Softness and Hydrodynamic Interactions Regulate Lipoprotein Transport in Crowded Yolk Environments

TL;DR

This study investigates how the softness of lipoproteins and hydrodynamic interactions influence their transport in crowded yolk environments, revealing significant diffusion slowdown due to complex interactions.

Contribution

It provides direct experimental evidence of LDL cage dynamics in yolk plasma and highlights the combined effects of hydrodynamics and particle softness on diffusion.

Findings

LDLs exhibit approximately 100-fold reduction in diffusion at high concentrations

Hydrodynamic interactions and particle softness critically slow down LDL mobility

Yolk plasma remains liquid despite dense packing and reduced LDL dynamics

Abstract

Low-density lipoproteins (LDLs) serve as nutrient reservoirs in egg yolk for embryonic development and as promising drug carriers. Both roles critically depend on their mobility in densely crowded biological environments. Under these crowded conditions, diffusion is hindered by transient confinement within dynamic cages formed by neighboring particles, driven by solvent-mediated hydrodynamic interactions and memory effects -- phenomena that have remained challenging to characterize computationally and experimentally. Here, we employ megahertz X-ray photon correlation spectroscopy to directly probe the cage dynamics of LDLs in yolk-plasma across various concentrations. We find that LDLs undergo anomalous diffusion, experiencing $\approx$ 100-fold reduction in self-diffusion at high concentrations compared to dilute solutions. This drastic slowing-down is attributed to a combination of hydrodynamic interactions, direct particle-particle interactions, and the inherent softness of LDL particles. Despite reduced dynamics, yolk-plasma remains as a liquid, yet sluggish, balancing dense packing, structural stability, and fluidity essential for controlled lipid release during embryogenesis.