Facile and Large-scale Fabrication of Biodegradable Thermochromic Fibers Based on Poly(lactic acid)

To investigate the feasibility of developing biobased and biodegradable thermochromic fibers,poly(lactic acid)(PLA)fibers with visual temperature indicator functionality were fabricated using a scalable melt spinning technique(spinning speed 800 m/min),where PLA and thermochromic microcapsules were used as fiber-forming polymers and color indicators,respectively.The effect of thermochromic microcapsules on the mechanical properties and reversible color-changing function of PLA fibers was systematically investigated to achieve high tenacity and sensitive color-changing function.The difference in the fiber performance was connected to changes in the multilayer structure.The results show that PLA fibers exhibit excellent tenacity of 3.7-4.7 cN/dtex and reversible and stable thermochromic behavior over 31℃.The high fraction of mesophase within TPLA-1 fiber plays an important role in its tenacity.Meanwhile,the low-concentration of microcapsules(~1 wt%)with good dispersion could act as a nucleating agent inside the PLA matrix and contribute to the formation of microcrystals in the amorphous between primary lamellae,which is also beneficial to maintain the tenacity of the fibers.The agglomeration of high-concentration microcapsules within PLA fibers hampered the formation of mesophase,resulting in a decrease in fiber tenacity.Aside from the content of microcapsules,the agglomeration of high-concentration microcapsules(>5 wt%)is the main reason that limits the substantial increase in fiber color depth.This study opens up new possibilities for degradable thermochromic fibers produced using standard industrial spinning technology.

Bio‑imitative Synergistic Color‑Changing and Shape‑Morphing Elastic Fibers with a Liquid Metal Core

The systematic integration of color-changing and shape-morphing abilities into entirely soft devices is a compelling strategy for creating adaptive camouflage,electronic skin,and wearable healthcare devices.In this study,we developed soft actuators capable of color change and programmable shape morphing using elastic fibers with a liquid metal core.Once the hollow elastic fiber with the thermochromic pigment was fabricated,liquid metal(gallium)was injected into the core of the fiber.Gallium has a relatively low melting point(29.8℃);thus,fluidity and metallic conductivity are preserved while strained.The fiber can change color by Joule heating upon applying a current through the liquid metal core and can also be actuated by the Lorentz force caused by the interaction between the external magnetic field and the magnetic field generated around the liquid metal core when a current is applied.Based on this underlying principle,we demonstrated unique geometrical actuations,including flower-like blooming,winging butterflies,and the locomotion of coil-shaped fibers.The color-changing and shape-morphing elastic fiber actuators presented in this study can be utilized in artificial skin,soft robotics,and actuators.