Structure and Nanomechanics of Dry and Hydrated Intermediate Filament Films and Fibers Produced from Hagfish Slime Fibers.

Intermediate filaments (IFs) are known for their extensibility, flexibility, toughness, and their ability to hydrate. Using keratin-like IFs obtained from slime fibers from the invertebrate Atlantic hagfish ( Myxine glutinosa), films were produced by drop-casting and coagulation on the surface of a MgCl2 buffer. Drop-casting produced self-supporting, smooth, and dense films rich in ß-sheets (61%), whereas coagulation formed thin, porous films with a nanorough surface and a lower ß-sheet content (51%). The films hydrated and swelled immediately when immersed in water and did not dissolve. X-ray diffraction showed that the ß-crystallites remained stable upon hydration, that swelling presumably happens in the amorphous C-terminal tail-domains of the IFs, and that high salt conditions caused a denser network mesh size, suggesting polyelectrolyte behavior. Hydration resulted in a roughly 1000-fold decrease in apparent Young's modulus from 109 to 106 Pa as revealed by atomic force microscopy nanoindentation. Nanoindentation-based power-law rheology and stress-relaxation measurements indicated viscoelasticity and a soft-solid hydrogel character for hydrated films, where roughly 80% of energy is elastically stored and 20% is dissipated. By pulling coagulation films from the buffer interface, macroscopic fibers with highly aligned IF ß-crystals similar to natural hagfish fibers were produced. We propose that viscoelasticity and strong hydrogen bonding interactions with the buffer interface are crucial for the production of such long biomimetic fibers with aligned ß-sheets. This study demonstrates that hagfish fiber IFs can be reconstituted into functional biomimetic materials that are stiff when dry and retain the ability to hydrate to become soft and viscoelastic when in water.

Lipid self-assembled structures for reactivity control in food.

Lipid self-assembled structures (SASs) have recently gained considerable interest for their potential applications, especially for sustained nutrient release and protein crystallization. An additional property, which is underexploited, is their ability to control chemical reactions in food products. Here, we concentrate on SASs formed by phospholipids (PLs) and monoglycerides (MGs), those compounds being the most natural surfactants and therefore, the best compatible with food products, in view of providing new functionalities through the formation of SASs. In this work, the phase behaviour of these amphiphiles when mixed with oil and water is described and compared. Subsequently, we address the influence of these structures to the oxidation and Maillard-type reactions. Finally, we show that SASs formed by MGs can strongly increase the yield of key aroma impact compounds generated by Maillard-type reactions when compared with the reaction performed in aqueous precursor solutions. Various SASs are compared. In particular, addition of oil to a reversed bicontinuous structure formed by MG leads to a reversed microemulsion, which, considering its low viscosity, is particularly suitable for food products and act as a very efficient reactor system. The influence of oil and precursors on phase behaviour is discussed and related to the efficiency of the Maillard reactions.This article is part of the themed issue 'Soft interfacial materials: from fundamentals to formulation'.

Mechanically Enhanced Liquid Interfaces at Human Body Temperature Using Thermosensitive Methylated Nanocrystalline Cellulose.

The mechanical performance of materials at oil/water interfaces after consumption is a key factor affecting hydrophobic drug release. In this study, we methylated the surface of nanocrystalline cellulose (NCC) by mercerization and dimethyl sulfate exposure to produce thermosensitive biopolymers. These methylated NCC (metNCC) were used to investigate interfacial thermogelation at air/water and medium-chain triglyceride (MCT)/water interfaces at body temperature. In contrast to bulk fluid dynamics, elastic layers were formed at room temperature, and elasticity increased significantly at body temperature, which was measured by interfacial shear and dilatational rheology in situ. This unique phenomenon depends on solvent quality, temperature, and polymer concentration at interfaces. Thus, by adjusting the degree of hydrophobicity of metNCC, the interfacial elasticity and thermogelation of the interfaces could be varied. In general, these new materials (metNCC) formed more brittle interfacial layers compared to commercial methylcellulose (MC A15). Thermogelation of methylcellulose promotes attractive intermolecular forces, which were reflected in a change in self-assembly of metNCC at the interface. As a consequence, layer thickness and density increased as a function of temperature. These effects were measured by atomic force microscopy (AFM) images of the displaced interface and confirmed by neutron reflection. The substantial structural and mechanical change of methylcellulose interfaces at body temperature represents a controllable encapsulation parameter allowing optimization of lipid-based drug formulations.

Inorganic-organic elastomer nanocomposites from integrated ellipsoidal silica-coated hematite nanoparticles as crosslinking agents.

We report on the synthesis of nanocomposites with integrated ellipsoidal silica-coated hematite (SCH) spindle type nanoparticles which can act as crosslinking agents within an elastomeric matrix. Influence of the surface chemistry of the hematite, leading either to dispersed particles or crosslinked particles to the elastomer matrix, was studied via swelling, scattering and microscopy experiments. It appeared that without surface modification the SCH particles aggregate and act as defects whereas the surface modified SCH particles increase the crosslinking density and thus reduce the swelling properties of the nanocomposite in good solvent conditions. For the first time, inorganic SCH particles can be easily dispersed into a polymer network avoiding aggregation and enhancing the properties of the resulting inorganic-organic elastomer nanocomposite (IOEN).

Self-assembly of rod-coil block copolymers from weakly to moderately segregated regimes.

We report on the self-assembly behaviour of two homologue series of rod-coil block copolymers in which, the rod, a pi -conjugated polymer, is maintained fixed in size and chemical structure, while the coil is allowed to vary both in molecular weight and chemical nature. This allows maintaining constant the liquid crystalline interactions, expressed by Maier-Saupe interactions, omega , while varying the tendency towards microphase separation, expressed by the product between the Flory-Huggins parameter and the total polymerization degree, chi N . Therefore, the systems presented here allow testing directly some of the theoretical predictions for the self-assembly of rod-coil block copolymers in a weakly segregated regime. The two rod-coil block copolymer systems investigated were poly(DEH-p-phenylenevinylene-b-styrene), whose self-assembly takes place in the very weakly segregated regime, and poly(DEH-p-phenylenevinylene-b-4vinylpyridine), for which the self-assembly behaviour occurs under increased tendency towards microphase separation, hereby referred to as moderately segregated regime. Experimental results for both systems are compared with predictions based on Landau expansion theories.

Surface Energetics Evolution during Processing of Epoxy Resins.

The surface energetics evolution throughout the entire curing process of two epoxy resins is predicted using a previously developed semiempirical relationship between surface tension and the solubility parameter. Evolution of the temperature and time of both the solubility parameter and density is investigated and used for this prediction, as is the concept of molar volume or mass of the interacting element. The theoretical prediction is compared with measured surface tensions. Experimental data are determined at different times during an isothermal curing process by the Wilhelmy wetting force method for surface tension with viscous drag corrections. Once corrections for viscous effects on measured surface tensions are made, very good agreement is found for the surface energetics evolution. Moreover, the total surface energies of solid cured epoxy resins, which cannot be directly measured, can be estimated with this prediction. Finally, this study provides a tool for further understanding the final adhesive properties of polymeric material considering the time evolution of surface energetics during processing. Copyright 2000 Academic Press.