Controllable fabrication of biocompatible microhelices based on the liquid rope coiling effect due to the phase viscosity difference

Microhelices with unique structures can achieve numerous functions mimicking micromotors and thus attract increasing attention from various fields especially in biomedical engineering. However, fabrication of biocompatible microhelices with controllable structures and favorable mechanical strengths still remains challenging. Here, we report a facile and efficient method for controllable fabrication of biocompatible microhelices with designable structures and enough mechanical strengths based on the liquid rope coiling effect due to phase viscosity differences. A two-stage microfluidic system is designed to generate all-aqueous-phase core-sheath microhelical flows without crosslinking, and the microhelical flows are subsequently utilized as templates for fabricating microhelices via UV-initiated curing of core flow segments. To demonstrate the efficiency of the proposed strategy, biocompatible photocurable polyethylene glycol diacrylate (PEGDA) solution, high-viscosity sodium alginate (NaAlg) solution and low-viscosity deionized water are employed as the inner, middle and outer phases respectively. The pitch (170 ∼ 500 μm), diameter (36 ∼ 87 μm), amplitude (0.52 ∼ 1.4 mm) and length (1.8 ∼ 5.6 mm) of PEGDA microhelices are precisely controlled by adjusting device dimensions, fluid viscosities, flowrates, and UV-irradiation time periods. The fabricated PEGDA microhelices exhibit outstanding mechanical strength. Furthermore, magnetic microhelices are successfully fabricated by incorporating Fe 3 O 4 nanoparticles into PEGDA solutions, which exhibit excellent motion performance in a magnetic field. The proposed strategy provides an efficient method for controllable fabrication of biocompatible microhelices with designable structures and functions for potential applications in various fields. • Biocompatible microhelices with designable structures are fabricated with helical flows as templates. • All-aqueous-phase core-sheath microhelical flows are generated with the liquid rope coiling effect. • The liquid rope coiling effect for forming microhelical flows is chiefly caused by phase viscosity difference. • Functional microhelices exhibit excellent mechanical strengths and magnetic-field-driven motion performances.