Understanding the Complex Rheology of Human Blood Plasma

Blood plasma (BP) is a borderline non-Newtonian fluid. Few studies have characterized the rheology of BP and even less focused on understanding its subtle viscoelastic traits, which were only somewhat recently acknowledged. We use passive microrheology to measure the bulk response of human plasma samples under shear at body and ambient temperatures. Evidence of subdiffusive behavior in the mean-squared displacement is observed at the highest frequencies probed, which we attribute to the stress relaxation of protein molecules or chains. Jeffreys-like complex shear moduli were computed thereof. The microenvironments of albumin, fibrinogen, and gamma-globulin solutions (key plasma proteins) were probed as well. Single proteins in an aqueous buffer showed no signs of viscoelasticity within experimental resolution. Conversely, mixed together, they appear to promote the same kind of short-term elastic behavior seen in plasma. All in all, a fresh look at the shear rheology of BP is presented.