Special issue on “Ultrasound-assisted engineering of materials for biomedical uses”

[no abstract available

Mechanofluorescent Polymer Brush Surfaces that Spatially Resolve Surface Solvation

Polymer brushes, consisting of densely end-tethered polymers to a surface, can exhibit rapid and sharp conformational transitions due to specific stimuli, which offer intriguing possibilities for surface-based sensing of the stimuli. The key toward unlocking these possibilities is the development of methods to readily transduce signals from polymer conformational changes. Herein, we report on single-fluorophore integrated ultrathin (<40 nm) polymer brush surfaces that exhibit changing fluorescence properties based on polymer conformation. The basis of our methods is the change in occupied volume as the polymer brush undergoes a collapse transition, which enhances the effective concentration and aggregation of the integrated fluorophores, leading to a self-quenching of the fluorophores’ fluorescence and thereby reduced fluorescence lifetimes. By using fluorescence lifetime imaging microscopy, we reveal spatial details on polymer brush conformational transitions across complex interfaces, including at the air–water–solid interface and at the interface of immiscible liquids that solvate the surface. Furthermore, our method identifies the swelling of polymer brushes from outside of a direct droplet (i.e., the polymer phase with vapor above), which is controlled by humidity. These solvation-sensitive surfaces offer a strong potential for surface-based sensing of stimuli-induced phase transitions of polymer brushes with spatially resolved output in high resolution

An engineered nanosugar enables rapid and sustained glucose-responsive insulin delivery in diabetic mice

Glucose-responsive insulin-delivery platforms that are sensitive to dynamic glucose concentration fluctuations and provide both rapid and prolonged insulin release have great potential to control hyperglycemia and avoid hypoglycemia diabetes. Here, biodegradable and charge-switchable phytoglycogen nanoparticles capable of glucose-stimulated insulin release are engineered. The nanoparticles are "nanosugars" bearing glucose-sensitive phenylboronic acid groups and amine moieties that allow effective complexation with insulin (approximate to 95% loading capacity) to form nanocomplexes. A single subcutaneous injection of nanocomplexes shows a rapid and efficient response to a glucose challenge in two distinct diabetic mouse models, resulting in optimal blood glucose levels (below 200 mg dL(-1)) for up to 13 h. The morphology of the nanocomplexes is found to be key to controlling rapid and extended glucose-regulated insulin delivery in vivo. These studies reveal that the injected nanocomplexes enabled efficient insulin release in the mouse, with optimal bioavailability, pharmacokinetics, and safety profiles. These results highlight a promising strategy for the development of a glucose-responsive insulin delivery system based on a natural and biodegradable nanosugar

The structure of cardiac glycogen in healthy mice

Transmission electron micrographs of glycogen extracted from healthy mouse hearts reveal aggregate structures around 133 nm in diameter. These structures are similar to, but on average somewhat smaller than, the alpha-particles of glycogen found in mammalian liver. Like the larger liver glycogens, these new particles in cardiac tissue appear to be aggregates of beta-particles. Free beta-particles are also present in liver, and are the only type of particle seen in skeletal muscle. They have diameters from 20 to 50 nm. We discuss the number distributions of glycogen particle diameters and the implications for the structure-function relationship of glycogens in these tissues. We point out the possible implications for the study of glycogen storage diseases, and of non-insulin dependent diabetes mellitus. (C) 2012 Elsevier B.V. All rights reserved

Integrated FRET Polymers Spatially Reveal Micro‐ to Nanostructure and Irregularities in Electrospun Microfibers

Abstract A spatial view of macroscopic polymer material properties, in terms of nanostructure and irregularities, can help to better understand engineering processes such as when materials may fail. However, bridging the gap between the molecular‐scale arrangement of polymer chains and the spatially resolved macroscopic properties of a material poses numerous difficulties. Herein, an integrated messenger material that can report on the material micro‐ to nanostructure and its processes is introduced. It is based on polymer chains labeled with fluorescent dyes that feature Förster resonance energy transfer (FRET) dependent on chain conformation and concentration within a host polymer material. These FRET materials are integrated within electrospun polystyrene microfibers, and the FRET is analyzed by confocal laser scanning microscopy (CLSM). Importantly, the use of CLSM allows a spatial view of material nanostructure and irregularities within the microfibers, where changes in FRET are significant when differences in fiber geometries and regularities exist. Furthermore, changes in FRET observed in damaged regions of the fibers indicate changes in polymer conformation and/or concentration as the material changes during compression. The system promises high utility for applications where nano‐to‐macro communication is needed for a better understanding of material processes

Lactosylated Glycogen Nanoparticles for Targeting Prostate Cancer Cells

Glyconanoparticles that exhibit multivalent binding to lectins are desirable for molecular recognition and therapeutic applications. Herein we explore the use of glycogen nanoparticles as a biosourced glycoscaffold for engineering multivalent glyconanoparticles. Glycogen nanoparticles, a naturally occurring highly branched polymer of glucose, was functionalized with lactose, achieved through copper­(I)-catalyzed alkyne–azide cycloaddition chemistry, for targeted interaction with lectins ex situ and on prostate cancer cells. The lactosylated glycogen, which contains terminal β-galactoside moieties, is termed galacto-glycogen (GG), and is found to interact strongly with peanut agglutinin (PNA), a β-galactoside-specific lectin, as observed by optical waveguide lightmode spectroscopy, dynamic light scattering, and quartz crystal microbalance measurements. The GG nanoparticles exhibit multivalent binding to PNA with an affinity constant of 3.4 × 10⁵ M^–1, and the GG–PNA complex cannot be displaced by lactose, demonstrating the competitive binding of GG to the lectin. These GG nanoparticles were tested for association with prostate cancer cell membranes in vitro, where the particles exhibited a high affinity for the membrane, as observed from flow cytometry and confocal microscopy. This is inferred to result from specific extracellular galectin-1 targeting. Furthermore, the GG nanoparticles induce aggregation between prostate cancer cells. Our results highlight a strategy for engineering a biosourced polysaccharide with surface moieties that exhibit strong multivalent interactions with lectins, and targeted interaction with prostate cancer cells

