High-sensitivity wearable sensor based on micro-needle structure design assisted by 3D printing
Shengting Zhang, Wanqi Jia, Xu Ting, Ao Guo, Yuteng Liu, Guangli Liu, Xiaoming Yang, Ping Liu, Runhuai Yang, Cong Sui
Abstract
Currently, most commercial knee joint motion sensors focus on large flexion angles, often overlooking subtle movements. Inspired by natural nanostructures like nanofibers and micro-needle arrays, this study presents a highly sensitive hydrogel sensor based on micro-needle deformation. By amplifying variations in contact area and needle deformation, the sensor significantly boosts sensitivity to small displacements. Utilizing digital light processing micro/nano additive manufacturing technology (DLP 3D printing), we have successfully engineered a polyacrylamide (PAMS) hydrogel sensor adept at precisely detecting minor displacements on the skin surface of the knee joint. In light of the challenges associated with detecting micro-needle deformation, we established the sensor's sensitivity index, denoted as GF', defined by the formula GF', = (ΔR/R 0 )/d, where d is specified as 100 μm in accordance with clinical requirements. The sensor attains an optimal sensitivity of 7.73 while simultaneously exhibiting exceptional recognition capabilities and advantages in signal-to-noise ratio when detecting micro-displacements of 20 μm. Experimental validation indicates that this hydrogel sensor demonstrates high sensitivity in monitoring intricate motion patterns, including knee joint twisting and relative sliding. In preliminary experiments, the sensor enabled non-invasive dynamic monitoring of biomechanical axis deviations in lower limbs caused by knee joint deformities via epidermal sensing, demonstrating potential for future submillimeter-level resolution of mechanical anomalies. This advancement opens new technological avenues and offers potential solutions for motion rehabilitation assessment and high-precision motion monitoring. • DLP-printed pyramid microneedle amplifies 20 μm detection via deformation/contact-area. • GF’ = 7.74 sensitivity achieved in complex biomechanical monitoring (GF’ = (ΔR/R0)/d). • PAMS hydrogel maintains >90 % cell viability with skin-safe biocompatibility. • >99 % bacterial inhibition against E. coli / S. aureus enables clinical use. • Multi-directional knee motion tracking validates rehabilitation applications.