In Vitro Biological Impact of Nanocellulose Fibers on Human Gut Bacteria and Gastrointestinal Cells

A 28-Day Repeated Oral Administration Study of Mechanically Fibrillated Cellulose Nanofibers According to OECD TG407

The impact of oral administration of mechanically fibrillated cellulose nanofibers (fib-CNF), a commonly used nanofiber, on toxicity and health remains unclear, despite reports of the safety and beneficial effects of chitin-based nanofibers. Thus, evaluating the oral toxicity of fib-CNF in accordance with OECD Test Guideline 407 (TG407) is essential. This study aimed to assess the safety of orally administered fib-CNF through an acute toxicity study in rats, following the OECD TG407 guidelines for 4 weeks. CNF "BiNFi-s" FMa-10005, derived from mechanically fibrillated pulp cellulose, was administered via gavage to male and female Crl:CD(SD) rats at doses of 50, 150, 500, and 1000 mg/kg/day for 28 days, with a control group receiving water for injection. The study evaluated the toxic effects of repeated administration, and the rats were monitored for an additional 14 days post-administration to assess recovery from any toxic effects. The results showed no mortality in either sex during the administration period, and no toxicological effects related to the test substance were observed in various assessments, including general condition and behavioral function observations, urinalysis, hematological examination, blood biochemical examination, necropsy findings, organ weights, and histopathological examination. Notably, only female rats treated with 1000 mg/kg/day of CNF exhibited a consistent reduction in body weight during the 14-day recovery period after the end of treatment. They also showed a slight decrease in pituitary and liver weights. However, hematological and blood biochemical tests did not reveal significant differences, suggesting a potential weight-suppressive effect of CNF ingestion.

Exploring xylan removal via enzymatic post-treatment to tailor the properties of cellulose nanofibrils for packaging film applications

Hemicellulose plays a key role in both the production of cellulose nanofibrils (CNF) and their properties as suspensions and films. While the use of enzymatic and chemical pre-treatments for tailoring hemicellulose levels is well-established, post-treatment methods using enzymes remain relatively underexplored and hold significant promise for modifying CNF film properties. This study aimed to investigate the effects of enzymatic xylan removal on the properties of CNF film for packaging applications. The enzymatic post-treatment was carried out using an enzymatic cocktail enriched with endoxylanase (EX). The EX post-treated-CNFs were characterized by LALLS, XRD, and FEG-SEM, while their films were characterized in terms of physical, morphological, optical, thermal, mechanical, and barrier properties. Employing varying levels of EX facilitated the hydrolysis of 8 to 35 % of xylan, yielding CNFs with different xylan contents. Xylan was found to be vital for the stability of CNF suspensions, as its removal led to the agglomeration of nanofibrils. Nanostructures with preserved crystalline structures and different morphologies, including nanofibers, nanorods, and their hybrids were observed. The EX post-treatment contributed to a smoother film surface, improved thermostability, and better moisture barrier properties. However, as the xylan content decreased, the films became lighter (lower grammage), less strong, and more brittle. Thus, the enzymatic removal of xylan enabled the customization of CNF films' performance without affecting the inherent crystalline structure, resulting in materials with diverse functionalities that could be explored for use in packaging films.

Dual roles of nanocrystalline cellulose extracted from jute (Corchorus olitorius L.) leaves in resisting antibiotics and protecting probiotics

Antibiotics can cure diseases caused by bacterial infections, but their widespread use can have some side effects, such as probiotic reduction. There is an urgent need for such agents that can not only alleviate the damage caused by antibiotics, but also maintain the balance of the gut microbiota. In this study, we first characterized the nanocrystalline cellulose (NCC) extracted from plant jute (Corchorus olitorius L.) leaves. Next, we evaluated the protective effect of jute NCC and cellulose on human model gut bacteria (Lacticaseibacillus rhamnosus and Escherichia coli) under antibiotic stress by measuring bacterial growth and colony forming units. We found that NCC is more effective than cellulose in adsorbing antibiotics and defending the gut bacteria E. coli. Interestingly, the low-dose jute NCC clearly maintained the balance of key gut bacteria like Snodgrassella alvi and Lactobacillus Firm-4 in bees treated with tetracycline and reduced the toxicity caused by antibiotics. It also showed a more significant protective effect on human gut bacteria, especially L. rhamnosus, than cellulose. This study first demonstrated that low-dose NCC performed satisfactorily as a specific probiotic to mitigate the adverse effects of antibiotics on gut bacteria.

