Modelling, simulation, and experimental characterization of particle sedimentation inside a horizontal syringe

Sedimentation is the settling of solid particles in a liquid medium driven by gravity. This phenomenon poses significant challenges in experimental lab-on-chip (LOC) applications, as they often involve a biological sample to be loaded inside a syringe for prolonged periods (e.g. 3D bioprinting, microfluidic cytometers). Mitigating solutions such as mechanical agitators or buffer adjustments exist, but increase the complexity and cost of the setup. In this work, we developed a model of particle sedimentation inside a horizontal syringe, which highlights the importance of several parameters: syringe radius, particle terminal velocity in the buffer, syringe outlet position, and flow-rate. The model provides a simple way to estimate the concentration half-life (t1/2), i.e. the time required for the concentration to halve, which is useful during the experiment design process. The model was initially tested numerically and then validated experimentally. Additionally, the applicability of the model to predict sedimentation of biological particles was experimentally demonstrated. Lastly, the model was used to develop guidelines for the design of setups with minimized sedimentation.