Ultracompliant Hydrogel-Based Neural Interfaces Fabricated by Aqueous-Phase Microtransfer Printing

Hydrogel-based electronics are ideally suited for neural interfaces because they exhibit ultracompliant mechanical properties that match that of excitable tissue in the brain and peripheral nerve. Hydrogel-based multielectrode arrays (MEAs) can conformably interface with tissues to minimize inflammation and improve the reliability to enhance signal transduction. However, MEA substrates composed of swollen hydrogels exhibit low toughness and poor adhesion when laminated on the tissue surface and also present incompatibilities with processes commonly used in MEA fabrication. Here, a strategy to fabricate an ultracompliant MEA is described based on aqueous-phase transfer printing. This technique employs redox active adhesive motifs in hygroscopic polymer precursors that simultaneously form hydrogels through sol–gel phase transitions and bond to materials in the underlying microelectronic structures. Specifically, in situ gelation of four-arm-polyethylene glycol-grafted catechol [PEG-Dopa]₄ hydrogels induced by oxidation using Fe³⁺ produces conformal adhesive contact with the underlying MEA, robust adhesion to electronic sub-structures, and rapid dissolution of water-soluble sacrificial release layers. MEAs are integrated on hydrogel-based substrates to produce free-standing ultracompliant neural probes, which are then laminated to the surface of the dorsal root ganglia in feline subjects to record single-unit neural activity.