Jute (Corchorus olitorius L.) Nanocrystalline Cellulose Inhibits Insect Virus via Gut Microbiota and Metabolism

Natural plant nanocrystalline cellulose (NCC), exhibiting a number of exceptional performance characteristics, is widely used in food fields. However, little is known about the relationship between NCC and the antiviral effect in animals. Here, we tested the function of NCC in antiviral methods utilizing honey bees as the model organism employing Israeli acute paralysis virus (IAPV), a typical RNA virus of honey bees. In both the lab and the field, we fed the IAPV-infected bees various doses of jute NCC (JNCC) under carefully controlled conditions. We found that JNCC can reduce IAPV proliferation and improve gut health. The metagenome profiling suggested that IAPV infection significantly decreased the abundance of gut core bacteria, while JNCC therapy considerably increased the abundance of the gut core bacteria Snodgrassella alvi and Lactobacillus Firm-4. Subsequent metabolome analysis further revealed that JNCC promoted the biosynthesis of fatty acids and unsaturated fatty acids, accelerated the purine metabolism, and then increased the expression of antimicrobial peptides (AMPs) and the genes involved in the Wnt and apoptosis signaling pathways against IAPV infection. Our results highlighted that JNCC could be considered as a prospective candidate agent against a viral infection.

Tackling the cytotoxicity and genotoxicity of cellulose nanofibers from the banana rachis: A new food packaging alternative

Cellulose nanofibrils from the banana rachis are a good alternative as packaging materials, food packaging, stabilizing agents, and functional food ingredients. To address the potential effects of ingested banana rachis cellulose nanofibrils (BR-CNFs), their toxicity in vitro and in vivo was evaluated using Caco-2 intestinal cells and mice, respectively. The results showed that BR-CNFs did not cause cytotoxic effects at the concentrations evaluated on Caco-2 cells. In addition to cytotoxicity tests, genotoxicity assays using comet assay indicated that Caco-2 cells showed no DNA damage at the concentrations of CNFs tested. Finally, acute in vivo cytotoxicity assays indicated that mice showed no sign of pathogenesis or lesions in the liver, kidney, or small intestine when treated with a single dose of BR-CNFs. Moreover, when the mice were treated daily for a month with BR-CNFs no hyperplasia or hypertrophy was observed in any of the organs evaluated. Additionally, biochemical parameters such as blood chemistry, creatinine, liver enzymes, and renal function showed that the BR-CNFs do not cause organ damage. Overall, this study shows that BR-CNFs are neither cytotoxic nor genotoxic. In conclusion, these studies are essential to guarantee the safety of this high value-added product in the food industry.

The emergence of hybrid cellulose nanomaterials as promising biomaterials

Cellulose nanomaterials (CNs) are promising green materials due to their unique properties as well as their environmental benefits. Among these materials, cellulose nanofibrils (CNFs) and nanocrystals (CNCs) are the most extensively researched types of CNs. While they share some fundamental properties like low density, biodegradability, biocompatibility, and low toxicity, they also possess unique differentiating characteristics such as morphology, rheology, aspect ratio, crystallinity, mechanical and optical properties. Therefore, numerous comparative studies have been conducted, and recently, various studies have reported the synergetic advantages resulting from combining CNF and CNC. In this review, we initiate by addressing the terminology used to describe combinations of these and other types of CNs, proposing "hybrid cellulose nanomaterials" (HCNs) as the standardized classifictation for these materials. Subsequently, we briefly cover aspects of properties-driven applications and the performance of CNs, from both an individual and comparative perspective. Next, we comprehensively examine the potential of HCN-based materials, highlighting their performance for various applications. In conclusion, HCNs have demonstraded remarkable success in diverse areas, such as food packaging, electronic devices, 3D printing, biomedical and other fields, resulting in materials with superior performance when compared to neat CNF or CNC. Therefore, HCNs exhibit great potential for the development of environmentally friendly materials with enhanced properties.

