Biomimetic double network hydrogels: Combining dynamic and static crosslinks to enable biofabrication and control cell-matrix interactions

Hydrogels are promising candidates for recapitulation of the native extracellular matrix (ECM), yet recreating molecular and spatiotemporal complexity within a single network remains a challenge. Double network (DN) hydrogels are a promising step towards recapitulating the multicomponent ECM and have enhanced mechanical properties. Here, we investigate DNs based on dynamic covalent and covalent bonds to mimic the dynamicity of the ECM and enable biofabrication. We also investigate the spatiotemporal molecular attachment of a bioactive adhesive peptide within the networks. Using oxidized alginate (dynamic network, Schiff base) and polyethylene glycol diacrylate (static network, acrylate polymerization) we find an optimized procedure, where the dynamic network is formed first, followed by the static network. This initial dynamically cross-linked hydrogel imparts self-healing, injectability, and 3D printability, while the subsequent DN hydrogel improves the stability of the 3D gels and imparts toughness. Rheology and compression testing show that the toughening is due to the combination of energy dissipation (dynamic network) and elasticity (static network). Furthermore, where we place adhesive sites in the network matters; we find distinct differences when an adhesive peptide, Arg-Gly-Asp (RGD), is attached to the different networks. This DN strategy bring us closer to understanding and recreating the complex multicomponent ECM—pushing us past a materials view of cell adhesion—while enabling injectabiltiy and printing of tough hydrogels.     

Characterization of aluminum phosphate nanoparticles formed in a water well

In a drinking water well in Nethen, Germany, a yellowish precipitate, dominated by aluminum and phosphorus, affected the operation of the submersible pump by mechanically blocking the impellers. So far, aluminum-dominated well incrustations have been documented in only two cases and their mineralogical characterization was insufficient. The aim of the present study is to (1) present a third finding of Al-incrustations in wells, (2) provide a mineralogical and geochemical in-depth characterization of the precipitate, and (3) try to explain the reason for the problems it causes for drinking water production from this well. The yellow precipitate consists of nanoparticle aggregates and is a short-range ordered phase that could be described as a modified form of evansite with phosphate being the major anion, accompanied by some sulfate and carbonate. Additionally, aggregation with hydrous silicates and organic material is present, which could be simply adsorbed or co-precipitated. The precipitate formed as shallow acidic groundwater containing dissolved aluminum entered the well through a leaky casing seal. In the well it mixed with deeper groundwater of higher pH, causing Al-phosphate precipitations. The aggregates tended to accumulate at the entrance slots of the pump which therefore became blocked and had to be replaced.     

Lanthanide‐Based Functional Misfit‐Layered Nanotubes

The synthesis of nanotubes from layered compounds has generated substantial scientific interest. “Misfit” layered compounds (MLCs) of the general formula [(MX)_1+x]_m[TX₂]_n, where M can include Pb, Sb, rare earths; T=Cr, Nb, and X=S, Se can form layered structures, even though each sub‐system alone is not necessarily a layered or a stable compound. A simple chemical method is used to synthesize these complex nanotubes from lanthanide‐based misfit compounds. Quaternary nanotubular structures formed by partial substitution of the lanthanide atom in nanotubes by other elements are also confirmed. The driving force and mechanism of formation of these nanotubes is investigated by systematic temperature and time‐dependent studies. A stress‐inducement mechanism is proposed to explain the formation of the nanotubes. The resulting materials may find applications in fields that include thermoelectrics, light emitters, and catalysis and address fundamental physical issues in low dimensions.     

Analysis of Dopant Atom Distribution and Quantification of Oxygen Vacancies on Individual Gd‐Doped CeO2 Nanocrystals

This work reports the analysis of the distribution of Gd atoms and the quantification of O vacancies applied to individual CeO₂ and Gd‐doped CeO₂ nanocrystals by electron energy‐loss spectroscopy. The concentration of O vacancies measured on the undoped system (6.3±2.6 %) matches the expected value given the typical Ce³⁺ content previously reported for CeO₂ nanoparticles. The doped nanoparticles have an uneven distribution of dopant atoms and an atypical amount of O vacant sites (37.7±4.1 %). The measured decrease of the O content induced by Gd doping cannot be explained solely by the charge balance including Ce³⁺ and Gd³⁺ ions.     

An accelerated Poincaré-map method for autonomous oscillators

A novel time-domain method for finding the periodic steady state of a free-running electrical oscillator is introduced. The method is based on the extrapolation technique MPE. The new method is applied to a family of artificial benchmark problems and to a real circuit (Colpitt’s oscillator). It turns out to have super-linearly convergence properties in both cases. Full implementational details are provided.     

Optimized 3D-NMR sampling for resonance assignment of partially unfolded proteins

Resonance assignment of NMR spectra of unstructured proteins is made difficult by severe overlap due to the lack of secondary structure. Fortunately, this drawback is partially counterbalanced by the narrow line-widths due to the internal flexibility. Alternate sampling schemes can be used to achieve better resolution in less experimental time. Deterministic schemes (such as radial sampling) suffer however from the presence of systematic artifacts. Random acquisition patterns can alleviate this problem by randomizing the artifacts. We show in this communication that quantitative well-resolved spectra can be obtained, provided that the data points are properly weighted before FT. These weights can be evaluated using the concept of Voronoi cells associated with the data points. The introduced artifacts do not affect the direct surrounding of the peaks and thus do not alter the amplitude and frequency of the signals. This procedure is illustrated on 60-residue viral protein, which lacks any persistent secondary structure and thus exhibits major signal overlap.