Recent Progress in Active Mechanical Metamaterials and Construction Principles

Abstract

Active mechanical metamaterials (AMMs) (or smart mechanical metamaterials) that combine the configurations of mechanical metamaterials and the active control of stimuli-responsive materials have been widely investigated in recent decades. The elaborate artificial microstructures of mechanical metamaterials and the stimulus response characteristics of smart materials both contribute to AMMs, making them achieve excellent properties beyond the conventional metamaterials. The micro and macro structures of the AMMs are designed based on structural construction principles such as, phase transition, strain mismatch, and mechanical instability. Considering the controllability and efficiency of the stimuli-responsive materials, physical fields such as, the temperature, chemicals, light, electric current, magnetic field, and pressure have been adopted as the external stimuli in practice. In this paper, the frontier works and the latest progress in AMMs from the aspects of the mechanics and materials are reviewed. The functions and engineering applications of the AMMs are also discussed. Finally, existing issues and future perspectives in this field are briefly described. This review is expected to provide the basis and inspiration for the follow-up research on AMMs.

Keywords: active mechanical metamaterials; construction principles; engineering applications; multi functions; stimuli-responsive materials.

Figure 1

Summary of active mechanical metamaterials, their construction principles, classifications, and applications. Primary applications of AMMs are listed, including: a) Stealth cloak.^{[ 48 ]} Copyright 2014, Nature Publishing Group. b) Electronic skin.^{[ 49 ]} Copyright 2019, Wiley‐VCH. c) Soft robot.^{[ 50 ]} Copyright 2020, Wiley‐VCH. d) Microfluidics.^{[ 28 ]} Copyright 2020, Nature Publishing Group. e) Flexible batteries.^{[ 51 ]} Copyright, 2020, American Chemical Society. f) Wearable devices.^{[ 52 ]} Copyright 2019, Nature Publishing Group. g) Bionic gripper.^{[ 53 ]} Copyright 2020, Wiley‐VCH. h) Anti‐impact structure.^{[ 46 ]} Copyright 2020, American Association for the Advancement of Science. i) Vascular stent.^{[ 54 ]} Copyright 2018, Wiley‐VCH.

Figure 2

Metamaterials based on phase transition principle. a) Compression behaviors of the 2D metamaterials with the different material layout at 25 and 70 °C.^{[ 61 ]} Copyright 2019, American Physical Society. b) Reversible actuation of the bird‐like robot.^{[ 62 ]} Copyright 2018, American Association for the Advancement of Science. c) The programmable deformation of the smart window under temperature changing.^{[ 18 ]} Copyright 2018, Wiley‐VCH. d) Two layers of the chain‐mail fabrics in the soft state.^{[ 67 ]} Copyright 2021, Nature Publishing Group.

Figure 3

Metamaterials based on strain mismatch. a) NTE metamaterials that composed of different thermal expansion coefficient materials.^{[ 11 ]} Copyright, 2016, American Chemical Society. b) 3D adjustable thermal expansion deformation.^{[ 73 ]} Copyright 2019, Wiley‐VCH. c) Kirigami structures with positive expansion effects.^{[ 74 ]} Copyright 2021, Wiley‐VCH. d) Hydrogel‐driven helical structure.^{[ 76 ]} Copyright 2013, Nature Publishing Group. e) Soft mechanical metamaterials with negative swelling behavior.^{[ 77 ]} Copyright 2018, American Association for the Advancement of Science.

Figure 4

Metamaterials based on mechanical instability. a) Buckling deformation of double beam sensitive to strain rate.^{[ 86 ]} Copyright 2020, American Association for the Advancement of Science. b) Porous metamaterials with tunable mechanical behaviors.^{[ 90 ]} Copyright 2014, American Physical Society. c) 2D to 3D transformation process of soccer‐shaped active metamaterials.^{[ 101 ]} Copyright 2016, Wiley‐VCH. d) Bionic self‐folding flap robot based on mechanical instability principle.^{[ 104 ]} Copyright 2020, American Association for the Advancement of Science. e) The crawling of the python like robot with kirigami skin.^{[ 31 ]} Copyright 2019, National Academy of Sciences.

Figure 5

Thermal‐responsive active metamaterials. a) Uniaxial stretching diagram of 4D printing auxetic metamaterials.^{[ 121 ]} Copyright 2020, Wiley‐VCH. b) The actuation and recovery of a flower and bi‐stable lattices.^{[ 35 ]} Copyright 2021, Elsevier. c) Display of the drug release function of SMP‐hydrogel stent.^{[ 136 ]} Copyright 2021, American Association for the Advancement of Science. d) Composition and deformation principle of super‐elastic thermal‐responsive metamaterials.^{[ 138 ]} Copyright 2020, Wiley‐VCH. e) Bi‐material multi‐stable metamaterials and the three‐dimension configuration in a stable state.^{[ 20 ]} Copyright 2019, Elsevier. f) The assembly deforms in sequence during the heating process to realize multi‐shape response functions.^{[ 37 ]} Copyright 2020, Elsevier.