Factors affecting the fate of nanoencapsulates post administration

Nanoencapsulation has found numerous applications in the food and nutraceutical industries. Micro and nanoencapsulated forms of bioactives have proven benefits in terms of stability, release, and performance in the body. However, the encapsulated ingredient is often subjected to a wide range of processing conditions and this is followed by storage, consumption, and transit along the gastrointestinal tract. A strong understanding of the fate of nanoencapsulates in the biological system is mandatory as it provides valuable insights for ingredient selection, formulation, and application. In addition to their efficacy, there is also the need to assess the safety of ingested nanoencapsulates. Given the rising research and commercial focus of this subject, this review provides a strong focus on their interaction factors and mechanisms, highlighting their prospective biological fate. This review also covers various approaches to studying the fate of nanoencapsulates in the body. Also, with emphasis on the overall scope, the need for a new advanced integrated common methodology to evaluate the fate of nanoencapsulates post-administration is discussed.

Recent advances in qualitative and quantitative characterization of nanocellulose-reinforced nanocomposites: A review

Nanocellulose has received immense consideration owing to its valuable inherent traits and impressive physicochemical properties such as biocompatibility, thermal stability, non-toxicity, and tunable surface chemistry. These features have inspired researchers to deploy nanocellulose as nanoscale reinforcement materials for bio-based polymers. A simple yet efficient characterization method is often required to gain insights into the effectiveness of various types of nanocellulose. Despite a decade of continuous research and booming growth in scientific publications, nanocellulose research lacks a measuring tool that can characterize its features with acceptable speed and reliability. Implementing reliable characterization techniques is critical to monitor the specifications of nanocellulose alone or in the final product. Many techniques have been developed aiming to measure the nano-reinforcement mechanisms of nanocellulose in polymer composites. This review gives a full account of the scientific underpinnings of techniques that can characterize the shape and arrangement of nanocellulose. This review aims to deliver consolidated details on the properties and characteristics of nanocellulose in biopolymer composite materials to improve various structural, mechanical, barrier and thermal properties. We also present a comprehensive description of the safety features of nanocellulose before and after being loaded within biopolymeric matrices.

KR-12 Derivatives Endow Nanocellulose with Antibacterial and Anti-Inflammatory Properties: Role of Conjugation Chemistry

This work combines the wound-healing-related properties of the host defense peptide KR-12 with wood-derived cellulose nanofibrils (CNFs) to obtain bioactive materials, foreseen as a promising solution to treat chronic wounds. Amine coupling through carbodiimide chemistry, thiol-ene click chemistry, and Cu(I)-catalyzed azide-alkyne cycloaddition were investigated as methods to covalently immobilize KR-12 derivatives onto CNFs. The effects of different coupling chemistries on the bioactivity of the KR12-CNF conjugates were evaluated by assessing their antibacterial activities against Escherichia coli and Staphylococcus aureus. Potential cytotoxic effects and the capacity of the materials to modulate the inflammatory response of lipopolysaccharide (LPS)-stimulated RAW 245.6 macrophages were also investigated. The results show that KR-12 endowed CNFs with antibacterial activity against E. coli and exhibited anti-inflammatory properties and those conjugated by thiol-ene chemistry were the most bioactive. This finding is attributed to a favorable peptide conformation and accessibility (as shown by molecular dynamics simulations), driven by the selective chemistry and length of the linker in the conjugate. The results represent an advancement in the development of CNF-based materials for chronic wound care. This study provides new insights into the effect of the conjugation chemistry on the bioactivity of immobilized host defense peptides, which we believe to be of great value for the use of host defense peptides as therapeutic agents.

Responses of Rat Mesenchymal Stromal Cells to Nanocellulose with Different Functional Groups

Cellulose nanofibrils (CNFs) are multiscale hydrophilic biocompatible polysaccharide materials derived from wood and plants. TEMPO-mediated oxidation of CNFs (TO-CNF) turns some of the primary hydroxyl groups to carboxylate and aldehyde groups. Unlike carboxylic functional groups, there is little or no information about the biological role of the aldehyde groups on the surface of wood-based CNFs. In this work, we replaced the aldehyde groups in the TO-CNF samples with carboxyl groups by another oxidation treatment (TO-O-CNF) or with primary alcohols with terminal hydroxyl groups by a reduction reaction (TO-R-CNF). Rat mesenchymal stem/stromal cells (MSCs) derived from bone marrow were seeded on polystyrene tissue culture plates (TCP) coated with CNFs with and without aldehyde groups. TCP and TCP coated with bacterial nanocellulose (BNC) were used as control groups. Protein adsorption measurements demonstrated that more proteins were adsorbed from cell culture media on all CNF surfaces compared to BNC. Live/dead and lactate dehydrogenase assays confirmed that all nanocellulose biomaterials supported excellent cell viability. Interestingly, TO-R-CNF samples, which have no aldehyde groups, showed better cell spreading than BNC and comparable results to TCP. Unlike TO-O-CNF surfaces, which have no aldehyde groups either, TO-R-CNF stimulated cells, in osteogenic medium, to have higher alkaline phosphatase activity and to form more biomineralization than TCP and TO-CNF groups. These findings indicate that the presence of aldehyde groups (280 ± 14 μmol/g) on the surface of TEMPO-oxidized CNFs might have little or no effect on attachment, proliferation, and osteogenic differentiation of MSCs.

