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    Gelation kinetics of thiol-methylsulfone (MS) hydrogel formulations for 3D cell culture
    (Washington, D.C. : American Chemical Society, 2022) de Miguel-Jiménez, Adrián; Ebeling, Bastian; Paez, Julieta I.; Fink-Straube, Claudia; Pearson, Samuel; del Campo, Aranzazu
    Crosslinking chemistries that allow hydrogel formation within minutes are essential to achieve homogeneous networks and cell distributions in 3D cell culture. Thiol-methylsulfone (MS) crosslinking chemistry offers minutes-scale gelation under near-physiological conditions showing many desirable attributes for 3D cell encapsulation. Here we investigate the gelation kinetics and mechanical properties of PEG-based hydrogels formed by thiol-tetrazole methylsulfone (TzMS) crosslinking as a function of buffer, crosslinker structure, and degree of TzMS functionalization. Appropriate buffer selection ensured constant pH throughout crosslinking. The formulation containing cell adhesive ligand RGD and enzymatically-degradable peptide VPM gelled in ca. 4 min at pH 7.5, and stiffness could be increased from hundreds of Pascals to > 1 kPa by using excess VPM. The gelation times and stiffnesses for these hydrogels are highly suitable for 3D cell encapsulations, and pave the way for reliable 3D cell culture workflows in pipetting robots.
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    Cascade Synthesis of Pyrroles from Nitroarenes with Benign Reductants Using a Heterogeneous Cobalt Catalyst
    (Weinheim : Wiley-VCH, 2020) Ryabchuk, Pavel; Leischner, Thomas; Kreyenschulte, Carsten; Spannenberg, Anke; Junge, Kathrin; Beller, Matthias
    A bifunctional 3d-metal catalyst for the cascade synthesis of diverse pyrroles from nitroarenes is presented. The optimal catalytic system Co/NGr-C@SiO2-L is obtained by pyrolysis of a cobalt-impregnated composite followed by subsequent selective leaching. In the presence of this material, (transfer) hydrogenation of easily available nitroarenes and subsequent Paal–Knorr/Clauson-Kass condensation provides >40 pyrroles in good to high yields using dihydrogen, formic acid, or a CO/H2O mixture (WGSR conditions) as reductant. In addition to the favorable step economy, this straightforward domino process does not require any solvents or external co-catalysts. The general synthetic utility of this methodology was demonstrated on a variety of functionalized substrates including the preparation of biologically active and pharmaceutically relevant compounds, for example, (+)-Isamoltane. © 2020 The Authors. Published by Wiley-VCH GmbH
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    Redox-triggerable Luciferin-Bioinspired Hydrogels as Injectable and Cell-encapsulating Matrices
    (Washington, D.C. : American Chemical Society, 2022) Jin, Minye; Gläser, Alisa; Paez, Julieta I.
    Over the past few decades there has been a great interest in developing smart hydrogels that are stimuli-responsive, due to their ability to respond to variations caused by external stimuli. These materials are exploited for biomedical applications such as biosensors, injectable scaffolds, drug delivery and tissue engineering. Recently, our group reported firefly-inspired hydrogel matrices for 3D cell culture. This platform exhibited certain advantages like rapid gelation rate and tunability of mechanical and biological properties. However, this firstly reported system did not allow for fine control of the gelation onset because the crosslinking reaction started as soon as the two precursors were mixed. Moreover, one of its precursors demonstrated poor storage stability in aqueous solution. These limitations restrict its application as injectable matrices. In this article, we endow the luciferin-inspired hydrogels with redox-triggering capability, to overcome the limitations of the previous system and to widen its application range. We achieve this goal by introducing protected macromers as hydrogel polymeric precursors that can be activated in the presence of a mild reductant, to trigger gel formation in situ with high degree of control. We demonstrate that the regulation of intrinsic (e.g., structure of protecting group, reductant type) and extrinsic (e.g., pH, temperature) parameters of the triggering reaction can be used to modulate key materials properties. This novel upgraded redox-triggerable system enables precise control over gelation onset and kinetics, thus facilitating its utilization as injectable hydrogel without negatively impacting its cytocompatibility. Our findings expand the current toolkit of chemically-based stimuli-responsive hydrogels.