Fig. 3: Gas–liquid two-phase flow for fibers fabrication.

A_1–4 Bubble flow pattern in the needle. The respective bubble flow pattern formed B_1–4 microscopic images of the gel fibers and C_1–4 microscopic images of the dehydrated fibers, along with D_1–4 SEM images (Q_g = 4.40, 5.35, 6.83 cm³/s, Q_l = 0.05 cm³/s, C = 25 mg/mL and collection rate of 15 rpm). CFD simulations at Q_g/Q_l ratios of E 80 (single bubble, Q_g = 4.0 cm³/s Q_l = 0.05 cm³/s, C = 25 mg/mL), F 110 (slug bubble, Q_g = 5.5 cm³/s Q_l = 0.05 cm³/s, C = 25 mg/mL) and G 140 (annular jet, Q_g = 7.0 cm³/s Q_l = 0.05 cm³/s, C = 25 mg/mL) reveal the interface deformation and flow field dynamics of the two-phase flow. H Optical images further capture the critical stages of gel fiber detachment from the needle tip, illustrating single bubble, slug flow, and annular jet interactions with the gel fibers. I Schematic of the bubble-triggered structural transitions in gel fibers. J Ternary phase diagram showing fiber morphology regions formed by controlling gas pressure (Pr), spinning drop concentration (C), and syringe advance speed (V). Bubble signal curves detected by the photoelectric sensor under different Q_g/Q_l conditions and the corresponding changes in K cavity spindle spacing (L₁), L solid spindle spacing (L₂), and M tooth spacing (L₃). Scale bar: B, C: 0.5 mm, D: 300 μm, E–H, and K–M: 500 μm.