Abstract:

Objective Although silk fibroin （SF） has excellent biocompatibility and cell affinity， its mechanical properties （such as strength and toughness） do not always meet the long-term mechanical support requirements of tissue engineering scaffolds in pure state. To address such problems， a SF-based polycaprolactone （PCL） composite fibers with high strength and high toughness were prepared by wet spinning technology， aiming to provide satisfactory mechanical properties， biodegradability， spinnability， and good biocompatibility between SF and PCL. This work seeks to create a sustainable and high-performance fiber alternative to existing synthetic biomaterials.

Method The composite fibers were fabricated using a green wet-spinning process by focusing on the effects of the mass ratio of SF to PCL. SF solution was blended with varying concentrations of PCL （10%-30%）， and the mixture was extruded through a microfluidic-inspired spinneret into a coagulation bath （alcohol aqueous solution） maintained at （25 ± 2） ℃. The structural and mechanical properties of the resulting fibers were characterized using scanning electron microscopy for morphology， Fourier-transform infrared spectroscopy for molecular interactions， and X-ray diffraction for crystallinity. Tensile strength， elongation at break， and Young's modulus were evaluated through mechanical testing.

Results The SF-based composite fibers exhibited uniform morphology with an average diameter of （315.38 ± 3.32） μm without bead formation. Mechanical performance varied with PCL content， where pure SF fibers showed a tensile strength of （26.45 ± 2.53） MPa， while SF/PCL₂₀ （20% PCL） achieved the optimal balance with a strength of （27.86 ± 0.54） MPa， a fracture elongation of （331.90 ± 24.52）%， and enhanced toughness. In contrast， higher PCL content （SF/PCL₃₀） led to reduced strength （12.31 ± 2.25） MPa， indicating a limit of the PCL content. Structural analyses confirmed improved molecular orientation and β-sheet formation in SF， facilitated by PCL-induced crystallization during wet spinning. The fibers also demonstrated superior aqueous stability and controlled degradability compared to pure SF materials. Notably， the SF/PCL₂₀ fiber's mechanical properties surpassed those of many electrospun SF-based composite fibers， approaching the performance of natural silk.

Conclusion The wet-spun SF-based composite fibers combine the biocompatibility of SF with the toughness of PCL， and successfully improve the mechanical properties of SF. The SF/PCL₂₀ formulation achieves an optimal trade-off between strength， ductility， and processability， making it suitable for demanding biomedical applications such as load-bearing sutures， tissue scaffolds， and drug delivery systems. The introduction of PCL effectively mitigated the brittleness of SF materials. The composite fibers exhibited significant improvements in both ductility and toughness， indicating their promising potential in the field of biomedical fibers， including surgical sutures and tissue engineering scaffolds. This study highlights the efficacy of green wet-spinning as a sustainable alternative to solvent-intensive electrospinning and provides a framework for designing advanced bio-hybrid fibers. Future work should focus on scaling up production and evaluating in vivo performance.

Key words: medical material, composite fiber, silk fibroin, polycaprolactone, wet spinning, microstructure, mechanical property