The development of flexible three-dimensional integrated circuits (3D-ICs) enables high-density electrical connections, miniaturization, and multifunctional applications. Unlike rigid circuit boards, flexible 3D-ICs can be applied to various surfaces, making them particularly relevant for wearable electronics, biomedical sensors, and soft robotics.
A recent review article in the KeAi Journal Wearable Electronics explores the use of gallium-based liquid metals as conductive materials for the next generation of flexible 3D-ICs. These metals offer high electrical conductivity, mechanical flexibility, and biocompatibility but present challenges in fabrication, including high-resolution structuring, interlayer stability, and oxidation issues that affect performance and durability.
“We noted that fabricating these circuits remains challenging particularly in achieving high-resolution patterning, ensuring interlayer stability, and addressing oxidation issues that impact performance and durability,” shares co-corresponding author Xiaodong Chen. “Hence, we focused on 3D printing-based fabrication methods that allow precise, scalable deposition of liquid metals.”
To address these challenges, researchers are turning to additive manufacturing techniques such as 3D printing. Compared to traditional methods like screen printing and microchannel molding, processes such as direct ink writing offer more precise control over structuring. Coaxial printing enhances stability by encapsulating the liquid metal, while hybrid printing techniques enable complex, multi-layer interconnections.
“A key advantage of 3D printing is its ability to operate at room temperature, making it compatible with soft, stretchable, and bio-integrated substrates,” says the co-corresponding author Dianpeng Qi. “This feature allows flexible circuits to be printed directly onto polymers, hydrogels, and even textiles, paving the way for highly adaptable and functional electronic systems,”
Despite these advantages, liquid metals pose challenges due to their high surface tension and oxidation tendency. Strategies such as doping with nanoparticles like carbon nanotubes or nickel improve mechanical stability and adhesion of printed circuits.
“To address this, researchers have explored ink modification strategies, such as doping with nanoparticles like carbon nanotubes and nickel, which enhance mechanical stability and adhesion while improving circuit durability,” says first author Ruiwen Tian. “Additionally, core-shell structures and oxide-layer engineering help regulate liquid metal flow, enabling more precise patterning. Beyond ink modifications, auxiliary printing techniques further refine fabrication.”
In addition to ink optimization, complementary printing techniques are also being explored. Freeze-assisted printing stabilizes liquid metal through controlled cooling, while hydrogel-supported printing suspends liquid metal in a gel matrix, enabling freeform 3D structures. Liquid-phase printing, on the other hand, facilitates rapid solidification in a fluid medium, forming well-defined conductive pathways.
“Additionally, embedding magnetic particles into liquid metal allows for remotely guided circuit formation, enabling reconfigurable electronics with tunable properties,” says Qi. “These approaches expand the possibilities for liquid metal circuits, offering new pathways to create adaptive, self-healing, and reprogrammable electronic systems.”
Beyond 3D printing, alternative fabrication methods utilize the wetting properties, phase transformations, and magnetic control of liquid metals. Selective wettability structuring guides the metal through laser-patterned surfaces, while phase transformation techniques create pre-formed conductive traces from gallium-indium alloys that can be reconfigured when heated. By embedding magnetic particles, liquid metal can also be remotely controlled, enabling adaptive and self-healing electronics.
“Ensuring that flexible 3D ICs can maintain electrical integrity under repeated mechanical stress is crucial, especially for applications in wearable healthcare monitoring, bioelectronic implants, and robotic systems,” Qi adds. “Future research should focus on developing self-healing and reconfigurable circuits to extend device lifespan, optimizing biocompatibility for seamless integration with biological tissues, and leveraging AI-driven fabrication to enhance precision and scalability.”
Despite these advancements, challenges remain in scalability, reproducibility, and long-term stability. Particularly in the fields of wearable medical devices, bioelectronic implants, and robotics, it is essential that flexible 3D-ICs maintain electrical integrity under mechanical stress. Future research is focused on self-healing and reconfigurable circuits, improving biocompatibility, and utilizing AI-driven fabrication techniques to enhance precision and scalability.
By combining the unique properties of liquid metals with advanced manufacturing techniques, new opportunities arise for developing intelligent, high-performance flexible electronics in human-machine interaction applications.
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