Figure 6

Chemical‐response active metamaterials. a) Samples with patterns on both sides and the deformed shapes.^{[ 143 ]} Copyright 2017, Wiley‐VCH. b) Initial state and the hydration state of the 2D and 3D auxetic metamaterials.^{[ 145 ]} Copyright 2020, Elsevier. c) Shape memory demonstration of the wax‐based polymers.^{[ 148 ]} Copyright 2017, Wiley‐VCH. d) The swelling process of square lattices with different unit configurations (plate #1, plate #2).^{[ 149 ]} Copyright 2016, Wiley‐VCH. e) Photolithographic patterning of gels and swelling‐induced cooperative deformation.^{[ 150 ]} Copyright 2017, American Association for the Advancement of Science.

Figure 7

Light‐responsive active metamaterials. a) Comparison of compression results of light‐response metamaterials with and without light source stimulation on the local region.^{[ 161 ]} Copyright 2020, Wiley‐VCH. b) Origami metamaterials with different numbers of pop‐up units and the schematic of unfolding effect under light stimulation.^{[ 162 ]} Copyright 2020, American Physical Society. c) Five typical modes of square twist origami antenna engagement.^{[ 24 ]} Copyright 2020, Wiley‐VCH. d) Light‐controlled microrobot.^{[ 157 ]} Copyright 2017, Wiley‐VCH. e) SLiRs (somatosensory light‐driven robots) centipede shows two kinds of movements: Waving forward and rotate turning.^{[ 53 ]} Copyright 2020, Wiley‐VCH. f) Flexible rolling of light‐responsive ratchet robot.^{[ 50 ]} Copyright 2020, Wiley‐VCH.

Figure 8

Electro‐responsive active metamaterials. a) The reprogramming process of the origami pattern by overheating.^{[ 167 ]} Copyright 2020, Wiley‐VCH. b) The transformation modes of the robot fabric, and the display of its bearing capacity.^{[ 168 ]} Copyright 2020, National Academy of Sciences. c) Reproduced with permission.^{[ 169 ]} Copyright 2018, Wiley‐VCH. d) Reproduced with permission.^{[ 170 ]} Copyright 2019, Wiley‐VCH, are schematics of the internal structures of laminated electro‐thermal response metamaterials. e) The lithiation process of auxetic lattices with different beam sizes.^{[ 171 ]} Copyright 2019, Nature Publishing Group. f) Micrometer‐scale origami quadruped robot and origami duck transformed from flat sheets.^{[ 45 ]} Copyright 2021, American Association for the Advancement of Science. g) The configuration of a cell and the layer‐by‐layer collapse of the metamaterials under uniaxial compression.^{[ 172 ]} Copyright 2019, Elsevier.

Figure 9

Magneto‐responsive active metamaterials. a) The infilling process of MRFs into cuboctahedron lattices.^{[ 27 ]} Copyright 2018, American Association for the Advancement of Science. b) Three typical deformation patterns of the magnetic meshes.^{[ 178 ]} Copyright 2019, Wiley‐VCH. c) Deformation under the magnetic field of asymmetric joints and the metamaterials array composed of cells with asymmetric joints.^{[ 29 ]} Copyright 2020, Wiley‐VCH. d) The deformations of the samples fabricated by DIW.^{[ 179 ]} Copyright 2018, Nature Publishing Group. e) Several programmable folding modes of Kresling origami assemblies.^{[ 180 ]} Copyright 2020, National Academy of Sciences. f) The ON and OFF state of the m‐bit bi‐stable cell and the tiled array with programmable mechanical properties.^{[ 181 ]} Copyright 2021, Nature Publishing Group. g) From left to right: the deformation of the M‐SMPs structures at 22 and 90 °C, with an upward magnetic field.^{[ 182 ]} Copyright 2020, American Physical Society. h) Metamaterials assembled by micro‐magnetic quadrupole modules.^{[ 183 ]} Copyright 2019, American Association for the Advancement of Science.

Figure 10

Pressure‐responsive metamaterials. a) The bearing capacity of the laminated structures with the change of internal pressure.^{[ 196 ]} Copyright 2018, Wiley‐VCH. b) Deformed states of the bending metamaterial under pressures from 0 to 0.025MP.^{[ 197 ]} Copyright 2020, Springer Nature. c) The deformation of the square lattices with alternatively arranged holes of different sizes.^{[ 30 ]} Copyright 2020, Elsevier. d) Specimen and the deformation process of the pneumatic negative stiffness metamaterials.^{[ 198 ]} Copyright 2020, Elsevier. e) The construction details of the inner pneumatic actuator and kirigami skin.^{[ 97 ]} Copyright 2018, American Association for the Advancement of Science. f) Schematics of the hydraulic actuated autonomic perspiration robot fingers.^{[ 204 ]} Copyright 2020, American Association for the Advancement of Science.

Figure 11

Functions of active mechanical metamaterials. a) Top view of the initial triangular micro‐cellular structures and assembled micro‐cellular structures.^{[ 209 ]} Copyright 2021, Nature Publishing Group. b) Three morphing pasta shapes of initial and cooked state. From top to bottom are ring, saddle, box.^{[ 211 ]} Copyright 2021, American Association for the Advancement of Science. c) Metamaterial voxels and the multi‐unit modules.^{[ 46 ]} Copyright 2020, American Association for the Advancement of Science. d) Origami metamaterials with functions of shapes reconfigurable and acoustic waveguides.^{[ 213 ]} Copyright 2016, American Association for the Advancement of Science. e) Contraction and deployment of the auxetic tensegrity actuator under strong center magnetic field and weak left field.^{[ 44 ]} Copyright 2020, American Association for the Advancement of Science.