Dependence of Self-Assembled Peptide Hydrogel Network Structure on Local Fibril Nanostructure

Physically cross-linked, fibrillar hydrogel networks are formed by the self-assembly of β-hairpin peptide molecules with varying degrees of strand asymmetry. The peptide registry in the self-assembled state can be used as a design element to generate fibrils with twisting, nontwisting, or laminated morphology. The mass density of the networks varies significantly, and can be directly related to the local fibrillar morphology as evidenced by small angle neutron scattering (SANS) and in situ substantiation using cryogenic transmission electron microscopy (cryo-TEM) under identical concentrations and conditions. Similarly, the density of the network is dependent on changes in the peptide concentration. Bulk rheological properties of the hydrogels can be correlated to the fibrillar nanostructure, with the stiffer, laminated fibrils forming networks with a higher G′ as compared to the flexible, singular fibrillar networks

Survey, Excavation, and Geophysics at Songjiaheba—A Small Bronze Age Site in the Chengdu Plain

Archaeological survey in the Chengdu Plain of Sichuan Province has revealed settlement patterns surrounding Late Neolithic walled sites, including large numbers of small settlements from the Neolithic, Bronze Age, and Han Dynasty eras. Here geophysical survey and excavation at one of these small-scale sites dating to the Middle Bronze Age are reported, showing for the first time the value of high-resolution geophysics for evaluating site size and integrity in the Chengdu region

Materials construction through peptide design and solution assembly

Self-assembly of molecules is an attractive materials construction strategy due to its simplicity in application. By considering peptidic molecules in the bottom-up materials self-assembly design process, one can take advantage of inherently biomolecular attributes; intramolecular folding events, secondary structure, and electrostatic interactions; in addition to more traditional self-assembling molecular attributes such as amphiphilicty, to define hierarchical material structure and consequent properties. These self-assembled materials range from hydrogels for biomaterials to nanostructures with defined morphology and chemistry display for inorganic materials templating. The local nano- and overall network structure, and resultant viscoelastic and cell-level biological properties, of hydrogels that are formed via beta-hairpin self-assembly will be presented. Importantly, the hydrogels do not form until individual peptide molecules intramolecularly fold into a beta-hairpin conformation. Subsequently, specific, intermolecular assembly occurs into a branched nanofibrillar network. These peptide hydrogels are potentially excellent scaffolds for tissue repair and regeneration due to inherent cytocompatibility, porous morphology, and shear-thinning but instant recovery viscoelastic properties. Slight design variations of the peptide sequence allow for tunability of the self-assembly/hydrogelation kinetics as well as the tunability of the local peptide nanostructure and hierarchical network structure. In turn, by controlling hydrogel self-assembly kinetics, one dictates the ultimate stiffness of the resultant network and the kinetics through which gelation occurs. Examples of peptide primary structure alteration and the alteration of bulk network properties will be discussed. During assembly and gelation, desired components can be encapsulated within the hydrogel network such as drug compounds and/or living cells. The system can shear thin but immediately reheal to preshear stiffness on the cessation of the shear stress. Additionally, a new system comprised of coiled coil motifs designed theoretically to assemble into two-dimensional nanostructures not observed in nature will be introduced. The molecules and nanostructures are not natural sequences and provide opportunity for arbitrary nanostructure creation with peptides

Exploiting the CH-π interactions in supramolecular hydrogels of aromatic carbohydrate amphiphiles

A novel class of supramolecular hydrogels derived from amino sugars is reported, where the self-assembly of aromatic carbohydrate amphiphiles is driven by CH-π interactions, rather than π–π stacking and H-bonding associated with gelators based on aromatic peptide amphiphiles. Spectroscopic data is provided as evidence for this mode of self-assembly and in silico studies revealed that a combination of CH-π and T-stacking of the fluorenyl groups contribute to the formation of the aggregated structures

Interfaces in Diblocks: A Study of Miktoarm Star Copolymers

We study AB$_n$ miktoarm star block copolymers in the strong segregation limit, focussing on the role that the AB interface plays in determining the phase behavior. We develop an extension of the kinked-path approach which allows us to explore the energetic dependence on interfacial shape. We consider a one-parameter family of interfaces to study the columnar to lamellar transition in asymmetric stars. We compare with recent experimental results. We discuss the stability of the A15 lattice of sphere-like micelles in the context of interfacial energy minimization. We corroborate our theory by implementing a numerically exact self-consistent field theory to probe the phase diagram and the shape of the AB interface.Comment: 12 pages, 11 included figure

Toy amphiphiles on the computer: What can we learn from generic models?

