STAR ink comprises microscale gallium particles uniformly dispersed in a hydrophilic polyurethane matrix dissolved in a neutral solvent (DMSO). After printing, a controlled thermal process induces pH shift and chemical sintering of particles through solvent decomposition, enabling the formation of conductive and structurally modifiable electronics without the limitations of high surface tension or premature solidification found in conventional gallium inks.
The printed electronics achieve a high resolution of ~50μm, electrical conductivity of 2.27×10^6 S/m, and a mechanical stiffness tuning ratio of over 1,465. Demonstrations include a transformative PCB that switches between a rigid portable device and a wearable pulse sensor, and a brain-implantable neural probe that stiffens for insertion and softens in vivo to reduce tissue damage. The probe enables dual-function optogenetic stimulation and electrophysiological recording, maintaining performance even under strain.
This work overcomes long-standing challenges in liquid metal electronics and opens new horizons for reconfigurable systems in wearable healthcare, implantable neural engineering, and soft robotics. The innovation demonstrates scalable manufacturing, stable biocompatibility, and multifunctional capabilities through a simple, room-temperature solution process.