Abstract:

Objective Silk based conductive gel fiber shows broad application prospects in human motion monitoring, disease diagnosis and treatment, human-computer interaction and other fields by virtue of its one-dimensional structure advantage. However, introducing carbon based conductive media to endow silk with conductive properties would reduce the transparency and mechanical ductility of the material. In order to solve the problems of opacity and poor mechanical ductility, silk fibroin (SF) and acrylamide (AAm) were employed as raw materials to fabricate silk fibroin-polyacrylamide hydrogel fibers (SAHF) for outstanding flexibility and high transparency through a combination of UV-induced polymerization and self-lubricating spinning strategies.

Method Under UV-induced conditions, AAm was polymerized into polyacrylamide (PAAm) long chains. With the crosslinking agent, PAAm and SF interacted strongly multiple hydrogen bonds and chemical crosslinking, creating a stable 3D network structure. Due to the hydrophobic interaction between the PTFE tube and the spinning solution, the gel fibers were able to self-lubricate, thereby enabling the continuous production of SAHF. Ca²⁺ and Cl^- from CaCl₂, as conductive media, formed free charge carriers. Ca²⁺ engages in electrostatic attraction and complexation with SF carboxyl and PAAm amide groups. Cl^- interacts electrostatically with SF amino groups. These integrate ions into 3D network, conferring good conductivity.

Results SAHF demonstrated good mechanical properties, particularly in terms of stretchability, achieving a maximum tensile strain of 224%. This unprecedented mechanical performance stemmed from the strong intermolecular interactions between PAAm and SF. Importantly, these molecular-level interactions not only ensured exceptional mechanical stability during operation but also provide the material with superior flexibility and strength, enabling it to maintain performance under repeated stress cycles.

From a processing perspective, SAHF demonstrated excellent manufacturability and this significantly broadens its potential applications in emerging fields such as flexible electronic circuits, smart interactive textiles, and conformable sensor arrays. Furthermore, the materials demonstrated outstanding optical transparency, maintaining 91% transmittance. This unique combination of properties makes it particularly suitable for applications where both mechanical flexibility and optical clarity are required, such as transparent wearable devices and optical-electronic hybrid systems.

Additionally, SAHF exhibited a conductivity of 0.64 mS/cm, achieved through the synergistic combination of metal ion coordination between PAAm and SF and the carefully engineered network structure. This balanced combination of mechanical and electrical properties makes it particularly valuable for next-generation flexible electronic devices. When employed as a strain sensor, the fiber demonstrates a gauge factor of 0.31, allowing for sensitive detection of minute deformations. Its dynamic performance is equally impressive, featuring a rapid response time of 21 ms and recovery time of 47 ms, which enables real-time monitoring of mechanical stimuli with high reliability. By using SAHF to monitor pH changes in the human sweat environment, a strong linear relationship and good reproducibility between pH and the relative resistance of the sensor were found in different pH ranges, demonstrating the long-term stability of the sensor under different pH conditions and providing a new technological path for the development of wearable medical devices in the future.

Conclusion The above research results indicate that SAHF has flexibility and high transparency. In practical applications, strain sensors based on SAHF exhibit excellent performance and can accurately and reliably monitor human micro movements, meeting the technical requirements of daily motion monitoring equipment. Especially in the field of joint diagnosis, this sensor has shown significant application advantages due to its excellent sensitivity and dynamic response characteristics, providing a new technological approach for the development of wearable medical devices in the future.

Key words: silk fibroin, acrylamide, self-lubricating spinning, conductive gel fiber, strain sensing, flexible electronic device, smart wearable textiles