Cellulose Nanofiber-Coated Perfluoropentane Droplets: Fabrication and Biocompatibility Study

Purpose

To study the effect of cellulose nanofiber (CNF)-shelled perfluoropentane (PFP) droplets on the cell viability of 4T1 breast cancer cells with or without the addition of non-encapsulated paclitaxel.

Methods

The CNF-shelled PFP droplets were produced by mixing a CNF suspension and PFP using a homogenizer. The volume size distribution and concentration of CNF-shelled PFP droplets were estimated from images taken with an optical microscope and analyzed using Fiji software and an in-house Matlab script. The thermal stability was qualitatively assessed by comparing the size distribution and concentration of CNF-shelled PFP droplets at room temperature (~22°) and 37°C. The cell viability of 4T1 cells was measured using a 3-[4,5-dimethylthiazol-2yl]-2,5-diphenyltetrazolium bromide (MTT) assay. Additionally, a hemolysis assay was performed to assess blood compatibility of CNF-shelled PFP droplets.

Results

The droplet diameter and concentration of CNF-shelled PFP droplets decreased after 48 hours at both room temperature and 37°C. In addition, the decrease in concentration was more significant at 37°C, from 3.50 ± 0.64×10⁶ droplets/mL to 1.94 ± 0.10×10⁶ droplets/mL, than at room temperature, from 3.65 ± 0.29×10⁶ droplets/mL to 2.56 ± 0.22×10⁶ droplets/mL. The 4T1 cell viability decreased with increased exposure time and concentration of paclitaxel, but it was not affected by the presence of CNF-shelled PFP droplets. No hemolysis was observed at any concentration of CNF-shelled PFP droplets.

Conclusion

CNF-shelled PFP droplets have the potential to be applied as drug carriers in ultrasound-mediated therapy.

Toxicological Assessment of Cellulose Nanomaterials: Oral Exposure

Cellulose nanomaterials (CNMs) have emerged recently as an important group of sustainable bio-based nanomaterials (NMs) with potential applications in multiple sectors, including the food, food packaging, and biomedical fields. The widening of these applications leads to increased human oral exposure to these NMs and, potentially, to adverse health outcomes. Presently, the potential hazards regarding oral exposure to CNMs are insufficiently characterised. There is a need to understand and manage the potential adverse effects that might result from the ingestion of CNMs before products using CNMs reach commercialisation. This work reviews the potential applications of CNMs in the food and biomedical sectors along with the existing toxicological in vitro and in vivo studies, while also identifying current knowledge gaps. Relevant considerations when performing toxicological studies following oral exposure to CNMs are highlighted. An increasing number of studies have been published in the last years, overall showing that ingested CNMs are not toxic to the gastrointestinal tract (GIT), suggestive of the biocompatibility of the majority of the tested CNMs. However, in vitro and in vivo genotoxicity studies, as well as long-term carcinogenic or reproductive toxicity studies, are not yet available. These studies are needed to support a wider use of CNMs in applications that can lead to human oral ingestion, thereby promoting a safe and sustainable-by-design approach.

