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Multi-step control over self-assembled hydrogels of peptide-derived building blocks and a polymeric cross-linker

We present a detailed study of self-assembled hydrogels of bundled and cross-linked networks consisting of positively charged amyloid-like nanofibers and a triblock copolymer with negatively charged end blocks as a cross-linker. In a first step small oligopeptides self-assemble into macrocycles which are held together by reversible disulfide bonds. Interactions between the peptides cause the macrocycles to assemble into nanofibers, which form a reversible hydrogel. The physical properties of the hydrogel are tuned using various methods such as control over the fibre length, addition of a cross-linking copolymer, and addition of salt. We establish a relationship between the bulk mechanical properties, the properties of the individual fibers and the hydrogel morphology using characterization techniques operating at different length scales such as rheology, atomic force microscopy (AFM) and cryo transmission electron microscopy (Cryo-TEM). This allows for a precise control of the elastic behaviour of these networks.

Adapting to extreme events related to natural variability and climate change: the imperative of coupling technology with strong regulation and governance

In recent years there has been an increase in extreme events related to natural variability (such as earthquakes, tsunamis and hurricanes) and climate change (such as flooding and more extreme weather). Developing innovative technologies is crucial in making society more resilient to such events. However, little emphasis has been placed on the role of human decision-making in maximizing the positive impacts of technological developments. This is exacerbated by the lack of appropriate adaptation options and the privatization of existing infrastructure, which can leave people exposed to increasing risk. This work examines the need for more robust government regulation and legislation to complement developments and innovations in technology in order to protect communities against such extreme events.

Effect of peptide and guest charge on the structural, mechanical and release properties of β-sheet forming peptides

The effect of peptide charge on the self-assembly, gelation behavior, and model drug release profiles has been explored here for three octa-peptides, VEVKVEVK (VEK2), VKVKVEVK (VEK3), and VEVEVKVE (VEK1), that carry a net charge of 0, +2, and -2 at neutral pH, respectively. Transparent, self-supporting hydrogels were found to form above a critical concentration when the peptide charge modulus was >1 and this was independent of the sign of the charge. TEM, SAXS, and shear rheology revealed that there were no differences in hydrogel structure or mechanical properties when the peptides were at the same concentration and carried the same charge modulus. All peptides were found to form dense fibrillar networks formed by β-sheet rich single fibers where lateral aggregation of the fibers occurred and increased with decreasing charge modulus. Such behavior was found to correlate with an increase in hydrogel mechanical properties, demonstrating that fiber lateral aggregation is inextricably linked with the mechanical properties of these hydrogels. Two hydrophilic model drug molecules, namely napthol yellow (NY) and martius yellow (MY), were subsequently incorporated within the VEK1 and VEK3 hydrogels at pH 7 and although they did not effect the self-assembly of the peptide at a molecular level, they did effect the level of lateral fiber aggregation observed and, therefore, the mechanical properties of the hydrogels. The release of each molecule from the hydrogels was monitored over time and shown to be controlled by Fickian diffusion where the diffusion rate, D, was dependent on the ratio between the overall effective charges carried by the peptide, i.e., the fibrillar network, and the overall charges carried by the guest molecules, but independent from the hydrogel concentration and mechanical properties within the ranges investigated. This work highlights the possibility of controlling the rate of release of small drug molecules by manipulating the charges on the guest molecules as well as the charged state of the self-assembling peptide.

Adaptive evolution of loci covarying with the human African Pygmy phenotype

African Pygmies are hunter-gatherer populations from the equatorial rainforest that present the lowest height averages among humans. The biological basis and the putative adaptive role of the short stature of Pygmy populations has been one of the most intriguing topics for human biologists in the last century, which still remains elusive. Worldwide convergent evolution of the Pygmy size suggests the presence of strong selective pressures on the phenotype. We developed a novel approach to survey the genetic architecture of phenotypes and applied it to study the genomic covariation between allele frequencies and height measurements among Pygmy and non-Pygmy populations. Among the regions that were most associated with the phenotype, we identified a significant excess of genes with pivotal roles in bone homeostasis, such as PPPT3B and the height associated SUPT3H-RUNX2. We hypothesize that skeletal remodeling could be a key biological process underlying the Pygmy phenotype. In addition, we showed that these regions have most likely evolved under positive selection. These results constitute the first genetic hint of adaptive evolution in the African Pygmy phenotype, which is consistent with the independent emergence of the Pygmy height in other continents with similar environments.

Isotope fractionation by thermal diffusion in silicate melts

Isotopes fractionate in thermal gradients, but there is little quantitative understanding of this effect in complex fluids. Here we present results of experiments and molecular dynamics simulations on silicate melts. We show that isotope fractionation arises from classical mechanical effects, and that a scaling relation based on Chapman-Enskog theory predicts the behavior seen in complex fluids without arbitrary fitting parameters. The scaling analysis reveals that network forming elements (Si and O) fractionate significantly less than network modifiers (e.g., Mg, Ca, Fe, Sr, Hf, and U).