Research ArticleBIOENGINEERING

Harnessing surface-bound enzymatic reactions to organize microcapsules in solution

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Science Advances  18 Mar 2016:
Vol. 2, no. 3, e1501835
DOI: 10.1126/sciadv.1501835
  • Fig. 1 System geometry and components.

    Reagent-laden microcapsules are drawn toward the enzyme-coated square region in the middle. The enzyme catalyzes the decomposition of the reagent, changing the fluid density and thereby generating convective flows. The inset shows the structure of a capsule with a polymer shell and a core region of radius R containing the reagent.

  • Fig. 2 Stages of convective aggregation.

    (A) Initial uniform distribution of capsules containing the reagent. (B) The reagent, released out of capsules, diffuses toward the enzyme-coated square region (shown in blue) on the bottom where it decomposes, driving fluid motion and carrying capsules to the square patch. (C) After the reagent is consumed, the fluid flow stops. Simulations (see movie S1) were performed for 500 capsules with R = 15 μm and P = 10−6 m/s. Reagent concentration is shown with the color bar (in molar). Arrows show direction of the fluid flow. The capsules’ density distribution is shown with a red curve above each image in the left column.

  • Fig. 3 Dynamics of aggregating capsules.

    (A) Evolution of capsule areal concentration n/n0 above the enzyme patch. (B) Evolution of fluid velocity in the middle point of the domain. (C) Dynamics of maximal reagent concentration. (D) Dynamics of maximal temperature change (relative to the reference temperature). Simulations were performed for N = 500 capsules with P = 10−6 m/s.

  • Fig. 4 Effects of capsule size and number of capsules.

    (A to D) Maximal values of (A) relative concentration n/n0 and (B) fluid velocity in the middle point of the domain, (C) maximal (in the domain) reagent concentration, and (D) maximal temperature change (relative to the reference temperature) for different numbers N of capsules with P = 10−6 m/s. Dotted lines show limiting concentrations nlim/n0 corresponding to hexagonal close-packed arrangement of capsules on the bottom.

  • Fig. 5 Influence of capsule shell permeability P.

    (A and B) Evolution of capsule areal concentration n/n0 (A) and maximal reagent concentration (B) for different values of P. The simulations were performed for R = 15 μm and N = 1000.

  • Fig. 6 Effect of enzyme patch size on the final distribution of capsules.

    The top panels show capsule areal concentration n/n0 plotted as a function of the x coordinate along the line z = 2 mm. The bottom panels provide snapshots of capsule distribution in the (x,z) plane. The enzyme-covered region is shown with a red line. The simulations were performed for R = 15 μm, P = 10−6 m/s, and N = 1000.

  • Fig. 7 Stages of capsule aggregation into a square shape.

    (A to C) Early (A), intermediate (B), and final (C) simulation instances demonstrate decreasing reagent concentration (color map) and velocity (arrows) and increasing capsule concentration n/n0 (thick red line). Blue lines show circulation of the (A) four-vortex and (B) two-vortex flows. The enzyme-coated square on the bottom (shown with small blue squares) initiates the aggregation of N = 500 capsules with R = 20 μm and P = 10−6 m/s into a hollow square shape. The low capsule concentration region in the center is a result of downward flow in the middle. See movie S2 for details.

  • Fig. 8 Aggregation of capsules into different shapes.

    The enzyme-coated pattern on the bottom (shown with small blue squares) induces the aggregation of N = 1000 capsules with radius R = 15 (left column) and N = 500 capsules with radius 40 μm (right column) into the following shapes: circle (top row), crankshaft (middle row), and square (bottom row). The snapshots show the final positions of capsules after the entire reagent is consumed and convection stops. Movies S3 to S8 demonstrate the processes. P = 10−6 m/s for both cases.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/3/e1501835/DC1

    Movie S1. Convective aggregation of N = 500 capsules with radius R = 15 μm and shell permeability P = 10−6 m/s on a square-shaped enzyme-coated patch.

    Movie S2. Convective aggregation of N = 500 capsules with radius R = 20 μm and shell permeability P = 10−6 m/s on a square-shaped enzyme-coated pattern.

    Movies S3 to S5. Convective aggregation of N = 1000 capsules with radius R = 15 μm and shell permeability P = 10−6 m/s on enzyme-coated patterns into the following shapes: square, circle, and crankshaft.

    Movies S6 to S8. Convective aggregation of N = 500 capsules with radius R = 40 μm and shell permeability P = 10−6 m/s on enzyme-coated patterns into the following shapes: square, circle, and crankshaft.

  • Supplementary Materials

    This PDF file includes:

    • Legends for movies S1 to S8

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    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mov format). Convective aggregation of N = 500 capsules with radius R = 15 μm and shell permeability P = 10−6 m/s on a square-shaped enzyme-coated patch.
    • Movie S2 (.mov format). Convective aggregation of N = 500 capsules with radius R = 20 μm and shell permeability P = 10−6 m/s on a square-shaped enzyme-coated pattern.
    • Movies S3 to S5 (.mov format). Convective aggregation of N = 1000 capsules with radius R = 15 μm and shell permeability P = 10−6 m/s on enzyme-coated patterns into the following shapes: square, circle, and crankshaft.
    • Movies S6 to S8 (.mov format). Convective aggregation of N = 500 capsules with radius R = 40 μm and shell permeability P = 10−6 m/s on enzyme-coated patterns into the following shapes: square, circle, and crankshaft.

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