Flexible Force Sensors In article 2202142, Terry Tao Ye, Zhaoli Gao, Jian Yang, and co‐workers present the layout of the skin‐adhesive force sensor based on piezoelectric poly(l‐Lactic acid) and its potential applications in human behavior recognition, such as finger, wrist, and laryngeal knot movement. The sensor is composed of photocurable acrylate films, gold electrodes and poly(l‐Lactic acid) film with a sandwiched structure, the acrylate film is skin‐adhesive and transparent as a substrate. The piezoelectric signal of the sensor during swallowing is presented alongside with a human larynx. Finger pressing and wrist bending are listed in the bottom of cover.

The application of biodegradable films based on the piezoelectric effect of poly-l-lactic acid (PLLA) in sensors, transducers, actuators, and so on has gradually become one of the emerging research focuses. In this work, a flexible PLLA sensor with UV-curable acrylate film packaging is proposed for human behavior recognition. The acrylic films with different proportions have different mechanical and surface properties, showing good flexibility, ductility, and skin adhesion. The morphology and crystal structure of the PLLA films and UV curable substrate obtained under the various postprocessing conditions and different proportions are examined by scanning electron microscopy, X-ray diffraction, Raman, and ATR-FTIR spectroscopy. In addition, by comparing six groups of PLLA films with different treatment conditions, the device made on film stretched four times and annealed for 8 h has the best performance. This sensor has good response ability to impact, vibration, and bending strain, and can be applied to human behavior recognition, such as touch, wrist bending, and swallowing.