techniques that provide further electronic enhancements while reducing the foreign body reaction. Thus, this review should serve as a guide for creating long-term functional implants to enable future healthcare technologies and as a discussion on current ideas and progress within the field.

Soft, Implantable Bioelectronic Interfaces for Translational Research

“…For soft bioelectronics, biocompatibility and histology tests are also required to confirm the superior biointegration properties triggering lower immune response compared to state‐of‐the‐art implants. [ 31,32 ] In the case of epidural electrodes, there is no penetration by foreign material within the neural tissue. We only expected encapsulation of the implant by fibrotic tissue build‐up.…”

Opto‐E‐Dura: A Soft, Stretchable ECoG Array for Multimodal, Multiscale Neuroscience

“…In contrast to traditional rigid devices, they integrate well with biological tissues as a result of low mechanical mismatch and high conformability to curved biological structures. [ 1–3 ] Recently, soft and stretchable devices have been developed to interface with the central nervous system. Minev et al.…”

The rise of flexible electronics in neuroscience, from materials selection to in vitro and in vivo applications

“…This is the main factor that limits the correct operation of a long-term implant that should be desirably active for the entire lifetime of the patient. To minimize this mechanism, four strategies can be adopted: the usage of soft materials, the implementation of surface coating to prevent biofouling, the integration of drug delivery system to control the inflammatory mechanism and the engineering of autologous cell layer to suppress the tissue response [14]. On the implant side, other issues arise in term of durability and reliability.…”

“…Numerous review papers reported new findings in the part that is usually in contact with the brain, such as the electrode grid [10][11][12][13] and described physiological mechanisms underlying the implantation of these devices in the brain [14], but very few present all the fabrication methodologies that involve new materials and electronic design to allow the manufacturing of the whole system.…”