In Situ RheoNMR Correlation of Polymer Segmental Mobility with Mechanical Properties during Hydrogel Synthesis

Understanding polymer gelation over multiple length-scales is crucial to develop advanced materials. An experimental setup is developed that combines rheological measurements with simultaneous time-domain $^{1}$H NMR relaxometry (TD-NMR) techniques, which are used to study molecular motion (<10 nm) in soft matter. This so-called low-field RheoNMR setup is used to study the impact of varying degrees of crosslinking (DC) on the gelation kinetics of acrylic acid (AAc) and N,N′-methylene bisacrylamide (MBA) free radical crosslinking copolymerization. A stretched exponential function describes the T$_{2}$ relaxation curves throughout the gelation process. The stretching exponent β decreases from 0.90 to 0.67 as a function of increasing DC, suggesting an increase in network heterogeneity with a broad T$_{2}$ distribution at higher DC. The inverse correlation of the elastic modulus G′ with T2 relaxation times reveals a pronounced molecular rigidity for higher DC at early gelation times, indicating the formation of inelastic, rigid domains such as crosslinking clusters. The authors further correlate G′ with the polymer concentration during gelation using a T$_{1}$ filter for solvent suppression. A characteristic scaling exponent of 2.3 is found, which is in agreement with theoretical predictions of G′ based on the confining tube model in semi-dilute entangled polymer solutions

Reversible photodissipation of composite photochromic azobenzene-alginate supramolecular hydrogels

Supramolecular smart materials can quickly elicit macroscopic changes upon external stimulation. Here we report that an azobenzene-containing cyclic dipeptide can form composite supramolecular hydrogels with alginate based on the charge complementarity, at lower loading than the critical gelation concentrations of either component. The gels can reversibly dissipate to fluids with UV light. They can also encapsulate and photorelease fluorescent cargo. Upon treatment of the gels with aqueous calcium salts, the alginate component is permanently cross-linked and the photochromic component is solubilized

Reprocessing of Instruments for Minimal Invasive Surgery - State of the Art and Prospects

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Die Weiterentwicklung des Instrumentariums der minimal-invasiven Chirurgie (MIC) vollzieht sich in Richtung einer Miniaturisierung mechanischer Komponenten, einer Kombination mehrerer Funktionen in einem Gerät und der Einführung neuer Techniken, insbesondere zur blutungsarmen und thermisch schonenden Durchtrennung von Blutgefäßen. Diese Entwicklungstendenzen haben Auswirkungen auf die Aufbereitungsfähigkeit der Geräte. Sie wirken sich in der Regel erschwerend aus. Hierbei stellt insbesondere die Reinigung, also die Entfernung der Anschmutzungen aus kleinen Lumina, filigranen Gelenken, von der Waschflotte schwer erreichbaren Toträumen etc. besonders hohe Anforderungen. Hinzu kommt, daß der Nachweis des Reinigungserfolges schwer zu führen ist und bisher kein in der Routine praktikables, allgemein akzeptiertes Standardnachweisverfahren eingeführt werden konnte. Es werden ein Überblick über die im Zusammenhang mit der Aufbereitung von Instrumenten der MIC auftretenden Problemstellungen gegeben und Lösungsansätze diskutiert.The development of instruments for minimal invasive surgery (MIS) is moving in the direction of the miniaturization of mechanical components, a combination of multiple functions in a single instrument, and the introduction of new techniques, in particular those reducing bleeding and thermal damage when cutting blood vessels. These tendencies have consequences for the reprocessability of the instruments, usually making reprocessing more difficult. In particular cleaning the removal of contaminations from tiny lumina, joints, etc., is highly demanding. In addition, proof of successful cleaning is difficult, and no standardised method of doing this in practice is currently available. An overview of the problems associated with the reprocessing of instruments for minimal invasive surgery is given, and a numbers of possible solutions are discussed

Citation guide

The German version of the citation guide is available at https://doi.org/10.21256/zhaw-24167

Dual-faced borax mediated synthesis of self-healable hydrogels merging dynamic covalent bonding and micellization

Intrinsic self-healing hydrogels with excellent mechanical properties are still difficult to achieve. Here, we presented a facile method to integrate dynamic boronate ester bonds and Pluronic F127 (PF127) micelle cross-links into one hydrogel system via a borax catalyzed thiol–ene click reaction and borax–diol chemistry. The hydrogel was capable of elongating up to 340% and self-healing approximately 90% of its initial stress within 24 h. Moreover, the hydrogel could endure a compressive strain of 80% without fracture, and exhibited excellent shape recovery and fatigue resistance ability as determined by the cyclic compressive loading–unloading test at 60% strain, providing a new facile route to design multifunctional hydrogels with spontaneous self-healing ability, good stretchability and excellent compressive properties

Protection-Group-Free Synthesis of Sequence-Defined Macromolecules via Precision λ-Orthogonal Photochemistry

An advanced light-induced avenue to monodisperse sequence-defined linear macromolecules via a unique photochemical protocol is presented that does not require any protection-group chemistry. Starting from a symmetrical core unit, precision macromolecules with molecular weights up to 6257.10 g mol−1 are obtained via a two-monomer system: a monomer unit carrying a pyrene functionalized visible light responsive tetrazole and a photo-caged UV responsive diene, enabling an iterative approach for chain growth; and a monomer unit equipped with a carboxylic acid and a fumarate. Both light-induced chain growth reactions are carried out in a λ-orthogonal fashion, exciting the respective photosensitive group selectively and thus avoiding protecting chemistry. Characterization of each sequence-defined chain (size-exclusion chromatography (SEC), high-resolution electrospray ionization mass spectrometry (ESI-MS), and NMR spectroscopy), confirms the precision nature of the macromolecules