Porous hydrogel sensors have attracted significant attention in fields such as smart wearables and medical monitoring due to their high sensitivity. However, existing fabrication methods typically degrade the surface smoothness of hydrogels when introducing porous structures and face significant challenges in removing fillers completely. To address these challenges, we herein introduce a novel one-step, thermosensitive spray-coating technique for the preparation of aircell hydrogel (ACH). This method leverages the rapid cooling of a thermoresponsive gelatin methacryloyl solution through atomization, enabling rapid cross-linking within seconds and air bubbles encapsulated in situ. Additionally, the transient flow of the pre-gel facilitates the repair of voids formed by ruptured surface bubbles, leading to the creation of the ACH with uniformly distributed inner air bubbles and a smooth outer surface. The mold-free fabrication method is independent of substrate surface properties, enabling the creation of a porous hydrogel film with a thickness as thin as 163 μm. Furthermore, the dual-crosslinked network endows the ACH with excellent anti-swelling properties, and the physical crosslinking between gelatin molecules allows the ACH to self-heal. The ACH exhibits excellent sensitivity in deformation sensing and can even successfully track minor external forces, which enables it to effectively complete various tasks such as facial expression recognition, pitch differentiation, and motion detection. By integrating the ACH into a sensing glove, we also demonstrate the significant potential of the ACH for applications in human-machine interaction and tactile sensing. Ultimately, the ACH sensors are also applied to motion mapping and machine tactile feedback, indicating their promising potential in human-machine interaction.

Electrocardiogram (ECG) monitoring is crucial for cardiovascular health assessment, yet often encumbered by bulky equipment, limited mobility, and professional application requirements of traditional ECG monitoring systems. Moreover, hydrogel-based bioelectrodes are facing challenges of high impedance and poor overall circuit flexibility. Addressing these multifaceted challenges, this study introduces a revolutionary approach through the development of a flexible electronic skin (e-skin) incorporating a novel dual-bridge ionic-electronic amphoteric (DBIEA) hydrogel. Our proposed dual-bridge strategy for synthesizing DBIEA hydrogel yields materials with excellent electrical conductivity (~ 5000 S/m) and unique ion-electron amphoteric properties. When applied as bioelectrodes, these hydrogels demonstrate tremendous potential in biological signal monitoring. Utilizing these DBIEA hydrogel, we develop an all-stretchable e-skin (ECG-Skin) for continuous 12-lead ECG monitoring. This ECG-Skin is characterized by its ultra-lightweight design, with a total mass not exceeding 20 g and a thickness of less than 1 mm. It exhibits superior signal quality, simplifies the ECG monitoring process by eliminating the need for medical professionals, and offers exceptional wearability. In the emotion recognition task utilizing ECG-Skin for monitoring 12-lead ECG, the convolutional neural networks (CNN)-based classification achieves an accuracy rate of 98.429%. These features collectively provide unprecedented portability in ECG monitoring technology.