A bit of a stretch? Characterising the mechanical properties of cell monolayers

One cell thick monolayers are the simplest tissues found in multicellular organisms, yet they fulfil critical roles in normal physiology lining blood vessels and the gastrointestinal tract. A key function of cell monolayers is to resist mechanical forces and act as physical barriers separating the internal environment from the exterior. Despite their intrinsically mechanical function, our knowledge of their mechanics is poor due to challenges in culturing and handling these fragile tissues. Research in the LCN by Andrew Harris and a team of collaborators led by Dr Guillaume Charras has now characterised the mechanical properties of these simple tissues.

Using a novel culture system in which collagen is used as a sacrificial scaffold, monolayers freely suspended between two test rods could be generated and their mechanics assessed. This approach revealed that monolayers are nearly 100 fold stiffer than their constituent cells due to the formation of specialised structures that interface the skeletons of adjacent cells into a tissue. Remarkably, monolayers could more than double in length before failing through fracture at intercellular junctions. Finally, depending on the stress applied, monolayers could behave either as a solid (at low stress) or as a fluid (at high stress).

Building on these advances, the team will now combine measurements of monolayer elasticity and ultimate strength with biological perturbations to dissect the role of proteins forming intercellular junctions in the establishment of monolayer mechanical properties. In addition, the method will enable investigations into genetic mutations and autoimmune diseases that cause pathologies resulting in a fragilisation of patient tissues.

Full details on this publication can be found in the Proceedings of the National Academy of Sciences of the USA:

Figure 1: (A) a monolayer cultured between two test rods is stretched until failure. At 126% extension, monolayers failed through the formation of cracks in the cellular material (arrowheads). (B) Deformations in a monolayer at 46% extension at the cellular level.

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