Amount, characteristics and safety of nano-scale cellulose fibrils

The aim of the study was to analyse the amount and properties of the finest fraction of cellulose nanofibrils (CNF), as well as to study its toxicity to humans as part of its safety assessment. A finely ground CNF was fractionated into four separate size fractions using a MicroFracon device, which utilises a tube flow fractionation principle. The two finest fractions, comprising around 20% of the original material, were collected and combined for further studies. Estimates for the dimensions of fibrils in the fraction were obtained with an in-line image analysis of the MicroFracon device, and transmittance measuremens were used for indirect information of the particle size. The morphological studies performed with state-of-the art methods, such as scanning electron (SEM) and atomic force microscopy (AFM), showed that the fraction was quite monodisperse, contrary to the original, heterogeous CNF sample, and consisted of thin, long fibrils. The cytotoxicity of the fraction was assessed by performing the short-term cytotoxicity studies in vitro, including estimates of the highest tolerated dose (HTD) and total protein content (TPC). Sublethality on human cells was studied with the RNA inhibition test, while Ames test was used to evaluate the genotoxicity of the fraction and test with nematode for studying its potential systemic effects. Some indication of cytotoxicity was observed in the TPC test with the highest sample concentration. However, the significance of this result should be addressed in relation to the other toxicity tests, in which no toxicity was observed. And most importantly, no indication of toxicity was found in the in vivo test.