Computational and experimental design of fast and versatile magnetic soft robotic low Re swimmers

Abstract

Miniaturized magnetic soft robots have shown extraordinary capabilities of contactless manipulation, complex path maneuvering, precise localization, and quick actuation, which have equipped them to cater to challenging biomedical applications such as targeted drug delivery, internal wound healing, and laparoscopic surgery. However, despite their successful fabrication by several different research groups, a thorough design strategy encompassing the optimized kinematic performance of the three fundamental biomimetic swimming modes at miniaturized length scales has not been reported till now. Here, we resolve this by designing magnetic soft robotic swimmers (MSRSs) from the class of helical and undulatory low Reynolds number (Re) swimmers using a fully coupled, experimentally calibrated computational fluid dynamics model. We study (and compare) their swimming performance, and report their steady-state swimming speed for different non-dimensional numbers that capture the competition by magnetic loading, non-linear elastic deformation and viscous solid-fluid coupling. We investigate their stability for different initial spatial orientations to ensure robustness during real-life applications. Our results show that the helical 'finger-shaped' swimmer is, by far, the fastest low Re swimmer in terms of body lengths per cycle, but that the undulatory 'carangiform' swimmer proved to be the most versatile, bi-directional swimmer with maximum stability.

Figures (13)

• Figure 1: Schematic representation of the fabrication procedure adopted for finger-shaped MSRS.
• Figure 2: Schematic representation of the magnetic soft robotic swimmers: (a) finger-shaped, (b) field-induced, (c) drag-induced, (d) carangiform-like, and (e) anguilliform-like. All the swimmers propel along the +ve x direction. The magnetic field vector B is represented by a green arrow, using a rotating magnetic field in (a) - (c) and an oscillating field in (d) and (e).
• Figure 3: Schematic representation of the experimental setup: the finger-shaped MSRS immersed within the fluid medium is subjected to magnetic fields for net propulsion.
• Figure 4: Comparison of the chronological snapshots of the experimental observations (top row) with the model predictions (bottom row) for the finger-shaped helical swimmer during one swimming cycle. Here, t and T represent current time instant and cycle time period, respectively. For movies of the swimmers, see the Supplementary Information.
• Figure 5: Comparing experiments and model: swimming speed vs. M$_\text{n}$ for (a) F$_\text{n}$=20 and (b) F$_\text{n}$=30 for the finger-shaped helical MSRS. The red and blue circles denote two separate experiments, the computational data points are represented by two error bars denoting the standard deviation. The numerical data is fitted by a regression curve (indicated by a black solid line).