Fabrication of high-strength collagen fibers via a novel integrated liquid crystal and microfluidic spinning.

Collagen is an ideal raw material for biological fibers, yet achieving long-range structural order and the resultant high-strength fibers without toxic crosslinkers remains a major challenge. This work integrates ultrasonic fragmentation with dialysis concentration to induce a stable lyotropic liquid crystalline (LC) collagen dope at a concentration as low as 3.3%, which is significantly lower than previously reported. Ultrasonic treatment reduced collagen fragment length to 10-30 nm, lowering steric hindrance and enhancing molecular mobility, thereby promoting nematic LC formation. Rheological analysis revealed that at 3.7%, the spinning dope exhibited a characteristic viscosity plateau in the low shear rate range of 1-5 s-1, indicating shear-induced alignment of nematic LC domains, which defines the optimal spinning window. Using 4.0% LC dope and an optimized ethanol flow rate of 0.30 mL/min in microfluidic spinning process, the resultant collagen fibers achieved a high tensile strength of 2.21 cN/dtex and a thermal denaturation temperature of 120.8 °C. Increasing the spinning dope concentration progressively reduced lateral molecular packing distance, transformed the fiber surface from grooved to smooth, and enhanced thermal stability. This study establishes a rational, crosslinker-free strategy to fabricate high-performance pure collagen fibers with superior mechanical and thermal properties, providing critical theoretical and technical support for their application in absorbable surgical sutures and regenerative medicine.