Direct Laser Writing of Functional Strain Sensors in Polyimide Tubes

It is highly desirable to have an approach that can integrate the design, processing, and fabrication of sensitive components and sensing elements to enable robust development of a highly sophisticated, specialized, and customized force/strain sensing system. Herein, by applying the flexible direct laser writing carbonization (DLWc) technique to a polyimide tube and with assistance of finite element analysis simulation, we successfully demonstrate this concept through designing, fabricating, characterizing, and testing the versatile 3D tubular sensing system that is able to sense a multitude of signals in different application scenarios, including sensing gas pressure, contact force, liquid viscosity, and detecting wind flow and underwater ultrasound signals. Moreover, with packaging the tubular sensor in a compliant poly(dimethylsiloxane) elastomer matrix and embedding it in an insole, the DLWc created tubular sensing system has also been demonstrated in use for pressure mapping to enable foot function and gait analysis. The approach presented in our work—combining DLWc with complex structured sensitive components—offers a strategy for low-cost, high-throughput, and versatile development of the sensing system that can meet highly demanding and customized force and strain measurement applications.