14.15 - 15.30 hrs, room: 7
Chair: Han Gardeniers 

  • 14.15 - 14.30 | Vincent Siekman (PCF) - Understanding the growth dynamics of capillary bridges for enhanced grease lubrication

    In this study we (experimentally and numerically) explore the dynamic growth of the capillary bridge formed when a bearing ball gently touches an approximately 100 microm thin film of silicon oil on a glass substrate. Fluorescence microscopy measurements reveal the formation of a dimple, i.e. a local minimum in the height profile, near the oil-ball contact, resulting in a large resistance to oil flow towards the oil bridge. Describing the flow in the thin film with lubrication theory, while the driving pressure is predicted by the momentary curvature of the liquid bridge, we calculate the height profile as a function of time. These profiles match, for a wide variety of initial film thicknesses, very well with the experimentally observed evolution of the capillary bridge and with the dimple profiles obtained from the fluorescence measurements. 

  • 14.35 - 14.50 | Alessia Broccoli (BIOS) - Accessibility Study of Porous Materials at the Single Particle Level as Evaluated within a Multiplexed Microfluidic Chip with Fluorescence Microscopy

    Molecular transport is a key aspect in the applications of most functional porous materials, as it determines their performances as adsorbents, batteries, and solid catalysts. Therefore, understanding the relevant diffusion processes is essential for designing superior materials. Uptake and release experiments of UV-active or fluorescent probes can elucidate mass transfer and directly provide an accessibility measure of porous particles. In this study, we present a novel microfluidic-based approach for assessing the accessibility of porous materials at the single particle level. It consists of the use of a multiplexed polydimethylsiloxane (PDMS) microfluidic device to monitor the uptake of fluorescent molecules in porous particles over time. The device enables the performance of multiple uptake experiments in parallel, allowing for a comparison of different particles under the same conditions and capturing interparticle heterogeneities often obscured by traditional bulk techniques.

  • 14.55 - 15.10 | Yu Na (DBE, AMBER) - A novel chemical strategy to improve the interfacial adhesion of thiol-norbornene polyethylene glycol hydrogels to PDMS-based microfluidic platforms

    Hydrogels are often incorporated in microfluidic platforms as ECM-mimicking scaffolds to provide a controlled dynamic cell culture environment. However, poor adhesion between the hydrogel and PDMS-based substrates can compromise cell culture performance, leading to hydrogel delamination. Herein, we apply a novel chemical strategy called interpenetration, using the combination of hydrophobic and hydrophilic initiators, along with in-situ photopolymerization of poly(ethylene) glycol (PEG) thiol-norbornene hydrogel, to enhance the interfacial adhesion of hydrogels to PDMS. The results demonstrate the tunable mechanical properties of the hydrogel matrix and improved adhesion strength via the interpenetration approach, together with the high biocompatibility of the hydrogel matrix during cell culture in the microfluidic platform. Our findings provide an effective hydrogel incorporation method to improve control for on-platform cell culture.

  • 15.15 - 15.30 | Keerthana Mohan (MCS) - Additives influence thermocavitation-induced microjets

    The study of thermocavitation jetting is relevant for several applications, including needle-free injection and 3D printing. A laser focused on the closed end of a glass microchannel filled with liquid induces cavitation (bubble growth and collapse) and forms microjets traveling outside the microchannel. The maximum bubble size is proportional to the amount of absorbed optical energy and also depends on the liquid filling volume. We studied a nozzle-free rectangular channel that can produce jets with distinct shapes and breakup behaviour. The interplay between instabilities such as axis-switching, bubble collapse, and capillary instability led to a slender jet of ~50 µm diameter and ~17 m/s velocity, which was identified as suitable for needle-free injection and investigated further. We also tested solutions of three different types of additives: surfactants, viscous, and viscoelastic additives of varying concentrations to assess their influence on the formation and breakup of the jet. We observed that viscous and viscoelastic additives delay jet breakup, but surfactants had no measurable effect. Moreover, the presence of the viscous additives led to slower (~13 m/s) and thinner (~30 µm) jets. 

    *This research was funded by the European Research Council (ERC) under the European Union Horizon 2020 Research and Innovation Program (Grant Agreement No. 851630)