Investigating the two-dimensional (2D) diffusion dynamics of multi-component surfactant systems is challenging due to the difficulty in establishing well-defined initial boundaries both temporally and spatially. To overcome this challenge, we employed two key strategies. First, we utilized a merging droplet technique which provides controlled spatiotemporal initial conditions, enabling in-situ measurement of multi-component surfactant diffusion. Second, we designed a model multi-component surfactant system comprising oxidized dioleoylphosphatidylcholine (oxDOPC) and cholesterol (Chol) through controlled UV-induced oxidation of DOPC. By using 1H nuclear magnetic resonance (NMR) spectroscopy and numerical simulations of diffusion with a moving boundary, we quantified the molecular profiles and diffusivities of miscible and immiscible species in oxDOPC-Chol system. Furthermore, we determined the line tension of oxDOPC domain from the elastic relaxation of its deformed shape. This work provides significant methodological advancements for studying molecular mixing in multi-component interfacial materials, including systems involving membrane proteins and lipid rafts.

Human diseases affect various cell types within the local niche, but the multicellular responses of human diseases have not been collectively assessed across organs. Here, we categorize multicellular responses of human diseases based on a remapped human cell atlas, incorporating 12 million single-cell transcriptome profiles acquired from an automated data collection pipeline. Additional curation expands the collection up to 46 million cells, covering 160 disease conditions across 49 distinct organ identities. From the re-aligned atlas of single-cell transcriptome data, we constructed a hierarchical cell classification framework comprising 32 major cell types and 165 cell subtype annotations. Systematic profiling of disease and organ association patterns of cellular subtype reveals archetypes of human diseases repeatedly found across organs, including a multicellular phenotype highly specific to the tumor microenvironment. The universal cell atlas could serve as a reference for unbiased deconvolution of spatial transcriptome datasets, revealing spatial distribution patterns associated with immunotherapy responses. Collectively, our study provides foundational resources for cross-tissue cell type annotation, presents a comprehensive multicellular overview of disease-associated responses across human tissues, and highlights multicellular responses in tumor microenvironments. Seongryong Kim, Sungmin Cheong, Suho Lee, Yeju Kim, Jong-Eun Park. Cross-tissue atlas of human disease identifies tumor-specific components in tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6265.

Lipid rafts, which are dynamic nanodomains in the plasma membrane, play a crucial role in intermembrane processes by clustering together and growing in size within the plane of the membrane while also aligning with each other across different membranes. However, the physical origin of layer by layer alignment of lipid rafts remains to be elucidated. Here, by using fluorescence imaging and synchrotron X-ray reflectivity in a phase-separated multilayer system, we find that the alignment of raft-mimicking Lo domains is regulated by the distance between bilayers. Molecular dynamics simulations reveal that the aligned state is energetically preferred when the intermembrane distance is small due to its ability to minimize the volume of surface water, which has fewer water hydrogen bonds (HBs) compared to bulk water. Our results suggest that water HB-driven alignment of lipid rafts plays a role as a precursor of intermembrane processes such as cell-cell fusion, virus entry, and signaling.

Despite technological advances in biomolecule detections, evaluation of molecular interactions via potentiometric devices under ion-enriched solutions has remained a long-standing problem. To avoid severe performance degradation of bioelectronics by ionic screening effects, we cover probe surfaces of field effect transistors with a single film of the supported lipid bilayer, and realize respectable potentiometric signals from receptor-ligand bindings irrespective of ionic strength of bulky solutions by placing an ion-free water layer underneath the supported lipid bilayer. High-energy X-ray reflectometry together with the circuit analysis and molecular dynamics simulation discovered biochemical findings that effective electrical signals dominantly originated from the sub-nanoscale conformational change of lipids in the course of receptor-ligand bindings. Beyond thorough analysis on the underlying mechanism at the molecular level, the proposed supported lipid bilayer-field effect transistor platform ensures the world-record level of sensitivity in molecular detection with excellent reproducibility regardless of molecular charges and environmental ionic conditions.

