Cell-size space effects on phase separation of binary polymer blends

Abstract

Within living cells, a diverse array of biomolecules is present at high concentrations. To better understand how molecular behavior differs under such conditions (collectively described as macromolecular crowding), the crowding environment has been reproduced inside artificial cells. We have previously shown that the combination of macromolecular crowding and microscale geometries imposed by the artificial cells can alter the molecular behaviors induced by macromolecular crowding in bulk solutions. We have named the effect that makes such a difference the cell-size space effect (CSE). Here, we review the underlying biophysics of CSE for phase separation of binary polymer blends. We discuss how the cell-size space can initiate phase separation, unlike nano-sized spaces, which are known to hinder nucleation and phase separation. Additionally, we discuss how the dimensions of the artificial cell and its membrane characteristics can significantly impact phase separation dynamics and equilibrium composition. Although these findings are, of themselves, very interesting, their real significance may lie in helping to clarify the functions of the cell membrane and space size in the regulation of intracellular phase separation.

Confinement-Induced Fractionation and Liquid–Liquid Phase Separation of Polymer Mixtures

“…In our simulations with polydisperse Dextran chains, we drew the molecular weight of each polymer from a Gaussian distribution, targeting and . The PEG chains were kept monodisperse throughout, which is consistent with the rather small polydispersity of reported in the experimental literature for low-molecular-weight PEG [ 7 , 17 , 44 ]. In all simulations, we selected the number of PEG and Dextran chains so that and , averaged over the entire droplet volume, which lies in the mixed one-phase regime of the bulk phase diagram (see Section 3.1 ).…”

“…The discrepancy between the initial estimate and the final value of is rather large, and we can only speculate about its origin: Clark extracted from experimental coexistence curves using Flory–Huggins solution theory [ 38 ], which ignores the polymer architecture and thus the branching of the Dextran chains. Further, a monodisperse molecular weight distribution is assumed in his treatment, although generally available Dextran polymers typically have a broad molecular weight distribution [ 7 , 17 , 18 , 22 , 44 ]. Finally, we used a rather coarse-grained description, which maps about 40 monomers onto a single bead, resulting in a larger entropy of mixing in the simulations compared to the experiments [ 32 ].…”

“…Therefore, we performed simulations at two smaller radii, i.e., and , which should still allow us to capture the effect of confinement on the phase behavior. Further, we considered mixtures containing either monodisperse or polydisperse Dextran chains, since high-molecular-weight Dextran usually has a broad molecular weight distribution; for example, the Dimova group used Dextran chains with and dispersities in the range of [ 7 , 41 , 44 ], while the Yanagisawa group used Dextran with and [ 17 , 18 ]. In our simulations with polydisperse Dextran chains, we drew the molecular weight of each polymer from a Gaussian distribution, targeting and .…”

“…Experimentally, confinement effects have been studied using DNA-based protocells [ 12 , 13 ] or water-in-oil droplets containing polymer mixtures such as polyethylene glycol (PEG) and bovine serum albumin, PEG and DNA, or PEG and Dextran, serving as a synthetic cytoplasm [ 14 , 15 , 16 , 17 ]. At sufficiently high concentrations, these polymer mixtures separate into two coexisting aqueous compartments, which can be used to localize additional components such as proteins [ 14 , 15 ].…”

Biophysical Reviews: Turning the page from 2022 to 2023

“…The second notable aspect of this Issue was the prize-winning review article by Assoc. Prof. Miho Yanagisawa-the 2023 recipient of the Michèle Auger Award for Young Scientists' Independent Research' (Yanagisawa 2022). Written on the topic of how μm-sized encapsulation can influence the physical chemistry of adsorption and phase transition events from their normal behavior observed in bulk liquid, the review also serves to introduce the author's research theme of "cell-sized space effects" and provides much food for thought to readers on the chemistry operating within the crowded interior of the cell (Yanagisawa 2022).…”