Cell-Size Space Regulates the Behavior of Confined Polymers: From Nano- and Micromaterials Science to Biology

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.

Multimolecular Competition Effect as a Modulator of Protein Localization and Biochemical Networks in Cell-Size Space

Cells are small, closed spaces filled with various types of macromolecules. Although it is shown that the characteristics of biochemical reactions in vitro are quite different from those in living cells, the role of the co-existence of various macromolecules in cell-size space remains still elusive. Here, using a constructive approach, it is demonstrated that the co-existence of various macromolecules themselves has the ability to tune protein localization for spatiotemporal regulation and a biochemical reaction system in a cell-size space. Both experimental and theoretical analyses reveal that enhancement of interfacial effects by a large surface-area-to-volume ratio facilitates membrane localization of molecules in the cell-size space, and the interfacial effects are alleviated by competitive binding to lipid membranes among multiple proteins even if their membrane affinities are weak. These results indicate that competition for membrane binding among various macromolecules in the cell-size space plays a role in regulating the spatiotemporal molecular organization and biochemical reaction networks. These findings shed light on the importance of surrounding molecules for biochemical reactions using purified elements in small spaces.

Cell-Sized Confinements Alter Molecular Diffusion in Concentrated Polymer Solutions Due to Length-Dependent Wetting of Polymers

Living cells are characterized by the micrometric confinement of various macromolecules at high concentrations. Using droplets containing binary polymer blends as artificial cells, we previously showed that cell-sized confinement causes phase separation of the binary polymer solutions because of the length-dependent wetting of the polymers. Here, we demonstrate that the confinement-induced heterogeneity of polymers also emerges in single-component polymer solutions. The resulting structural heterogeneity also leads to a slower transport of small molecules at the center of cell-sized droplets than that in bulk solutions. Coarse-grained molecular simulations support this confinement-induced heterogeneous distribution by polymer length and demonstrate that the effective wetting of the shorter chains at the droplet surface originates from the length-dependent conformational entropy. Our results suggest that cell-sized confinement functions as a structural regulator for polydisperse polymer solutions that specifically manipulates the diffusion of molecules, particularly those with sizes close to the correlation length of the polymer chains.

Emerging biomaterials for tumor immunotherapy

BACKGROUND

The immune system interacts with cancer cells in various intricate ways that can protect the individual from overproliferation of cancer cells; however, these interactions can also lead to malignancy. There has been a dramatic increase in the application of cancer immunotherapy in the last decade. However, low immunogenicity, poor specificity, weak presentation efficiency, and off-target side effects still limit its widespread application. Fortunately, advanced biomaterials effectively contribute immunotherapy and play an important role in cancer treatment, making it a research hotspot in the biomedical field.

MAIN BODY

This review discusses immunotherapies and the development of related biomaterials for application in the field. The review first summarizes the various types of tumor immunotherapy applicable in clinical practice as well as their underlying mechanisms. Further, it focuses on the types of biomaterials applied in immunotherapy and related research on metal nanomaterials, silicon nanoparticles, carbon nanotubes, polymer nanoparticles, and cell membrane nanocarriers. Moreover, we introduce the preparation and processing technologies of these biomaterials (liposomes, microspheres, microneedles, and hydrogels) and summarize their mechanisms when applied to tumor immunotherapy. Finally, we discuss future advancements and shortcomings related to the application of biomaterials in tumor immunotherapy.

CONCLUSION

Research on biomaterial-based tumor immunotherapy is booming; however, several challenges remain to be overcome to transition from experimental research to clinical application. Biomaterials have been optimized continuously and nanotechnology has achieved continuous progression, ensuring the development of more efficient biomaterials, thereby providing a platform and opportunity for breakthroughs in tumor immunotherapy.

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'.

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

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.