Electrospinning Machine | Flexible Silk-Fibroin-Based Electroluminescent Fiber with External-Field-Driven Touch Response and Triboelectric Sensing for Smart Wearables

Flexible and lightweight electroluminescent electronic products have attracted widespread attention in the field of smart textiles. However, current electroluminescent devices mainly rely on petroleum-based matrices, complex high-voltage power sources, and embedded sensors, which limits their suitability for sustainable, lightweight, and visually intuitive wearable electronics.

Figure 1. a) Preparation process of silk-fibroin-based electroluminescent fiber (SFELF). b) Morphological changes of SFELF during preparation. c, d) Electroluminescence mechanism of SFELF. e) Formation of the local electric field at the contact between the external electrode and the luminescent layer in SFELF and its principle of promoting luminescence.

Based on this, a research team consisting of Associate Professor Yao Yijun, Professor Zhang Pengfei, and Dr. Zhang Zhenfang from Xi'an Polytechnic University collaborated to fabricate a flexible, high-brightness, coaxially-structured silk fibroin-based alternating current electroluminescent fiber (SFELF) using conjugated electrospinning, coating, and encapsulation techniques. By precisely designing the luminescent layer matrix with silk fibroin and adjusting its β-sheet-rich secondary structure, the resulting SFELF exhibits outstanding mechanical toughness (5.29 MJ m⁻³) and high brightness (up to 366 cd m⁻²), surpassing counterparts based on polydimethylsiloxane and cellulose matrices. This fiber maintains stable brightness after more than 10,000 bending cycles, demonstrating superior mechanical durability and stability. Even after the structural outer electrode is removed, the fiber retains its sensitive touch-activated luminescence properties, which can be modulated by external electric or thermal fields without requiring an external power source. This luminescence phenomenon can be achieved by touching with a finger or metallic material. Regarding potential smart textile applications, the SFELF integrates triboelectric and liquid sensing capabilities, enables real-time visual monitoring, and offers significant potential for human-machine interaction. The related research findings were published under the title "Flexible Silk-Fibroin-Based Electroluminescent Fiber with External-Field-Driven Touch Response and Triboelectric Sensing for Smart Wearables" in the journal Advanced Functional Materials.

Figure 2. a) Silver-plated nylon yarn, b) fiber coated with dielectric layer, c) appearance and surface morphology of silk-fibroin-based electroluminescent fiber (SFELF). d–i) Scanning electron microscopy (SEM) images and energy dispersive spectroscopy (EDS) images of the cross-section of silk-fibroin-based electroluminescent fiber (SFELF).

Figure 3. a) System snapshots at 0, 10, 20, 60, 80, and 100 nanoseconds (ns). b) Root mean square deviation (RMSD) of silk fibroin (SF) fragments. c) Centroid distance between copper-doped zinc sulfide (ZnS:Cu) and silk fibroin (SF); d) Binding energy between ZnS:Cu and SF. e) Active amino acid residues at the interface between ZnS:Cu and SF.

Figure 4. a) Light transmittance of silk fibroin (SF) film. b) Fourier transform infrared spectroscopy of degummed silk fibroin, silk fibroin-coated polyvinylidene fluoride fiber (SFF), and silk-fibroin-based electroluminescent fiber. c) Fourier transform infrared spectroscopy of SFELF under different acidification degrees. d) Secondary structure proportion of SFELF and acidified silk-fibroin-based electroluminescent fiber (when citric acid content is 0, it represents SFELF; "SFEFL" in the original text is a typo for "SFELF"). e) X-ray diffraction spectra of polyvinylidene fluoride (PVDF), SFELF, and Acid-SFELF. f) Mechanical properties of SFF, SFELF, and Acid-SFELF. g) Luminescence cycle stability of SFELF.

Figure 5. a) Photoluminescence image of silk-fibroin-based electroluminescent fiber (SFELF). b) Photoluminescence spectrum of SFELF. c) CIE color coordinate diagram of SFELF photoluminescence. d) Change of SFELF luminescence brightness with voltage. e) Spectral changes of SFELF at different voltages (frequency: 50 kHz). f) Change of SFELF luminescence brightness with frequency (electric field strength: 3 V·μm⁻¹; L₀: luminescence brightness at 50 kHz, L: luminescence brightness at different frequencies). g) Luminescence spectra of SFELF at different frequencies (electric field strength: 3 V·μm⁻¹). h) CIE color coordinate diagram of SFELF luminescence color changing with frequency (electric field strength: 3 V·μm⁻¹). i) Optical display of SFELF. j) Comparison of luminescence brightness between SFELF and other ACEL devices. k) SFELF embroidered on fabric.

Figure 6. a) Touch luminescence mechanism of silk-fibroin-based electroluminescent fiber (SFELF) driven by electric field. b) Luminescence state of SFELF when touched in an electric field environment. c) Luminescence disappearance of SFELF when not touched in an electric field environment. d) Sliding luminescence phenomenon of SFELF in an electric field environment. e) Luminescence appearance of SFELF touched by different materials. f) Touch luminescence appearance of SFELF at different temperatures. g) Touch luminescence mechanism of SFELF driven by thermal field.

Figure 7. a) Triboelectric sensing mechanism of silk-fibroin-based electroluminescent fiber (SFELF). b) Maximum open-circuit voltage of SFELF. c) Maximum short-circuit current of SFELF. d) Wireless Bluetooth transmission of triboelectric signals from SFELF through chip connection. e) SFELF for monitoring wrist movement signals. f) Schematic diagram of SFELF for jaundice treatment. g) Schematic diagram of SFELF application in medical health. h) SFELF and SFELF without external electrode sewn on a white T-shirt to form "smiley face" (made of SFELF) and "sad face" (made of SFELF without external electrode) patterns. i) Response when pressing the "sad face": I) "Smiley face" luminescence at different frequencies; II) "Sad face" response to liquid and luminescence at different frequencies; III) Generation of triboelectric signals.

Conclusion
This study successfully prepared a silk-fibroin-based electroluminescent fiber (SFELF) with a coaxial structure. This fiber architecture is flexible and has high luminescence brightness, consisting of an inner electrode, dielectric layer, luminescent layer, and outer electrode. This fiber not only possesses electrically stimulated luminescence characteristics but also has touch luminescence capability driven by electric/thermal field-force coupling, synchronous triboelectric sensing function, and liquid detection capability. By constructing the luminescent layer matrix with silk fibroin (SF) and regulating the β-sheet content in its secondary structure, this alternating current electroluminescent fiber (SFELF) exhibits excellent toughness (5.29 MJ/m³) and high luminescence brightness (up to 366 cd/m²), with performance superior to reported counterparts based on polydimethylsiloxane (PDMS), thermoplastic polyurethane (TPU), or cellulose. Notably, the fiber maintains stable brightness after over 10,000 bending cycles, reflecting excellent stability. Interestingly, even after removing the external electrode, SFELF can achieve sensitive touch luminescence under thermal field modulation, effectively eliminating the dependence of alternating current electroluminescent (ACEL) fibers on a power source. Additionally, SFELF has triboelectric sensing capability, enabling wireless Bluetooth transmission of triboelectric signals through chip connection; meanwhile, the fiber can detect various liquids, including water, saline, simulated urine, and fluorescent solutions. These multifunctional sensing characteristics make SFELF a potential preferred material for smart textiles, human-machine interaction, and multi-environment real-time visual monitoring.

https://doi.org/10.1002/adfm.202514650