Multi-material 3D printing of self-powered sensors based on ionic thermoelectric hydrogels

The development of self-powered wearable electronics is hindered by the mismatch between rigid thermoelectric generators and deformable body contours in conventional manufacturing methods. Here, we present a 3D-printable ionic hydrogel based on a gelatin and κ-carrageenan matrix that meets the flow, recovery, and structural requirements of multi-material direct ink writing. Our ink design consists of gelatin and κ-carrageenan, where the latter modulates the viscoelasticity of the precursor and enables the formation of a double-network porous structure, thereby enhancing mechanical robustness and facilitating ion transport. High-fidelity 3D architectures can be printed, and an in-situ silicone encapsulation effectively suppresses dehydration, extending operational lifetime. Geometry-optimised features such as wavy structures further improve strain responsiveness by increasing ion-migration pathways. With an SO₄²⁻/SO₃²⁻ redox couple, the hydrogel reaches a Seebeck coefficient of 3.96 mV K⁻¹ and maintains stable thermoelectric output during deformation. Demonstrations of temperature sensing, motion detection, and encoded signal output validate the capability of this integrated printing strategy to produce monolithic, long-lasting, and form-adaptive self-powered wearable devices.