RESUMEN

Strong and tough hydrogels are promising candidates for flexible electronics, biomedical devices, and so on. However, the conflict between improving the mechanical strength and toughness properties of polysaccharide-based hydrogels remains unsolved. Herein, a strategy is proposed to produce a hierarchically structured cellulose hydrogel that combines solution annealing and dual cross-linking treatment approaches. The solution annealing considerably increases the hydrophobic stacking and chemical cross-linking of the cellulose chains, thereby facilitating their subsequent self-assembly and recrystallization during the chemical and physical cross-linking processes. The cellulose hydrogels exhibit superposed chemically and physically cross-linked domains comprising homogeneous nanoporous network structures, which in turn are composed of interconnected cellulose nanofibers and cellulose II crystallite hydrates. These cellulose hydrogels exhibit a high water content of 76-84% and excellent mechanical properties that compare favorably to those of biomacromolecule-based hydrogels. The prepared hydrogels exhibit a mechanical strength and work of fracture of 21 ± 3 MPa and 2.6 ± 0.4 MJ m-3 under compression, and 7.2 ± 0.7 MPa and 5.9 ± 0.6 MJ m-3 under tension, respectively. It is anticipated that this strategy will be applicable to other biomacromolecules and crystalline polymers, and that it will enable the construction of other hydrogels exhibiting high mechanical performances.

RESUMEN

Fluorescent materials span multiple applications from biological probes and chemical sensing to optoelectronic systems. Although great efforts have been made toward developing classes of fluorescent materials, 100,000+ traditional fluorescent dyes still suffer from the obstacle of aggregation-caused quenching (ACQ). Thus, designing fluorescent materials with excellent optical performance from ACQ luminogens remains challenging. In this work, we prepared fluorescent amphiphilic quaternized ß-chitin (QC-F) via nucleophilic addition between the amino groups of QC and isothiocyanate groups of fluorescein isothiocyanate (FITC). Due to the covalent anchoring of the QC backbone, steric hindrance of the bulky acetamido groups, electrostatic repulsion of the quaternary ammonium groups, and homogeneous distribution of FITC units, the FITC units were spatially and electronically isolated, and the QC-F series exhibited unique fluorescent behaviors. The QC-F series could be used to observe their interactions with microbial cells through fluorescence imaging to gain insights into the QC antibacterial mechanism. Moreover, with their favorable cytocompatibility, the QC-F series are also suitable for cell imaging. Thus, the present work will broaden the applications of chitin and conventional ACQ luminogens.

Asunto(s)

Antibacterianos , Quitina , Antibacterianos/farmacología , Quitina/farmacología , Fluoresceína , Fluoresceína-5-Isotiocianato , Colorantes Fluorescentes/farmacología

RESUMEN

Chitin is the second most abundant natural polysaccharide with biocompatibility, biodegradability, and bioactivity. Homogeneous modification of chitin is an efficient way to improve or to impart new properties to chitin. Here, amide-modified ß-chitin (AMC), hydroxyethyl ß-chitin (HEC), and hydroxybutyl ß-chitin (HBC) through Michael addition, Williamson reaction, and ring-opening addition, were homogeneously synthesized from aqueous KOH/urea solution, respectively, with controlled structures and uniform properties. The reactions mainly occur at the hydroxyl groups of C-6 positions of ß-chitin chains due to mild conditions, and the obtained ß-chitin derivatives with high DS values are water-soluble. AMC could transform from sol to gel at acidic condition or upon adding Fe3+ due to the presence of partial carboxylate groups. As a specific highlight, HEC and HBC could thermally form smart hydrogels at physiological temperature, with cytocompatibility and blood biocompatibility, which is very useful as drug/ cell carriers for biomedical applications. The remarkably mild and "green" condition of aqueous KOH/urea solution for the synthesis of chitin derivatives has pioneered a better way to exploit its great diversity of the natural, sustainable polysaccharide.

RESUMEN

Here, we present the preparation of hydrophobic nanoporous cellulose gel-g-poly(glycidyl methacrylate) (NCG-g-PGMA) nanocomposites by surface-initiated atom transfer radical polymerization (SI-ATRP) of glycidyl methacrylate (GMA) monomers and hydrophobic modification with pentadecafluorooctanoyl chloride (C7F15COCl) on the cellulose nanofibrils of the NCG. The successful grafting of PGMA and hydrophobic modification of C7F15CO- groups on the NCG was evaluated by Fourier transform infrared (FTIR) spectroscopy. X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirmed that the SI-ATRP and hydrophobic modification did not change the microscopic morphology and structure of the NCG-g-PGMA nanocomposites. Dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) showed remarkable thermomechanical properties and moderate thermal stability. The method has tremendous promise to use NCG as a platform for SI-ATRP and produce new functional NCG-based nanomaterials.