3D printing hydrogel with structural design via vat photopolymerization for strain sensing

Due to the constraints of photoinitiators and mechanical properties, vat photopolymerization 3D printable hydrogels are still the focus of current research. Drawing inspiration from the water-soluble modification of the photoinitiator diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), a rapid and expedient UV-curable hydrogel with remarkable strength and toughness has been developed using polymerizable micelles. The incorporation of polymerizable micelles not only significantly enhances the solubility of TPO, an efficient commercial photoinitiator, thereby eliminating the need for specific organic solvents, but also serves as physical crosslinking points for polymer chains. Moreover, by harnessing the abundant hydrogen bonding present in glycerol and plant cellulose, the precursor hydrogel exhibits a rapid layer-by-layer printing capability of 6 s per layer, accompanied by an enhanced mechanical toughness reaching 4.55 MJ/m³. The hydrogel-based resistance sensor demonstrates wide-ranging detection capabilities and high sensitivity. It has the gauge factor (GF) of 2.28 within low strains (<100 %) and can maintain a high linear GF of 5.84 even under large strains (200–500 %). This allows the hydrogel-based sensor to have a significant change in relative resistance when detecting human limb movements. The lattice structure design imparts a notable pressure sensitivity of 1.13 KPa−1. Additionally, the utilization of a glycerol/water binary solvent ensures excellent water retention properties. Furthermore, the hydrogel exhibits significant advantages in capacitive sensors owing to its printed surface gradient bulge structure. Consequently, the hydrogel developed in this study possesses exceptional printing abilities, high strength, and impressive toughness, making it a valuable option for the design and fabrication of flexible electronic devices.