Wireless Miniature Magnetic Phase-Change Soft Actuators

Abstract

Wireless miniature soft actuators are promising for various potential high-impact applications in medical, robotic grippers, and artificial muscles. However, these miniature soft actuators are currently constrained by a small output force and low work capacity. To address such challenges, a miniature magnetic phase-change soft composite actuator is reported. This soft actuator exhibits an expanding deformation and enables up to a 70 N output force and 175.2 J g^-1 work capacity under remote magnetic radio frequency heating, which are 10⁶ -10⁷ times that of traditional magnetic soft actuators. To demonstrate its capabilities, a wireless soft robotic device is first designed that can withstand 0.24 m s^-1 fluid flows in an artery phantom. By integrating it with a thermally-responsive shape-memory polymer and bistable metamaterial sleeve, a wireless reversible bistable stent is designed toward future potential angioplasty applications. Moreover, it can additionally locomote inside and jump out of granular media. At last, the phase-change actuator can realize programmable bending deformations when a specifically designed magnetization profile is encoded, enhancing its shape-programming capability. Such a miniature soft actuator provides an approach to enhance the mechanical output and versatility of magnetic soft robots and devices, extending their medical and other potential applications.

Keywords: high work capacity; magnetic soft composites; miniature wireless soft devices; phase-change materials; programmable shape deformation.

Figure 1. Phase-change magnetic soft actuator with inflation behavior.

a) Schematic showing the inflation process of the cylindrical phase-change actuator under magnetic-RF heating. b) Scanning electron microscope (SEM) image of the composed double-layer film for the actuator. c) Experimental camera video snapshots exhibit the corresponding inflation process of the actuator under magnetic-RF heating. d) Ultrasound imaging video snapshots exhibiting the inflation process of the cylindrical actuator inside a porcine coronary artery ex-vivo. The images in (c) and (d) are obtained from Movies S1 and S3 (Supporting Information), respectively.

Figure 2. Characterization and optimization of the magnetic phase-change soft actuator.

a) The maximum internal pressure of the phase-change actuator with a fixed 70.8 mm³ volume under magnetic-RF heating as a function of the internal low-boiling point liquid content. b) The internal pressure of the actuator under magnetic-RF heating with different weight ratios of the Fe₃O₄NPs content. Note that the actuator volume is fixed to 70.8 mm³. c) The body length elongation ratio and radial expansion ratio of the actuator as a function of the inner pressure under magnetic-RF heating. The actuator’s maximum inflation ratio and internal pressure with different d) skin thicknesses and e) moduli of the composed materials in the inflation process. f) The calculated output forces under different volume inflation ratios. The data are presented as mean values ± standard deviation for 3 times measured.

Figure 3. Actively controlled soft inflating balloon toward future angioplasty applications.

Schematic illustrates a) the locomotion and inflation, and b) blocking process of the magnetic phase-change actuator under a rotating magnetic field and magnetic-RF heating, respectively. Note, the amplitude and frequency of the rotating magnetic field are about 40 mT and 0.5–2 Hz, respectively. A series of pictures illustrate the corresponding c) locomotion, d) inflation, and e) blocking process in the “Y”-shaped water full-filled glass tube. The images in (c)–(e) are obtained from Movie S4 (Supporting Information).

Figure 4. Proof-of-concept demonstration of the reversible bistable stent application.

a) Schematic and camera image showing the design of the reversible stent. b) A series of camera images showing the operating process of the reversible stent with different power inputs of the magnetic-RF heating. c) The images exhibit the “open” and “close” process of the reversible stent in the Ecoflex soft tube and d) the corresponding stenting force in this process. e) The ultrasound images demonstrate that the reversible stent opens inside the porcine coronary artery ex-vivo. The images shown in (b), (c), and (e) are obtained from Movies S5, S6, and S7 (Supporting Information), respectively.

Figure 5. Soft-bodied locomotion capability of the proposed actuator inside granular media.

a) The Schematic illustrates the vertical lifting process of the magnetic phase-change actuator inside a granular media by turning the magnetic-RF heating system on and off at regular intervals. b) The corresponding camera images of this lifting process. c) The Schematic shows the explosion and jumping behavior of the magnetic phase-change actuator in granular media under magnetic-RF heating (P3 power input). d) The corresponding images of the explosion and jumping process. The images shown in (b) and (c) are obtained from Movies S8 and S9 (Supporting Information), respectively.

Figure 6. Sheet-shaped magnetic phase-change soft actuator with walking and expanding behavior.

a) The schematic illustrates the bending and expanding behaviors of the actuator under magnetic torques and magnetic-RF heating, respectively. b) A series of images showing the walking and inflation behavior of the magnetic phase-change soft robot inside a glass tube under magnetic torques and magnetic-RF heating, respectively. These images are obtained from Movie S11 (Supporting Information).