Microfluidic Controlled Mass-Transfer and Buckling for Easy Fabrication of Polymeric Helical Fibers

Abstract

Microfluidic fabrication of helical microfibers is still a big challenge. The reason is that this always includes designing the necessary geometrical channels and chemical conditions to first form a flowing liquid jet, which has to be continually reacting and rapidly evolving in time from viscous liquid to a flexible solid to maintain the helical structure inside the microfluidic channels. In this report, dextran aqueous solution and liquid PEG400 are infused separately into the inner and outer channels of a simple single emulsion microfluidic device, respectively. The formed two phase stream then enters a widening collection tube, where automatically formation of dextran helical fiber happened due to water shifting and widening of the channel cooperatively induced buckling. Various experimental conditions that influence the amplitudes, wavelengths, and diameters of the formed helical fibers are discussed.

Bioinspired Polymeric Helical and Superhelical Microfibers via Microfluidic Spinning

“…For simplicity, here, the inner phase was either 4.0 wt% CCS or 8.0 wt% PVA in water, or 8.0 wt% PUU3‐12 in N , N ‐dimethylformamide (DMF) or 8.0 wt% EVOH in dimethyl sulfoxide (DMSO). Similar to our previous report, other concentrations of these polymer solutions can also be used to get helical fibers . Liquid poly(ethylene glycol) 400 (PEG400) or 80 wt% PEG800 or 70 wt% PEG1000 (the number denotes the molecular weight of PEG) in H 2 O with similar viscosities (Figure S1, Supporting Information) was used as the outer phase, to exclude the viscosity influence on the morphology of the fibers (Figure g–i).…”

“…When it entered into a wider collection tube II (d 2 > d 1 , Figure a), solid polymeric helical fibers automatically formed (Figure a,c). We attributed this to the synergy effect of the mass‐transfer between the dispersed inner and the continuous outer phase and the widening of collection tube II . First, once the inner polymeric solution met with the continuous outer phase in tube I, the solvent in the jet (water or DMF or DMSO) began to diffuse into the outer phase because of osmotic pressure, while the polymer still remained in the jet, due to its immiscibility with the outer phase.…”

“…First, once the inner polymeric solution met with the continuous outer phase in tube I, the solvent in the jet (water or DMF or DMSO) began to diffuse into the outer phase because of osmotic pressure, while the polymer still remained in the jet, due to its immiscibility with the outer phase. Thus shrinkage of the jet occurred, leading to the accumulation of elastic energy and the buildup of stress, which could be released via folding of the straight jet . Second, the suddenly widening of tube II created a velocity difference between the straight inner jet and the outer continuous phase, imposing viscous drag on and folding of the jet .…”

“…Similar to our previous report, other concentrations of these polymer solutions can also be used to get helical fibers. [34] Liquid poly(ethylene glycol) 400 (PEG400) or 80 wt% PEG800 or 70 wt% PEG1000 (the number denotes the molecular weight of PEG) in H 2 O with similar viscosities (Figure S1, Supporting Information) was used as the outer phase, to exclude the viscosity influence on the morphology of the fibers (Figure 3g-i). These two liquids were pumped separately into the inner and outer channels, a straight jet of the inner polymeric solution formed in tube I.…”

Controllable Microfluidic Fabrication of Microstructured Materials from Nonspherical Particles to Helices

“…[6,7] Compared with spherical microparticles, microstructured materials with other different shapes can show unique properties in various fields for advanced applications such as targeting www.advancedsciencenews.com www.mrc-journal.de 3D helical shapes. Although microfluidic technique can produce helical microfibers from coiled jet templates, [37,38] fabrication of particulated microstructured materials with helical shapes still remains difficult. Such helical microstructured materials can be typically produced by 3D direct laser writing, [14] bending of multilayer metals that deposited or grown on a sacrificed substrate, [39] and depositing metal coatings on diced xylem vessels of plants; [40] however, these techniques usually suffer from troublesome fabrication process and limited materials choice.…”