Printed Stretchable Liquid Metal Electrode Arrays for In Vivo Neural Recording

Abstract

The adoption of neural interfacing into neurological diagnosis is severely hampered by the complex, costly, and error‐prone manufacturing methods, requiring new fabrication processes and materials for flexible neural interfacing. Here a strategy for fabricating highly stretchable neural electrode arrays based on screen printing of liquid metal conductors onto polydimethylsiloxane substrates is presented. The screen‐printed electrode arrays show a resolution of 50 µm, which is ideally applicable to neural interfaces. The integration of liquid metal–polymer conductor enables the neural electrode arrays to retain stable electrical properties and compliant mechanical performance under a significant (≈108%) strain. Taking advantage of its high biocompatibility, liquid metal electrode arrays exhibit excellent performance for neurite growth and long‐term implantation. The stretchable electrode arrays can spontaneously conformally come in touch with the brain surface, and high‐throughput electrocorticogram signals are recorded. Based on stretchable electrode arrays, real‐time monitoring of epileptiform activities can be provided at different states of seizure. The method reported here offers a new fabrication strategy to manufacture stretchable neural electrodes, with additional potential utility in diagnostic brain–machine interfaces.

Flexible and stretchable polymer optical fibers for chronic brain and vagus nerve optogenetic stimulations in free-behaving animals

“…The strain at break of the POFs is higher than 150%, implying a superior stretchability compared to the reported polymer-based optical implants for in vivo optogenetics [ 29 , 36 ]. In addition, we did not observe noticeable cracks or significant influence on the output power of the POFs after repeated 100% stretching deformation, which implies an excellent mechanical stability of the fabricated optical waveguides [ 37 – 39 ]. Those advantages greatly expand the potential applications of optogenetics and enable optical delivery in soft tissues even with large deformations.…”

Strategies for interface issues and challenges of neural electrodes

“…4): (i) Charge transfer by electrons: traditional neural electrode materials such as metal and carbon employ free electrons as movable charge carriers to communicate with biological tissues. 55,62 Because of their outstanding electrical conductivity and biological stability, they can be implanted in vivo for a long time and have been extensively investigated; 63 (ii) charge transfer by ions: hydrogels are essentially ionic conductive materials, which reveal favorable promise in neural interfaces due to their inherent biocompatibility, flexibility, and compliance with nerve tissues; 11,21,64–66 and (iii) charge transfer via an electron–ion synergistic effect: the electrode materials include not only conductive polymers with soft, flexible and mechanically adjustable properties, 67,68 but also the composite materials which are constituted with both ion-conductive and electron-conductive materials.…”

“…A high charge storage capacity and charge injection limit enhance the stimulating capability of the electrode (Table S1†). In addition, the flexible stretchable/bendable 27,28 electrodes can withstand large mechanical deformations and conformal well with soft dynamic biological tissues, which improves the fidelity and stability of the signal transmission. Simultaneously, high-density neural electrodes can achieve multi-site acquisition of the same neuron activity, 29,30 so that more waveform information can be used to distinguish neuron signals from multiple sources to ensure the authenticity of the information.…”

Flexible and Stretchable Liquid Metal Electrodes Working at Sub-Zero Temperature and Their Applications

“…Although Galinstan shows outstanding properties including flexibility and stretchability even under cold conditions, its high surface tension and rapid oxidation rate hinder the fabrication of desirable patterns for electronic devices and circuits in comparison with other functional materials [13][14][15]. Various methods for Galinstan patterning thus have been developed and enhanced, including microfluidic injection [16][17][18][19][20][21], photolithography [22,23], stencil lithography [24][25][26][27], imprint lithography [28], microcontact printing [29,30], and composite material synthesis [31]. Each of these methods has individual advantages (i.e., high processability, high resolution limits, high stability, or cost-effective fabrication); however, integrating all the advantageous elements is still a challenge.…”