Tunable Pressure Sensor of f-Carbon Dot-Based Conductive Hydrogel with Electrical, Mechanical, and Shape Recovery for Monitoring Human Motion

The reversible volume memories of the inner structures of soft materials with controllable hydrophilic–hydrophobic balance have been widely recognized, for example, hydrogels used in pressure sensors. Mechanical stimuli, such as pressure, vibration, and tensile, may influence the deformation of the hydrogel while simultaneously changing the electronic signal. Here, we designed a hydrophobic carbon dot nanoparticle (f-CD) mixed with polyvinyl alcohol and catechol-conjugated chitosan to obtain a hydrogel suitable for pressure and vibration sensor applications. The hydrophobicity of loaded f-CD plays an important role in mechanical performance and electronic signal acquisition. It also affects the different rheological reversibility and shape recovery as an impact on the volume transition. These characteristics are influenced by the compactness, dimensional structure, and density of the fabricated hydrogel. As a result, hydrogels with high hydrophobicity have a stiff structure (shear modulus 8123.1 N·m–2) compared to that of the hydrophilic hydrogel (ranging between 6065.7 and 7739.2 N·m–2). Moreover, the mechanically dependent volume transition hydrogel affects the electronic resistivity (up to 17.3 ± 1.3%) and capacitance change (up to 145%) when compressed with different forces. The hydrogel with a controlled hydrophobic–hydrophilic inner structure shows a unique sensitivity and great potential for various applications in wearable electronic skins, real-time clinical health-care monitoring, and human–computer interactions.