Tadpole-Like Flexible Microswimmers with the Head and Tail Both Magnetic

Abstract

In analogy to eukaryotic cells that move by beating the flagella, magnetically powered micro/nanorobots with flexible filaments are capable of eluding the limitation of the scallop theorem to generate net displacement in a three-dimensional space, but they are limited by complicated fabrication and low speed. Here, we demonstrate a tadpole-like flexible microswimmer with a head and tail that are both magnetic by developing a magnetically assisted in situ polymerization method. The flexible microswimmer consists of a magnetic-bead head fixed to a nanochain bundle of magnetic nanoparticles (tail), and the tail length and stiffness can be adjusted simply by changing the duration and strength of the applied magnetic field during fabrication, respectively. For the microswimmer under an oscillating magnetic field, the magnetic head generates an undulatory motion, which can be further increased by the flexible magnetic tail. The magnetically induced undulation of the head and tail generates a traveling wave propagating through its flexible tail, resulting in efficient tadpole-like propulsion of the microswimmer. The flexible microswimmer runs at a maximum motion speed when the tail length is ∼5 times the diameter of the magnetic head, corresponding to ∼half the wavelength of the undulatory motion. The flexible microswimmers reported here are promising for active sensing and drug delivery, as the tails can be designed with various responsive hydrogels, and the results are expected to advance flexible micro/nanorobots.

One-step formation of polymorphous sperm-like microswimmers by vortex turbulence-assisted microfluidics

“…In this study, inspired by spermatozoa's morphology and function, we proposed an asymmetrical design with polymorphous head and flexible tail for endowing microswimmer both propelling and loading abilities at low Reynold environment. Different to the manufacture of traditional microswimmers [35][36][37][38][39][40][41] (Supplementary Table S2), the proposed VTAM approach enables the fabrication of biocompatible asymmetrical magnetic microswimmers with tail in one step. It not only provides high moveable ability but also achieves bionic semipermeable membrane encapsulation, offering sustain release capability for targeted drug delivery.…”

Evolution of the Microrobots: Stimuli-Responsive Materials and Additive Manufacturing Technologies Turn Small Structures into Microscale Robots

“…Next to LCE and hydrogel-based actuators-which respond to light, heat, and chemical stimuli and find more applications comprising moving parts-magnetic systems cover a broad, somewhat complementary, spectrum of the research performed in microrobotics (Figure 5), focusing more on motion and spatial control. As organic materials do not show inherent magnetic properties, most magnetic microactuators consist of composites comprising magnetic particles (e.g., FePt, NdFeB, and Cr2O) or superparamagnetic iron oxide nanoparticles (SPIONs) dispersed in a soft matrix [112][113][114]. In this way, one can still take advantage of the common lithographic, molding, As organic materials do not show inherent magnetic properties, most magnetic microactuators consist of composites comprising magnetic particles (e.g., FePt, NdFeB, and Cr 2 O) or superparamagnetic iron oxide nanoparticles (SPIONs) dispersed in a soft matrix [112][113][114].…”

“…As organic materials do not show inherent magnetic properties, most magnetic microactuators consist of composites comprising magnetic particles (e.g., FePt, NdFeB, and Cr2O) or superparamagnetic iron oxide nanoparticles (SPIONs) dispersed in a soft matrix [112][113][114]. In this way, one can still take advantage of the common lithographic, molding, As organic materials do not show inherent magnetic properties, most magnetic microactuators consist of composites comprising magnetic particles (e.g., FePt, NdFeB, and Cr 2 O) or superparamagnetic iron oxide nanoparticles (SPIONs) dispersed in a soft matrix [112][113][114]. In this way, one can still take advantage of the common lithographic, molding, and printing techniques used in microfabrication, suffering only minor drawbacks connected to the different optical and rheological properties of the composites compared to the pure resins [100].…”

“…Besides molecular interactions, other forces can drive self-assembly and be effective even on larger scales, interfacing large particles as well as devices. Among such interactions, we find magnetic, dipolar, electrostatic, chemical, optical, and acoustic ones, thus displaying a plethora of opportunities to control the aggregation of particles and communication between them and allowing the simultaneous manipulation of large collections of microrobots [98,113,150,[173][174][175][176]. Large swarms of microrobots can, in fact, be more suited to accomplish tasks that are too complicated for single microdevices, allowing for parallel processing and better task allocation.…”

Magnetic Control of Nonmagnetic Living Organisms

“…This lag primarily stems from the challenge of not being able to simply “shrink” or miniaturize traditional robots to the micron scale without compromising their functionality. Instead, emerging bottom-up strategies are being developed that prioritize the utilization of active colloidal particles capable of sensing and responding to external stimuli with programmable motility, , although they often lack the comprehensive functional aspects of traditional robots . While inspired by biological matter, these synthetic active materials fall short of the hierarchical complexity found in living colloids .…”