Abstract
Cellulose nanofibrils (CNF) are renewable bio-based materials with high specific area, which makes them ideal candidates for multiple emerging applications including for instance on-demand drug release. However, in-depth chemical and structural characterization of the CNF surface chemistry is still an open challenge, especially for low weight percentage of functionalization. This currently prevents the development of efficient, cost-effective and reproducible green synthetic routes and thus the widespread development of targeted and responsive drug-delivery CNF carriers. We show in this work how we use dynamic nuclear polarization (DNP) to overcome the sensitivity limitation of conventional solid-state NMR and gain insight into the surface chemistry of drug-functionalized TEMPO-oxidized cellulose nanofibrils. The DNP enhanced-NMR data can report unambiguously on the presence of trace amounts of TEMPO moieties and depolymerized cellulosic units in the starting material, as well as coupling agents on the CNFs surface (used in the heterogeneous reaction). This enables a precise estimation of the drug loading while differentiating adsorption from covalent bonding (∼1 wt% in our case) as opposed to other analytical techniques such as elemental analysis and conductometric titration that can neither detect the presence of coupling agents, nor differentiate unambiguously between adsorption and grafting. The approach, which does not rely on the use of 13C/15N enriched compounds, will be key to further develop efficient surface chemistry routes and has direct implication for the development of drug delivery applications both in terms of safety and dosage.
Highlights
Wood-derived cellulose nds industrial applications in a wide range of elds, from paper products to buildings, cosmetics, foodstuffs or medical industry,[1,2] with numerous kinds of industrially produced cellulosic materials
We show that dynamic nuclear polarization (DNP) enhanced solid-state NMR can be used to unravel the surface chemistry of an innovative nanocellulose drug carrier even in the case of a very low level of gra ing (
The starting Cellulose nanofibrils (CNF)-t material was prepared by controlled TEMPO oxidation to achieve a high degree of oxidation, as already described by Isogai et al in 2011.7 The rst step of functionalization corresponds to a catalyzed amidation with furfurylamine performed in water using a large excess of both reactants and reagents. 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS) were used as coupling agents, and multiple washing steps were conducted in an effort to remove all the molecules that were not covalently bound, including the by-products issued from the coupling (EDC-urea, NHS) and excess of amine
Summary
Cellulose nano brils (CNFs),[3,4,5] which triggered a strong and lasting scienti c enthusiasm. In line with a sustainable green strategy compatible with ecological concerns and medical applications, it is becoming increasingly important to perform these surface reactions in aqueous conditions employing readily available reagents/ catalysts with minimal sensitivity to water This further decreases the kinetic and activation efficiency of the carboxylic groups compared to the use of organic solvent.[21] All in all, the lack of techniques able to report on low level of CNF surface modi cations impedes the development of efficient, cost-effective and reproducible green synthetic routes and the widespread development of targeted and responsive drug-delivery CNF carriers. This new CNF-t based complex represents a smart drug carrier formulation with “on-demand” API release abilities in the presence of esterases
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