Advanced Characterization of Soft Cosmetic Film Deposits with X-Ray Microtomography.

Cosmetic materials are complex soft compounds, including pigments, emulsifiers, film-formers, and fillers. After evaporation or absorption, they form a residue of inert ingredients called the cosmetic film. This thin layer, deposited on the skin, enhances complexion by smoothing texture, concealing imperfections, and evening skin tone.

Age-tailored artificial skin model for cosmetic film development.

Thin film deposition is essential in the cosmetic industry, where formulations such as foundations and concealers rely on uniform layer formation to conceal pores and texture irregularities for a natural and even appearance. However, variations in skin topography, influenced by factors such as aging, genetics, and environmental exposure, can significantly affect the behavior of these films. Aging, in particular, leads to increased skin roughness and wrinkles, creating challenges to achieve consistent cosmetic deposition in diverse age groups.

Excipient-free nanotransformation of hydrophilic macromolecules using aqueous counter collision for enhanced bioavailability.

The demand for sustainable, eco-friendly biopolymer transdermal delivery systems has increased owing to growing environmental awareness. In this study, we used aqueous counter collision (ACC), a nontoxic nanotransformation method, to convert high- and ultrahigh-molecular-weight hydrophilic macromolecules into their corresponding nanoparticles (NPs). Hyaluronic acid (HA) and crosslinked HA (CLHA) were chosen as the model compounds.

Regulation of Interfacial Anchoring Orientation of Anisotropic Nanodumbbells.

Nanoparticles exhibiting geometrical and chemical anisotropies hold promise for environmentally responsive materials with tunable mechanical properties. However, a comprehensive understanding of their interfacial behaviors remains elusive. In this paper, we control the interfacial anchoring orientation of polystyrene nanodumbbells by adjusting interparticle forces.

Tubulin Double Helix: Lateral and Longitudinal Curvature Changes of Tubulin Protofilament.

By virtue of their native structures, tubulin dimers are protein building blocks that are naturally preprogrammed to assemble into microtubules (MTs), which are cytoskeletal polymers. Here, polycation-directed (i.e.

Minireview - Microtubules and Tubulin Oligomers: Shape Transitions and Assembly by Intrinsically Disordered Protein Tau and Cationic Biomolecules.

In this minireview, which is part of a special issue in honor of Jacob N. Israelachvili's remarkable research career on intermolecular forces and interfacial science, we present studies of structures, phase behavior, and forces in reaction mixtures of microtubules (MTs) and tubulin oligomers with either intrinsically disordered protein (IDP) Tau, cationic vesicles, or the polyamine spermine (4+). Bare MTs consist of 13 protofilaments (PFs), on average, where each PF is made of a linear stack of αβ-tubulin dimers (i.

Comparison between 102k and 20k Poly(ethylene oxide) Depletants in Osmotic Pressure Measurements of Interfilament Forces in Cytoskeletal Systems.

The proliferation of successful, cell-free reconstitutions of cytoskeletal networks have prompted measurements of forces between network elements via induced osmotic pressure by the addition of depletants. Indeed, it was through osmotic pressurization that Tau, an intrinsically disordered protein found in neuronal axons, was recently discovered to mediate two distinct microtubule (MT) bundle states, one widely spaced and a second tightly packed, separated by an energy barrier due to polyelectrolyte repulsions between opposing Tau projection domains on neighboring MT surfaces. Here, we compare interfilament force measurements in Tau coated MT bundles using PEO20k (poly(ethylene oxide), = 20000), a commonly used inert depletant, and recently published measurements with PEO102k.

Synchrotron small-angle X-ray scattering and electron microscopy characterization of structures and forces in microtubule/Tau mixtures.

Tau, a neuronal protein known to bind to microtubules and thereby regulate microtubule dynamic instability, has been shown recently to not only undergo conformational transitions on the microtubule surface as a function of increasing microtubule coverage density (i.e., with increasing molar ratio of Tau to tubulin dimers) but also to mediate higher-order microtubule architectures, mimicking fascicles of microtubules found in the axon initial segment.

Paclitaxel suppresses Tau-mediated microtubule bundling in a concentration-dependent manner.

Background: Microtubules (MTs) are protein nanotubes comprised of straight protofilaments (PFs), head to tail assemblies of αβ-tubulin heterodimers. Previously, it was shown that Tau, a microtubule-associated protein (MAP) localized to neuronal axons, regulates the average number of PFs in microtubules with increasing inner radius observed for increasing Tau/tubulin-dimer molar ratio Φ at paclitaxel/tubulin-dimer molar ratio Λ=1/1.

