Structural design advances pave the way for next-generation wearable sensors

Tactile sensors are widely used in robotics, prosthetics, wearable devices, and healthcare monitoring. These devices detect and convert external stimuli such as pressure and force into electrical signals, facilitating effective environmental detection. Scientists have made extensive efforts to improve the performance of tactile sensors in terms of sensing range and sensitivity. In this context, mechanical metamaterials are highly promising. Specifically, auxetic mechanical metamaterials (AMMs)-possessing a negative Poisson’s ratio-enable inward contraction and localized strain concentration upon compression. These counterintuitive behaviors render them lucrative options for designing sensors and actuators with excellent properties.

However, existing AMM technology suffers from fabrication and integration challenges.

Addressing this knowledge gap, a team of researchers from the Seoul National University of Science and Technology, led by Mr. Mingyu Kang, the first author of the study and a Master’s course student in the Department of Mechanical Design and Robot Engineering, and including Dr. Soonjae Pyo, an Associate Professor in the Department of Mechanical System Design Engineering, have proposed a novel 3D AMM-based tactile sensing platform based on a cubic lattice with spherical voids and fabricated using digital light processing-based 3D printing. Their breakthrough findings were made available online and published in the journal Advanced Functional Materials on July 6, 2025.

The researchers explored the tactile sensing platform, utilizing 3D-printed auxetic metamaterials in both capacitive and piezoresistive sensing modes. While the sensor responds to pressure via electrode spacing and dielectric distribution modulation in the first mode, the latter mode leverages a conformally coated network of carbon nanotubes that alters resistance under load.

“The unique negative Poisson’s ratio behavior utilized by our technology induces inward contraction under compression, concentrating strain in the sensing region and enhancing sensitivity. Beyond this fundamental mechanism, our auxetic design further strengthens sensor performance in three critical aspects: sensitivity enhancement through localized strain concentration, exceptional performance stability when embedded within confined structures, and crosstalk minimization between adjacent sensing units. Unlike conventional porous structures, this design minimizes lateral expansion, improving wearability and reducing interference when integrated into devices such as smart insoles or robotic grippers. Furthermore, the use of digital light processing-based 3D printing enables precise structural programming of sensor performance, allowing geometry-based customization without changing the base material,” remarks Mr. Kang.

The team showcased two proof-of-concept scenarios highlighting the novelty of their work: a tactile array for spatial pressure mapping and object classification, as well as a wearable insole system with gait pattern monitoring and pronation type detection capabilities.

According to Dr. Pyo: “The proposed sensor platform can be integrated into smart insoles for gait monitoring and pronation analysis, robotic hands for precise object manipulation, and wearable health monitoring systems that require comfortable sensing without disrupting daily life. Importantly, the auxetic structure preserves its sensitivity and stability even when confined within rigid housings, such as insole layers, where conventional porous lattices typically lose performance. Its scalability and compatibility with various transduction modes also make it suitable for pressure mapping surfaces, rehabilitation devices, and human-robot interaction interfaces that require high sensitivity and mechanical robustness.”

In the next decade, auxetic-structured 3D-printed tactile sensors could form the backbone of next-generation wearable electronics, enabling continuous, high-fidelity monitoring of human movement, posture, and health metrics. Their structural adaptability and material independence could drive the creation of custom-fit, application-specific sensors for personalized medicine, advanced prosthetics, and immersive haptic feedback systems.

As additive manufacturing becomes more accessible, mass-customized tactile interfaces with programmable performance may become standard in consumer products, healthcare, and robotics.