Polymeric membrane artificial RBCs 1 micron and larger

The fate of intravenously injected nylon membrane artificial cells containing hemolysate has been studied (Chang, 1964, 1965, 1972a). A suspension of 5^±2.5^ diameter (mean ± standard deviation) nylon membrane artificial rbc's was infused intravenously over a period of 1.5 min, and samples were obtained from the anesthetized cat during and following the infusion.

The arterial level rose steeply during infusion, but upon discontinuation of the infusion, the level fell rapidly (Fig. 5.4). Thus, most of the artificial cells successfully completed one or more circulations, after which they were removed rapidly from the bloodstream. Experiments using 51Cr-labeled nylon membrane artificial cells showed that most of them were removed by the lung, liver, or spleen. Collodion membrane artificial cells are also removed rapidly from the circulation. Thus, it appears that nylon and collodion membrane artificial cells smaller than rbc's are rapidly removed from the circulation. During the infusion, there is a fall in arterial blood pressure and an increase in venous pressure and other signs compatible with pulmonary embolism. These artificial rbc's do not have the deformability of rbc's that allows the latter to pass through capillaries of smaller diameters.

Can artificial rbc's survive longer if they are made much smaller in order that they can pass through the capillaries? Unfortunately, it has long been known that even submicron foreign particles are removed very rapidly from the circulation (Halpern et al., 1958). After all, this is part of the body's defence against circulating microorganisms and other foreign particles. Thus, we looked into another factor, the surface

Fig. 5.4. Circulation time of artificial rbc's after infusion (from Chang 1965, 1972a).

property of artificial cells (Chang, 1964, 1965, 1972a). Red blood cells and other formed elements of blood have a negative surface charge due to the presence of n-acetylneuraminic acid containing mucopolysaccharide on the red blood cell membrane (Cook et al., 1961). Danon and Marikovsky (1961) found that the younger rbc's were about 30% more strongly charged than the older ones obtained from the same blood sample. All this information led us to look into the effects of surface properties on circulation time for rbc's, foreign particles, and artificial rbc's (Chang, 1965,1972a).

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