Sperm-shaped magnetic microrobots: Fabrication using electrospinning, modeling, and characterization

Abstract

We use electrospinning to fabricate sperm-shaped magnetic microrobots with a range of diameters from 50 µm to 500 µm. The variables of the electrospinning operation (voltage, concentration of the solution, dynamic viscosity, and distance between the syringe needle and collector) to achieve beading effect are determined. This beading effect allows us to fabricate microrobots with similar morphology to that of sperm cells. The bead and the ultra-fine fiber resemble the morphology of the head and tail of the sperm cell, respectively. We incorporate iron oxide nanoparticles to the head of the sperm-shaped microrobot to provide a magnetic dipole moment. This dipole enables directional control under the influence of external magnetic fields. We also apply weak (less than 2 mT) oscillating magnetic fields to exert a magnetic torque on the magnetic head, and generate planar flagellar waves and flagellated swim. The average speed of the sperm-shaped microrobot is calculated to be 0.5 body lengths per second and 1 body lengths per second at frequencies of 5 Hz and 10 Hz, respectively. We also develop a model of the microrobot using elastohydrodynamics approach and Timoshenko-Rayleigh beam theory, and find good agreement with the experimental results.

Magnetically Powered Biodegradable Microswimmers

“…Inspired by natural swimmers that swim with high efficiency and speed utilizing undulatory locomotion [25][26][27][28][29], the microswimmer was designed with multiple cylinders connected through springs to mimic the travelling-wave moment. The applied spring in the microswimmer can undergo flexible deformation under an external magnetic field to lead to the mechanical bending of the swimmer.…”

“…One advisable solution is adopting the efficient propulsion mechanism of body and caudal fin deformations to break the symmetry, hence achieving net propulsion in the low Re regime. Examples include fish-like multilink nanowire swimmers containing flexible porous Ag hinges [25], nanoswimmers made up of an elastic polypyrrole tail and flexible polymer bilayer hinges [26], multi-segment undulatory microswimmers containing joints and incorporating the use of a U-type transmission [27], sperm-shaped microswimmers made of flexible SU-8 or ultra-fine fiber tails [28,29], and so on. Besides, it is also highly important that the microrobots are made of a material that suits its usage and purpose, especially considering that many are used in complex environments such as in the human body [30].…”

“…In addition, structures with interfacing of rigid and soft parts are prone to repeated damage [34], increasing the likelihood of structural collapse during release and swimming. Although other undulatory microswimmers constructed by a single substrate may possess enhanced structural integrity, they lack biodegradability [27][28][29], which might create difficulties when applied in real-time in vivo environments as it can activate thrombi, potentially harming the organism. This limits its capabilities for use, especially in future applications within the human body.…”

Biologically Inspired Microrobotics

“…respectively. We rewrite (28) using (29), and devise a proportional control input (B → K p e) to obtain the following error dynamics:…”

“…Experimental and simulation frequency response of sperm-shaped microrobots. The average speed is calculated from 10 trials for each frequency[29]. The maximum swimming speed is observed at frequency of 10 Hz.…”