Research ArticleMATERIALS SCIENCES

Programmable droplet manipulation by a magnetic-actuated robot

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Science Advances  14 Feb 2020:
Vol. 6, no. 7, eaay5808
DOI: 10.1126/sciadv.aay5808
  • Fig. 1 Scheme and demonstration of the magnetic-actuated robot.

    (A) Scheme of the droplet manipulation system. (B) Parameters describing the magnetic-actuated robot. (C to F) Typical behaviors of the droplets manipulated by the robot. Droplets can be transported (C), split (D), released (E), and rotated (F) by the robot. The gray arrows represent the moving direction of the robots. The moving speed is 2 mm/s. The volume of the droplets is 250 μl. Scale bar, 5 mm.

  • Fig. 2 Diagram and mechanical analysis of the droplet manipulation.

    (A) Phase diagram showing the diverse behaviors of the droplet with the variation of D/d and V. (B) Mechanical analysis explaining the actuating ability of the robot. Three forces, including the adhesion force between the liquid and the beads (Fa), the adhesion force between the liquid and the substrate (ffront), and the resilience force due to the deformation of the droplet (Fe), determine the movement of the TCL at the front end of the droplet (the upper scheme). Two main forces (Fe and frear) affect the movement of the TCL at the rear end of the droplet (the lower scheme).

  • Fig. 3 Generality demonstration of the robot.

    (A) Oil droplet manipulation under water. The oil droplets (100 μl) are CCl4-dissolved with Br2 (left) and styrene (right). The robot transports the left droplet to mix with the right one. (B) Water droplet manipulation under oil (n-heptadecane). The droplets (50 μl) are water-dissolved with KSCN (left) and FeCl3 (right), respectively. The left droplet is captured by the robot and transported to the right one. (C) Gas bubble manipulation under water. A superhydrophobic robot can successively collect the gas bubbles (20 μl). The white dotted line indicates the trajectory of the robot. (D) Manipulation of a water droplet on the upright surface. The robot transports a 20-μl water droplet to move up and down with a speed of 2 mm/s. (E) Manipulation of a water droplet inside a tube. A droplet (20 μl) is actuated by the robot to capture the impurity inside a tube. After 1 min, the impurity is dissolved and taken away by the droplet. The red dashed circle indicates the location of the impurity. The black arrow indicates the movement of the droplet. Scale bars, 10 mm.

  • Fig. 4 Chemical and simulated medical applications using the robot.

    (A) Demonstration of stepwise chemical reactions. The robot split a daughter drop of 1.5 μl from a NaOH droplet and transport it to an indicator droplet (phenolphthalein). In the second step, the robot leaves the indicator droplet, splits a daughter drop from a HCl droplet, and then moves back to the indicator droplet. The volumes of the NaOH droplet, the indicator droplet, and the HCl droplet are all 250 μl. (B) Simulation of the calculi removal. The robot transports a droplet of drug to calculi placed on the substrate. The calculi are collected and taken away from the substrate. (C) Simulation of the vascular clearance. The drug droplet and the plaque placed inside a tube filled with water. The drug droplet is transported to the plaque by the robot. After 1 min, the plaque is dissolved and taken away. The black arrow indicates the movement of the droplet. The moving speed is 2 mm/s. Scale bars, 10 mm.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/6/7/eaay5808/DC1

    Section S1. Mechanical analysis of the droplet behaviors manipulated by the magnetic-actuated robot

    Section S2. Detailed analysis of the phase diagram

    Section S3. Analysis of factors affecting droplet manipulation behaviors

    Section S4. Principle of the bead surface modification

    Section S5. Analysis of factors influencing the volume of daughter drops

    Section S6. Quantitative evaluation of the mixing efficiency

    Fig. S1. Scheme of the magnetic-actuated robot.

    Fig. S2. Contact angle characterization.

    Fig. S3. Micro-droplet manipulation.

    Fig. S4. Demonstration of the droplet behaviors influenced by D/d and V.

    Fig. S5. Demonstration of the luminol reaction.

    Fig. S6. Demonstrations of the drug delivery using the magnetic-actuated robot.

    Movie S1. Typical behaviors of the droplets manipulated using the magnetic-actuated robot.

    Movie S2. Demonstration of the droplet behaviors influenced by D/d and V.

    Movie S3. Generality demonstration of the magnetic-actuated robot.

    Movie S4. Display of the stepwise acid-based neutralization reactions.

    Movie S5. Display of the luminol reaction.

    Movie S6. Simulation of the calculi removal.

    Movie S7. Simulation of the drug delivery.

    Movie S8. Simulation of the vascular clearance.

  • Supplementary Materials

    The PDF file includes:

    • Section S1. Mechanical analysis of the droplet behaviors manipulated by the magnetic-actuated robot
    • Section S2. Detailed analysis of the phase diagram
    • Section S3. Analysis of factors affecting droplet manipulation behaviors
    • Section S4. Principle of the bead surface modification
    • Section S5. Analysis of factors influencing the volume of daughter drops
    • Section S6. Quantitative evaluation of the mixing efficiency
    • Fig. S1. Scheme of the magnetic-actuated robot.
    • Fig. S2. Contact angle characterization.
    • Fig. S3. Micro-droplet manipulation.
    • Fig. S4. Demonstration of the droplet behaviors influenced by D/d and V.
    • Fig. S5. Demonstration of the luminol reaction.
    • Fig. S6. Demonstrations of the drug delivery using the magnetic-actuated robot.
    • Legends for movies S1 to S8

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mov format). Typical behaviors of the droplets manipulated using the magnetic-actuated robot.
    • Movie S2 (.mov format). Demonstration of the droplet behaviors influenced by D/d and V.
    • Movie S3 (.mov format). Generality demonstration of the magnetic-actuated robot.
    • Movie S4 (.mov format). Display of the stepwise acid-based neutralization reactions.
    • Movie S5 (.mov format). Display of the luminol reaction.
    • Movie S6 (.mov format). Simulation of the calculi removal.
    • Movie S7 (.mov format). Simulation of the drug delivery.
    • Movie S8 (.mov format). Simulation of the vascular clearance.

    Files in this Data Supplement:

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