Oil-in-Water-in-Oil Multinanoemulsions for Templating Complex Nanoparticles

Bio-Based Multicompartment Photonic Pigments: Unlocking Non-Iridescent Pure RGB Structural Colors for Versatile Chromatic Engineering

Non-iridescent photonic glass pigments of block copolymers show great potential for sustainable structural coloration. However, the ability to create accurate RGB color mixtures for real-world applications is limited by the prevalent use of non-degradable, fossil oil-derived components and the difficulty in achieving pure red hues. This work presents an alternative strategy for achieving more sustainable structural coloration by fabricating composite photonic pigments through controlled self-assembly of water, vegetable oil, and biodegradable bottlebrush block copolymers (BBCPs) in a complex emulsion system. The obtained photonic balls feature unprecedented multicompartment structures characterized by a short-range ordered assembly of water nanodroplets stabilized by the BBCPs, along with oil droplets stabilized by these nanodroplets, which substantially enhances resistance to Ostwald ripening. Furthermore, a new structural model is introduced to eliminate disordered scattering, successfully creating a pure red structural color and overcoming a long-standing limitation in versatile chromatic engineering.

A Close Look at Molecular Self-Assembly with the Transmission Electron Microscope

Molecular self-assembly is pervasive in the formation of living and synthetic materials. Knowledge gained from research into the principles of molecular self-assembly drives innovation in the biological, chemical, and materials sciences. Self-assembly processes span a wide range of temporal and spatial domains and are often unintuitive and complex. Studying such complex processes requires an arsenal of analytical and computational tools. Within this arsenal, the transmission electron microscope stands out for its unique ability to visualize and quantify self-assembly structures and processes. This review describes the contribution that the transmission electron microscope has made to the field of molecular self-assembly. An emphasis is placed on which TEM methods are applicable to different structures and processes and how TEM can be used in combination with other experimental or computational methods. Finally, we provide an outlook on the current challenges to, and opportunities for, increasing the impact that the transmission electron microscope can have on molecular self-assembly.

Improved delivery system for celastrol-loaded magnetic Fe3O4/α-Fe2O3 heterogeneous nanorods: HIF-1α-related apoptotic effects on SMMC-7721 cell

Fe₃O₄/α-Fe₂O₃ heterogeneous nanorods were prepared by a rapid combustion method with α-FeOOH nanorods as precursors. Fe₃O₄/α-Fe₂O₃ heterogeneous nanorods with a saturation magnetization of 33.2 emu·g^-1 were obtained using 30 mL of absolute ethanol at a calcination temperature of 300 °C. Their average length was around 140 nm, and average diameter was about 20 nm. To improve the dispersion characteristics of the Fe₃O₄/α-Fe₂O₃ heterogeneous nanorods in aqueous solution, citric acid and PEG were applied to modify the nanorod surface via the Mitsunobu reaction. The results showed that the hydrodynamic size range of Fe₃O₄/α-Fe₂O₃/CA-PEG-celastrol was 250-500 nm, the surface potential was -15 mV, and the saturation magnetization was approximately 23 emu·g^-1. The drug loading capacity of Fe₃O₄/α-Fe₂O₃/CA-PEG was larger than the non-PEG modified version. Fe₃O₄/α-Fe₂O₃/CA-PEG-celastrol had slow-release characteristics and was sensitive to changes in pH. Application of a magnetic field significantly promoted the inhibition of SMMC-7721 human liver cancer cell growth after treatment with Fe₃O₄/α-Fe₂O₃/CA-PEG-celastrol. Celastrol and Fe₃O₄/α-Fe₂O₃/CA-PEG-celastrol increased the production of reactive oxygen species in SMMC-7721 cells and promoted apoptosis and apoptosis-related proteins (p53, Bax, Bcl-2) were also changed. In addition, the expression of hypoxia-inducible factor 1α (HIF-1α) was enhanced. We may conclude that celastrol-loaded magnetic Fe₃O₄/α-Fe₂O₃ heterogeneous nanorods may be applied in the chemotherapy of human cancer with good biocompatibility and delivery.

Nanostructures, Faceting, and Splitting in Nanoliter to Yoctoliter Liquid Droplets

Contrary to everyday experience, where all liquid droplets assume rounded, near-spherical shapes, the temperature-tuning of liquid droplets to faceted polyhedral shapes and to spontaneous splitting has been recently demonstrated in oil-in-water emulsions. However, the elucidation of the mechanism driving these surprising effects, as well as their many potential applications, ranging from faceted nanoparticle synthesis through new industrial emulsification routes to controlled-release drug delivery within the human body, have been severely hampered by the micron-scale resolution of the light microscopy employed to date in all in situ studies. Thus, the thickness of the interfacially frozen crystalline monolayer, suggested to drive these effects, could not be directly measured, and the low limit on the droplet size still showing these effects remained unknown. In this study, we employ a combination of super-resolution stimulated emission depletion microscopy, cryogenic transmission and freeze-fracture electron microscopy, to study these effects well into the nanometer length scale. We demonstrate the occurrence of the faceting transition in droplets spanning an incredible 12 decades in volume from nanoliters to yoctoliters and directly visualize the interfacially frozen, few nanometer thick, crystalline monolayer suggested to drive these effects. Furthermore, our measurements allow placing an upper-limit estimate on the two-dimensional Young modulus of the interfacial nanometer-thick surface crystal in the smallest droplets, providing insights into the virtually unexplored domain of nanoelasticity.