Effect of Surface Modification on the Pulmonary and Systemic Toxicity of Cellulose Nanofibrils

Cellulose nanofibrils (CNFs) have emerged as sustainable options for a wide range of applications. However, the high aspect ratio and biopersistence of CNFs raise concerns about potential health effects. Here, we evaluated the in vivo pulmonary and systemic toxicity of unmodified (U-CNF), carboxymethylated (C-CNF), and TEMPO (2,2,6,6-tetramethyl-piperidin-1-oxyl)-oxidized (T-CNF) CNFs, fibrillated in the same way and administered to mice by repeated (3×) pharyngeal aspiration (14, 28, and 56 μg/mouse/aspiration). Toxic effects were assessed up to 90 days after the last administration. Some mice were treated with T-CNF samples spiked with lipopolysaccharide (LPS; 0.02-50 ng/mouse/aspiration) to assess the role of endotoxin contamination. The CNFs induced an acute inflammatory reaction that subsided within 90 days, except for T-CNF. At 90 days post-administration, an increased DNA damage was observed in bronchoalveolar lavage and hepatic cells after exposure to T-CNF and C-CNF, respectively. Besides, LPS contamination dose-dependently increased the hepatic genotoxic effects of T-CNF.

Boar seminal plasma improves sperm quality by enhancing its antioxidant capacity during liquid storage at 17°C

The objective of this study was to investigate the effects of different levels of seminal plasma (SP) on boar sperm quality, antioxidant capacity and bacterial concentrations during liquid storage at 17°C. Boar sperm was diluted with Beltsville Thawing Solution (BTS) consisting of 0, 25, 50 and 75% (v/v) of SP. Total motility, progressive motility and dynamic parameters were assessed by the computer assisted sperm analysis (CASA) system. Acrosome and plasma membrane integrity were measured by FITC-PNA/DAPI and SYBR-14/PI staining, respectively. In addition, total antioxidant capacity (T-AOC), malondialdehyde (MDA) content, and reactive oxygen species (ROS) levels were detected using commercial assay kits. Bacterial concentrations were assessed by turbidimetric assay. Our results showed that 25% SP markedly improved total motility, progressive motility, sperm dynamic parameters, acrosome integrity compared with 0, 50 and 75% SP (P < 0.05). In addition, 25% SP significantly increased T-AOC but decreased MDA content and ROS levels compared with 0, and 75% SP (P < 0.05). Moreover, 25% SP significantly decreased the bacterial concentrations in extended semen compared with 50% and 75% SP, however, which was higher than with 0% SP (P < 0.05). These results suggest that 25% SP can promote boar sperm quality through enhancing its antioxidant capacity during liquid storage.

Overview of potential adverse health effects of oral exposure to nanocellulose

Nanocellulose is an emerging material for which several food-related applications are foreseen, for example, novel food, functional food, food additive or in food contact materials. Nanocellulose materials can display a range of possible shapes (fibers, crystals), sizes and surface modifications. For food-related applications in the EU, information on the safety of substances must be assessed. The present review summarizes the current knowledge on (possible) adverse health effects of nanocellulose upon oral exposure, keeping EU regulatory aspects in mind. The overview indicates that toxicity data, especially from in vivo studies, are limited and outcomes are not unambiguous. The hazard assessment is further complicated by: the diversity in morphologies and surface modifications, lack of standard reference materials, limited knowledge about intestinal fate and absorption, analytical difficulties in biological matrices, dispersion issues, the possible presence of impurities and interferences within biological assays. Two subchronic in vivo toxicity studies show no indications of toxicity for two specific nanocellulose materials, even at high doses. However, these studies may have missed certain early or nano-specific toxic effects, such as inflammation potential, for which other, subacute studies provide some indications. Most in vitro studies show no cytotoxicity; however, several indicate that effects on oxidative stress and inflammatory responses depend on differences in size or surface treatments. Further, too few studies assessed genotoxicity of nanocelluloses. Therefore, immunotoxicity, oxidative stress and genotoxicity require further attention, as do absorption and effects on nutrient uptake. Recommendations for future research facilitating the safety assessment and safe-by-design of nanocellulose in food-related applications are provided.

Nanocelluloses - Nanotoxicology, Safety Aspects and 3D Bioprinting

Nanocelluloses have good rheological properties that facilitate the extrusion of nanocellulose gels in micro-extrusion systems. It is considered a highly relevant characteristic that makes it possible to use nanocellulose as an ink component for 3D bioprinting purposes. The nanocelluloses assessed in this book chapter include wood nanocellulose (WNC), bacterial nanocellulose (BNC), and tunicate nanocellulose (TNC), which are often assumed to be non-toxic. Depending on various chemical and mechanical processes, both cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC) can be obtained from the three mentioned nanocelluloses (WNC, BNC, and TNC). Pre/post-treatment processes (chemical and mechanical) cause modifications regarding surface chemistry and nano-morphology. Hence, it is essential to understand whether physicochemical properties may affect the toxicological profile of nanocelluloses. In this book chapter, we provide an overview of nanotoxicology and safety aspects associated with nanocelluloses. Relevant regulatory requirements are considered. We also discuss hazard assessment strategies based on tiered approaches for safety testing, which can be applied in the early stages of the innovation process. Ensuring the safe development of nanocellulose-based 3D bioprinting products will enable full market use of these sustainable resources throughout their life cycle.

