I Can red blood cells be considered colloids? (soft matter physics)

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Hi,

I was studying soft matter physics when a question arose between a friend and me. Namely if red blood cells can be considered to be a colloid. Colloids as it was presented to us had 3 criteria: high diffusion so the particles wouldn't form a sediment, a small reynolds number and a surface size much bigger than the solvent.

On first sight, RBC's seemed to fit these criteria, but they still separate from the plasma in 1-2 days. This is slow, but does this mean they can not be considered colloids or does this mean they are simply unstable colloids?

A following question was whether stacks of red blood cells or so called "rouleaux" could be considered colloids (as well). Here, our intuition said no, but besides a higher reynolds number and presumed faster sedimentation we didn't find good arguments.

Can anyone shed a bit of light on the situation?
 

Andy Resnick

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Hi,

I was studying soft matter physics when a question arose between a friend and me. Namely if red blood cells can be considered to be a colloid. Colloids as it was presented to us had 3 criteria: high diffusion so the particles wouldn't form a sediment, a small reynolds number and a surface size much bigger than the solvent.

On first sight, RBC's seemed to fit these criteria, but they still separate from the plasma in 1-2 days. This is slow, but does this mean they can not be considered colloids or does this mean they are simply unstable colloids?
RBC's are too large to consider whole blood as a colloid (blood plasma is a colloidal fluid, tho). In addition, the RBC cytoplasm (or any cytoplasm) can be modeled as a disordered colloid.

 

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