Haemodynamics around confined microscopic cylinders

Motivated by the recent developments in the research of untethered microrobots for performing minimally invasive procedures inside blood vessels, we have devised a novel microfluidic experiment for studying the haemodynamics around different types of cylinders confined inside a straight, long, 270×100μm channel. Two test sections are studied: flow past a confined circular cylinder and past a confined elliptic cylinder. The two cylinders cause a channel blockage of about 28%. We consider a continuous regime for the blood flow, since its pulsatile nature is barely felt in the regions of the human body further away from the heart, and Reynolds numbers (Re) in the range of 0.05–100, which allow to replicate a variety of flow conditions. Human blood is emulated using non-particulate polymer solutions with rheological properties analogue to those of the biofluid. Pressure drop measurement, micro-Particle Image Velocimetry and streak imaging techniques are employed to study the viscoelastic haemodynamics in the test sections, characterised by elasticity numbers (El) in the approximate interval of 1–30. Our findings include a striking dampening effect on the acceleration of the flow in the contractions between the elliptic cylinder and the channel walls, due to the elasticity of blood, and steeper pressure drops and longer recovery lengths measured in the test section of the elliptic obstacle, caused by a stronger shear stress field characterising this flow geometry and higher strain accumulation in its wake, respectively, compared to the circular cylinder. •Non-linear pressure drop vs. flow rate growth in blood-like flows past cylinders.•Shear-thinning explains a slow-growing evolution for Ma