A critical review of the current knowledge regarding the biological impact of nanocellulose

Abstract

Several forms of nanocellulose, notably cellulose nanocrystals and nanofibrillated cellulose, exhibit attractive property matrices and are potentially useful for a large number of industrial applications. These include the paper and cardboard industry, use as reinforcing filler in polymer composites, basis for low-density foams, additive in adhesives and paints, as well as a wide variety of food, hygiene, cosmetic, and medical products. Although the commercial exploitation of nanocellulose has already commenced, little is known as to the potential biological impact of nanocellulose, particularly in its raw form. This review provides a comprehensive and critical review of the current state of knowledge of nanocellulose in this format. Overall, the data seems to suggest that when investigated under realistic doses and exposure scenarios, nanocellulose has a limited associated toxic potential, albeit certain forms of nanocellulose can be associated with more hazardous biological behavior due to their specific physical characteristics.

Keywords: Cellulose nanocrystals; Exposure; Hazard; Human health; Nano-object-cell interactions; Nanocellulose; Nanofibers; Nanotoxicology; Risk.

Fig. 1

Transmission electron microscopy images of selected nanocellulose types. CNCs isolated by HCl (a) and H₂SO₄ hydrolysis (b) from bacterial cellulose, H₂SO₄ hydrolysis from tunicate mantles (c) or wood pulp (f) and nanofibrillated cellulose obtained by enzymatic (d), mechanical (e), or 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO) mediated oxidative (g) degradation of wood pulp. The figure is reprinted with permission from Sacui et al. [96] © (2014) American Chemical Society

Fig. 2

Life cycle of nanocellulose based composite materials where 5 different stages can be identified: production of raw materials or isolation (Stage 1), manufacture (Stage 2), transportation (Stage 3), consumer use (Stage 4) and disposal (Stage 5). Adapted from Shatkin et al. [70], with permission of The Royal Society of Chemistry

Fig. 3

Length dependent clearance of CNCs by macrophages. Confocal laser scanning microscopy images of the triple-cell co-culture model exposed to 0.56 ± 0.25 μg/cm² rhodamine-labeled CNCs isolated from cotton (green a–d) or 0.67 ± 0.09 μg/cm² CNCs isolated from tunicates (e–h) via the ALICE system. Co-cultures were either immediately fixed (a, e) or after 1 (b, f), 24 (c, g), or 48 h (d, h) post exposure and stained for cytoskeleton (red) and nuclei (cyan). Images are presented as surface rendering (top), xz-projection of the z-stacks (middle), or twofold optical zoom (bottom). Boxes indicate digitally enlarged (×2) areas. Arrow shows fiber-F-actin interactions. Scale bars 30 μm. Reprinted with permission from Endes et al. [79] © 2015 American Chemical Society