Stem Cell Nuclei's Rare Sponge-Like Properties Help Them Transition Into Specialized Cells
A super-absorbent sponge is auxetic, meaning that it can expand when stretched instead of getting thinner, which would generally happen with conventional materials. Auxeticity can be found in several manmade and naturally occurring substances. But now scientists have found auxetic properties in the most unlikely of places - stem cells. Their study, which added auxeticity to the ever increasing repertoire of the body's master cells, was conducted at the University of Cambridge.
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Auxetic materials show extraordinarily different properties in that they get fatter when stretched and contract when compressed. These properties allow them to have high shock resistance and energy absorption, making them useful as sponge mops, packing material, and shock absorbing materials like knee pads or shoulder pads. What surprised the material scientists was that the nuclei of stem cells, which can be developed into different types of specialized cells, were also auxetic.
"This is a pretty bizarre finding and very unexpected," said Dr. Kevin Chalut, from the Wellcome Trust-Medical Research Council Cambridge Stem Cell Institute, in a statement. "When the stem cell is in the process of transforming into a particular type of cell, its nucleus takes on an auxetic property, allowing it to 'sponge up' essential materials from its surroundings. This property has not, to my knowledge, been seen before at a cellular level and is highly unusual in the natural world."
The auxetic properties, however, are not present throughout the life of the cell. They only appear in the stem cell's nucleus when it is in the transformation stage, changing from an embryonic, non-specific stem cell into a differentiated, tissue-specific cell, such as that of the heart. The scientists tested the cells' auxeticity by treating the fluid surrounding the nucleus - called cytoplasm - with a colored dye while it was transitioning. When the nucleus stretched, it absorbed the dye, indicating that it had expanded and become porous. Scientists speculate that the cells may be absorbing molecules from the surrounding cytoplasm, which help them to develop into specialized cells.
Natural auxetic materials are difficult to come by and considering that they have huge potential in a number of applications, scientists can use this research as a stepping stone for further studies. Scientists are already aware of a number of highly ordered auxetic materials such as the auxetic honeycomb. But the transitional stem cells are considered disordered auxetic material, and scientists are still trying to find more like them.
"There is clearly a lot we can learn from nature," Chalut said. "We are already seeing auxeticity explored for its super-absorption properties, but despite great technological effort, auxetic materials are still rare and there is still much to discover about them in order to manufacture them better. To overcome this, materials scientists can do what has become de rigueur in their discipline: they can learn from nature. Studying how auxeticity has evolved in nature will guide research into new ways to produce auxetic materials, which might have many diverse applications in our everyday life."
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