An aircell hydrogel for ultra-sensitive human-machine interaction

A novel conductive hydrogel, termed AirCell Hydrogel and developed by Tianjin University researchers, exhibits an ultra-high sensitivity of 18.9. Its smooth surface enables conformal adhesion that effectively suppresses motion artifacts, while its porous interior structure lowers the Young's modulus during deformation tracking.

The work, reported in the International Journal of Extreme Manufacturing, achieved high-accuracy human–machine collaborative interaction and is expected to play a significant role in remote surgical operations, virtual reality, and related fields.

Surface defects and residual components in porous hydrogels are key factors limiting their sensing applications.

"Existing porous hydrogels are typically fabricated by foaming, phase separation, sacrificial templating, and the like," said Faze Chen, corresponding author on the paper and Associate Professor at the School of Mechanical Engineering, Tianjin University. "They face challenges such as surfaces riddled with pores and residual contaminants trapped inside. This prevents them, when used as sensing patches, from fully capturing motion signals and also results in poor biocompatibility. Therefore, why not adopt an additive-like approach to construct internal pores instead of performing these complex treatments on the precursor solution?"

Porous structures with a high specific surface area have been shown to effectively enhance the sensitivity of hydrogel sensors. They have recently emerged as a novel research strategy for reducing response hysteresis and lowering detection limits.

However, existing fabrication methods often cannot produce a smooth surface to maximize skin contact area, and the non-degradable residues prevent the hydrogel's use for in vivo signal detection. Moreover, because the one-pot fabrication process involves wetting at the solution–mold interface, the resulting gel thickness reaches several millimeters.

Chen's group formulated a temperature‐sensitive pre‐gel solution and, by spray-induced atomization cooling, achieved a quasi-3D-printed bubble-gel structure. This method requires no additional dopants and is mold-free, and surface defects of the gel are instantaneously repaired by the flowing solution to yield a smooth exterior.

The core–shell crosslinked double-network endows the AirCell Hydrogel with exceptional mechanical properties. The researchers conducted a comprehensive evaluation of its adhesion, self-healing, and anti-swelling performance. In sensing applications, it can accurately detect a variety of human motions—including facial expressions, hand gestures, throat movements, and pulse beats—enabling a robotic hand to mirror the movements of a human hand.

"A major highlight of this work is that the AirCell Hydrogel exhibits a sandwich structure, achieving a bubble interlayer while retaining a smooth surface—something that similar studies have not accomplished," said co-author Ye Tian, Associate Professor at Northeastern University. "Moreover, its micrometer-scale tunable thickness makes it indispensable for high-precision, miniaturized sensing applications."

The researchers are continuing their work, aiming to introduce covalent crosslinking to enhance the gel sensors’ tolerance to extreme environments. They also plan to integrate a three-dimensional programmable motion platform and precisely control the spraying area to achieve macroscopic structuring of the bubble hydrogel sensors.

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