TEMPO-oxidized cellulose nanofibril/polyvalent cations hydrogels: a multifaceted view of network interactions and inner structure

Abstract

In the last years, hydrogels from renewable biopolymers and low-cost row materials are a hot topic for biomedical applications. In this context, cellulose nanofibrils are considered suitable building blocks for the synthesis of many biocompatible products, with a variety of chemical-physical properties. Herein we report a multi-technique and multi-scale study, from the molecular to the nanometric length scale, of the sol–gel transition observed in aqueous solutions of TEMPO-oxidized nano-sized cellulose fibrils (TOCNFs), when in the presence of polyvalent cations (Mg2+ and Ca2+). We combine the data from Small Angle Neutron Scattering (SANS), which provide information about the inner structure of the nanofibril, with those from UV Resonant Raman (UVRR) spectroscopy, which is a sensitive probe of the intra- and inter-molecular interactions in the gel and the liquid state. The transition between the gel and the liquid phases is investigated as a function of the concentration of both TOCNFs and cations, the nature of the latter, and the pH at which the phenomenon is observed. SANS analysis reveals that ion concentration induces an anisotropic swelling in the nanofibrils which, at the same time, become more and more flexible. The nanofibrils flexibility is also dependent on TOCNF concentration and pH value. UVRR allows us to elucidate the structural organization and hydrogen-bonding properties of water in aqueous TOCNF dispersions and gels, showing how water molecules partially lose their typical bulk-like tetrahedral organization when ions are added, and the gel phase is formed. Graphical abstract

Environmental safety of nanocellulose: an acute in vivo study with marine mussels Mytilus galloprovincialis

“…13,50 The first step consisted of the TEMPO-mediated oxidation of cellulose. 51,52 Cotton linters pulp was suspended in a keg containing TEMPO (0.22 g, 1.38 mmol) and KBr (1.54 g, 12.9 mmol) at a final cellulose concentration of 2% w/w (final volume: 570 mL). The oxidation process was promoted by adding dropwise an aqueous solution of NaClO (12.5% w/w aqueous solution, 43.7 mL) to the cellulose suspension under vigorous magnetic stirring.…”

“…These results agree with previous observations of greater fiber dispersion in NSW and stronger surface adhesion to the cell membrane, which can override electrostatic repulsion with TOCNF negative charges. 52,76 In addition, mussel gill cells are covered by a mucus made of acid and neutral polysaccharides with an active role in particle ingestion via cilia-transported mucus masses. 77 Although no concentration-dependent effects were observed in ASCh-ChE activity, both CN fibers affected the cholinergic function via an indirect mechanism (i.e., cell membrane interaction) rather than direct binding to the AChE enzyme.…”