Flexible Ink That Changes Shape with Heat

Researchers at KAIST have developed an innovative “shape-shifting” electronic ink that changes its stiffness based on temperature. This breakthrough enables electronics that are both firm and flexible—depending on how and where they’re used. It opens new possibilities in wearable health devices, soft robotics, and biomedical implants.

How It Works

The ink is composed of gallium microdroplets suspended in a polymer-based solvent. At room temperature, gallium remains solid, giving the ink rigidity. When slightly heated (just above body temperature), the gallium melts, the surrounding polymer breaks down, and the ink becomes soft and electrically conductive.

• The oxide shell surrounding each gallium droplet is removed when heated in an acidic environment, allowing the particles to merge into a liquid form.

• This switchable behavior makes the ink highly suitable for applications that require structural support during manufacturing or insertion, followed by flexibility during operation.

Technical Highlights

• Achieves a stiffness drop of over 1,400 times when heated.

• Maintains high conductivity despite its flexibility.

• Allows micro-scale printing down to 50 micrometers.

• Compatible with common industrial techniques like screen printing, spray coating, and dip coating.

Demonstrated Use Cases

Two real-world prototypes demonstrated by the team include:

1. A wearable skin patch that stays rigid while off-body (for handling and durability), then softens on skin contact for user comfort.

2. A brain implant that remains firm during surgical placement but softens afterward, reducing tissue irritation and improving biocompatibility.

Why This Innovation Matters

• Bridges the gap between hard and soft electronics: Traditional materials require trade-offs between structure and comfort. This ink enables both.

• Enhances medical device safety and usability: Implants can now be designed to insert easily and then soften to reduce inflammation or discomfort.

• Supports advanced wearable tech: Devices can conform more naturally to the body, making long-term use safer and more comfortable.

• Lowers barriers to manufacturing: The ink integrates easily into standard production processes, making it scalable and commercially viable.