Ionic shape-morphing microrobotic end-effectors for environmentally adaptive targeting, releasing, and sampling

Abstract

Shape-morphing uses a single actuation source for complex-task-oriented multiple patterns generation, showing a more promising way than reconfiguration, especially for microrobots, where multiple actuators are typically hardly available. Environmental stimuli can induce additional causes of shape transformation to compensate the insufficient space for actuators and sensors, which enriches the shape-morphing and thereby enhances the function and intelligence as well. Here, making use of the ionic sensitivity of alginate hydrogel microstructures, we present a shape-morphing strategy for microrobotic end-effectors made from them to adapt to different physiochemical environments. Pre-programmed hydrogel crosslinks were embedded in different patterns within the alginate microstructures in an electric field using different electrode configurations. These microstructures were designed for accomplishing tasks such as targeting, releasing and sampling under the control of a magnetic field and environmental ionic stimuli. In addition to structural flexibility and environmental ion sensitivity, these end-effectors are also characterized by their complete biodegradability and versatile actuation modes. The latter includes global locomotion of the whole end-effector by self-trapping magnetic microspheres as a hitch-hiker and the local opening and closing of the jaws using encapsulated nanoparticles based on local ionic density or pH values. The versatility was demonstrated experimentally in both in vitro environments and ex vivo in a gastrointestinal tract. Global locomotion was programmable and the local opening and closing was achieved by changing the ionic density or pH values. This ‘structural intelligence’ will enable strategies for shape-morphing and functionalization, which have attracted growing interest for applications in minimally invasive medicine, soft robotics, and smart materials.

Study on Magnetic Control Systems of Micro-Robots

“…In 2021, Zheng et al (2021) designed ionic shape-morphing micro-robotic end-effectors (ISMEs) that can be used for environmental targeting, releasing and sampling, and have a gripping motion. The magnetic nanoparticles are encapsulated in an alginate monolayer, and the ISMEs are controlled by the external magnetic field to reach the target position.…”

“…The system consists of 8 electromagnetic coils with DT4 cores, which are distributed diagonally. The structure of this coil system is the same as that used by Diller et al (2013) and Li et al (2020), as shown in Figure 2D (Zheng et al, 2021). The specific modeling configuration of this electromagnetic coils is shown in Figure 1E (Pourkand and Abbott, 2018).…”

“…Researchers believe FIGURE 2 | (A) External electromagnetic system has 8 electromagnetic coils distributed diagonally to control a micro robot with two pseudopods to perform magnetic walking (Li et al, 2020). (B) The process of magnetic walking of a micro-robot by alternately raising the left and right feet (Li et al, 2020) (C) Indirect pushing of non-magnetic microbeads (Li et al, 2020) (D) Octupole magnetic system provides magnetic drive in rotating field and gradient field to ISMEs (Zheng et al, 2021).…”

Recent progress in actuation technologies of micro/nanorobots

“…Inspired by the movement process of starfish preying on shellfish, Zheng et al [25] designed a sea star-like microrobot, the flexible tentacles of which can effectively conform to the outer contours of any target with autonomous deformation in a liquid environment for grasping and releasing. The robot has multiple actuation modes, for example, through trapping of magnetic microspheres or through encapsulating magnetic nanomaterials in the robot body, as shown in Figure 1.…”

A Review of Microrobot’s System: Towards System Integration for Autonomous Actuation In Vivo

“…The micromachines applied to non-invasive medical interventions have attracted numerous attention since being proposed by Albert Hibbs and Richard Feynman in 1959. After decades of development, it has made great progress in a variety of microrobot fields, including actuation, control, navigation, and functionalization, laying the foundation for future clinical applications [ 1 , 3 , 5 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ]. However, how to accurately deliver microrobots to a specified position to perform medical tasks is still an unsolved problem due to the fact that manual control is inefficient and imprecise.…”