Abstract
We report a versatile method for the generation of complex-shaped three-dimensional multi-compartmental (3D-MC) microparticles. Complex-shaped microparticles have recently received much attention for potential application in self-assemblies, micromachines, and biomedical and environmental engineering. Here, we have developed a method based on 3D nonequilibrium-induced microflows (Marangoni and diffusional flows) of microdroplets that are discharged from the tip of a thin capillary in a simple centrifugal microfluidic device. The microparticle shapes can be tuned by the partial dissolution of specific compartments and by the deformation of the precursor microdroplets by manipulating the 3D microflows. We believe that this method will have wide applications in nano- and microscience and technologies.
Highlights
Microflows induced by the nonequilibrium condition of the solutions before solidification (Fig. 1a, (II) and (III)), though no deformation is induced without microflows (Fig. 1a, (I))
The calcium alginate (Ca-alg) gel in all parts was dissolved by removing the Ca2+ ions with the Ca-chelating agent of ethylenediamine-tetraacetic acid (EDTA)
We showed that the dominant control parameter for deformation using the diffusional flow was the gelling speed of the Na-Alg, which was controlled by varying the Ca2+ concentration (Fig. 3b,c and Supplementary Fig. S3); we showed that the dominant control parameter for deformation using the Marangoni flow was the surface tension difference between the solutions, which was controlled by changing the concentration of the surfactant (Fig. 4d and Supplementary Fig. S4)
Summary
Microflows induced by the nonequilibrium condition of the solutions before solidification (Fig. 1a, (II) and (III)), though no deformation is induced without microflows (Fig. 1a, (I)). For the deformation of droplets, we used a diffusional flow (Fig. 1a, (II)) and a Marangoni flow (Fig. 1a, (III)). The diffusional flow is driven by the difference in molecular concentration between the two solutions; the solution flows from higher- to lower-concentration regions. The Marangoni flow is driven by the difference in surface tension between the two solutions, and it flows from solutions with lower to higher surface tensions. Both microflows continued until the difference between the two solutions relaxed into the equilibrium state; the degree of deformation could be kinetically tuned by controlling the time necessary for droplet solidification. The kinetic tunability by 3D deformation is one of the unique features of this method; previous methods generally produced equilibrated shapes after the completion of deformation
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