(Nanowerk Spotlight) Creating electronic circuits that can bend and flex while maintaining reliable electrical connections presents significant engineering challenges. Traditional electronics rely on solid metals like copper and gold, which provide excellent conductivity but can fail when subjected to repeated bending or stretching. This limitation affects applications where electronics need to conform to irregular shapes or maintain function while being deformed.
Current manufacturing methods for flexible electronics primarily create two-dimensional patterns on flat or slightly curved surfaces. These techniques, including stencil printing, injection filling, and direct ink writing, effectively produce thin conductive layers but cannot build truly three-dimensional electronic structures. When attempting to create 3D patterns, manufacturers must often stack multiple 2D layers or use complex post-processing steps, leading to reliability issues at layer interfaces.
Liquid metals, particularly gallium-based alloys, offer an alternative approach due to their unique properties. These materials remain fluid at room temperature while maintaining electrical conductivity comparable to solid metals. However, their fluid nature creates manufacturing challenges – they tend to merge unpredictably and resist precise patterning, especially in three-dimensional configurations.
A research team in Singapore and China has developed a method to control liquid metal flow for creating three-dimensional electronic patterns within flexible structures. Their approach, detailed in Advanced Functional Materials (“Capillarity-Assisted 3D Patterning of Liquid Metal”), combines 3D printing with controlled fluid dynamics to guide liquid metal into specific patterns. Rather than building up layers, it creates complete 3D structures in a single process. The technique allows electronic pathways to traverse multiple directions and levels simultaneously, enabling complex circuits that previous methods could not achieve.
Capillarity-assisted 3D patterning of liquid metal (LM) in a DLP-printed hierarchical lattice matrix. a) Schematic of the 3D patterning process. b–d) Digital images of the lattice structure at various fabrication stages (top) and corresponding microscopic images of pillar surface in the horizontal cross-section of the liquid path (bottom): b) as-printed structure with a pixelized smooth surface, c) LMP-deposited pillar after liquid infusion and ethanol evaporation, and d) electrically conductive LM circuit after sintering, which illuminates a green LED. (Image: Reprinted with permission by Wiley-VCH Verlag)
The researchers use digital light processing to create lattice structures containing networks of channels between 496 and 2480 micrometers in diameter. These channels guide liquid metal through capillary action – the physical phenomenon that moves liquids through narrow spaces. The team demonstrated that smaller channels, particularly those around 496 micrometers, provide better control over liquid metal movement.
To improve control over the liquid metal, the researchers developed a mixture combining microscopic metal droplets suspended in ethanol with a polymer called polyvinylpyrrolidone. This mixture flows predictably through the printed channels and settles into defined patterns. Applied pressure then merges the droplets into continuous electrical pathways.
The resulting structures achieve an electrical conductivity of 377,000 siemens per meter while retaining flexibility. In testing, the circuits maintained electrical performance through 1,000 cycles of stretching and bending. The technique allows stretching up to 100% of original length while maintaining electrical function.
The team created several test devices to demonstrate practical applications. They produced electromagnetic interference shields that blocked more than 90% of incoming signals. They built pressure sensors with response times of 175 milliseconds and multi-circuit structures capable of independently controlling separate electronic components while being twisted or bent.
This manufacturing process reduces complexity compared to existing methods. The entire fabrication cycle, from printing the structure to creating functional circuits, takes minutes and requires no specialized equipment beyond the printer itself. The process works at room temperature and uses commercially available materials.
The researchers identify several specific paths for advancing this technology. High-resolution 3D printing techniques, particularly projection micro-stereolithography and two-photon polymerization, could refine feature sizes from the current 496 micrometers down to micron and sub-micron scales. This miniaturization would enable more complex circuits in smaller spaces while potentially improving the precision of liquid metal patterning.
The team also suggests optimizing the resin formulation used in printing. Adding specific photoabsorbing materials could reduce unwanted curing effects and enhance the dimensional accuracy of the microchannels that guide the liquid metal. This improvement would allow for more precise control over electrical pathways.
Current mechanical methods for activating the liquid metal circuits, while effective, could potentially damage very small features. The researchers propose two alternatives: evaporation-induced sintering, which would work by controlling the composition of the liquid metal mixture, and acoustic sintering, which would use sound waves to merge metal particles without physical pressure. These techniques could enable more delicate and precise electronic structures.
The manufacturing process currently works well for small devices but faces challenges in scaling up to larger productions. The researchers outline several approaches to address this, including optimizing the liquid metal mixture for faster flow through channels and developing automated systems for the sintering process.
These improvements could enable applications requiring higher precision or smaller scale than currently possible. The researchers particularly note the potential for creating more sophisticated medical implants and microscale sensors once these refinements are implemented.
Get our Nanotechnology Spotlight updates to your inbox!
Thank you!
You have successfully joined our subscriber list.
Become a Spotlight guest author! Join our large and growing group of guest contributors. Have you just published a scientific paper or have other exciting developments to share with the nanotechnology community? Here is how to publish on nanowerk.com.
