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Aging is a process that affects not only living beings. Many materials, such as plastics and glasses, also age – that is, they slowly change over time as their particles try to pack better – and there are already computer models to describe it. Biological materials, such as living tissues, can exhibit glasses-like behavior, except that the particles are actual cells or bacteria that have their own propulsion. Researchers at the University of Göttingen have now used computer simulations to explore the aging behavior of these “living” glass systems. There was a surprise that particle activity can actually drive aging, which has potential consequences for a number of applications. Their research was published in Physical Review Letters.
In materials such as glass and plastics, their particles clump better over time (i.e. they age). But if this process is disturbed by mechanical deformation, for example if a solid is bent, the materials return to their previous state and are therefore “rejuvenated”. To model what happens in biological systems, physicists at the University of Göttingen have developed extensive computer simulations of a model of a glass made up of active particles (a living glass). Just as would happen in a real biological system, each particle in the simulation has its own propelling force; this is modeled as a random change of direction over time. Then the researchers varied the time scale of these changes in direction. When this time frame is short, the particles are randomly pushed as if at a higher temperature, and this is known to produce aging. But when the changes of direction are slow, the particles try to go in the same direction and this should act as a local deformation, thus stopping aging. However, the simulations here have shown something interesting and unexpected: when particle activity is very persistent, it actually pushes aging in living glass systems.
“We were really surprised when we saw that persistent active propulsion can cause aging. We expected it to function as a small-scale deformation in the material that would rejuvenate it,” comments Dr. Rituparno Mandal of the Institute of Theoretical Physics at the University of Göttingen. He goes on to say, “But in reality, local deformation is so slow that the particles can actually follow the flow and use their motion to find low-energy arrangements. In fact, they pack better.”
Senior author Professor Peter Sollich, also from the University of Göttingen, added: “The research highlights important characteristics of glass behavior in active materials that do not have comparable behavior in conventional glass. This could have implications for many processes. biologics where glass-like effects have been identified, including cell behavior in wound healing, tissue development and cancer metastasis. “
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