A Virginia Tech lab prints a silicone filled with droplets of liquid gallium-indium alloy, then stretches the droplets during printing so heat flows along them. A 2025 paper reports 9.9 W/mK along the droplet direction, about 40 times unfilled silicone. The work is early research aimed at custom heat sinks and stretchable wearables.
Key facts
Composite: EGaIn droplets of about 10 to 100 microns in PDMS silicone
Thermal conductivity along droplets: 9.9 W/mK, about 40 times unfilled silicone
Droplet stretching is set by nozzle flow versus print bed speed
Research from Virginia Tech's VT MADE, led by Michael Bartlett
Context EGaIn is eutectic gallium-indium, an alloy of roughly three parts gallium to one part indium that stays liquid at room temperature; PDMS is a common silicone elastomer.
How is the composite made and printed?
Graduate student Hugh Grennan of the Soft Materials and Structures Lab at VT MADE mixes EGaIn into uncured PDMS. The mixing breaks the metal into separate droplets of roughly 10 to 100 microns, each protected by a thin oxide layer. Roughly an hour of oven curing solidifies the silicone while the droplets stay liquid. The material is printed from a syringe-fed machine.
How does printing steer the heat?
Droplet shape depends on the ratio between the speed at which material leaves the nozzle and the speed of the print bed. A suitable ratio stretches round droplets into long, thin ones, so heat can travel along each droplet from a source to a sink. A 2025 paper in Advanced Functional Materials, co-authored by lab head Michael Bartlett, reports 9.9 W/mK along that direction, about 40 times the unfilled silicone. A 2024 paper in Additive Manufacturing credits the oxide layer with helping droplets keep their shape.
What about the self-healing circuit demo?
In a cast slab, pressing a line with an indenter merges droplets into a conductive track that lit an LED. After the track was cut with a razor blade, pressing again near the cut restored the light, though faintly, because the metal flows around the damage. Named uses are custom heat sinks and stretchable wearables, plus directed cooling in vehicles, robots and electronics.
What it means
This is laboratory research shown in a video, not a product. For manufacturers the relevant point is the principle: print parameters, not only material choice, can set the direction of thermal conductivity. Syringe-fed printing of a metal-filled elastomer has no qualification route, no supplier and no stated cost per part. Small and mid sized European companies in thermal management or wearables can follow the papers, but should not plan around it within a normal project timeline.
Frequently asked questions
How much does the printing raise thermal conductivity?
A 2025 paper co-authored by Michael Bartlett reports 9.9 W/mK along the droplet direction, about 40 times that of unfilled silicone.
Why does the material stay conductive after being cut?
The droplets are liquid metal, so pressing near a cut lets the metal flow together again and rebuild a conductive path, as shown with an LED.