Surface functionalization and size modulate the formation of reactive oxygen species and genotoxic effects of cellulose nanofibrils

BACKGROUND

Cellulose nanofibrils (CNFs) have emerged as a sustainable and environmentally friendly option for a broad range of applications. The fibrous nature and high biopersistence of CNFs call for a thorough toxicity assessment, but it is presently unclear which physico-chemical properties could play a role in determining the potential toxic response to CNF. Here, we assessed whether surface composition and size could modulate the genotoxicity of CNFs in human bronchial epithelial BEAS-2B cells. We examined three size fractions (fine, medium and coarse) of four CNFs with different surface chemistry: unmodified (U-CNF) and functionalized with 2,2,6,6-tetramethyl-piperidin-1-oxyl (TEMPO) (T-CNF), carboxymethyl (C-CNF) and epoxypropyltrimethylammonium chloride (EPTMAC) (E-CNF). In addition, the source fibre was also evaluated as a non-nanosized material.

RESULTS

The presence of the surface charged groups in the functionalized CNF samples resulted in higher amounts of individual nanofibrils and less aggregation compared with the U-CNF. T-CNF was the most homogenous, in agreement with its high surface group density. However, the colloidal stability of all the CNF samples dropped when dispersed in cell culture medium, especially in the case of T-CNF. CNF was internalized by a minority of BEAS-2B cells. No remarkable cytotoxic effects were induced by any of the cellulosic materials. All cellulosic materials, except the medium fraction of U-CNF, induced a dose-dependent intracellular formation of reactive oxygen species (ROS). The fine fraction of E-CNF, which induced DNA damage (measured by the comet assay) and chromosome damage (measured by the micronucleus assay), and the coarse fraction of C-CNF, which produced chromosome damage, also showed the most effective induction of ROS in their respective size fractions.

CONCLUSIONS

Surface chemistry and size modulate the in vitro intracellular ROS formation and the induction of genotoxic effects by fibrillated celluloses. One cationic (fine E-CNF) and one anionic (coarse C-CNF) CNF showed primary genotoxic effects, possibly partly through ROS generation. However, the conclusions cannot be generalized to all types of CNFs, as the synthesis process and the dispersion method used for testing affect their physico-chemical properties and, hence, their toxic effects.

A systematic review on the effects of nanomaterials on gut microbiota

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Nanomaterials have been shown to affect gut microbiota (GM) both in vivo and in vitro.

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The effects have been shown to depend on size, dose, dose duration and functional groups.

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In general, more studies seem to indicate dose-dependent adverse effects of NMs towards GM.

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Standardized protocols are needed for characterization of NMs, dosing, and test systems (both in vitro and in vivo).

Some nanomaterials (NMs) have been shown to possess antimicrobial activity and cause GM dysbiosis. Since NMs are being used widely, a systematic assessment of the effects of NMs on GM is warranted. In this systematic review, a total of 46 in vivo and 22 in vitro studies were retrieved from databases and search engines including Science-Direct, Pubmed and Google scholar. Criteria for assessment of studies included use of in vitro or in vivo studies, characterization of NMs, use of single or multiple doses as well as consistency of results. GM dysbiosis has been studied most widely on TiO₂, Ag, Zn-based NMs. There was moderate evidence for GM dysbiosis caused by Zn- and Cu-based NMs, Cu-loaded chitosan NPs and Ag NMs, and anatase TiO₂ NPs, as well as low evidence for SWCNTs, nanocellulose, SiO₂, Se, nanoplastics, CeO_2, MoO₃ and graphene-based NMs. Most studies indicate adverse effects of NMs towards GM. However, more work is required to elucidate the differences on the reported effects of NM by type and sex of organisms, size, shape and surface properties of NMs as well as effects of exposure to mixtures of NMs. For consistency and better agreement among studies on GM dysbiosis, there is need for internationally agreed protocols on, inter alia, characterization of NMs, dosing (amounts, frequency and duration), use of sonication, test systems (both in vitro and in vivo), including oxygen levels for in vitro models.

