Bio Focus: Swelled gels crack cells
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els crack cells
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mode of hydraulic tissue fracture by studying small islands of cell sheets (comprised of 15–20 epithelial cells each) that were micropatterned onto the surface of a polyacrylamide gel. This system was placed under controllable states of stretch during which the cells could be monitored by optical microscopy (see Figure). After uncovering the curious result of post-strain fracture (see Figure), the researchers conducted traction force microscopy, which is an optical technique that permits quantification of stress levels in the cell monolayer (a technique previously developed by corresponding author Xavier Trepat). The results were surprising. “One of the most striking things about these experiments,” said corresponding author Marino Arroyo, “is that fracture occurs when tension is lowest. You’re used to seeing cracks when you pull, but not when you compress, so this was very unexpected.” To explain the unique fracturing phenomena, the researchers then considered the role of the polyacrylamide substrate, turning to the poroelastic theory of hydrogel mechanics. This theory posits that hydrogels should experience time-dependent swelling when relaxed from a state of tension. To support the utility of poroelastic theory for explaining their experimental system, including the initial observation
MRS BULLETIN
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VOLUME 40 • MAY 2015
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www.mrs.org/bulletin
383
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