Gas bubbles can be trapped and then manipulated with laser light. In this report, we propose the detailed optical trapping mechanism of gas bubbles confined inside a thin light-absorbing liquid layer between two glass plates. The necessary condition of bubble trapping in this case is the direct absorption of light by the solution containing a dye. Due to heat release, fluid whirls propelled by the surface Marangoni effect at the liquid/gas interface emerge and extend to large distances. We report the experimental microscopic observation of the origin of whirls at an initially flat liquid/air interface as well as at the curved interface of a liquid/gas bubble and support this finding with advanced numerical simulations using the finite element method within the COMSOL Multiphysics platform. The simulation results were in good agreement with the observations, which allowed us to propose a simple physical model for this particular trapping mechanism, to establish the origin of forces attracting bubbles toward a laser beam and to predict other phenomena related to this effect.

The transport of bio-particles in viscous flows exhibits a rich variety of dynamical behaviour, such as morphological transitions, complex orientation dynamics or deformations. Characterising such complex behaviour under well controlled...

The development of vascular networks on-chip is crucial for the long-term culture of three-dimensional cell aggregates such as organoids, spheroids, tumoroids, and tissue explants. Despite the rapid advancement of microvascular network systems and organoid technology, vascularizing organoids-on-chips remains a challenge in tissue engineering. Moreover, most existing microfluidic devices poorly reflect the complexity of in vivo flows and require complex technical settings to operate. Considering these constraints, we developed an innovative platform to establish and monitor the formation of endothelial networks around model spheroids of mesenchymal and endothelial cells as well as blood vessel organoids generated from pluripotent stem cells, cultured for up to 15 days on-chip. Importantly, these networks were functional, demonstrating intravascular perfusion within the spheroids or vascular organoids connected to neighbouring endothelial beds. This microphysiological system thus represents a viable organ-on-chip model to vascularize biological tissues and should allow to establish perfusion into organoids using advanced microfluidics.