Generic coarse-grained models are designed such that they are (i) simple and (ii) computationally efficient. They do not aim at representing particular materials, but classes of materials, hence they can offer insight into universal properties of these classes. Here we review generic models for amphiphilic molecules and discuss applications in studies of self-assembling nanostructures and the local structure of bilayer membranes, i.e. their phases and their interactions with nanosized inclusions. Special attention is given to the comparison of simulations with elastic continuum models, which are, in some sense, generic models on a higher coarse-graining level. In many cases, it is possible to bridge quantitatively between generic particle models and continuum models, hence multiscale modeling works on principle. On the other side, generic simulations can help to interpret experiments by providing information that is not accessible otherwise.Comment: Invited feature article, to appear in Macromolecular Rapid Communication

Technical note Flood map development by coupling satellite maps and three-dimensional drafting software: Case study of the Sarawak River Basin

Flood maps are important for local authorities in designing mitigation plans to minimise damage and loss due to flooding. In recent years, flood events in the Sarawak River Basin, Malaysia have caused damage to property, loss of life and disruption of productive activities. Currently, the available flood map for Sarawak River Basin is generated using InfoWorks River Simulation (InfoWorks RS) and spot levels are captured using the Light Detection and Ranging (LiDAR) system. However, the high cost of this flood mapping technique has motivated the development of an advanced but low-cost flood mapping method. This study was carried out to test the feasibility of using Google Earth coupled with Autocad Civil 3D in generating flood maps. Google Earth was used to obtain the elevation data, while Autocad Civil 3D was used to plot the water level surface. Data for the maximum water level, recorded since 1960, for 12 water level stations were fed into the model for flood map generation. This research confirmed that Autocad Civil 3D coupled with Google Earth is feasible for generating an updated and accurate flood map, after comparison with 2 flood maps developed previously.Keywords: Autocad Civil 3D, flood map, Google Eart

Peptide hydrogels from twisted ribbon aggregates

We have studied the rheology of an aqueous solution phase formed in the model peptide system A10K (A=alanine, K=lysine), where the short hydrophobic peptides self-assemble into twisted ribbon structures consisting of laminated beta-sheets. The ribbons are crystalline in 2 dimensions, therefore rigid, and they are weakly charged. The average ribbon lengths, \u3cL \u3e≈ 60 nm, corresponding to an aspect ratio, L/d≈10. With increasing concentration a transition from a viscous liquid into a gel-like solid occurs around a volume fraction f ≈ 0.02, that we identify as the overlap concentration f*. Coinciding with the overlap concentration is also a phase transition, from the low concentration isotropic liquid phase to a nematic phase. This concentration is significantly lower than what is predicted for hard rods by Onsager theory for this given aspect ratio. We attribute this to the ribbon charge and long range electrostatic interactions, stabilizing the nematic phase. In this nematic phase, the storage modulus G’ increases strongly with increasing Please click Additional Files below to see the full abstract

Phase Behavior of Polyelectrolyte Block Copolymers in Mixed Solvents

We have studied the phase behavior of the poly(n-butyl acrylate)-b-poly(acrylic acid) block copolymer in a mixture of two miscible solvents, water and tetrahydrofuran (THF). The techniques used to examine the different polymers, structures and phases formed in mixed solvents were static and dynamic light scattering, small-angle neutron scattering, nuclear magnetic resonance and fluorescence microscopy. By lowering the water/THF mixing ratio X, the sequence unimers, micron-sized droplets, polymeric micelles was observed. The transition between unimers and the micron-sized droplets occurred at X = 0.75, whereas the microstructuration into core-shell polymeric micelles was effective below X = 0.4. At intermediate mixing ratios, a coexistence between the micron-sized droplets and the polymeric micelles was observed. Combining the different aforementioned techniques, it was concluded that the droplet dispersion resulted from a solvent partitioning that was induced by the hydrophobic blocks. Comparison of poly(n-butyl acrylate) homopolymers and poly(n-butyl acrylate)-b-poly(acrylic acid) block copolymers suggested that the droplets were rich in THF and concentrated in copolymers and that they were stabilized by the hydrophilic poly(acrylic acid) moieties.Comment: 11 pages, 12 figures, to appear in Macromolecule

Linking micellar structures to hydrogelation for salt-triggered dipeptide gelators

Some functionalised dipeptides can form hydrogels when salts are added to solutions at high pH. We have used surface tension, conductivity, rheology, optical, confocal and scanning electron microscopy, 1H NMR and UV-Vis spectroscopy measurements to characterise fully the phase behaviour of solutions of one specific gelator, 2NapFF, at 25 °C at pH 10.5. We show that this specific naphthalene–dipeptide undergoes structural transformations as the concentration is increased, initially forming spherical micelles, then worm-like micelles, followed by association of these worm-like micelles. On addition of a calcium salt, gels are generally formed as long as worm-like micelles are initially present in solution, although there are structural re-organisations that occur at lower concentrations, allowing gelation at lower than expected concentration. Using IR and SANS, we show the differences between the structures present in the solution and hydrogel phases