Self-Assembly of Nano- to Macroscopic Metal–Phenolic Materials

The self-assembly of molecular building blocks into well-defined macroscopic materials is desirable for developing emergent functional materials. However, the self-assembly of molecules into macroscopic materials remains challenging, in part because of limitations in controlling the growth and robustness of the materials. Herein, we report the molecular self-assembly of nano- to macroscopic free-standing materials through the coordination of metals with natural phenolic molecules. Our method involves a simple and scalable solution-based template dipping process in precomplexed metal–phenolic solutions, enabling the fabrication of free-standing macroscopic materials of customized architectures (2D and 3D geometries), thickness (about 10 nm to 5 μm), and chemical composition (different metals and phenolic ligands). Our macroscopic free-standing materials can be physically folded and unfolded like origami, yet are selectively degradable. Furthermore, metal nanoparticles can be grown in the macroscopic free-standing films, indicating their potential for future applications in biotechnology and catalysis

Mechanofluorescent Polymer Brush Surfaces that Spatially Resolve Surface Solvation

Polymer brushes, consisting of densely end-tethered polymers to a surface, can exhibit rapid and sharp conformational transitions due to specific stimuli, which offer intriguing possibilities for surface-based sensing of the stimuli. The key toward unlocking these possibilities is the development of methods to readily transduce signals from polymer conformational changes. Herein, we report on single-fluorophore integrated ultrathin (<40 nm) polymer brush surfaces that exhibit changing fluorescence properties based on polymer conformation. The basis of our methods is the change in occupied volume as the polymer brush undergoes a collapse transition, which enhances the effective concentration and aggregation of the integrated fluorophores, leading to a self-quenching of the fluorophores’ fluorescence and thereby reduced fluorescence lifetimes. By using fluorescence lifetime imaging microscopy, we reveal spatial details on polymer brush conformational transitions across complex interfaces, including at the air–water–solid interface and at the interface of immiscible liquids that solvate the surface. Furthermore, our method identifies the swelling of polymer brushes from outside of a direct droplet (i.e., the polymer phase with vapor above), which is controlled by humidity. These solvation-sensitive surfaces offer a strong potential for surface-based sensing of stimuli-induced phase transitions of polymer brushes with spatially resolved output in high resolution

Mechanofluorescent Polymer Brush Surfaces that Spatially Resolve Surface Solvation

Polymer brushes, consisting of densely end-tethered polymers to a surface, can exhibit rapid and sharp conformational transitions due to specific stimuli, which offer intriguing possibilities for surface-based sensing of the stimuli. The key toward unlocking these possibilities is the development of methods to readily transduce signals from polymer conformational changes. Herein, we report on single-fluorophore integrated ultrathin (<40 nm) polymer brush surfaces that exhibit changing fluorescence properties based on polymer conformation. The basis of our methods is the change in occupied volume as the polymer brush undergoes a collapse transition, which enhances the effective concentration and aggregation of the integrated fluorophores, leading to a self-quenching of the fluorophores’ fluorescence and thereby reduced fluorescence lifetimes. By using fluorescence lifetime imaging microscopy, we reveal spatial details on polymer brush conformational transitions across complex interfaces, including at the air–water–solid interface and at the interface of immiscible liquids that solvate the surface. Furthermore, our method identifies the swelling of polymer brushes from outside of a direct droplet (i.e., the polymer phase with vapor above), which is controlled by humidity. These solvation-sensitive surfaces offer a strong potential for surface-based sensing of stimuli-induced phase transitions of polymer brushes with spatially resolved output in high resolution

Mapping the Three‐Dimensional Nanostructure of the Ionic Liquid–Solid Interface Using Atomic Force Microscopy and Molecular Dynamics Simulations

Abstract Ionic liquids (ILs) are a widely investigated class of solvents for scientific and industrial applications due to their desirable and “tunable” properties. The IL–solid interface is a complex entity, and despite intensive investigation, its true nature remains elusive. The understanding of the IL–solid interface has evolved over the last decade from a simple 1D double layer, to a 2D ordered interface, and finally a liquid‐specific, complex 3D ordered liquid interface. However, most studies depend solely on one technique, which often only examine one aspect of the interfacial nanostructure. Here, a holistic study of the protic IL–solid interface is presented, which provides a more detailed picture of IL interfacial solvation. The 3D nanostructure of the ethylammonium nitrate (EAN)–mica interface is investigated using a combination of 1D, 2D, and 3D amplitude modulated‐atomic force microscopy and molecular dynamics simulations. Importantly, it is found that the EAN–mica interface is more complex than previously reported, possessing surface‐adsorbed, near‐surface, surface‐normal, and lateral heterogeneity, which propagates at relatively large distances from the solid substrate. The work presented in this study meaningfully enhances the understanding of the IL–solid interface