Can a combined shear and pressure-driven mechanism control the optimal droplet migration in Microfluidics?

Studies on surfactant-laden droplets in tubular Poiseuille flows have revealed intriguing cross-stream migration behaviours under low surface Péclet number limits. However, droplet dynamics in rectangular channels, driven by combined shear and pressure, present new opportunities in biomedical lab-on-a-chip devices. So, what could be the optimal design for a microfluidic device—shear-driven, pressure-driven, or a combination of both—to achieve controlled droplet migration? To answer this, we investigate surfactant-laden droplet steering in combined flows, emphasising the influence of a thermal dipole generated by living cells within the droplet and its interaction with a non-isothermal environment. Our findings highlight that subject to specific conditions, thermocapillary effects and the strength of the thermal dipole can significantly enhance the Marangoni effect and modify the cross-stream migration velocities. Moreover, we explore how varying the internal dipole strength modulates fluid jet velocities near the droplet centre, which is crucial for microfluidic control. Further, transitioning from Poiseuille to Couette profiles in rectangular channels proves advantageous for precise droplet manipulation, offering insights for optimising microfluidic assays.