Methods: We report a synchrotron SAXS and TEM study of the phase behavior of microtubules as a function of varying concentrations of paclitaxel (1/32≤Λ≤1/4) and Tau (human isoform 3RS, 0≤Φ≤1/2) at room temperature.

Tau mediates microtubule bundle architectures mimicking fascicles of microtubules found in the axon initial segment.

Tau, an intrinsically disordered protein confined to neuronal axons, binds to and regulates microtubule dynamics. Although there have been observations of string-like microtubule fascicles in the axon initial segment (AIS) and hexagonal bundles in neurite-like processes in non-neuronal cells overexpressing Tau, cell-free reconstitutions have not replicated either geometry. Here we map out the energy landscape of Tau-mediated, GTP-dependent 'active' microtubule bundles at 37 °C, as revealed by synchrotron SAXS and TEM.

The effect of multivalent cations and Tau on paclitaxel-stabilized microtubule assembly, disassembly, and structure.

In this review we describe recent studies directed at understanding the formation of novel nanoscale assemblies in biological materials systems. In particular, we focus on the effects of multivalent cations, and separately, of microtubule-associated protein (MAP) Tau, on microtubule (MT) ordering (bundling), MT disassembly, and MT structure. Counter-ion directed bundling of paclitaxel-stabilized MTs is a model electrostatic system, which parallels efforts to understand MT bundling by intrinsically disordered proteins (typically biological polyampholytes) expressed in neurons.

Surface charge effects on optical trapping of nanometer-sized lipid vesicles.

Optical trapping of nanometer-sized lipid vesicles has been challenging due to the low refractive index contrast of the thin lipid bilayer to the aqueous medium. Using an "optical bottle", a recently developed technique to measure interactions of nanoparticles trapped by an infrared laser, we report, for the first time, quantitative measurements of the trapping energy of charged lipid vesicles. We found that the trapping energy increases with the relative amount of anionic lipids (DOPG) to neutral lipids (DOPC) in vesicles.

Spontaneous unilamellar polymer vesicles in aqueous solution.

A unilamellar polymeric vesicle is a self-assembled structure of a block copolymer that forms a spherical single bilayer structure with a hydrophobic interlayer and a hydrophilic surface. Due to their enhanced colloidal stability and mechanical property, controllable surface functionality, or tunable membrane thickness, polymeric vesicles are useful in nano and bio-science, providing potential applications as nanosized carriers for catalysts, drugs, and enzymes. For fabrication of a unilamellar vesicle, however, preparative procedures with a few steps are inherently required.

Transformation of taxol-stabilized microtubules into inverted tubulin tubules triggered by a tubulin conformation switch.

Bundles of taxol-stabilized microtubules (MTs)--hollow tubules comprised of assembled αβ-tubulin heterodimers--spontaneously assemble above a critical concentration of tetravalent spermine and are stable over long times at room temperature. Here we report that at concentrations of spermine several-fold higher the MT bundles (B(MT)) quickly become unstable and undergo a shape transformation to bundles of inverted tubulin tubules (B(ITT)), the outside surface of which corresponds to the inner surface of the B(MT) tubules. Using transmission electron microscopy and synchrotron small-angle X-ray scattering, we quantitatively determined both the nature of the B(MT)-to-B(ITT) transformation pathway, which results from a spermine-triggered conformation switch from straight to curved in the constituent taxol-stabilized tubulin oligomers, and the structure of the B(ITT) phase, which is formed of tubules of helical tubulin oligomers.

Simple super-resolution live-cell imaging based on diffusion-assisted Förster resonance energy transfer.

Despite the recent development of several super-resolution fluorescence microscopic techniques, there are still few techniques that can be readily employed in conventional imaging systems. We present a very simple, rapid, general and cost-efficient super-resolution imaging method, which can be directly employed in a simple fluorescent imaging system with general fluorophores. Based on diffusion-assisted Förster resonance energy transfer (FRET), fluorescent donor molecules that label specific target structures can be stochastically quenched by diffusing acceptor molecules, thereby temporally separating otherwise spatially overlapped fluorescence signals and allowing super-resolution imaging.

Ion specific effects in bundling and depolymerization of taxol-stabilized microtubules.

Microtubules (MTs) are nanometer scale hollow cylindrical biological polyelectrolytes. They are assembled from alpha/beta-tubulin dimers, which stack to form protofilaments (PFs) with lateral interactions between PFs resulting in the curved MT. In cells, MTs and their assemblies are critical components in a range of functions from providing tracks for the transport of cargo to forming the spindle structure during mitosis.