A detailed understanding of the mechanistic principles which govern peptide and protein selfassembly is of considerable biomedical and biotechnological importance. Owing to the diversity of peptide and protein sequences which have been shown to aggregate into ordered structures, the ability to self-assemble is now recognized as an inherent feature of the polypeptide backbone. It is therefore of utmost importance to elucidate the rules governing the self-assembly process. De novo designed oligopeptides, based on sequences of alternating hydrophilic and hydrophobic residues and containing complementary charge distributions, have shown the potential to self-assemble into hydrogels rich in β-sheet secondary structure. Here we present and characterize the unexpected self-assembly and hydrogel formation of AK-16, an alanine-rich oligopeptide, whose sequence does not abide by typical rules which allow for peptide self-organization. AK-16 spontaneously forms soluble, thermodynamically unstable β-sheet-rich aggregates, which can be stabilized by salt addition to yield a self-supporting macroscopic hydrogel. The AK-16 hydrogel exhibits the ability to encapsulate and slowly release a model protein. This one-charge-type system represents a novel class of selfassembling oligopeptides, in which the initial conformational instability can be exploited to tune the viscosity and physicochemical properties of the resultant hydrogel. This study provides insight for the future de novo design of self-assembling oligopeptides.

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In this paper, we present the analyses of surface tension of surfactant-stabilized dispersions of carbon nanotubes. This method allows one to study interactions of carbon nanotubes with surfactants at different levels of nanotube loading when optical methods fall short in quantifying the level of nanotube separation. Sodium dodecyl sulfate was used as a stabilizing agent to uniformly disperse single-walled carbon nanotubes in an aqueous media. We show that surface tension is very sensitive to small changes of nanotube and surfactant concentrations. The experimental data suggest that, at moderate concentrations, surfactant displaces carbon nanotubes from the air-water interface and the nanotubes are mostly moved into the bulk of the liquid. By analyzing the surface tension as a function of surfactant concentration, we obtained the dependence of critical micelle concentration on nanotube loading. We then constructed the adsorption isotherm for dodecyl sulfate on carbon nanotubes and bundles of carbon nanotubes. The results of these experiments enabled us to extend the phase diagram of the produced dispersions to a broader range of surfactant and nanotube concentrations.

Wet-spun stimuli-responsive composite fi bers made of covalently crosslinked alginate with a high concentration of single-walled carbon nanotubes (SWCNTs) are electroconductive and sensitive to humidity, pH, and ionic strength, due to pH-tunable water absorbing properties of the covalently crosslinked alginate. The conductivity depends on the material swelling in humid atmosphere and aqueous solutions: the greater the swelling, the smaller is the electrical conductivity. The covalently crosslinked fi bers reversibly deform during the swelling/shrinking. In the swollen state, the fi bers are less conductive, while they return to the same level of conductivity after shrinking. This unique reversible change of electroconductivity of the SWCNT-alginate fi bers is due to the elastic deformation of the alginate network in the area of electrical contacts between SWCNT bundles arrested in the alginate matrix. Fibers of this kind can be used as a simple, robust, disposable, and biocompatible platform for electrotextiles, biosensors, and fl exible electronics in biomedical and biotechnological applications.

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