Abstract
Wood-derived nanofibrillated cellulose (NFC) has long been recognized as a valuable nanomaterial for food-related applications. However, the safety of NFC cannot be predicted just from the chemical nature of cellulose, and there is a need to establish the effect of the nanofibers on the gastrointestinal tract, to reassure the safe use of NFC in food-related products. The present work selected the intestinal cells Caco-2 and the gut bacteria Escherichia coli and Lactobacillus reuteri to evaluate the in vitro biological response to NFC. NFC materials with different surface modifications (carboxymethylation, hydroxypropyltrimethylammonium substitution, phosphorylation and sulfoethylation) and unmodified NFC were investigated. The materials were characterized in terms of surface functional group content, fiber morphology, zeta potential and degree of crystallinity. The Caco-2 cell response to the materials was evaluated by assessing metabolic activity and cell membrane integrity. The effects of the NFC materials on the model bacteria were evaluated by measuring bacterial growth (optical density at 600 nm) and by determining colony forming units counts after NFC exposure. Results showed no sign of cytotoxicity in Caco-2 cells exposed to the NFC materials, and NFC surface functionalization did not impact the cell response. Interestingly, a bacteriostatic effect on E. coli was observed while the materials did not affect the growth of L. reuteri. The present findings are foreseen to contribute to increase the knowledge about the potential oral toxicity of NFC and, in turn, add to the development of safe NFC-based food products.
Highlights
IntroductionIn the era of nanotechnology, nanocellulose (NC) has emerged as a highly interesting material for a wide range of industrial (e.g., packaging and electronics) and biomedical (e.g., wound care and tissue engineering) applications [1,2]
In the era of nanotechnology, nanocellulose (NC) has emerged as a highly interesting material for a wide range of industrial and biomedical applications [1,2]
We have previously shown that fiber morphology is influenced by the presence of proteins, observing fiber agglomeration when functionalized nanofibrillated cellulose (NFC) materials were suspended in cell culture media [27]
Summary
In the era of nanotechnology, nanocellulose (NC) has emerged as a highly interesting material for a wide range of industrial (e.g., packaging and electronics) and biomedical (e.g., wound care and tissue engineering) applications [1,2]. The physicochemical properties of NFC materials, such as fiber dimensions, degree of crystallinity, aspect ratio, specific surface area and degree of branching of the nanofibrils, depend on the raw material, the pretreatments used in the manufacturing process and the post-manufacturing chemical modifications [7] These materials characteristics may affect the interactions between the cellulose nanofibers and biological systems and the materials’ hazard to human health and the environment. As for other nanomaterials, it is believed that, in order to reach the full potential of NFC applications, the materials’ safety aspects have to be considered at early stages of product development [8] In this sense, the number of studies aiming to understand the potential hazard of NC materials, including NFC, has increased during the last years [9,10]. We selected four NFC materials with the following surface functionalizations: carboxymethylated, hydroxypropyltrimethylammonium, phosphorylated and sulfoethylated NFCs, together with the unmodified NFC, to investigate the effect of nanofiber surface modification on the GIT
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