Rapidly deployable and morphable 3D mesostructures with applications in multimodal biomedical devices

Abstract

Structures that significantly and rapidly change their shapes and sizes upon external stimuli have widespread applications in a diversity of areas. The ability to miniaturize these deployable and morphable structures is essential for applications in fields that require high-spatial resolution or minimal invasiveness, such as biomechanics sensing, surgery, and biopsy. Despite intensive studies on the actuation mechanisms and material/structure strategies, it remains challenging to realize deployable and morphable structures in high-performance inorganic materials at small scales (e.g., several millimeters, comparable to the feature size of many biological tissues). The difficulty in integrating actuation materials increases as the size scales down, and many types of actuation forces become too small compared to the structure rigidity at millimeter scales. Here, we present schemes of electromagnetic actuation and design strategies to overcome this challenge, by exploiting the mechanics-guided three-dimensional (3D) assembly to enable integration of current-carrying metallic or magnetic films into millimeter-scale structures that generate controlled Lorentz forces or magnetic forces under an external magnetic field. Tailored designs guided by quantitative modeling and developed scaling laws allow formation of low-rigidity 3D architectures that deform significantly, reversibly, and rapidly by remotely controlled electromagnetic actuation. Reconfigurable mesostructures with multiple stable states can be also achieved, in which distinct 3D configurations are maintained after removal of the magnetic field. Demonstration of a functional device that combines the deep and shallow sensing for simultaneous measurements of thermal conductivities in bilayer films suggests the promising potential of the proposed strategy toward multimodal sensing of biomedical signals.

Keywords: Lorentz force; deployable and morphable 3D mesostructures; instability; magnetic force; mechanically guided assembly.

Fig. 1.

Schematic illustrations of 3D mesostructures actuated by Lorentz forces and magnetic forces. (A) Schematic illustration of the 2D precursor in an exploded view to show the layer construction. (B–F) Optical images and FEA results of a deployed 3D ribbon mesostructure, actuated by applying the Lorentz force. (Scale bar, 2 mm.) (C–F) Optical images and FEA results of four different stable configurations for the assembled 3D mesostructure, which can be triggered by applying different Lorentz forces (through control of the electrical current). (Scale bars, 2 mm.) (G) Schematic illustration of the 2D precursor in an exploded view to show the layer construction, including a nickel layer (600 nm) sandwiched between two polyimide (PI) layers (∼7 μm each) with a thickening layer (PI, ∼8 μm). (H) Array of magnetic architectures deformed under an external magnetic field, with the Bottom illustrating deformations of four unit cells. (Scale bars, 10 mm.)

Fig. 2.

Programmable deformations in mechanically assembled 3D mesostructures actuated by Lorentz forces. (A) Scaling laws and experimental results for the maximum out-of-plane displacement of the suspended serpentine mesostructure as a function of the combined parameter, BIL²H³/(Eb²h³λ). (Scale bars, 4 mm.) (B) Optical images and FEA results for a highly deployable 3D mesostructure. The rightmost panel shows the distribution of the maximum principal strain. (Scale bars, 4 mm.) (C and D) Experimental and FEA results that illustrate actuated deformations in two 3D mesostructures, controlled by the Lorentz force. (Scale bars, 4 mm.) (E) Measured temperature distribution of 3D mesostructures when the electrical currents are applied. (F) Time responses of vibrational amplitudes at two endpoints of wings (marked as #1 and #2) in a butterfly-shaped mesostructure, for alternating currents with three different frequencies (5, 65, and 145 Hz, from Left to Right). The images on the Right show vibrational modes at the two lowest resonant frequencies. (Scale bars, 4 mm.)

Fig. 3.

Reconfigurable 3D mesostructures that can be reshaped by Lorentz forces. (A) FEA results that show the normalized maximum out-of-plane displacement versus the current applied to the suspended serpentine mesostructure. (Scale bars, 4 mm.) (B) Scaling laws and experimental results for the critical current of the suspended serpentine mesostructure as a function of the combined parameter, Ebh³λ/(BL^1.5H^2.5). (C–E) Optical images and FEA results that illustrate different stable configurations of reconfigurable 3D mesostructures. (Scale bars, 4 mm.) (F) Similar results for an origami-shaped reconfigurable mesostructure with four stable states. (Scale bars, 4 mm.) (G) Similar results for a reconfigurable origami mesostructure with six stable states. (Scale bars, 4 mm.)

Fig. 4.

Deployable and reconfigurable 3D mesostructures achieved through use of magnetic materials. (A) Optical images of the as-assembled and actuated configurations for a C-shaped structure. (Scale bars, 4 mm.) (B) Optical images that show actuated deformations in a 2D kirigami mesostructure with unidirectional cuts. (Scale bars, 4 mm.) (C) Similar results for another 2D kirigami mesostructure with bidirectional cuts. (Scale bars, 4 mm.) (D) Optical images of the kirigami mesostructure with the same pattern as that in C, and two different metal thicknesses (300 and 600 nm). (Scale bars, 4 mm.) (E–G) Optical images that illustrate different stable configurations of reconfigurable 3D mesostructures that can be reshaped by applying external magnetic fields. (Scale bars, 4 mm.) (H) Optical images and 2D precursors for the serpentine mesostructures with different distribution of magnetic material on each straight ribbon. The leftmost panel shows the profiles of deformed shapes. (Scale bars, 4 mm.)

Fig. 5.

A biomedical device for simultaneous measurements of thermal conductivities of bilayer materials. (A) Schematic illustration of the deployable, biomedical device for deformable process and measurement. (B) Optical images of biomedical device in different operational modes (states 1, 2, and 3). (Scale bars, 4 mm.) (C) Changes in temperature (ΔT) as a function of the thickness of Sylgard 184 silicone elastomer (h_S184) for two different states at a measurement time of 30 s. (D) Heat penetration depth induced by sensing units with small and large heaters on a semi-infinite, homogeneous medium. (E) Cross-sectional schematic image (Left) for measuring the thermal conductivities of a bilayer film, and contour plots of ΔT in terms of k_top and k_bottom for states 2 and 3 (Middle and Right).