Decoding the spleen
It is common knowledge that the heart pumps blood and the stomach digests food, but very few people can explain what the human spleen is for.
Scientists can tell you that a major function of the spleen is to remove aged and abnormal red blood cells from circulation and recycle them, acting like a blood filter. However, the exact way the spleen filters these cells remains a mystery.
To solve this puzzle, a new paper published in the Proceedings of the National Academy of Sciences by Richard and Loan Hill Department of Biomedical Engineering Assistant Professor Zhangli Peng and his collaborators Annie Viallat and Emmanuèle Helfer from Aix Marseille University in France combined microfluidic experiments and multiscale modeling to reveal the physical mechanisms of this filtration process.
Peng and his team discovered that 8-micron-sized healthy red blood cells can pass through 0.28-micron rigid slits in a microfluidic device they designed to mimic the spleen without any problem or damage at 37 degrees Celsius, which is the average human body temperature. Interestingly, they found that at room temperature a significant amount of red blood cells became stuck in the slits.
Anyone who has tried to move a couch through a small doorway knows how difficult it can be to try and move a large object through a smaller opening, so how exactly is the red blood cell able to pass through such small slits? Peng explained that at body temperature the cell’s cytoskeleton unfolds, allowing the cell to deform into a shape close to two spheres connected by a narrow tether, which in principle can pass through any gap no matter how small it is.
“This is a major milestone because many people have simulated this cell path, but no one has previously validated the path and components of the cells,” Peng said. “This is the first systematic comparison between a real experiment and simulation.”