Research ArticleMICROSTRUCTURES

Sequence-encoded colloidal origami and microbot assemblies from patchy magnetic cubes

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Science Advances  04 Aug 2017:
Vol. 3, no. 8, e1701108
DOI: 10.1126/sciadv.1701108
  • Fig. 1 Magnetic field–driven assembly of patchy microcubes and their modes of self-reconfiguration.

    (A) Schematic of the experimental setup used to assemble and manipulate the patchy microcubes. A uniform magnetic field was generated by a collinear pair of electromagnets (1 and 2), and a magnetic field gradient was imposed by a single electromagnet (3). (B) Micrograph of an aqueous dispersion of single-side cobalt-coated patchy microcubes (the superimposed yellow lines represent the magnetic patches; scale bar, 20 μm). (C) Example of a linear chain of patchy microcubes formed upon the application of a uniform magnetic field. (D) Reversible self-reconfiguration of the linear chain in (C) into a structure of two closed loops upon removing the applied field (movie S1). (E) Schematics of the assembly pathways for the two basic unit doublets, AA and AB, which correspond to assembled particles on the same side and opposite sides of the assembled magnetic films, respectively.

  • Fig. 2 Reconfiguration patterns of short chains of microcubes driven by dipole-field and residual dipole-dipole interactions.

    (A to I) Snapshots of the reconfiguration patterns intrinsic to AA, AAA, and AAB sequences. After the applied field is removed, the microcube chains self-fold (A and B, D and E, and G and H) until (i) a ground state configuration is attained [for example, (B)], (ii) a metastable structure is formed [for example, (E)], or (iii) a sterically restricted conformation is attained [for example, (H)]. When the external field is imposed again, (i) the ground state configuration C is retained [for example, (C)], (ii) the metastable AAA structure usually reconfigures into AC [for example, (F)], and (iii) the partially wrapped structure AAB reattains its initial stretched state [for example, (I)]. Scale bar, 20 μm. (J) Change in the magnetic dipolar energy per microcube during the reconfiguration process as a function of the interdipolar angle Embedded Image, the angle between planes of magnetic patches on adjacent microcubes, adapting self-folding toward the ground state. The inset shows the interaction between two dipoles of finite length 2l in terms of the unit vector of each dipole, Embedded Image and Embedded Image, and the position vector Embedded Image between Embedded Image and Embedded Image.

  • Fig. 3 Examples of dynamic reconfiguration of chain sequences comprising four microcubes.

    (A) Snapshots of field-on and field-off states of the four particle colloidal isomers (that is, ABBA and BBAA). Scale bar, 20 μm. (B) Dependence of folding rate measured for the initial 0.5 s of the ABBA microcube sequence on the applied magnetic field strength after the field is removed. The folding rate is linearly dependent on the square of the strength of initially applied magnetic field. The error bars correspond to the SD of the folding rate per the square of the field strength from five different ABBA structures.

  • Fig. 4 Microcube assemblies as prototypes of microbots for transporting cells and as colloidal origami.

    (A to E) Snapshots of a microbot comprising six microcubes (BABBAB) used for transporting a yeast cell. (A) Spatial migration of the assembly in its open state under uniform external magnetic field with longitudinally imposed gradient. (B) The microcube chain is brought to the yeast cell by attraction along the gradient. (C) The cluster self-closes upon removing the uniform field, which results in the capture of the yeast cell. (D) The microbot is transported to the target location by a magnetic gradient force. (E) Finally, the cell is released by reactivating the uniform magnetic field. (F to J) Distribution of magnetic field intensity around the BABBAB assembly during each stage of manipulation shown in (A) to (E), as calculated by COMSOL Multiphysics. (K and L) Snapshots of a repeatedly self-reconfigurable multicube chain as an example of programmable colloidal origami. Scale bars, 20 μm (A and K).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/8/e1701108/DC1

    Supplementary Results and Discussion

    fig. S1. An example set of images from an optical microscope, an SEM, and an SEM with an EDS overlay of an assembled chain of patchy microcubes.

    fig. S2. Example of the assembly of patchy microcubes under a uniform magnetic field.

    fig. S3. Magnetic hysteresis curve of a collection of dried Co-coated patchy microcubes.

    fig. S4. Calculation of the dipole-dipole interaction energy for patchy microcube doublets as a function of bending angle in the absence of an external magnetic field.

    fig. S5. The kinetics of the self-reconfiguration of four particle clusters expressed by mean interparticle (≡ interdipolar) angle Formula.

    fig. S6. Chain reorientation techniques for reprogramming the relative sequence of a microbot assembly (BAABBAABB).

    fig. S7. Chain reorientation technique to program the sequence of a microbot.

    movie S1. Magnetic field–driven actuation of an assembled chain.

    movie S2. Self-folding and irreversible transition of assembled chains with sequences of AA, AAA, and AAAA.

    movie S3. Reversible actuation of chains with sequences of ABBB, ABBA, and BBAA.

    movie S4. Cell capture and transport by a microbot prototype.

    movie S5. BAABBAABB chain conversion process.

    movie S6. Programmed assembly of a chain with an ABBA sequence.

    References (34, 35)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Results and Discussion
    • fig. S1. An example set of images from an optical microscope, an SEM, and an SEM with an EDS overlay of an assembled chain of patchy microcubes.
    • fig. S2. Example of the assembly of patchy microcubes under a uniform magnetic field.
    • fig. S3. Magnetic hysteresis curve of a collection of dried Co-coated patchy microcubes.
    • fig. S4. Calculation of the dipole-dipole interaction energy for patchy microcube doublets as a function of bending angle in the absence of an external magnetic field.
    • fig. S5. The kinetics of the self-reconfiguration of four particle clusters expressed by mean interparticle (≡ interdipolar) angle δ .
    • fig. S6. Chain reorientation techniques for reprogramming the relative sequence of a microbot assembly (BAABBA→ABB).
    • fig. S7. Chain reorientation technique to program the sequence of a microbot.
    • Legends for movies S1 to S6
    • References (34, 35)

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.avi format). Magnetic field–driven actuation of an assembled chain.
    • movie S2 (.avi format). Self-folding and irreversible transition of assembled chains with sequences of AA, AAA, and AAAA.
    • movie S3 (.avi format). Reversible actuation of chains with sequences of ABBB, ABBA, and BBAA.
    • movie S4 (.avi format). Cell capture and transport by a microbot prototype.
    • movie S5 (.avi format). BAABBAABB chain conversion process.
    • movie S6 (.avi format). Programmed assembly of a chain with an ABBA sequence.

    Files in this Data Supplement: