Biomedical subjects

Raffaele Mezzenga

Publications and source records attributed to Raffaele Mezzenga.

9 recordsLinked to original sources

PubMed2006

Liquid-crystalline polymers from cationic dendronized polymer-anionic lipid complexes.

The use of cationic dendronized polymers as a polyelectrolytic system for templating thermotropic liquid-crystalline phases (LC) via complexation and self-assembly with counter-charged ionic lipids is described. The topology of the LC phases resulting from the self-assembly process, their lattice parameter, and the interpenetration of lipid chains is discussed via birefringency analysis and small-angle X-ray scattering. Depending on the generation of the dendronized polymer and the length of the alkyl chains, amorphous, lamellar, and columnar tetragonal phases are observed. A structural model is proposed which accounts for the systematic variations of alkyl chain length as well as polymer generation. Owing to the reversible nature of the ionic complexation, this process proves high relevance for nanoporous channels, biomimetic, transport, and nanotemplating applications.

Journal Article↗

PubMed2006

Emulsion-templated fully reversible protein-in-oil gels.

We have developed a new method allowing us to transform low-viscous apolar fluids into elastic solids with a shear elastic modulus of the order of 10(3)-10(5) Pa. The elasticity of the elastic solid is provided by a percolating 3D network of proteins, which are originally adsorbed at the interface of an oil-in-water emulsion template. By cross-linking the protein films at the interface and upon removal of water, the template is driven into a structure resembling a dry foam where the protein interfaces constitute the walls of the foam and the air is replaced by oil confined within polyhedral, closely packed droplets. Depending on the density of the protein network, the final material consists of chemically unmodified oil in a proportion of 95 to 99.9%. The physical properties of the elastic solid obtained can be tuned by changing either the average diameter size of the emulsion template or the cross-linking process of the protein film. However, the original low-viscosity emulsion can be restored by simply rehydrating the solidified fluid. Therefore, the present procedure offers an appealing strategy to build up solid properties for hydrophobic liquids while preserving the low viscosity and ease of manufacturing.

Emulsions↗

PubMed2005

Cross linking and rheological characterization of adsorbed protein layers at the oil-water interface.

The dilatational rheological properties of cross-linked protein layers adsorbed at the oil-water interface were investigated with help of a modified drop tensiometer allowing successive replacements of the external phase. This setup enables one to perform cross-linking reactions at the interface only, that is, without any contact between the cross-linking agent and protein molecules in solution, under continuous monitoring of the interfacial tension. The mechanical properties of the resulting interface were investigated with dilatational large strain experiments. Measured rheological properties were related to the expected stability of an emulsion against disproportionation by considering the ratio of the interfacial elasticity to the interfacial tension. In an attempt to increase this ratio to improve the resistance against disproportionation, experiments were performed with densified protein layers obtained via reduction of the droplet area prior to cross linking. To highlight the influence of the protein morphology on the dilatational rheological properties of the cross-linked adsorbed layers, experiments were performed with random coil (beta-casein) as well as globular (beta-lactoglobulin) proteins. Glutaraldehyde was used as a cross-linking agent. Experiments were performed at 55 degrees C and pH 7.0 in 20 mM imidazole buffer for later comparison with enzymatically cross-linked adsorbed protein layers. The present work demonstrated substantial qualitative and quantitative differences in the interfacial rheological properties of cross-linked random coil and globular proteins.

Adsorption↗

PubMed2005

Polysaccharide-induced order-to-order transitions in lyotropic liquid crystals.

We report on the order-to-order transitions of lyotropic liquid crystals formed by self-assembled monogylcerides and water in the presence of polysaccharides of various molecular weights. The phase diagram of monoglyceride-water-polysaccharide systems, their morphology, and the topology of liquid crystalline structures were determined by combining optical cross-polarization, oscillatory shear rheometry, and small-angle X-ray scattering. The presence of hydrophilic mono-, oligo-, and polysaccharides in the water domains of liquid crystalline phases resulted in a general decrease of the cubic-to-hexagonal transition temperature. Provided that the sugar could fit within the water channels, the decrease was observed to be dependent on the polysaccharide concentration but independent of its molecular weight. For isotropic bicontinuous cubic phases, monomeric sugars such as glucose were reported to shrink the lattice parameter of the structure without inducing phase transitions. However, when a polymeric form of glucose was used, such as dextran, transitions from the gyroidal Ia3d cubic phase to double diamond Pn3m cubic phases were observed at well-defined molecular weights of polysaccharide. These results were interpreted in terms of size exclusions of polymer sugars by the water domains of the liquid crystal phases as well as the different topologies of water channels. Molecular dynamics simulations of polysaccharides in the water environment were performed to support these findings.

Crystallization↗

PubMed2005

Shear rheology of lyotropic liquid crystals: a case study.

We have investigated the rheological properties of lyotropic liquid crystals (LCs) formed by self-assembled neutral lipids and water, their relationship with the topology of the structure, and their dependence on temperature and water content. The phase diagram of a representative monoglyceride-water system, determined by combining cross-polarized optical microscopy and small-angle X-ray scattering (SAXS), included four structures: lamellar, hexagonal, gyroid bicontinuous cubic (Ia3d), and double diamond bicontinuous cubic (Pn3m), as well as several regions of two-phase coexistence of some of the above structures. Rheology in the linear viscoelastic regime revealed a specific signature that was characteristic of the topology of each structure considered. The order-order transitions lamellar-to-cubic and cubic-to-hexagonal, as well as the order-disorder transitions from each LC to an isotropic fluid, were easily identified by following the development of the storage and loss moduli, G' and G'', respectively. The viscoelastic properties of both bicontinuous cubic phases were shown to be strongly frequency-dependent, following a pseudo-Maxwell behavior, with multiple relaxation times. Cubic-to-cubic transitions were nicely captured by scaling the longest relaxation time, tau, with either temperature or water volume fraction. Therefore, the set of the three main parameters used to establish the rheological behavior of the structure, that is, G', G'', and relaxation time, tau, constitutes a consistent ensemble to identify the structures of the liquid crystal. Finally, relaxation spectra, extracted for all liquid crystalline phases, allowed an additional possible identification criterion of the various structures considered.

Journal Article↗

PubMed2005

Understanding foods as soft materials.

Foods make up some of the most complex examples of soft condensed matter (SCM) with which we interact daily. Their complexity arises from several factors: the intricacy of components, the different aggregation states in which foods are encountered, and the multitude of relevant characteristic time and length scales. Because foodstuffs are governed by the rules of SCM physics but with all the complications related to real systems, the experimental and theoretical approaches of SCM physics have deepened our comprehension of their nature and behaviour, but many questions remain. In this review we discuss the current understanding of food science, by considering established SCM methods as well as emerging techniques and theoretical approaches. With their complexity, heterogeneity and multitude of states, foods provide SCM physics with a challenge of remarkable importance.

Biocompatible Materials↗

PubMed2004

Design of double emulsions by osmotic pressure tailoring.

A method was developed allowing in situ adjustment of water-in-oil-in-water double emulsion (W/O/W) morphologies by tailoring the osmotic pressure of the water phases. The control of internal droplet size is achieved by altering the chemical potential of the external and internal water phases by dissolving neutral linear polysaccharides of suitable molecular weights. As a consequence of the different chemical potentials in the two aqueous phases, transport of water takes place modifying the initial morphology of the double emulsion. Self-diffusion 1H nuclear magnetic resonance (1H NMR) was used to assess transport mechanisms of water in oil, while a numerical model was developed to predict the swelling/shrinking behavior of W/O/W double emulsions. The model was based on a two-step procedure in which the equilibrium size of a single internal water droplet was first predicted and then the results of the single droplet were extended to the entire double emulsion. The prediction of the equilibrium size of an internal droplet was derived by the equalization of the Laplace pressure with the osmotic pressure difference of the two aqueous phases, as modeled by mean-field theory. The double emulsion equilibrium morphologies were then predicted by upscaling the results of a single drop to the droplet size distribution of the internal W/O emulsion. Good agreement was found between the theoretical predictions and the measurement of double emulsion droplet size distribution. Therefore, the present model constitutes a valuable tool for in situ control of double emulsion morphology and enables new possible applications of these colloidal systems.

Colloids↗

PubMed2003

Templating organic semiconductors via self-assembly of polymer colloids.

A route for producing semiconducting polymer blends is demonstrated in which a doped pi-conjugated polymer is forced into a three-dimensionally continuous minor phase by the self-assembly of colloidal particles and block copolymers. The resulting cellular morphology can be viewed as a high-internal phase polymeric emulsion. Compared with traditional blending procedures, this process reduces the percolation threshold for electrical conductivity by a factor of 10, increases the conductivity by several orders of magnitude, and simultaneously improves thermal stability. Following this route, new applications can be envisaged for semiconducting polymer blends that require only minimal concentrations of doped pi-conjugated polymer.

Journal Article↗

PubMed2002

Enthalpic, entropic, and square gradient contributions to the surface energetics of amine-cured epoxy systems.

The evolution of surface tension during polymerization of three amine-cured epoxy systems was investigated. Due to the chemical reaction of the epoxy groups with primary and secondary amines, the energetic status of an epoxy-amine system increased during polymerization. At the same time, the polymerization process induced entropic variations, also contributing to the evolution of surface energetics. A simple relation expressing the surface tension as a function of the bulk energy, the entropy of the system, and the square gradient of the polymer density was derived. The bulk and surface energetics were expressed in terms of solubility parameter and surface tension, respectively. The former was predicted using the Van Krevelen group contribution method, while the latter was directly measured using the Wilhelmy wetting method. Results indicated that, in all the three epoxy-amine systems under investigation, a unique relationship combining the surface tension, the bulk energy, the entropy, and the density square gradient of the system could be used. On the basis of the present study, and taking into account all contributory factors, it was concluded that the enthalpy component to the surface energetics is the dominant contribution.

Journal Article↗