Researchers strengthen silicone bonding in soft devices

Houston, Texas – Engineers at Rice University have developed a method to significantly improve the bonding strength of silicone in soft devices, without altering the base materials or introducing new treatments.

The researchers found that the degree of curing at the time of bonding directly impacts how well silicone elastomers adhere.

Their findings, published in Science Advances, provide a predictive framework that connects curing time and temperature with adhesion performance.

“This gives us a kind of clock,” said Daniel Preston, corresponding author and assistant professor of mechanical engineering.

“It tells us when the material has partially cured enough to be handled but is still fresh enough to form strong chemical bonds.”

Silicone elastomers are used widely in soft robotics and biomedical devices due to their flexibility and chemical stability.

However, bonding cured silicone components has been a known challenge, with weak adhesion often leading to leaks or failure under strain.

To address this, the Rice team introduced a “reaction coordinate,” a dimensionless metric that tracks curing progress under varying thermal conditions.

The team demonstrated that bonding within a specific curing window leads to significantly stronger adhesion, while overcuring results in weak interfaces.

Using standard peel tests, the researchers showed that adhesion strength declines sharply beyond a defined reaction threshold.

To validate the model, the team fabricated soft pneumatic actuators with and without curing control.

Devices bonded within the optimal window showed improved pressure tolerance and 50% greater bending curvature.

In a separate trial, 3D-printed silicone structures achieved more than 200% improvement in interlayer adhesion when built using reaction coordinate guidance.

According to Preston, the framework could benefit manufacturers of medical implants, wearable electronics, and soft robotics, especially in additive manufacturing.

The approach does not rely on chemical treatments or plasma bonding, and can be implemented using existing materials and processes.

The research was supported by the US National Science Foundation and NASA.