Surfactant-free diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide dissolution for rapidly photocurable, high-strength ionic hydrogels for vat photopolymerization of graded sensing lattices

Surfactant-free phosphoric acid dissolution of TPO for vat photopolymerization • Rapid gelation (3.3 s) and high fracture strength (430 kPa) achieved • Stable ionic conductivity retained over 30 days • The improved BCC lattice sensor eliminates the pressure-insensitive plateau region. • Wearable and soft robotic lattice manipulator applications demonstrated The vat photopolymerization (VPP) of high-performance hydrogels is constrained by the limited aqueous solubility of the highly efficient photoinitiator diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO). Here, we report a surfactant-free strategy to directly dissolve TPO using phosphoric acid (PA), enabling a rapidly photocurable and high-strength PT-AP (PA/TPO-Acrylamide/PEGDA) ionic hydrogel. The PT-AP precursor exhibits rapid liquid-to-solid gelation (3.3 s) at a low energy dosage of 13.16 mJ cm −2 , while retaining considerable mechanical properties after curing. The cured PT-AP ionic hydrogel achieves a strength of 430 kPa, a Young's modulus of 137.5 kPa and a toughness of 1530.71 kJ m −3 . It also demonstrates high ionic conductivity (25.11 mS cm −1 ) with stable retention within 30 days. Comprehensive printability assessments using test geometries and classic strut-based lattices confirm the high VPP manufacturing capacity of PT-AP ionic hydrogel. Furthermore, a continuously graded beam-diameter BCC lattice capacitive sensor is developed, which suppresses the pressure-insensitive plateau and yields high sensitivity over the full dynamic range. Finally, applications in wearable devices and flexible lattice manipulators displayed the potential of this platform for soft sensing and human-machine interaction. This work establishes a surfactant-free TPO dissolution method as a high-efficiency VPP material foundation for developing strong, conductive, and long-term stable ionic hydrogel.