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1. Liquid-liquid phase separation promotes animal desiccation tolerance

   https://doi.org/10.1073/pnas.2014463117  

   Belott, Clinton ; Janis, Brett ; Menze, Michael A. ( October 2020 , Proceedings of the National Academy of Sciences)

   Proteinaceous liquid-liquid phase separation (LLPS) occurs when a polypeptide coalesces into a dense phase to form a liquid droplet (i.e., condensate) in aqueous solution. In vivo, functional protein-based condensates are often referred to as membraneless organelles (MLOs), which have roles in cellular processes ranging from stress responses to regulation of gene expression. Late embryogenesis abundant (LEA) proteins containing seed maturation protein domains (SMP; PF04927) have been linked to storage tolerance of orthodox seeds. The mechanism by which anhydrobiotic longevity is improved is unknown. Interestingly, the brine shrimpArtemia franciscanais the only animal known to express such a protein (AfrLEA6) in itsmore »anhydrobiotic embryos. Ectopic expression ofAfrLEA6 (AWM11684) in insect cells improves their desiccation tolerance and a fraction of the protein is sequestered into MLOs, while aqueousAfrLEA6 raises the viscosity of the cytoplasm. LLPS ofAfrLEA6 is driven by the SMP domain, while the size of formed MLOs is regulated by a domain predicted to engage in protein binding.AfrLEA6 condensates formed in vitro selectively incorporate target proteins based on their surface charge, while cytoplasmic MLOs formed inAfrLEA6-transfected insect cells behave like stress granules. We suggest thatAfrLEA6 promotes desiccation tolerance by engaging in two distinct molecular mechanisms: by raising cytoplasmic viscosity at even modest levels of water loss to promote cell integrity during drying and by forming condensates that may act as protective compartments for desiccation-sensitive proteins. Identifying and understanding the molecular mechanisms that govern anhydrobiosis will lead to significant advancements in preserving biological samples.

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2. Topology control of human fibroblast cells monolayer by liquid crystal elastomer

   https://doi.org/10.1126/sciadv.aaz6485  

   Turiv, Taras ; Krieger, Jess ; Babakhanova, Greta ; Yu, Hao ; Shiyanovskii, Sergij V. ; Wei, Qi-Huo ; Kim, Min-Ho ; Lavrentovich, Oleg D. ( May 2020 , Science Advances)

   Eukaryotic cells in living tissues form dynamic patterns with spatially varying orientational order that affects important physiological processes such as apoptosis and cell migration. The challenge is how to impart a predesigned map of orientational order onto a growing tissue. Here, we demonstrate an approach to produce cell monolayers of human dermal fibroblasts with predesigned orientational patterns and topological defects using a photoaligned liquid crystal elastomer (LCE) that swells anisotropically in an aqueous medium. The patterns inscribed into the LCE are replicated by the tissue monolayer and cause a strong spatial variation of cells phenotype, their surface density, and numbermore »density fluctuations. Unbinding dynamics of defect pairs intrinsic to active matter is suppressed by anisotropic surface anchoring allowing the estimation of the elastic characteristics of the tissues. The demonstrated patterned LCE approach has potential to control the collective behavior of cells in living tissues, cell differentiation, and tissue morphogenesis.« less
3. Liquid crystal elastomer foams with elastic properties specifically engineered as biodegradable brain tissue scaffolds

   https://doi.org/10.1039/c7sm01949a  

   Prévôt, M. E. ; Andro, H. ; Alexander, S. L. ; Ustunel, S. ; Zhu, C. ; Nikolov, Z. ; Rafferty, S. T. ; Brannum, M. T. ; Kinsel, B. ; Korley, L. T. ; et al ( January 2018 , Soft Matter)

