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Two-Way Stretch


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cells react to stretch
Biomaterials combine living cells with an artificial gel-like medium. Such materials are being explored for use, among other things, in synthetic replacement tissues and organs. But some traits of biomaterials have been puzzling scientists for many years. Prof. Samuel Safran and Dr. Rumi De of the Institute's Materials and Interfaces Department, together with Dr. Assaf Zemel, formerly a postdoc in Safran's group and now at the University of California, Davis, have proposed a solution to one of those puzzles.
When the gel is stretched, say by pulling on either end, the cells respond by reducing the stress on their connections to the medium. But the timing of that stretch affects the way the cells orient themselves: When the gel is stretched slowly, the cells align parallel to the direction of the externally imposed stretch, but if it's stretched quickly, that alignment is nearly perpendicular.
What causes the difference? The scientists propose that in both cases a cell adjusts itself to maintain an optimal amount of stretch in the medium. In slow stretching, the cells, which tend to contract, have time to align themselves and take the steps needed to counteract the external stretch, as though steeling themselves for a tug-of-war. When the stretching is quick, however, they don't have enough time to develop this careful balancing of forces. Turning about 90 degrees effectively takes them out of the game of tug-of-war, since the medium cannot pull on the cells in this position.
This research, which appeared recently in Nature Physics, may aid in designing and processing biomaterials with specific properties, and may have implications for research in wound healing and muscle growth, as well as elucidating the behavior of cancer cells and more.
Prof. Samuel Safran's research is supported by the estate of David Turner. Prof. Safran is the incumbent of the Fern and Manfred Steinfeld Professorial Chair.

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