Swimming in Synthetic Mucus: Advantages and Limitations to a Modular Approach
This paper demonstrates the performance of modular magnetic bead based microswimmers inside synthetic mucus environments. The microswimmers under investigation are composed of chemically bonded magnetic spheres and are actuated using rotating magnetic fields. While these microswimmers have been well characterized in Newtonian fluids, their viability inside biomimetic mucus environments, has not been well defined. Understanding their performance inside such environments will provide insights into how to better design microswimmers for in vivo based tasks, such as drug delivery and minimally invasive surgery. Synthetic mucus was fabricated by mixing deionized water with mucin from a porcine stomach in varying concentrations. These formulations were analyzed using a Discovery Hybrid Rheometer 3 (DHR-3) and verified to have nonlinear viscoelastic properties. SEM imaging of the formulations revealed a heterogeneous fiber network, which is common in most biological mucus environments. Three types of microswimmers were investigated: a standard three bead achiral microswimmer, a two bead “snowman” swimmer, and a single bead swimmer. These microswimmer derivatives were characterized through velocity vs. frequency curves and directional controllability tests.
The results of both the tests were peculiar. Three bead achiralmicroswimmers could not form in high concentrations of mucus and were generally unstable during experiments. However, both snowman and single bead swimmers performed beyond expectations. This is the first documented case of symmetric particle aggregates, and more importantly, single particles, swimming without any additional geometric features normally required of low Reynolds number swimming. Single particles, when actuated, were shown to have a non-linear velocity vs. frequency relationship, which was repeated through multiple trials. Snowman swimmers exhibited consistent performance and had a linear velocity relationship, but were found to be significantly slower than the single bead swimmers. Both constructs could be directed to traverse complex trajectories, but internally generated flows tended to offset their desired directions. Due to magnetic dipole differences, swarms of single particles could be directed to swim in different directions under the same control input. These results indicate that such mucus environments can facilitate swimming without additional geometric properties such as chirality or flexibility. The single bead swimmers demonstrated in this paper may very well be the simplest microswimmer that could be used for in vivo drug delivery applications.
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Rogowski, Louis, "Propagation in Synthetic Mucus: Advantages and Limitations to a Modular Approach" (2018). Mechanical Engineering Research Theses and Dissertations. 8.