   Tissue regeneration requires 3-dimensional (3D) smart materials as scaffolds to promote transport of nutrients. To mimic mechanical properties of extracellular matrices, biocompatible polymers have been widely studied and a diverse range of 3D scaffolds have been produced. We propose the use of responsive polymeric materials to create dynamic substrates for cell culture, which goes beyond designing only a physical static 3D scaffold. Here, we demonstrated that lactone- and lactide-based star block-copolymers (SBCs), where a liquid crystal (LC) moiety has been attached as a side-group, can be crosslinked to obtain Liquid Crystal Elastomers (LCEs) with a porous architecture using a salt-leachingmore »method to promote cell infiltration. The obtained SmA LCE-based fully interconnected-porous foams exhibit a Young modulus of 0.23 ± 0.07 MPa and a biodegradability rate of around 20% after 15 weeks both of which are optimized to mimic native environments. We present cell culture results showing growth and proliferation of neurons on the scaffold after four weeks. This research provides a new platform to analyse LCE scaffold–cell interactions where the presence of liquid crystal moieties promotes cell alignment paving the way for a stimulated brain-like tissue.« less
4. Core–shell droplets and microcapsules formed through liquid–liquid phase separation of a colloid–polymer mixture

   https://doi.org/10.1039/D1SM01091C  

   Dang, Steven ; Brady, John ; Rel, Ryle ; Surineni, Sreenidhi ; O’Shaughnessy, Conor ; McGorty, Ryan ( September 2021 , Soft Matter)

   Microcapsules allow for the controlled containment, transport, and release of cargoes ranging from pharmaceuticals to fragrances. Given the interest from a variety of industries in microcapsules and other core–shell structures, a multitude of fabrication strategies exist. Here, we report on a method relying on a mixture of temperature-responsive microgel particles, poly( N -isopropylacrylamide) (pNIPAM), and a polymer which undergo fluid–fluid phase separation. At room temperature this mixture separates into colloid-rich (liquid) and colloid-poor (gas) fluids. By heating the sample above a critical temperature where the microgel particles shrink dramatically and develop a more deeply attractive interparticle potential, the droplets ofmore »the colloid-rich phase become gel-like. As the temperature is lowered back to room temperature, these droplets of gelled colloidal particles reliquefy and phase separation within the droplet occurs. This phase separation leads to colloid-poor droplets within the colloid-rich droplets surrounded by a continuous colloid-poor phase. The gas/liquid/gas all-aqueous double emulsion lasts only a few minutes before a majority of the inner droplets escape. However, the colloid-rich shell of the core–shell droplets can solidify with the addition of salt. That this method creates core–shell structures with a shell composed of stimuli-sensitive microgel colloidal particles using only aqueous components makes it attractive for encapsulating biological materials and making capsules that respond to changes in, for example, temperature, salt concentration, or pH.« less
5. Pore condensation and freezing is responsible for ice formation below water saturation for porous particles

   https://doi.org/10.1073/pnas.1813647116  

   David, Robert O. ; Marcolli, Claudia ; Fahrni, Jonas ; Qiu, Yuqing ; Perez Sirkin, Yamila A. ; Molinero, Valeria ; Mahrt, Fabian ; Brühwiler, Dominik ; Lohmann, Ulrike ; Kanji, Zamin A. ( April 2019 , Proceedings of the National Academy of Sciences)

   Ice nucleation in the atmosphere influences cloud properties, altering precipitation and the radiative balance, ultimately regulating Earth’s climate. An accepted ice nucleation pathway, known as deposition nucleation, assumes a direct transition of water from the vapor to the ice phase, without an intermediate liquid phase. However, studies have shown that nucleation occurs through a liquid phase in porous particles with narrow cracks or surface imperfections where the condensation of liquid below water saturation can occur, questioning the validity of deposition nucleation. We show that deposition nucleation cannot explain the strongly enhanced ice nucleation efficiency of porous compared with nonporous particlesmore »at temperatures below −40 °C and the absence of ice nucleation below water saturation at −35 °C. Using classical nucleation theory (CNT) and molecular dynamics simulations (MDS), we show that a network of closely spaced pores is necessary to overcome the barrier for macroscopic ice-crystal growth from narrow cylindrical pores. In the absence of pores, CNT predicts that the nucleation barrier is insurmountable, consistent with the absence of ice formation in MDS. Our results confirm that pore condensation and freezing (PCF), i.e., a mechanism of ice formation that proceeds via liquid water condensation in pores, is a dominant pathway for atmospheric ice nucleation below water saturation. We conclude that the ice nucleation activity of particles in the cirrus regime is determined by the porosity and wettability of pores. PCF represents a mechanism by which porous particles like dust could impact cloud radiative forcing and, thus, the climate via ice cloud formation.

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