Public defence in Engineering Physics, M.Sc. Tytti Kärki

Title of the thesis: Perspectives on Capillary Bridges: Quasi-Two-Dimensional Droplets and Living Bridges

Thesis defender: Tytti Kärki
Opponent: Professor Jean-François Joanny, College de France
Custos: Professor Jaakko Timonen, Aalto University School of Science

Liquids have various fascinating properties and can behave in many different ways. For example, they can form droplets or thin films and connect surfaces through so-called capillary bridges, as seen in wet sand. Although these phenomena are mundane, understanding them is important in many research fields and technological applications. Similarly, as fluids can deform and flow, cells in tissues can move collectively and reorganize, making the study of liquids also valuable for understanding living systems.

In this doctoral thesis, capillary bridges were utilized to investigate the behavior of both liquid droplets and living tissues. A simple droplet model based on capillary bridges was developed, allowing to study complex interactions of liquids both experimentally and theoretically in a well-controlled system. Furthermore, this thesis demonstrated that cells can form capillary bridges between two surfaces, revealing a novel analogy between liquids and living tissues. Although the bridges made of cells resembled liquid capillary bridges, the interactions between cells and surfaces could result in rupture of the bridge.

The thesis demonstrates that capillary bridges can be an effective tool for investigating the behavior of both simple droplets and complex living tissues. They enable the examination of how liquids and tissues shape themselves, organize, and interact with surfaces, providing insights for example to design micro- and nanofluidic systems as well as for understanding tissue behavior and stability.

Keywords: capillarity, capillary phenomena, capillary bridge, interfacial tension, surface tension, contact angle, moving contact line, contact line dynamics, Hele-Shaw cell, droplets, quasi-two-dimensional droplets, vapor pressure, Marangoni effect, cellular aggregate, spheroids, physics of biological tissues

Thesis available for public display 7 days prior to the defence at Aalto University's public display page.