Implantable liquid metal-based flexible neural microelectrode array and its application in recovering animal locomotion functions

Abstract

With significant advantages in rapidly restoring the nerve function, electrical stimulation of nervous tissue is a crucial treatment of peripheral nerve injuries leading to common movement disorder. However, the currently available stimulating electrodes generally based on rigid conductive materials would cause a potential mechanical mismatch with soft neural tissues which thus reduces long-term effects of electrical stimulation. Here, we proposed and fabricated a flexible neural microelectrode array system based on the liquid metal GaIn alloy (75.5% Ga and 24.5% In by weight) and via printing approach. Such an alloy with a unique low melting point (10.35 °C) owns excellent electrical conductivity and high compliance, which are beneficial to serve as implantable flexible neural electrodes. The flexible neural microelectrode array embeds four liquid metal electrodes and stretchable interconnects in a PDMS membrane (500 µm in thickness) that possess a lower elastic modulus (1.055 MPa), which is similar to neural tissues with elastic moduli in the 0.1-1.5 MPa range. The electrical experiments indicate that the liquid metal interconnects could sustain over 7000 mechanical stretch cycles with resistance approximately staying at 4 Ω. Over the conceptual experiments on animal sciatic nerve electrical stimulation, the dead bullfrog implanted with flexible neural microelectrode array could even rhythmically contract and move its lower limbs under the electrical stimulations from the implant. This demonstrates a highly efficient way for quickly recovering biological nerve functions. Further, the good biocompatibility of the liquid metal material was justified via a series of biological experiments. This liquid metal modality for neural stimulation is expected to play important roles as biologic electrodes to overcome the fundamental mismatch in mechanics between biological tissues and electronic devices in the coming time.

Flexible fiber-based optoelectronics for neural interfaces

“…The combination of the mechanical compliance and stretchability of SEBS fibers with the biocompatibility of Ga-based liquid metal electrodes suggests the application of these structures in biological tissue interfaces. 86,256 Stretchable fibers have also been fabricated to form tunable optical waveguides by co-drawing transparent PC as the core material within the SEBS cladding. As PC is a glassy polymer, it plastically deformed following stretching of the PC/SEBS fiber with its structure coiling up into a helix upon release (Fig.…”

Liquid Metal Enabled Electrobiology: A New Frontier to Tackle Disease Challenges

“…Beyond skin electronics, LM shows great potential in electrobiology, including brain stimulation, used as a neural junction and for muscle stimulation, cosmetology and dieting, artificial organs, cardiac pacing, cancer therapy, immunization therapy even psychotherapy etc. Figure 3 presents the typical applications and perspectives of LM-enabled electrobiology, such as artificial retinas [ 69 ], cochlear implants [ 70 ], flexible sensors [ 71 ], energy harvesting during movement [ 72 ], electrical skin [ 66 , 73 ], electrical muscle stimulation [ 74 ], liquid metal bath electrodes [ 75 ], nerve connections [ 65 , 76 ], conformable tumor treatment, tumor treating fields [ 11 , 77 ], pace-making and defibrillation, liquid metal electrode array [ 78 ], etc. Both experimental studies and clinical trials will enlarge the application scopes of LM-enabled electrobiology therapy.…”

“…Most recently, a kind of LM electrode is developed which is useful in neuromuscular stimulation [ 74 ]. As shown in Figure 6 D, LM is attached to a flexible PDMS substrate.…”

“… LM-enabled electrobiology in disease therapy. Human model ( ); ( A ) Artificial retina reproduced with permission from [ 69 ]; ( B ) Cochlear implant [ 70 ]; ( C ) Flexible sensors [ 65 ]; ( D ) Electrical skin reproduced with permission from [ 66 , 73 ]; ( E ) Electrical muscle stimulation reproduced with permission from [ 74 ]; ( F ) Liquid metal bath electrode reproduced with permission from [ 75 ]; ( G ) Nerve connection reproduced with permission from [ 65 , 76 ]; ( H ) Conformable tumor treatment; ( I ) Tumor treating fields reproduced with permission from [ 11 , 77 ]; ( J ) Pace-making and defibrillation; ( K ) Liquid metal electrode array reproduced with permission from [ 78 ]. …”

Liquid-Metal Enabled Droplet Circuits

“…Liquid metal has recently been introduced into soft electronics and the biomedical field [ 15 ]. Liquid-metal sensors [ 16 , 17 ], memristors [ 18 ], diodes [ 19 ] and electrodes [ 20 , 21 , 22 ] have already been proposed for health monitoring and disease treatment ( Figure 2 A–C). Recently, some researches has been devoted to the study of liquid-metal droplets ( Figure 2 D), which show great potential in self-powered devices [ 23 , 24 ] and phagocytosis [ 25 ].…”