Highly Sensitive Anisotropic Multidirectional Strain Sensor through Direct-Write Micro-3D Printing Ordered Microfibers

Multidirectional strain sensors exhibit significant potential in flexible electronic devices, facilitating precise detection of complex movements. However, achieving both macroscopic and microscopic anisotropy in the conductive networks of strain sensors remains challenging, particularly in developing the high sensitivity and selectivity needed to effectively differentiate axial strains. Highly ordered microfiber is the key to realize high-selectivity multidirectional strain sensor. Herein, we proposed a micro-three-dimensional (3D) printing approach to fabricate highly ordered microfibers, which enables direct printing of orthogonally aligned microfibers for precise identification of in-plane strain directions. The process offers automated control of both microfiber alignment and spacing, streamlining the production of multidirectional strain sensors into a single integrated process. Polylactic acid (PLA) and polybutylene adipate-co-terephthalate (PBAT) were combined in a 75:25 ratio to create highly ordered fiber. There was significant anisotropy in the response to loads applied parallel and perpendicular to the fiber arrangement (maximum sensitivity ratio of 541:2.12), with a significant selectivity of 11.98, which can effectively distinguish between strains of different directions and magnitudes. Furthermore, it has an excellent performance with an operating range of 44%, a maximum gauge factor (GF = 541), good durability (stable performance after 500 stretching cycles), a low detection limit (2% strain), and a fast response (210 ms). This work proposes an efficient approach to solve the trade-off between high directional selectivity and high sensitivity by integrated preparation of cross-affecting highly ordered fibers, demonstrating potential for multidirectional sensors in human-machine motion detection and wearable electronics.