Biodegradable Tracer Particles for Underwater Particle Image Velocimetry

Particle Image Velocimetry (PIV) is an important tool for accurately measuring and visualizing fluid flow dynamics in various scientific and engineering fields. However, current commercial PIV particles (e.g., polymer and metal-coated microspheres) are typically not made with environmentally friendly materials and potentially pose longer term health risks for live animal experiments. As an alternative for PIV, we propose the use of biodegradable particles, which are nontoxic, more sustainable, readily accessible, and cost-effective. We tested a variety of food-grade and cosmetic-grade additives to identify suitable particles for PIV experiments in both fresh and saltwater (35 ppt). These particles closely match the density of water, with particle sizes ranging from 5 µm to 50 µm for applications of different scales. To test their feasibility and effectiveness, we conducted PIV experiments using both biodegradable options and commercial PIV particles (as a control) across different length scales, including a translating hydrofoil (2.5 cm) in freshwater, and swimming jellyfish (~10 cm) and brine shrimp (~ 5 mm) in saltwater. Compared to commercial PIV particles, our biodegradable particles not only demonstrated comparable laser scattering properties, but also accurately followed fluid velocities in various flow patterns (e.g., vortical flow, shear flow, etc.) with a low particle Stokes number (10^-6 - 10^-4), confirming their suitability for PIV applications. These particles’ biodegradability and minimal environmental impact make them a practical and effective choice for biological applications.