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

Impact of Polydispersity on Phase Separation: Insights from Polyethylene Glycol and Dextran Mixtures

The dynamic formation of (bio)molecular condensates has emerged as a key regulatory mechanism in cellular processes. Concepts from polymer physics can provide valuable insights into the underlying mechanisms and properties of these condensates. While stoichiometric interactions between chemically distinct molecules have traditionally been the primary focus for understanding and predicting the equilibrium behavior, recent attention has turned to the role of molecular diversity, particularly the interplay between molecules of similar types but varying chain lengths. To mimic such cellular conditions, we investigated the impact of molecular weight polydispersity using polyethylene glycol (PEG) and dextran (Dex) solutions through experiments and molecular simulations. Our findings reveal that polydisperse systems, which contain a higher fraction of short-chain components, exhibit a narrower two-phase region, along with reduced concentration differences and interfacial tension between the coexisting polymer-rich and polymer-poor phases. In these systems, the Dex-rich phase is enriched with longer Dex chains compared to the PEG-rich phase, with a gradual transition in chain length across their interface. However, polydispersity has no significant effects on the critical concentration and critical exponents. Finally, our study of condensation kinetics demonstrates that phase separation is not limited by the nucleation rate but instead by the diffusion-driven aggregation of polymers.

Ferguson Plot Analysis of Chaperone ClpB from Moderate Halophile

The Ferguson plot is a simple method for determining the molecular weight of native proteins and their complexes. In this study, we tested the validity of the Ferguson plot based on agarose native gel electrophoresis using multimeric chaperone protein, ClpB, derived from a moderate halophile that forms a native hexamer. The Ferguson plot showed a single band with a molecular weight of 1,500 kDa, approximately twice the size of the native hexamer. This result is consistent with the structure of other chaperons that form a double ring assembly comprising two hexameric units, i.e., a dodecamer. Supporting this, dynamic light scattering experiment showed two peaks, which likely correspond to the hexamer and dodecamer structures.

Phase separation in soft repulsive polymer mixtures: foundation and implication for chromatin organization

Given the wide range of length scales, the analysis of polymer systems often requires coarse-graining, for which various levels of description may be possible depending on the phenomenon under consideration. Here, we provide a super-coarse grained description, where polymers are represented as a succession of mesosopic soft beads which are allowed to overlap with others. We then investigate the phase separation behaviors in a mixture of such homopolymers based on mean-field theory, and discuss universal aspects of the miscibility phase diagram in comparison with the numerical simulation. We also discuss an extension of our analysis to mixtures involving random copolymers, which might be interesting in the context of chromatin organization in a cell nucleus.

Marangoni Droplets of Dextran in PEG Solution and Its Motile Change Due to Coil-Globule Transition of Coexisting DNA

Motile droplets using Marangoni convection are attracting attention for their potential as cell-mimicking small robots. However, the motion of droplets relative to the internal and external environments that generate Marangoni convection has not been quantitatively described. In this study, we used an aqueous two-phase system [poly(ethylene glycol) (PEG) and dextran] in an elongated chamber to generate motile dextran droplets in a constant PEG concentration gradient. We demonstrated that dextran droplets move by Marangoni convection, resulting from the PEG concentration gradient and the active transport of PEG and dextran into and out of the motile dextran droplet. Furthermore, by spontaneously incorporating long DNA into the dextran droplets, we achieved cell-like motility changes controlled by coexisting environment-sensing molecules. The DNA changes its position within the droplet and motile speed in response to external conditions. In the presence of Mg2+, the coil-globule transition of DNA inside the droplet accelerates the motile speed due to the decrease in the droplet's dynamic viscosity. Globule DNA condenses at the rear part of the droplet along the convection, while coil DNA moves away from the droplet's central axis, separating the dipole convections. These results provide a blueprint for designing autonomous small robots using phase-separated droplets, which change the mobility and molecular distribution within the droplet in reaction with the environment. It will also open unexplored areas of self-assembly mechanisms through phase separation under convections, such as intracellular phase separation.

Exploring Pore Formation and Gas Sensing Kinetics Using Conjugated Polymer-Small Molecule Blends

Controlling miscibility between mixture components helps induce spontaneous phase separation into distinct domain sizes, thereby resulting in porous conjugated polymer (CP) films with different pore sizes after selective removal of auxiliary components. The miscibility of the CP mixture can be tailored by blending auxiliary model components designed by reflecting the difference in solubility parameters with the CP. The pore size increases as the difference in solubility parameters between the matrix CP and auxiliary component increases. Electrical properties are not critically damaged even after forming pores in the CP; however, excessive pore formation enables pores to spread to the vicinity of the dielectric layer of CP-based field-effect transistors (FETs), leading to partial loss of the carrier-transporting active channel in the FET. The porous structure is advantageous for not only increasing detection sensitivity but also improving the detection speed when porous CP films are applied to FET-based gas sensors for NO2 detection. The quantitative analysis of the response-recovery trend of the FET sensor using the Langmuir isotherm suggests that the response speed can be improved by more than 2.5 times with a 50-fold increase in NO2 sensitivity compared with pristine CP, which has no pores.

