Effect of viscosity on microswimmers: a comparative study
Nsamela, A.; Sharan, P.; Garcia-Zintzun, A.; Heckel, S.; Chattopadhyay, P.; Wang, L.; Wittmann, M.; Gemming, T.; Sáenz, J.; Simmchen, J. (2021) ChemNanoMat, 7(9), 1042–1050. DOI: 10.1002/cnma.202100119
Summary
This study systematically compared the effect of viscosity on the swimming speed and motion patterns of four types of microswimmers with different propulsion mechanisms: two biological (bovine sperm cells and Bacillus subtilis bacteria) and two artificial (catalytic alginate microtubes and Janus Pt@SiO2 spherical microparticles). Experiments in glycerol and methylcellulose solutions of increasing viscosity revealed that viscosity affects each swimmer type differently depending on propulsion mechanism, size, and the viscoelastic properties of the medium. The work provides a framework for understanding microswimmer behavior in biologically relevant high-viscosity environments such as blood and mucus.
Key Findings
- Biological swimmers (sperm, bacteria) and artificial swimmers (catalytic tubes, Janus particles) respond differently to increased viscosity
- Sperm cells showed reduced velocity in glycerol but maintained motility in methylcellulose due to its viscoelastic properties
- B. subtilis bacteria were less affected by viscosity than sperm cells, likely due to their smaller size and different flagellar mechanics
- Artificial catalytic swimmers showed viscosity-dependent decreases in speed linked to reduced diffusion of fuel molecules
- Surface tension, catalyst activity, and diffusion coefficients all contribute to viscosity effects beyond simple drag
Our Contribution
Our group contributed to the biological aspects of this study, providing expertise on bacterial physiology and membrane properties relevant to understanding microswimmer behavior.
Significance
This comparative study provides systematic data on how viscosity affects diverse propulsion mechanisms, relevant for designing microswimmers for biomedical applications in viscous biological fluids.