On 2014 Oct 29, Benoit Kornmann commented:

This paper presents some spectacular features of membrane chemistry. If you are not into the topic, watching some of the featured movies will likely pique your interest.

It has long been known that different lipid species can have different affinity for each other, such that they may segregate into different phases, which can be visualized as subdomains on artificial membranes such as giant unilamellar vesicles (GUVs). Because a phase-separated membrane has a much lower entropy than a mixed one, phase separation can be achieved by lowering the temperature or increasing order in the membrane by stretching it.

In this paper, the authors bathed GUVs in a hypotonic solution. Because these GUVs are semi-permeable to water, they swell until they eventually rupture, causing a catastrophic leak that re-equilibrates pression. After the GUVs recover from rupture, they start swelling again, and go through several cycles of swelling-rupture until reaching osmotic equilibrium.

Here, the authors observe that, while in relaxed GUVs lipids are perfectly mixed, swelled GUVs show lipid phase separation. Mixing occurs right after each membrane rupture event; therefore, a cycle of separation-mixing follows the cycle of swelling-rupture of the GUV.

It was previously known that vesicles underwent cycles of swelling-rupture. It was also previously known that membrane tension favored lipid phase separation. It is also not clear whether these phenomena are relevant in the case of biological systems. Nonetheless, the movies presented here are spectacular and unveil unexpected and very complex dynamic behaviors of seemingly very simple chemical systems.

On 2014 Oct 29, Benoit Kornmann commented:

This paper presents some spectacular features of membrane chemistry. If you are not into the topic, watching some of the featured movies will likely pique your interest.

It has long been known that different lipid species can have different affinity for each other, such that they may segregate into different phases, which can be visualized as subdomains on artificial membranes such as giant unilamellar vesicles (GUVs). Because a phase-separated membrane has a much lower entropy than a mixed one, phase separation can be achieved by lowering the temperature or increasing order in the membrane by stretching it.

In this paper, the authors bathed GUVs in a hypotonic solution. Because these GUVs are semi-permeable to water, they swell until they eventually rupture, causing a catastrophic leak that re-equilibrates pression. After the GUVs recover from rupture, they start swelling again, and go through several cycles of swelling-rupture until reaching osmotic equilibrium.

Here, the authors observe that, while in relaxed GUVs lipids are perfectly mixed, swelled GUVs show lipid phase separation. Mixing occurs right after each membrane rupture event; therefore, a cycle of separation-mixing follows the cycle of swelling-rupture of the GUV.

It was previously known that vesicles underwent cycles of swelling-rupture. It was also previously known that membrane tension favored lipid phase separation. It is also not clear whether these phenomena are relevant in the case of biological systems. Nonetheless, the movies presented here are spectacular and unveil unexpected and very complex dynamic behaviors of seemingly very simple chemical systems.