Paulo A. L. Fernandes

Self-Assembly Made Durable: Water-Repellent Materials Formed by Cross-Linking Fullerene Derivatives

Fullerene flakes: A diacetylene-functionalized fullerene derivative self-organizes into flakelike microparticles (see picture). Both the diacetylene and C(60) moieties can be effectively cross-linked, which leads to supramolecular materials with remarkable resistivity to solvent, heat, and mechanical stress. Moreover, the surface of the cross-linked flakelike objects is highly durable and water-repellent.

Superstructures and superhydrophobic property in hierarchical organized architectures of fullerenes bearing long alkyl tails

Formation of hierarchically self-organized architectures in organic media and their non-wetting surface features of a series of fullerene-C60 derivatives bearing different numbers of long hydrocarbon chains (1–3) and semiperfluoro-alkyl tails (4) are investigated by means of a variety of techniques, including X-ray diffraction, differential scanning calorimetry, as well as spectroscopic and microscopic methods. All derivatives self-assemble into a bilayer arrangement with their fundamental structural subunit and lamellar distance ranging from 2.88 to 4.85 nm depending on the substituents. The hydrocarbon-C60 derivatives (1–3) provide well-defined three-dimensional microparticles having a nanoflaked outer surface morphology or microparticles composed of many plate-like units in 1,4-dioxane solution, both architectures enhancing the surface water-repellency. The microparticles with a nanoflaked-outer surface obtained from a C60 derivative with semiperfluoro-alkyl chains (4) in a diethoxyethane solution exhibit a surface water-repellency comparable to objects formed from the hydrocarbon-hybrid C60 derivatives. Taking into account the moderate hydrophobic nature of the C60 surface compared to the high hydrophobicity of the hydro- or fluoro-carbons, these results suggest that the C60 moieties are exposed to the outer surface in the supramolecular objects formed in polar solvent conditions and define their non-wetting properties.

Electron Transport and Electrochemistry of Mesomorphic Fullerenes with Long-Range Ordered Lamellae

Fullerenes, C60, modified with long alkyl chains form long-range ordered lamellar mesophases permitting a high C60 content. The mesomorphic fullerenes feature reversible electrochemistry and a comparably high electron carrier mobility making them attractive components for fullerene-based soft materials.

Mechanobiology: Correlation Between Mechanical Stability of Microcapsules Studied by AFM and Impact of Cell-Induced Stresses

Intracellular delivery of proteins, peptides, and other biomolecules [ 1,2 ] by microcapsules is of growing importance not only in applied biomedical research, but also in fundamental cell biology. [ 3 ] Although microcapsules [ 2 , 4–8 ] have the potential to reveal information about mechanobiology and cell mechanics, previous investigations of their mechanical properties have only been used for designing delivery vehicles with improved mechanical strength. [ 9–11 ] Accordingly, the force-deformation behavior of polyelectrolyte capsules has been intensively studied. [ 12–14 ] Several parameters such as temperature, number of layers, and encapsulated contents infl uence the mechanical properties of the capsules. It has been shown that incubation at high temperatures results in drastic changes of the morphology of polymeric capsules accompanied by increasing stiffness. [ 7 , 15–17 ] Furthermore, delivery and release, including pulsed release, [ 18 ] remotely controllable release, [ 1 ]

Quantitative Analysis of Scanning Transmission X-ray Microscopy Images of Gas-Filled PVA-Based Microballoons

We report on the quantitative analysis of scanning transmission X-ray microscopy (STXM) images of gas-filled, poly(vinyl alcohol) (PVA)-based microballoons (MB) in a water environment. A model for the transmitted intensity is proposed on the basis of a perfect spherical shell stabilizing the microballoon. An extension of this model to take into account the deformation of the MBs is also presented. Taking into consideration a density gradient of the shell and the STXM resolution, we were able to explain very precisely two types of experimental STXM profiles observed on gas-filled MBs. This enables the detailed characterization of MB properties such as radius and wall thickness and the determination of their wall density with unprecedented high resolution.

Elastic nanomembrane metrology at fluid–fluid interfaces using axisymmetric drop shape analysis with anisotropic surface tensions: deviations from Young–Laplace equation

Fluid–fluid interfaces are an attractive template for engineering nanomembranes via self-assembly. Although an increasing number of investigations of the local (∼10−10 m2) surface mechanics of a variety of materials, detailed studies of mechanical behavior and the constitutive parameters over larger areas (>10−6 m2) are relatively scarce. This is because of the limitations of quantitative experimental techniques due to the asymmetry of the length scales involved. Here, we discuss fabrication and characterization of a polysaccharide and polyamino acid-based nanomembrane having a thickness of approximately 200 nm and surface area of 25 × 10−6 m2 and present mechanical data for hyaluronic acid–poly-L-lysine nanomembranes using a modified pendant drop as a test frame. Covalent cross-linking of these molecules at fluid–fluid interfaces leads to the formation of supramolecular networks which confer properties such as mechanical rigidity that are outside of the description provided by equilibrium surface thermodynamics. A theoretical framework for data interpretation of purely elasticity interface systems is provided, and experimental signatures of anisotropic tension distributions on axisymmetric drop and bubble shapes are identified. By taking advantage of the mechanical transparency of the fluid–fluid interface, this method provides a means of accessing mechanical properties of ultrathin materials independent of artifacts, such as adhesion, introduced by a solid substrate.

Mechanism and kinetics of controlled drug release by temperature stimuli responsive protein nanocontainers

A new container composed of an inner gel core and an outer protein shell has been prepared by sonicating oil in an aqueous protein solution. Hydrophobic drugs can be loaded into the containers and released by thermal trigger. In this paper, we attempted to discover the release mechanism of the protein containers by means of individual carrier characterization and release data analysis. The mechanical and thermal properties of the containers were first investigated and associated with the release mechanism. At room temperature, the protein container was robust and elastic. Plastic deformation did not happen until the container was compressed above 70% deformation. Stirring the protein containers in a buffer solution could only release 15% of the encapsulated drug. The drug release was mainly from diffusion of the drug located in the outer layer of the gel core. When the temperature increases above the gel transition temperature, the gel core was liquefied and the protein container shrunk, which resulted in a squeezing-controlled quick release. Annealing the protein container at the increased temperature led to a complete release of encapsulated drug via a diffusion-controlled release mechanism.

Novel Characterization Techniques of Microballoons

With the development of innovative, more complex and ever smaller micro-systems there is a growing need to develop novel characterization techniques that can provide more detailed information about their properties. Fundamental aspects of these techniques are high resolution, measurements in liquid environment, force detection and chemical sensitivity on individual microballoons. In this chapter three characterization techniques based on AFM, RICM and STXM are presented and illustrated with some basic results obtained on PVA-based microballoons.