If you throw a rubber balloon filled with water against a wall, it will spread out and deform on impact, while the same balloon filled with honey, which is more viscous, will deform much less. If the balloon's elastic rubber was stiffer, an even smaller change in shape would be observed.
By simply analyzing how much a balloon changes shape upon hitting a wall, you can uncover information about its physical properties.
Although cells are not simple sacks of fluid, they also contain viscous and elastic properties related to the membranes that surround them; their internal structural elements, such as organelles; and the packed DNA arrangement in their nuclei. Because variations in these properties can provide information about cells' state of activity and can be indicative of diseases such as cancer, they are important to measure.
UCLA bioengineering researchers have taken advantage of cells' physical properties to develop a new instrument that slams cells against a wall of fluid and quickly analyzes the physical response, allowing for the identification of cancer and other cell states without expensive chemical tags.
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