While self-diffusion of surfactant molecules has long been investigated with FRAP, studying mutual diffusion involving two or more surfactants remains a challenge in biological physics, chemistry, etc., primarily due to hurdles in preparing well-defined initial conditions. The 'domain insertion method' is newly developed to generate a clear boundary between two lipid domains by coalescing a lipid-coated water droplet onto planar monolayer of another lipid. In this poster, we present our recent findings on two-dimensional mutual diffusion dynamics of UV-oxidized DOPC and cholesterol. Numerical simulations, NMR and IR spectroscopy results will be presented. Miscibility, diffusion coefficient and inter-domain line tension were measured. This study can be potentially implicated for assessing the interfacial mixing properties of two or more surfactants.

Lipid vesicles are a useful drug-encapsulating carrier in the field of nano-biotechnology. Inter-vesicle interaction in nanoscale, which is a crucial factor to determine the stability of vesicles, however, has not been actively studied so far due to the obstacles of nanometer-sized (∼100nm) and thin walled vesicular structure as well as the lack of measurement techniques. In this poster session, we present the quantitative measurement of intermolecular interaction of charged lipid vesicles by “optical bottle”, a technique to confine multi-particles into focused laser beam. This technique can probe osmotic second virial coefficient (B2) in wide range of vesicle concentration up to several volume percent, which is ten folds denser regime than conventional scattering technique. This work can be potentially implicated to studying quantitatively the interactions between various nanoparticles grafted with proteins, polymers, drugs, etc.

Ordered domains in cellular membranes, called lipid rafts, are involved in signal transduction, cellular transport, and disease development. They compartmentalize membrane proteins, thus provide functional hotspots for those cellular processes. Especially, when two membranes communicate, domain size growth and positional proximity between these domains in distinct membranes can be necessary for efficient cell-cell interaction, synaptic vesicle fusion, and drug delivery through vesicles. Here, using synchrotron X-ray reflectivity and fluorescence microscopy, we describe our recent findings that domain size and alignment in phase separated lipid multilayers can be controlled by salt concentration in aqueous phase. We also describe the effect of depletion force as well.

We investigated the effect of cholesterol on the vertical order of spin-coated supported dipalmitoylphosphatidylcholine (DPPC) multilayers by using synchrotron X-ray reflectivity with customized X-ray liquid cell. As increasing mol% of cholesterol up to 10%, the lamellar spacing of the DPPC multilayer increases, implying that cholesterol induces a tilt-to-untilt transition. The sharpening of X-ray intensity upon cholesterol binding, reflected in the FWHM plot, suggests that cholesterol enhances the vertical ordering of the DPPC multilayer. In addition, fluorescence microscopy experiment confirms a gel-to-liquid ordered (LO) phase transition between 5 and 7% cholesterol. As a result, in low cholesterol regime, the DPPC multilayer is not in a simple gel phase but in a ripple phase where lipids are vertically disordered due to the differently tilted chains which leads to undulations. Therefore, we conclude that the cholesterol-induced ripple-to-LO phase transition enhances the vertical order of the DPPC multilayer. While most of works on membrane structure and cholesterol effect have focused on the physical properties of lipid membrane in lateral direction, this paper suggested a new physical aspect of studying vertical structures of membrane.

We present a novel technique to measure diffusion coefficients of insoluble surfactant monolayers. We merge a surfactant-coated droplet with a fluorescently labeled planar monolayer. During the merging process, a monolayer on a droplet displaces the existing planar monolayer, leaving a dark area when viewed under a fluorescence microscope. We measure fractional intensities as the dyes recover, which allows diffusion coefficients to be computed. We validate this technique with the two most common phospholipid monolayers (DPPC and DOPC) and study the diffusion of their mixtures. The proposed technique has several advantages over the FRAP technique and is potentially capable of measuring the diffusion of any soluble/insoluble surfactant monolayers.