Cellular uptake of polymer gels by membrane wrapping

Biomolecular condensates are viscoelastic, liquid-liquid phase-separated droplets in the cytosol of biological cells. Lipid-bilayer membranes are abundant in cells and may interact with the condensates. We use a polymer-network model for microgels to characterize the engulfment of particles with 3D elasticity at fluid membranes. The physico-chemical parameters that control engulfment are size, shape and elasticity of the microgel, bending rigidity and tension of the membrane, and microgel-membrane adhesion strength.^1,2 The microgels are modeled by spring networks and the membranes by triangulated surfaces, with the microgels attached to the membranes via receptor-ligand bonds.³ Hertz theory is employed to characterize the microgel’s Young’s modulus and Poisson’s ratio. The interplay of microgel and membrane deformations is controlled by the competition between microgel elasticity and membrane bending rigidity. Our numerical simulations predict an increased stability of partial-wrapped states for microgels with lower Young’s moduli. There is a discontinuous transition from oblate to nearly spherical microgels with increasing wrapping fractions, irrespective of membrane tension. Volume and surface area of partial-wrapped microgels are significantly reduced compared with those of free microgels.³ Understanding condensate wrapping will facilitate the design of tunable and responsive polymeric gels for biomedical applications, e.g., targeted drug delivery vectors.