In the study of jellyfish locomotion, understanding the wakes and vortices they generate while swimming is a key area of exploration, according to researchers led by Wu. A particularly valuable method in this field is particle image velocimetry (PIV), which facilitates the investigation of flow phenomena and the mechanics of biomechanical propulsion. PIV operates by tracking tracer particles suspended in water that are illuminated with laser light. This method typically employs hollow glass spheres, polystyrene beads, aluminum flakes, or specially coated synthetic granules to boost light reflectivity.
While these materials are effective for flow measurements due to their appropriate size and density, they also carry significant costs—sometimes reaching $200 per pound. Additionally, they come with various health and environmental hazards; for instance, glass microspheres can irritate skin or eyes, and inhaling polystyrene beads and aluminum flakes poses risks as well. Moreover, these materials are not digestible by animals and can inflict internal injuries. To address these issues, several biodegradable alternatives—such as yeast cells, milk, microalgae, and potato starch—have emerged, presenting more affordable options priced as low as $2 per pound.
Wu identified starch particles as the most promising biodegradable tracers. To ascertain the most suitable type, an investigation was conducted on various starches, including corn starch, arrowroot starch, baking powder, jojoba beads, and walnut shell powder. Each particle type was introduced into water tanks containing moon jellyfish, with their movement being monitored using a PIV system. Performance assessments were conducted based on factors such as particle size, density, and laser-scattering capabilities.
The findings indicated that corn starch and arrowroot starch were the most effective candidates for PIV applications. Their density and uniform size distribution made them ideal, with arrowroot starch excelling in laser scattering tests. In contrast, corn starch was identified as advantageous for scenarios where larger tracer particles are necessary, demonstrating the capability to produce larger laser scattering dots during experiments. Both starch types delivered visualization performance on par with conventional synthetic PIV tracer materials, effectively depicting the flow structures generated by swimming jellyfish.
DOI: Physical Review Fluids, 2025. 10.1103/bg66-976x (About DOIs).