Toward the Formulation of Stable Micro and Nano Double Emulsions through a Silica Coating on Internal Water Droplets

Delivery systems able to coencapsulate both hydrophilic and hydrophobic species are of great interest in both fundamental research and industrial applications. Water-in-oil-in-water (w₁/O/W₂) emulsions are interesting systems for this purpose, but they suffer from limited stability. In this study, we propose an innovative approach to stabilize double emulsions by the synthesis of a silica membrane at the water/oil interface of the primary emulsion (i.e., inner w₁/O emulsion). This approach allows the formulation of stable double emulsions through a two-step process, enabling high encapsulation efficiencies of model hydrophilic dyes encapsulated in the internal droplets. This approach also decreases the scale of the double droplets up to the nanoscale, which is not possible without silica stabilization. Different formulation and processing parameters were explored in order to optimize the methodology. Physicochemical characterization was performed by dynamic light scattering, encapsulation efficiency measurements, release profiles, and optical and transmission electron microscopies.

Cross-talk between emulsion drops: how are hydrophilic reagents transported across oil phases?

Emulsion drops are frequently used as vessels, for example, to conduct biochemical reactions in small volumes or to perform screening assays at high throughputs while consuming minimal sample volumes. These applications typically require drops that do not allow exchange of reagents such that no cross-contamination occurs. Unfortunately, in many cases, reagents are exchanged between emulsion drops even if they have a low solubility in the surrounding phase, resulting in cross-contaminations. Here, we investigate the mechanism by which hydrophilic reagents are transported across an oil phase using water-oil-water double emulsion drops as a model system. Remarkably, even large objects, including 11 000 base pair double-stranded circular DNA are transported across oil shells. Importantly, this reagent transport, that is to a large extent caused by aqueous drops that spontaneously form at the water-oil interface, is not limited to double emulsions but also occurs between single emulsion drops. We demonstrate that the uncontrolled reagent transport can be decreased by at least an order of magnitude if appropriate surfactants that lower the interfacial tension only moderately are employed or if the shell thickness of double emulsions is decreased to a few hundreds of nanometers.

Controlling Complex Nanoemulsion Morphology Using Asymmetric Cosurfactants for the Preparation of Polymer Nanocapsules

Complex nanoemulsions, comprising multiphase nanoscale droplets, hold considerable potential advantages as vehicles for encapsulation and delivery as well as templates for nanoparticle synthesis. Although methods exist to controllably produce complex emulsions on the microscale, very few methods exist to produce them on the nanoscale. Here, we examine a recently developed method involving a combination of high-energy emulsification with conventional cosurfactants to produce oil-water-oil (O/W/O) complex nanoemulsions. Specifically, we study in detail how the composition of conventional ethoxylated cosurfactants Span80 and Tween20 influences the morphology and structure of the resulting complex nanoemulsions in the water-cyclohexane system. Using a combination of small-angle neutron scattering and cryo-electron microscopy, we find that the cosurfactant composition controls the generation of complex droplet morphologies including core-shell and multicore-shell O/W/O nanodroplets, resulting in an effective state diagram for the selection of nanoemulsion morphology. Additionally, the cosurfactant composition can be used to control the thickness of the water shell contained within the complex nanodroplets. We hypothesize that this degree of control, despite the highly nonequilibrium nature of the nanoemulsions, is ultimately determined by a competition between the opposing spontaneous curvature of the two cosurfactants, which strongly influences the interfacial curvature of the nanodroplets as a result of their ultralow interfacial tension. This is supported by a correlation between cosurfactant compositions that produces complex nanoemulsions and those that produce homogeneous mixed micelles in equilibrium surfactant-cyclohexane solutions. Ultimately, we show that the formation of complex O/W/O nanoemulsions is weakly perturbed upon the addition of hydrophilic polymer precursors, facilitating their use as templates for the formation of polymer nanocapsules.

Synthesis of Oil-Laden Poly(ethylene glycol) Diacrylate Hydrogel Nanocapsules from Double Nanoemulsions

Multiple emulsions have received great interest due to their ability to be used as templates for the production of multicompartment particles for a variety of applications. However, scaling these complex droplets to nanoscale dimensions has been a challenge due to limitations on their fabrication methods. Here, we report the development of oil-in-water-in-oil (O₁/W/O₂) double nanoemulsions via a two-step high-energy method and their use as templates for complex nanogels comprised of inner oil droplets encapsulated within a hydrogel matrix. Using a combination of characterization methods, we determine how the properties of the nanogels are controlled by the size, stability, internal morphology, and chemical composition of the nanoemulsion templates from which they are formed. This allows for identification of compositional and emulsification parameters that can be used to optimize the size and oil encapsulation efficiency of the nanogels. Our templating method produces oil-laden nanogels with high oil encapsulation efficiencies and average diameters of 200-300 nm. In addition, we demonstrate the versatility of the system by varying the types of inner oil, the hydrogel chemistry, the amount of inner oil, and the hydrogel network cross-link density. These nontoxic oil-laden nanogels have potential applications in food, pharmaceutical, and cosmetic formulations.

Marker patterning: a spatially resolved method for tuning the wettability of PDMS

This article presents a marker patterning method where a permanent ink is used as a masking layer. During plasma oxidation, the PDMS surfaces are protected leading to a simple and easy wettability patterning.