Improving the properties of polylactic acid/polypropylene carbonate blends through cardanol-induced compatibility enhancement

Cardanol (CD) is used as a reactive compatibilizer, and blended with polylactic acid (PLA) and polypropylene carbonate (PPC) resin (70/30(w/w)) to obtain a series of PLA/PPC/CD blends. The systematic study was conducted on the thermal properties, optical properties, rheological properties, mechanical properties, and microscopic morphology of the blend, by varying amounts of CD added to the blends. A detailed explanation and comprehensive analysis of the reaction mechanism between CD and PLA/PPC have been made. The study found that CD acts as a "bridge" between the PLA and PPC, forming the structure of a block copolymer (PLA-b-CD-b-PPC), and the copolymer can greatly improve the compatibility of PLA and PPC. When the amount of CD reaches 8 wt%, only one Tg is observed in the blend, simultaneously, PLA/PPC has already transitioned from a partially compatible system to a completely compatible system. At the same time, the addition of CD does not have any negative impact on the thermal stability of the PLA/PPC blend under processing temperature conditions, and the thermal stability of the PLA/PPC/CD blends can even be improved under extreme conditions. In addition, the addition of CD allows the PLA/PPC/CD blends to maintain a high light transmittance while reducing the opacity of the blend (the light transmittance remains above 92 %, and the opacity is reduced from 37 % to about 24 %), demonstrating excellent optical properties. Moreover, the elongation at break and impact strength of the PLA/PPC/CD blend both show a trend of first increasing and then decreasing with the increase of CD amount. When the CD amount varies within the range of 6- 8 wt%, the blends undergoes a brittle-ductile transition, and its toughness is greatly improved while the rigidity can also meet practical needs. When the amount of CD in the system increases to 12 wt%, the toughness of the blend reaches its peak, and its elongation at break and impact strength reach 513.24 % and 9211.5 J/m2 respectively (increased to 2442.84 % and 270.73 % of the PLA/PPC blend). Concurrently, the fracture surface of the blend exhibits large-scale plastic flow in the direction of the applied force, with marked shear yield phenomena, showing obvious characteristics of tough fracture.

Biophysical Reviews: peering into 2024

After introducing the winner of this year's Michèle Auger Award for Young Scientists' Independent Research, this Editorial for Volume 16 Issue 1 then describes the Issue contents. The Editorial concludes by providing a look into what lies ahead for 2024.

Biophysical Reviews: A goodbye to 2023

This Editorial for the IUPAB Biophysical Reviews journal (2023 volume 15 issue 6) first provides an overview of the contents of this "Regular Issue featuring an Issue Focus on the Computational Biophysics of Atomic Force Microscopy" before going on to highlight some of the notable work published in the journal throughout 2023. Highlights of the current Issue include the contributed review article by Antonio Benedetto, winner of the 2023 Michèle Auger Award for Young Scientists' Independent Research, the latest installment of the "Biophysical Reviews Top 5 Series" authored by Angela Dulhunty, and an Issue Focus on the topic of computational aspects of atomic force microscopy generated from an IUPAB-sponsored workshop held in 2022.

Biophysical Reviews: a call for nominations to the 2024 Michéle Auger Award

This editorial for volume 15 issue 3 first provides a brief introduction to the issue contents before then going on to open the call for nominations to the 2024 Michéle Auger Award for Young Scientists' Independent Research-the journal's single award.

Phase separation in supramolecular and covalent adaptable networks

Phase separation phenomena have been studied widely in the field of polymer science, and were recently also reported for dynamic polymer networks (DPNs). The mechanisms of phase separation in dynamic polymer networks are of particular interest as the reversible nature of the network can participate in the structuring of the micro- and macroscale domains. In this review, we highlight the underlying mechanisms of phase separation in dynamic polymer networks, distinguishing between supramolecular polymer networks and covalent adaptable networks (CANs). Also, we address the synergistic effects between phase separation and reversible bond exchange. We furthermore discuss the effects of phase separation on the material properties, and how this knowledge can be used to enhance and tune material properties.

Biophysical Reviews: And the winner is …

This Editorial (Vol. 15 Issue 2-Regular Issue) first announces the winner of the 2023 Michèle Auger Award for Young Scientists' Independent Research before then going on to describe the contents of the current Issue. The Editorial closes with a discussion of the pros and cons of writing in the formulation of scientific ideas.

Biophysical Reviews: Turning the page from 2022 to 2023

This Editorial (vol. 15 issue 1-Regular Issue featuring an Issue Focus on the "100th Anniversary of Har Gobind Khorana") first describes the issue contents before providing both, a look back at some journal highlights from 2022, and a look forward to what we can expect from 2023. The Editorial closes with a roundup of new journal access features and an acknowledgement of those supporting the journal.

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

The formation of (bio)molecular condensates via liquid-liquid phase separation in cells has received increasing attention, as these aggregates play important functional and regulatory roles within biological systems. However, the majority of studies focused on the behavior of pure systems in bulk solutions, thus neglecting confinement effects and the interplay between the numerous molecules present in cells. To better understand the physical mechanisms driving condensation in cellular environments, we perform molecular simulations of binary polymer mixtures in spherical droplets, considering both monodisperse and polydisperse molecular weight distributions for the longer polymer species. We find that confinement induces a spatial separation of the polymers by length, with the longer ones moving to the droplet center. This partitioning causes a distinct increase in the local polymer concentration near the droplet center, which is more pronounced in polydisperse systems. Consequently, the confined systems exhibit liquid-liquid phase separation at average polymer concentrations where bulk systems are still in the one-phase regime.

Biophysical Reviews: Publishing short and critical reviews written by key figures in the field

This Editorial for Issue 5 (Vol. 14 2022) of Biophysical Reviews begins with a short note of commemoration for the journal's founding chief editor Jean Garnier (1929-2022) who sadly passed away this month. Following this is a precis of the current Issue contents that begins with an introduction of the prizewinning article by Assoc. Prof. Miho Yanagisawa, winner of the 2022 Michèle Auger Award for Young Scientists' Independent Research. This Editorial concludes with a brief and somewhat subjective discussion of what features do and don't, help to make for a 'good journal'.