Description
Microfluidic technologies provide powerful tools for manipulating and sorting microscopic objects and play an important role in diagnostics and therapeutic research. Conventional sorting strategies are generally based on physical properties such as density or size, using techniques like centrifugation or microfluidic filtration, while more advanced approaches take advantage of how cells respond to external stimuli, including light or magnetic fields, enabling active sorting in microfluidic devices. Recently, cell deformability, have emerged as highly informative biomarkers, reflecting internal mechanical states linking to disease progression, immune activation, and differentiation [1, 2]. In confined microchannels, soft objects, including droplets, capsules, and biological cells, typically maintain mobility via a thin lubrication film that prevents direct contact with channel walls. However, recent research indicates that micro-scale wall textures can disrupt lubrication, causing soft objects to trap at low velocities but glide smoothly at higher speeds [3]. This surface roughness creates a sharp transition in frictional behavior compared to standard lubricated motion. Under a fixed flow condition, this mechanism introduces a critical role for deformability, as more rigid objects tend to experience higher resistance, while more deformable ones remain efficiently transported by the flow. Consequently, capsules consisting of a liquid core enclosed by an elastic membrane, resembling the mechanical behavior of living cells, serve as an ideal physical model to investigate these bio-inspired sorting mechanism.
The project focuses on exploiting friction-based transitions to design microfluidic devices that sort soft objects exclusively by deformability. By tunning surface topography and flow conditions, we investigate how objects with different mechanical properties follow distinct trajectories, enabling passive, mechanical sorting without external fields. To address this, we are developing a novel device using elastic capsules, produced via specific protocols to ensure defined mechanical properties. The work involves analyzing the physical interaction between capsules and textured channel walls, while quantifying how friction forces depend on parameters such as flow rate, surface texture geometry, capsule size, and deformability. Initial experiments focus on probing the behavior of single capsules, expecting stiffer ones to deviate while softer ones remain unperturbed. This framework aims to establishing the link between surface texture and particle deformability, laying the groundwork for future sorting applications.
References:
[1] Häner et al. Sorting of capsules according to their stiffness: from principle to application. Soft Matter 17, 3722 (2021).
[2] Urbanska et al. A comparison of microfluidic methods for high-throughput cell deformability measurements. Nat. Methods 17, 587 (2020).
[3] Keiser et al. Motion of Viscous Droplets in Rough Confinement: Paradoxical Lubrication. Phys. Rev. Lett. 122, 074501 (2019).