Research ArticleENGINEERING

In-air microfluidics enables rapid fabrication of emulsions, suspensions, and 3D modular (bio)materials

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Science Advances  31 Jan 2018:
Vol. 4, no. 1, eaao1175
DOI: 10.1126/sciadv.aao1175
  • Fig. 1 Concept of IAMF and guide to the article.

    (A) Chip-based microfluidics enables in-line control over droplets and particles, making it a versatile platform technology. A chip design where droplets (blue) are transported by a coflow (pink) is shown. (B) IAMF maintains the in-line control of chip-based microfluidics but relies on jet ejection and coalescence into air. Therefore, a wide range of droplets and particles can be produced at flow rates typically two orders of magnitude higher than with chip-based microfluidics. When combining reactive, solidifying microjets, IAMF also enables on-the-fly production and direct deposition of microparticles into 3D multiscale modular (bio)materials.

  • Fig. 2 Physical principles of IAMF.

    (A) High-speed photograph of IAMF operated in “drop-jet” mode. Here, a droplet train is ejected from actuated nozzle 1 and collides with a jet that is ejected from nozzle 2. (B) IAMF operated in “jet-jet” mode, as used for spinning fibers. (C) Schematic representation of in-air impact, encapsulation, and solidification mechanisms. Different surface tensions (σ1 > σ2) result in Marangoni-driven encapsulation of the droplet. (D and E) High-speed photographs of the “drop-jet” mode, in which (D) the droplets and (E) the jet are selectively labeled with a fluorescent dye. The droplets maintain a spherical shape during impact and encapsulation, whereas the jet spreads around the droplet within a few diameters of travel. (F and G) Alginate microparticles produced (F) without and (G) with Marangoni-driven encapsulation. (H) Phase diagram of particle shape as a function of surface tension gradient Δσ and the nozzle diameter D1 = D2. Symbols indicate spherical (o) or irregular (□) particles. The solid line refers to a basic model for the transition between these shape regimes. Scale bars, 1 mm (black) and 0.4 mm (white).

  • Fig. 3 IAMF enables high-throughput production of monodisperse microemulsions and microsuspensions with various compositions, sizes, and shapes.

    Schematic diagrams (left) indicate the relevant control parameters. (A to F) IAMF operated in “drop-jet” mode enabled the production of monodisperse (B) w/o emulsions, (C) double emulsions, (D) spherical particle suspensions, and (E) single-material and (F) multimaterial core-shell particles. alg, alginate; dex, dextran; TA, tyramine. (G to K) Tuning the microparticle size. (H to J) Particles produced using nozzle diameters of 20, 100, and 250 μm, respectively. (K) Probability P of the particle size as a function of nozzle diameter (indicated per curve) and actuation frequency. Colors from black to pale blue indicate increasing actuation frequencies of 2.3, 3.5, 4, 4.5, 5, 6, 7, and 8 kHz. (L to N) Elongated particles were made by increasing the relative jet velocity. (O) IAMF operated in “jet-jet” mode enabled the production of (P) straight and (Q) pearl-lace morphologies. (R) Throughput as a function of nozzle diameter for IAMF and chip-based droplet microfluidics (MF). The maximum per-nozzle throughput of monodispersed droplet production using chip-based microfluidics is limited by Ca = 0.1 and We = 1. The production throughput window of IAMF is determined by Weej = 1 (that is, minimum) and Weg = 0.2 (that is, maximum). Green circles are data points obtained using our IAMF setup. Red squares are data points obtained from previously reported studies on droplet microfluidics (2, 4452). Droplet production frequencies are indicated with gray dashed lines. Scale bars, 200 μm (unless otherwise indicated).

  • Fig. 4 One-step additive manufacturing and injection molding of 3D multiscale modular (bio)materials.

    (A) Modular freeforms with a controlled microarchitecture were manufactured by stacking of shape-stable core-shell particles. (B to D) A hollow cylinder was formed by deposition of the composite jet onto a rotating substrate. By altering the building blocks’ composition, the resulting microarchitecture consisted of (C) a liquid-filled foam or (D) a multimaterial modular solid, where the cross-linker for the core was added to the shell and vice versa. (E) To eject a modular filler, only the droplets’ cores are solidified in the air, whereas the slower solidifying shells enable seamless filling of the mold. (F to H) A modular construct was produced by filling a bone-shaped mold. Inset: Hydrogel construct while still in the mold. The 3D multiscale modular material consisted of MSCs (pink), encapsulated in alginate microspheres (green) that are embedded in dextran-tyramine hydrogel (red). (I) Injection-molded multiscale modular tissue construct with optimized cellular micro- and macroenvironments. The construct consisted of insulin-producing pancreatic β cells (MIN6; beige with blue nuclei) that were encapsulated in alginate microparticles (green). The cell-laden microparticles were encapsulated within a proangiogenic fibrin network that contained human endothelial and stem cells (pink with blue nuclei). The microenvironments supported MIN6 cell proliferation, whereas the macroenvironment supported the formation of an endothelial cellular network within 7 days of in vitro culture. HUVEC, human umbilical cord endothelial cell. Scale bars, 1 cm (B and F), 5 mm (G), and 100 μm (C, D, H, and I).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/1/eaao1175/DC1

    section S1. Rayleigh-Plateau breakup

    section S2. Shape control

    section S3. Comparing IAMF to droplet-based particle formation technologies

    section S4. IAMF with respect to additive manufacturing technologies

    fig. S1. Schematic of the setup.

    fig. S2. Ejection and breakup regimes.

    fig. S3. Overview of particles and fibers.

    fig. S4. Hydrogel templating.

    fig. S5. Particle size distributions.

    fig. S6. Elongation of droplets and particles.

    fig. S7. IAMF handheld device.

    fig. S8. Fiber-based modular materials.

    fig. S9. Characterization of IAMF-based cell microencapsulation.

    fig. S10. Viability and function of IAMF-processed cells.

    fig. S11. Overview of IAMF-based materials and throughput.

    fig. S12. Surface tension of ethanol/water mixtures.

    movie S1. One-step 3D modular printing a solid freeform.

    movie S2. Omnidirectional printing using IAMF handheld device.

    table S1. Detailed process parameters of key experiments.

    References (5383)

  • Supplementary Materials

    This PDF file includes:

    • section S1. Rayleigh-Plateau breakup
    • section S2. Shape control
    • section S3. Comparing IAMF to droplet-based particle formation technologies
    • section S4. IAMF with respect to additive manufacturing technologies
    • fig. S1. Schematic of the setup.
    • fig. S2. Ejection and breakup regimes.
    • fig. S3. Overview of particles and fibers.
    • fig. S4. Hydrogel templating.
    • fig. S5. Particle size distributions.
    • fig. S6. Elongation of droplets and particles.
    • fig. S7. IAMF handheld device.
    • fig. S8. Fiber-based modular materials.
    • fig. S9. Characterization of IAMF-based cell microencapsulation.
    • fig. S10. Viability and function of IAMF-processed cells.
    • fig. S11. Overview of IAMF-based materials and throughput.
    • fig. S12. Surface tension of ethanol/water mixtures.
    • Legends for movies S1 and S2
    • table S1. Detailed process parameters of key experiments.
    • References (53–83)

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    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.mp4). One-step 3D modular printing a solid freeform.
    • movie S2 (.mp4). Omnidirectional printing using IAMF handheld device.

    Files in this Data Supplement:

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