Capillary-size flow of human blood plasma: Revealing hidden elasticity and scale dependence

Viscosity and diffusion in life processes and tuning of fundamental constants

Viewed as one of the grandest questions in modern science, understanding fundamental physical constants has been discussed in high-energy particle physics, astronomy and cosmology. Here, I review how condensed matter and liquid physics gives new insights into fundamental constants and their tuning. This is based on two observations: first, cellular life and the existence of observers depend on viscosity and diffusion. Second, the lower bound on viscosity and upper bound on diffusion are set by fundamental constants, and I briefly review this result and related recent developments in liquid physics. I will subsequently show that bounds on viscosity, diffusion and the newly introduced fundamental velocity gradient in a biochemical machine can all be varied while keeping the fine-structure constant and the proton-to-electron mass ratio intact. This implies that it is possible to produce heavy elements in stars but have a viscous planet where all liquids have very high viscosity (for example that of tar or higher) and where life may not exist. Knowing the range of bio-friendly viscosity and diffusion, we will be able to calculate the range of fundamental constants which favour cellular life and observers and compare this tuning with that discussed in high-energy physics previously. This invites an inter-disciplinary research between condensed matter physics and life sciences, and I formulate several questions that life science can address. I finish with a conjecture of multiple tuning and an evolutionary mechanism.

Fundamental constants explain submillimeter liquid shear forces

From fundamental physical constants to the identification of liquid shear elasticity, over the past decade, new ways have emerged to understand viscosity.

The role of plasma in the yield stress of blood

BACKGROUND

Yielding and shear elasticity of blood are merely discussed within the context of hematocrit and erythrocyte aggregation. However, plasma might play a substantial role due its own viscoelasticity.

OBJECTIVE

If only erythrocyte aggregation and hematocrit would determine yielding, blood of different species with comparable values would present comparable yield stresses.

METHODS

rheometry (SAOS: amplitude and frequency sweep tests; flow curves) of hematocrit-matched samples at 37°C. Brillouin Light Scattering Spectroscopy at 38°C.

RESULTS

Yield stress for pig: 20mPa, rat: 18mPa, and human blood: 9mPa. Cow and sheep blood were not in quasi-stationary state supporting the role of erythrocyte aggregation for the development of elasticity and yielding. However, pig and human erythrocytes feature similar aggregability, but yield stress of porcine blood was double. Murine and ruminant erythrocytes both rarely aggregate, but their blood behavior was fundamentally different. Pig plasma was shear-thinning and murine plasma was platelet-enriched, supporting the role of plasma for triggering collective effects and gel-like properties.

CONCLUSIONS

Blood behavior near zero shear flow is not based solely on erythrocyte aggregation and hematocrit, but includes the hydrodynamic interaction with plasma. The shear stress required to break down elasticity is not the critical shear stress for dispersing erythrocyte aggregates, but the shear stress required to fracture the entire assembly of blood cells within their intimate embedding.