Scientists Decode Glass-Like Properties of Epithelial Tissues

Scientists at the Indian Institute of Science (IISc) have uncovered the underlying mechanics behind the puzzling glass-like behavior observed in epithelial tissues—dynamic systems that remain metabolically active yet exhibit solid-like properties. Their findings, recently published in Nature Communications, illuminate how a complex interplay between cellular biochemical activity and mechanical forces culminates in slow-moving, glassy dynamics despite cells’ inherent activity.

Epithelial tissues form protective layers lining organs and body surfaces, where cells are densely packed yet dynamically interactive. These tissues simultaneously display regions of sluggish cell movement adjacent to zones of rapid mobility, a phenomenon known as dynamic heterogeneity. This coexistence of fluid and solid behaviors is the hallmark of glassy materials, which maintain the disordered structure typical of liquids but behave mechanically like solids.

Traditional theoretical frameworks have struggled to reconcile this paradox. Passive models predict that glass-like states only emerge when cell activity drops and density increases to extreme levels. However, actively metabolizing cells, expected to promote fluid-like tissue behavior, nonetheless exhibit mechanical arrest. To investigate this contradiction, the IISc team combined sophisticated time-lapse microscopy with biomechanical measurements, tracking both the spatial organization of actin filaments and force distributions in epithelial monolayers.

Notably, the researchers identified slow oscillations in actin levels occurring on an hour-long timescale—far slower than the minute-scale fluctuations known from isolated cells. This suggested an emergent behavior arising from intercellular mechanical interactions within the dense tissue environment. Attempts to replicate these dynamics using conventional vertex models consistently predicted tissue fluidization rather than arrest, underscoring the models’ insufficiency.

By introducing a novel active vertex model incorporating mechanochemical feedback—a bidirectional coupling between intracellular biochemical states and mechanical forces at cell-cell interfaces—the team successfully reproduced the glassy behaviors observed experimentally. This feedback loop proved crucial: by modulating cell contractility in response to mechanical tension, the model captures how biochemical oscillations and mechanical crowding together enforce dynamical arrest.

This mechanochemical paradigm marks a significant shift from purely genetic or biochemical perspectives, emphasizing the essential role of mechanics in tissue-level phenomena such as wound healing, disease progression, and embryonic development. The findings also suggest broader applicability, hinting that similar feedback mechanisms may regulate collective behavior in various tissue types.

By bridging biochemical activity and physical interactions, this work opens new avenues to understand how cells collectively organize into mechanically robust yet dynamic architectures. It provides a conceptual framework for future bioengineering applications, where controlling tissue mechanical properties could influence regeneration and pathology. This study not only resolves a decades-old mystery but also sets the stage for exploring the rich mechanobiology underpinning living tissues.

Keywords

Epithelial tissue, glassy dynamics, mechanochemical feedback, cell mechanics, active matter, tissue fluidisation, actin oscillations, vertex model, dynamic heterogeneity