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.
Highlights
Sperm cells can move at a high speed in biofluids based on the flexible flagella, which inspire novel flagellar micro-/nanorobots to be designed
Sperm cell is typical with flagellar self-propulsive capability, which can move forward in low Reynolds number biofluids through the flagellum-generated transverse waves[18], and provides us with possibilities to realize effective flagellar propulsion at micro-/nanoscale
Under a magnetic field of 70 Gs, 40 Hz and precession angle at 30°, the nanorobot could be actuated forward to reach a high velocity at 4.86 μm/s, and backward velocity at 3.17 μm/s could be achieved when turning the precession axis around
Summary
Sperm cells can move at a high speed in biofluids based on the flexible flagella, which inspire novel flagellar micro-/nanorobots to be designed. Enlightened by periodic undulations of the sperms, artificial sperm-shaped micro-/nanorobots have attracted much attention, aimed to achieve biomimetics in structure and function Among these researches, some are focused on integrated synthesis based on micro lithography or electrospinning technique, to construct a composite structure containing a magnetic head with a flexible polymer t ail[24,25,26,27]. A F e3O4 microsphere could be connected with rigid Ni nanorod for sperm-shaped configuration, yet the desired flexibility and functionalization was lacked; or be linked with repolymerized bacterial flagellum to achieve flagellar propulsion, yet great diversity existed compared with the sperm’s s hape[28,29,30,31,32] Despite these tremendous efforts, to the best of our knowledge, no research has realized flexible sperm-like nanorobots with assembled head-to-tail structures. It is imperative to develop facile and reliable fabrication methods to construct artificial sperm-like nanorobots, and study the corresponding flagellar propulsion at low Reynolds numbers
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