Artificial flexible sperm-like nanorobot based on self-assembly and its bidirectional propulsion in precessing magnetic fields

Abstract

Sperm cells can move at a high speed in biofluids based on the flexible flagella, which inspire novel flagellar micro-/nanorobots to be designed. Despite progress in fabricating sperm-type robots at micro scale, mass fabrication of vivid sperm-like nanorobots with flagellar flexibility is still challenging. In this work, a facile and efficient strategy is proposed to produce flexible sperm-like nanorobots with self-assembled head-to-tail structure, and its bidirectional propulsion property was studied in detail. The nanorobots were composed of a superparamagnetic head and a flexible Au/PPy flagellum, which were covalently linked via biotin-streptavidin bonding with a high yield. Under precessing magnetic fields, the head drove the flexible tail to rotate and generated undulatory bending waves propagating along the body. Bidirectional locomotion was investigated, and moving velocity as well as direction varied with the actuating conditions (field strength, frequency, direction) and the nanorobot’s structure (tail length). Effective flagellar propulsion was observed near the substrate and high velocities were attained to move back and forth without U-turn. Typical modelling based on elastohydrodynamics and undulatory wave propagation were utilized for propulsion analysis. This research presents novel artificial flexible sperm-like nanorobots with delicate self-assembled head-to-tail structures and remarkable bidirectional locomotion performances, indicating significant potentials for nanorobotic design and future biomedical application.

Soft Millirobot Capable of Switching Motion Modes on the Fly for Targeted Drug Delivery in the Oviduct

“…According to the undulatory motion theory, the locomotion velocity is related to the magnetic field intensity and rotating frequency. 42 The forward speed is similar to that of snake-like gliding, reaching 1.5 mm/s under a magnetic field of 3 mT and 1 Hz.…”

“…The soft linkages contribute to effective undulatory propagation and a constant phase lag exists between the magnetic head and the flagellum. According to the undulatory motion theory, the locomotion velocity is related to the magnetic field intensity and rotating frequency . The forward speed is similar to that of snake-like gliding, reaching 1.5 mm/s under a magnetic field of 3 mT and 1 Hz.…”

“…The millirobot performs the sperm-like rotating to negotiate narrow channels, inspired by the flagellar beating of the sperm cells (Figure G). , The oviduct has an isthmus featured with a narrow channel . The magnetic millirobot with rolling mode cannot pass through the narrow channel due to dimension limitation, and the propelling force of the gliding mode is relatively weak to overcome the high hydrodynamic force near the walls within a narrow channel (Figure S10).…”

Enhancing magnetically driven microswimmer velocity via low Reynolds number hydrodynamic interactions

“…These developments can be categorized based on actuation control, designs, and fluid medium exploitations. For control, researchers have developed different actuation mechanisms for independent control of multiple magnetic swimmers (identical or/and non-identical) [44][45][46], bidirectional propulsion [47], turning maneuvers [48], and omnidirectional navigation [26,29]. In the design aspect, optimization of the swimmer's geometry and actuation parameters [25,49,50], multiple flagellated geometry [51][52][53], and flagellum with intrinsic curvature [54,55] are reported for maximization of swimmer performance.…”

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

“…Flexible microswimmers can adaptively deform according to local landscapes and navigate in three-dimensional space, setting them apart from surface-assisted microwalkers/rollers confined to boundaries and rigid-bodied helical microswimmers. Up until now, some flexible microswimmers with head–tail structures have been reported, such as the DNA-connected superparamagnetic particle chain attached to a red blood cell, DNA flagella linked to a magnetic microparticle, sperm cells loaded with magnetic nanoparticles, bead-on-string fibers fabricated by electrospinning, and (dual-) multisegment flexible wires prepared by a multistep electrochemical deposition method. − However, for these reported head–tail flexible micro/nanoswimmers, only one part (head or tail) is magnetic, and they generally feature a tail with a consistent diameter from the tip to the “neck” connection, differentiating from the tapering tail design observed in living organisms. Furthermore, their fabrication methods usually involve noble metals, expensive instruments, and tedious multiple steps, , while lacking the capability for facile control of the structural characteristics (e.g., tail length and stiffness) of the microswimmers.…”