Intermolecular interaction simultaneously mediated network morphology and β-sheet crystallization of silk fibroin/polyacrylamide hydrogel for its excellent adhesive strain sensing performances

Silk fibroin (SF), as a special natural polymer, is a good candidate for preparing flexible sensor due to its excellent biocompatibility, biodegradability and amphiphilic properties. However, the high and uncontrollable crystallization of SF makes it challenge to be utilized in excellent biomimetic SF hydrogel sensor. Neat SF hydrogel is brittle and not adhesive. Here, polyacrylamide (PAM) was introduced to the SF hydrogel to address this issue. Due to their strong intermolecular interaction, the network morphology of SF/PAM hydrogel was altered to non-Euclidean pore from Euclidean one. Meanwhile, its β-sheet crystallization was suppressed to nanoscale readily. These evolutions endow the SF/PAM hydrogel with not only enhanced mechanical properties but also excellent adhesion performance. Compared with that of neat PAM hydrogel, tensile strength, tensile failure strain, compressive strength (under 80% strain) and adhesion performance (on pig skin) of the SF8/PAM hydrogel are increased by 133.1%, 120.9%, 610.8% and 104.8%, respectively. Additionally, the amphiphilicity of SF could make the carbon nanotubes (CNTs) disperse well in hydrogel. CNT0.3/SF8/PAM hydrogel not only inherits but also improves the above properties. It exhibits excellent adhesive sensing performance with maximal gauge factor of 10.13, working strain range of 1000% and stability as long as over 500 cycles. The detection of six human activities was also demonstrated. This work affords a general strategy to achieve high-performance SF-based hydrogel and indicates that the SF/PAM hydrogel possesses great promise for applications in flexible wearable strain sensors.