Phase-change metal ink with pH-controlled chemical sintering for versatile and scalable fabrication of variable stiffness electronics
- Simok Lee
- Gun-Hee Lee
- Inho Kang
- Woojin Jeon
- Semin Kim
- Yejin Ahn
- Choong Yeon Kim
- Do A Kwon
- Michael D. Dickey
- Steve Park
- Seongjun Park
- Jae-Woong Jeong
2025-05-30
Variable stiffness electronics represent the forefront of adaptive technology, integrating rigid and soft electronics in a single system through dynamic mechanical modulation. While gallium’s high modulus tuning ratio and rapid phase transitions make it ideal for transformative electronic systems (TES), its liquid-state instability, high surface tension, and unintended phase transitions during processing pose substantial challenges. Here, we introduce STiffness-Adjustable temperature-Responsive ink (STAR ink), a chemically sinterable gallium composite electronic ink designed to overcome these obstacles. STAR ink enables high-resolution (~50 micrometers) circuit patterning, large-scale batch fabrication, and three-dimensional structure coating at room temperature. Through pH-controlled chemical sintering, STAR ink–based TES exhibits exceptional mechanical tunability (tuning ratio: 1465) and electrical conductivity (2.27 × 10 6 siemens per meter). Demonstrated applications—from multilayered variable stiffness printed circuit boards (PCBs) matching standard PCBs’ complexity to body-temperature responsive neural probe—underscore STAR ink’s potential for reconfigurable electronics across consumer electronics and biomedical devices.