Speaker
Description
Many microfluidics and lab-on-chip (LOC) systems rely on syringe-based systems for the precise movimentation and delivery of cells and microparticles. Despite their widespread use, these systems remain vulnerable to sedimentation (i.e. the gravity-driven settling of suspended particles) which leads to non-uniform sample concentrations, clogging, reduced reproducibility, and unreliable outcomes in diagnostic assays, microfluidic cytometry, and tissue engineering applications. This study introduces a dual approach to mitigate sedimentation, integrating predictive theoretical modelling with an active hardware-based solution.
First, we developed and validated a mathematical model that describes particle sedimentation dynamics within horizontally oriented syringes, the configuration most commonly employed in microfluidic setups [1]. The model provides estimates the concentration half-life, which is the time required for the effective particle concentration to decrease by 50%, as a function of system parameters: particle and buffer properties, syringe geometry, and operating flow rate. This predictive framework enables users to determine the usable lifetime of a sample before substantial particle loss occurs. Model predictions were validated through Finite Element Method (FEM) simulations and experimental studies using polymeric and biological particles. The results demonstrate that, in unstirred and suboptimal conditions, sedimentation can reduce the effective particle concentration by up to 90% within 25 minutes. Moreover, the model provides practical guidance for mitigating sedimentation, showing that appropriate choices of syringe barrel diameter and nozzle eccentricity can substantially extend the concentration half-life.
Successively, we developed the Syringe Electromagnetic Controller (SEC) [2], a compact and low-cost device designed to actively suppress sedimentation and thermal drift in syringe-based experiments. The SEC enables both stirring and temperature regulation within standard syringes through electromagnetic actuation. Compared with passive approaches and existing commercial systems, the SEC is inexpensive (<€50), open-source, and highly customizable, facilitating broad adoption in both academic and translational research. The device employs a magnetically actuated stir bar that oscillates inside the syringe, driven by an external electromagnetic coil mounted on a 3D-printed support. The same coil is also used to provide controlled heating, regulated via a closed-loop feedback system using a thermistor, achieving temperature stability within ±0.5 °C of the set point. Experimental validation confirmed that the SEC effectively prevents sedimentation of cells and microparticles for periods exceeding 25 minutes, maintaining stable flow, consistent sample concentrations, and temperature. Flow cytometry–based viability assays further showed that neither magnetic stirring nor localized heating significantly compromised cell health, with viability consistently exceeding 85%.
By combining predictive sedimentation modelling with real-time, active syringe control, this work establishes a robust framework for improving sample handling in syringe-based microfluidic workflows. The proposed solutions are readily applicable to 3D bioprinting, point-of-care diagnostics, and microfluidic screening platforms, where consistency, precision, and cell viability are essential. Overall, this integrated approach addresses a key limitation of current lab-on-chip technologies and enables more reliable, reproducible, and scalable biological experiments.