Characterization and Antibacterial Properties of Autoclaved Carboxylated Wood Nanocellulose

Abstract

Cellulose nanofibrils (CNFs) were obtained by applying a chemical pretreatment consisting of autoclaving the pulp fibers in sodium hydroxide, combined with 2,2,6,6tetramethylpiperidinyl-1-oxyl-mediated oxidation. Three levels of sodium hypochlorite were applied (2.5, 3.8, and 6.0 mmol/g) to obtain CNF qualities (CNF_2.5, CNF_3.8, and CNF_6.0) with varying content of carboxyl groups, that is, 1036, 1285, and 1593 μmol/g cellulose. The cytotoxicity and skin irritation potential (indirect tests) of the CNFs were determined according to standardized in vitro testing for medical devices. We here demonstrate that autoclaving (121 °C, 20 min), which was used to sterilize the gels, caused a modification of the CNF characteristics. This was confirmed by a reduction in the viscosity of the gels, a morphological change of the nanofibrils, by an increase of the ultraviolet−visible absorbance maxima at 250 nm, reduction of the absolute zeta potential, and by an increase in aldehyde content and reducing sugars after autoclaving. Fouriertransform infrared spectroscopy and wide-angle X-ray scattering complemented an extensive characterization of the CNF gels, before and after autoclaving. The antibacterial properties of autoclaved carboxylated CNFs were demonstrated in vitro (bacterial survival and swimming assays) on Pseudomonas aeruginosa and Staphylococcus aureus. Importantly, a mouse in vivo surgical-site infection model on S. aureus revealed that CNF_3.8 showed pronounced antibacterial effect and performed as good as the antiseptic Prontosan wound gel.

A Review on Cellulose-based Materials for Biomedicine

“…aeruginosa [76]. The physical, chemical, antibacterial activity of carboxylate CNF can be modified via treatment such as autoclaves [77]. The autoclave treatment at 121 °C for 20 min reduced the gels' viscosity, increased the ultraviolet-visible absorbance maxima at 250 nm, and increased the aldehyde content.…”

“…The autoclave treatment at 121 °C for 20 min reduced the gels' viscosity, increased the ultraviolet-visible absorbance maxima at 250 nm, and increased the aldehyde content. Autoclaved carboxylate CNF showed high antibacterial activity with minimal toxicity toward L929 mouse fibroblasts and reconstructed human epidermis (RhE) [77]. The antibacterial activity of carboxylate CNF with different oxidation levels was evaluated against P.aeruginosa and S.aureus [45,77].…”

“…Autoclaved carboxylate CNF showed high antibacterial activity with minimal toxicity toward L929 mouse fibroblasts and reconstructed human epidermis (RhE) [77]. The antibacterial activity of carboxylate CNF with different oxidation levels was evaluated against P.aeruginosa and S.aureus [45,77]. Oxygenated CNF exhibited higher antibacterial activity than non-oxygenated CNF dispersion [45,77].…”

“…The antibacterial activity of carboxylate CNF with different oxidation levels was evaluated against P.aeruginosa and S.aureus [45,77]. Oxygenated CNF exhibited higher antibacterial activity than non-oxygenated CNF dispersion [45,77].…”

“…The antibacterial of pure cellulose nanoparticles could be due to several mechanisms, including; decrease the mobility of bacteria cells [76], surrounding and entrapping the bacteria via the formation of a network [45], and reduced pH value due to the increase of aldehydes groups in CNFs [73,77]. However, further investigations should be carried out to understand the key parameters affecting the antibacterial activity of pure cellulose nanomaterials.…”