"Crowding is common in living systems at different length scales, from busy hallways down to dense cellular cytoplasm," said Ayusman Sen, Verne M. Willaman Professor of Chemistry and Distinguished Professor of Chemistry and Chemical Engineering at Penn State and one of the leaders of the research team. "The insides of cells are very, very crowded with proteins, macromolecules and organelles. Molecules that are involved in chemical reactions required by the cell must be transported through this crowded, viscous environment to find their partner reagents. If the environment is uniformly crowded, movement slows, but we know that the inside of a cell is non-uniform; there are gradients of macromolecules and other species. So, we were interested in how these gradients would influence transport at the nanoscale."
The researchers compared the movement of various "tracer" colloids -- insoluble particles suspended in a liquid -- through different environments using microfluidics. A microfluidic device can be filled with different solutions in which the researchers establish gradients -- from high to low -- of "crowder" macro-molecules in the fluid. The tracers, which can be large or small, hard or soft...
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