"Grainy Laser Speckle Patterns" Deliver More Sensitive Soft Pressure Sensors — and Could Heal Wounds

Researchers from China's Shanxi University have come up with a new approach to building high-sensitivity flexible capacitive pressure sensors — by using "grainy laser speckle patterns" to build microstructures in the sensor material.

"Wearable technologies utilizing flexible pressure sensors have made significant strides in finding applications in human–machine interaction, health monitoring, and electronic skin," the researchers explain by way of background to their work. "Capacitive pressure sensors suffer from an inherent limitation of low sensitivity. This is currently solved by embedding a micropattern into the electrodes or dielectric layers, which are tailored to augment the sensitivity and align with real-world application demands."

While embedded micropatterns solve the sensitivity problem, they introduce an issue of their own: the complexity of actually getting these micropatterns embedded in the target material. For this, the team turned to a pulsed laser system — using an approach known as laser speckle grayscale lithography to create "grainy laser speckle patterns" that, in turn, are responsible for random conical array (RCA) microstructures in the sensor.

To prove the concept, the team used the technique to produce capacitive pressure sensors from polydimethylsiloxane (PDMS), a flexible non-toxic material, which showcased ultra-high sensitivities up to 19.76kPa⁻¹ across a range of 0-100 Pascals of pressure, with a minimum detection of 1.9Pa. Impressively, the soft sensors also showed considerable resilience despite their sensitivity — delivering stable readings across 10,000 test cycles, the team reports.

The researchers are now investigating other applications for the technology, including treating materials for anti-reflection and anti-fog properties — and even in helping wounds to heal. "[RCA microstructures] can be applied to patches that promote wound healing," the team explains of this latter possibility, "because the conical microstructures can easily penetrate the skin, effectively deliver drugs to the target area, and maintain the local drug concentration for a long time."

The team's work has been published in the journal Light: Advanced Manufacturing under open-access terms.