1) Researchers developed anisotropic magnetic microcubes that can be assembled into microstructures using external electric and magnetic fields. 2) The magnetic field provides an alignment torque that controls the orientation of the cubes, while the electric field controls the assembly speed and frequency of polarization between the cubes. 3) By independently and simultaneously controlling the electric and magnetic fields, the assembled microcube structures can be actuated, transported, and used to complete tasks like capturing live yeast cells.

1. Assembly and Magnetic Actuation of Microbot Prototypes from Anisotropic
Patchy Microcubes
Nidhi Diwakar2, 4, Koohee Han1, 2, C. Wyatt Shields IV2, 3, Bhuvnesh Bharti1, 2, Gabriel López2, 3, and Orlin D. Velev1, 2
1Department of Chemical and Biomolecular Engineering, NCSU; 2NSF Research Triangle MRSEC; 3Department of Biomedical Engineering, Duke University;
4Department of Robotics Engineering, Worcester Polytechnic Institute
Field-Driven Assembly Process
Polarization
𝐇
AssemblyPlacement Attraction
𝐇 𝑬+
A combination of magnetic torque and dielectric polarization promotes
interaction between cubes and results in assemblies.
Magnetic field strength directly changes the alignment torque. Electric field
intensity controls assembly speed and frequency affects relative polarization.
Field-Induced Actuation
𝝁 𝟏 𝝁 𝟐
𝝁 𝟏 𝝁 𝟐
Eint
The angle between two dipole moments
𝐇
Field on
𝑬int =
𝝁 𝟏 ∙ 𝝁 𝟐
𝒓 𝟑
− 𝟑
𝝁 𝟏 ∙ 𝒓 𝝁 𝟐 ∙ 𝒓
𝒓 𝟓
Anisotropic Particle Fabrication
Source
Co VaporFerromagnetic
Coating [Co, Fe]
(100 nm)
Dielectric
material
[SU-8] (10 μm)
Triangle Materials Research Science and Engineering Center, Velev Research Group, North Carolina State University, Duke University
Acknowledgements
Experimental Set Up
Electrode
Electromagnets
Sample
Chamber 3 mm
H
E
20-30 μm
Paraffin
Barrier
Cover Slip
Side View
Assembly
DisassemblyThe magnetic and electric fields
can be controlled independently,
but act in parallel. 50 μm
Gradient-Directed Transportation
Electric Field
Gradient
External
Permanent Magnet
Application: Live Cell Capture
Navigation of Grabber Structure to Capture Live Yeast Cell
The grabber structure can be manipulated to move and capture a live cell using a
combination of both electric and magnetic gradients.
50 μm
Approach Capture Transport Release
Conclusions
Assembling Cubes 𝐻 + 𝐸 fields act together to assemble cubes
Actuating Chains Energy minimization drives folding behavior
Constructing Structures Combine staggered and linear chains
to yield useful structures
Transporting Grabbers External field gradients cause cube
movement
Capturing Live Targets Transport and actuate structures to
capture target objects
Microstructure Design Principles
+ =
A A AA
=+
A B AB
Linear
AAA
AAAA
AA
Staggered
20 μm
30 μm
50 μm
ABAB
ABA
AB
10 μm
Combination
ABBA
10 μm
Reversibly Actuatable