Abstract: 

Magnetic fiber robots have revealed great potential for future minimally invasive robotic surgery. However, with the miniaturization of fiber robots, the integration of functional microtools at the distal end becomes extremely challenging, since it requires assembling multifunctional structures on the curved surfaces of fiber ends, which typically have very small curvature radii. In this study, a submillimeter fiber robot with integrated micro-manipulation tool at the distal end is reported using a “Swiss roll” assembly strategy. This approach enables the one-step assembly of multiscale structures (mm-µm) from a 2D film to a 3D tool on the curved surface of the fiber robot. The multiscale structure consists of a millimeter-scale (mm) magnetic thin film with integrated micrometer-scale (µm) feature structures, which is inspired from the cat tongue covered by numerous little papillae. The fiber robot can perform multiple functions including endovascular clot grabbing, liquid delivery, and sampling under the manipulation of the magnetic field. The strategy provides a universal protocol for integrating and assembling functional components at the distal end of fiber robots, contributing significantly to the functionalization and miniaturization of interventional medical robots.

Figure 1 Design and functionalities of the magnetic fiber robot. a) Scheme of the magnetic fiber robot. The robot consists of a magnetic fiber body, an embedded capillary tube, and a micro-manipulation tool at the distal end. The magnetization direction between the robot body and the fiber end is orthogonal. b) A photograph of the robot with an outer diameter of 500 µm. The inset is an enlarged view of the fiber end. c) Images of the cat tongue, which is covered by many little papillae. d) The cat tongue-inspired design of the micro-manipulation tool at the fiber end. An array of microscale barbs is integrated on the soft magnetic film. The shape of the barb mimics that of bees’ barbs. e) The steering direction of the fiber body and the state of the micro-manipulation tool at the fiber end can be controlled using orthogonal magnetic fields. f) Functionalities of the magnetic fiber robot. i) Removal of obstruction; ii) Drug delivery; iii) Liquid biopsy.

Figure 2 Fabrication process and basic properties of the magnetic fiber robots. a) Fabrication process of the magnetic fiber robots. i) A magnetic PDMS film doped with NdFeB micro-particles was pre-designed with a pair of tips, which were bent backward and fixed; ii) These tips were magnetized through a magnetic field of 1 T while in this bent state; iii) An array of barbs was integrated onto this pair of tips using the TPP fabrication technique; iv) A capillary tube approached the film to facilitate the rolling like a “Swiss roll” process; v) The capillary tube after rolling was inserted into a PTFE tube. The suction pressure was applied to fill the PTFE tube with magnetic PDMS prepolymer, allowing the PDMS to encapsulate the capillary tube. This filling process was conducted under a magnetic field oriented along the fiber, allowing for the alignment of NdFeB particles. In this manner, the fiber robot body could be produced; vi) After curing, the PTFE tube at the distal end was peeled off, thus producing the magnetic fiber robot with an embedded capillary tube. b) A PDMS film is magnetized under a curled condition to simulate the opening and closing behavior of the micro-manipulation tool. c) A photograph of the closing behavior under the manipulation of magnetic fields. d) Demonstration of the bending behavior of the fiber body under external magnetic fields. e) Relationship between the bending angle and the applied magnetic field for PDMS films with different thicknesses. This relationship was measured under the experimental setup shown in (b) and (c). f) Relationship between the bending angle and the applied magnetic field for PDMS films with different mass ratios of NdFeB particles. This relationship was also measured in a way shown in (b) and (c). g) Relationship between the bending angle and the distance (depicted in (d)) for fiber robot bodies with different mass ratios of NdFeB particles.

Figure3 Modeling and simulation of the magnetic fiber robot. a) Analytical model for the deflection of the fiber robot. b) Euler–Bernoulli beam mechanics model. c) The deformation angle of the magnetic fiber robot at different distances from the magnet, which was calculated using the model. The magnetic field intensity and gradient data at different distances were derived from finite element simulation and curve fitting of the simulated magnetic field intensity data, respectively. d) Finite element analysis simulation of the bending deformation of the magnetic thin film using the COMSOL Multiphysics. e) Finite element analysis simulation of the bending deformation of the fiber robot in the COMSOL Multiphysics environment. The color bar on the right side represents the magnetic field strength generated by the permanent magnet.

DOI: 10.1002/adfm.202309424