Unravelling cationic cellulose nanofibril hydrogel structure: NMR spectroscopy and small angle neutron scattering analyses

Abstract

Stiff, elastic, viscous shear thinning aqueous gels are formed upon dispersion of low weight percent concentrations of cationically modified cellulose nanofibrils (CCNF) in water. CCNF hydrogels produced from cellulose modified with glycidyltrimethylammonium chloride, with degree of substitution (DS) in the range 10.6(3)-23.0(9)%, were characterised using NMR spectroscopy, rheology and small angle neutron scattering (SANS) to probe the fundamental form and dimensions of the CCNF and to reveal interfibrillar interactions leading to gelation. As DS increased CCNF became more rigid as evidenced by longer Kuhn lengths, 18-30 nm, derived from fitting of SANS data to an elliptical cross-section, cylinder model. Furthermore, apparent changes in CCNF cross-section dimensions suggested an "unravelling" of initially twisted fibrils into more flattened ribbon-like forms. Increases in elastic modulus (7.9-62.5 Pa) were detected with increased DS and H solution-state NMR T relaxation times of the introduced surface -N(CH) groups were found to be longer in hydrogels with lower DS, reflecting the greater flexibility of the low DS CCNF. This is the first time that such correlation between DS and fibrillar form and stiffness has been reported for these potentially useful rheology modifiers derived from renewable cellulose.

Surfactant controlled zwitterionic cellulose nanofibril dispersions

“…The parameter L c could not be determined within the probed q-range, therefore it was fixed at an arbitrary value of 1000 nm, L c c (2p/q min ) whereas r min was fixed to 1 nm, based on the SANS data obtained for CNF. 27 Solid-state NMR experiments were performed at room temperature using a Bruker Avance III spectrometer equipped with a 4 mm triple resonance probe operating at frequencies of 300.13 MHz ( 1 H) and 75.47 MHz ( 13 C). Quantitative 1D 13 C{ 1 H} direct polarization (DP) NMR experiments were conducted at an MAS rate of 10 kHz for ZCNF and OCNF powders tightly packed in an 80 mL rotor ( Fig.…”

“…20,21 This functionalization route involves the selective introduction of negatively charged carboxyl groups 17,19,22 by oxidation, followed by grafting of quaternary ammonium groups from the GTMACcationization. 21 Although pathways for the production of cellulose nanofibrils (CNFs) bearing oppositely charged moieties have been reported, 6,7 their self-assembly in aqueous media has not, to the best of our knowledge, been described, although the colloidal properties of oxidised cellulose nanofibrils (OCNFs) 18,[23][24][25] and quaternary ammonium salt grafted CNF 21,26,27 aqueous dispersions have been characterized. Here, we describe the functionalization and double-charged nature of ZCNFs revealed by 13 C nuclear magnetic resonance (NMR) spectroscopy and z-potential measurements.…”

Mechanically robust cationic cellulose nanofibril 3D scaffolds with tuneable biomimetic porosity for cell culture

“…Cellulose modified with GTMAC was prepared as described in ref. 50, using 3 mol equivalents of GTMAC relative to cellulose anhydroglucose units. The resultant ''cationic cellulose nanofibrils'' are henceforth abbreviated as CCNF.…”

Recent Advances in Modified Cellulose for Tissue Culture Applications

“…Cellulose surfaces bear a slight negative charge in aqueous media [ 109 ] and, to overcome this, the epoxide, glycidyltrimethylammonium chloride (GTMAC), has been used to introduce a positive charge onto the surface via introduction of quaternary ammonium moieties. Unlike chitosan, these cationised CNF have a permanent charge and can be dispersed in water to form stable hydrogels if the degree of GTMAC substitution along the nanofibril is high enough to charge stabilise the dispersed particles [ 67 ]. Bacterial cellulose films were chemically modified with GTMAC facilitating the attachment of MG-63 osteoblast cells through electrostatic interactions between the phosphate-lipid bilayer of the cell membrane and the positively charged quaternary ammonium group ( Figure 4 [ 22 ]).…”

“…Not only does cellulose have tuneable mechanical and structural properties, but it also can be readily functionalised due to the exposed hydroxyl groups on the surface of the fibrils, summarised in Scheme 1 . Common modifications include the TEMPO oxidation of the hydroxyl group to a carboxylic acid [ 68 ], cationisation by grafting of glycidyl trimethylammonium chloride to the surface to introduce a positive charge [ 67 ], sulfuric acid hydrolysis leading to sulfate half esters [ 69 ] and derivitisation to produce a range of cellulose esters and ethers [ 70 ]. Although different modifications of cellulose materials have been widely reviewed [ 45 , 71 , 72 ] and exploited for other applications such as water purification [ 73 ], drug delivery [ 74 ] and rheology modification [ 75 ], reports of use in tissue engineering applications are more recent.…”