human plasma on cell cultures

[Harald Heider]

Hi,

I am trying to add human plasma (derived from citrate blood) to cell 
cultures. The set-up is the following: HEK293 cells are cultured in 12 
well-plates in 1 ml of complete medium (DMEM with serum and 
antibiotics). Then 700 microliters of human plasma are added (without 
removing the medium). After 4h the whole stuff is coagulated! Does 
anybody know how to avoid blood clotting under these circumstances?

Harald

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