Advanced Functional Materials Based on Nanocellulose for Pharmaceutical/Medical Applications

Nanocelluloses (NCs), with their remarkable characteristics, have proven to be one of the most promising "green" materials of our times and have received special attention from researchers in nanomaterials. A diversity of new functional materials with a wide range of biomedical applications has been designed based on the most desirable properties of NCs, such as biocompatibility, biodegradability, and their special physicochemical properties. In this context and under the pressure of rapid development of this field, it is imperative to synthesize the successes and the new requirements in a comprehensive review. The first part of this work provides a brief review of the characteristics of the NCs (cellulose nanocrystals-CNC, cellulose nanofibrils-CNF, and bacterial nanocellulose-BNC), as well as of the main functional materials based on NCs (hydrogels, nanogels, and nanocomposites). The second part presents an extensive review of research over the past five years on promising pharmaceutical and medical applications of nanocellulose-based materials, which have been discussed in three important areas: drug-delivery systems, materials for wound-healing applications, as well as tissue engineering. Finally, an in-depth assessment of the in vitro and in vivo cytotoxicity of NCs-based materials, as well as the challenges related to their biodegradability, is performed.

Fluorescently Labeled Cellulose Nanofibers for Environmental Health and Safety Studies

An optimal methodology for locating and tracking cellulose nanofibers (CNFs) in vitro and in vivo is crucial to evaluate the environmental health and safety properties of these nanomaterials. Here, we report the use of a new boron-dipyrromethene (BODIPY) reactive fluorescent probe, meso-DichlorotriazineEthyl BODIPY (mDTEB), tailor-made for labeling CNFs used in simulated or in vivo ingestion exposure studies. Time-correlated single photon counting (TCSPC) fluorescence lifetime imaging microscopy (FLIM) was used to confirm covalent attachment and purity of mDTEB-labeled CNFs. The photoluminescence properties of mDTEB-labeled CNFs, characterized using fluorescence spectroscopy, include excellent stability over a wide pH range (pH2 to pH10) and high quantum yield, which provides detection at low (μM) concentrations. FLIM analysis also showed that lignin-like impurities present on the CNF reduce the fluorescence of the mDTEB-labeled CNF, via quenching. Therefore, the chemical composition and the methods of CNF production affect subsequent studies. An in vitro triculture, small intestinal, epithelial model was used to assess the toxicity of ingested mDTEB-labeled CNFs. Zebrafish (Danio rerio) were used to assess in vivo environmental toxicity studies. No cytotoxicity was observed for CNFs, or mDTEB-labeled CNFs, either in the triculture cells or in the zebrafish embryos.

Role of Surface Chemistry in the In Vitro Lung Response to Nanofibrillated Cellulose

Wood-derived nanofibrillated cellulose (NFC) has emerged as a sustainable material with a wide range of applications and increasing presence in the market. Surface charges are introduced during the preparation of NFC to facilitate the defibrillation process, which may also alter the toxicological properties of NFC. In the present study, we examined the in vitro toxicity of NFCs with five surface chemistries: nonfunctionalized, carboxymethylated, phosphorylated, sulfoethylated, and hydroxypropyltrimethylammonium-substituted. The NFC samples were characterized for surface functional group density, surface charge, and fiber morphology. Fibril aggregates predominated in the nonfunctionalized NFC, while individual nanofibrils were observed in the functionalized NFCs. Differences in surface group density among the functionalized NFCs were reflected in the fiber thickness of these samples. In human bronchial epithelial (BEAS-2B) cells, all NFCs showed low cytotoxicity (CellTiter-GloVR luminescent cell viability assay) which never exceeded 10% at any exposure time. None of the NFCs induced genotoxic effects, as evaluated by the alkaline comet assay and the cytokinesis-block micronucleus assay. The nonfunctionalized and carboxymethylated NFCs were able to increase intracellular reactive oxygen species (ROS) formation (chloromethyl derivative of 2',7'-dichlorodihydrofluorescein diacetate assay). However, ROS induction did not result in increased DNA or chromosome damage.

In Vitro Investigation of Thiol-Functionalized Cellulose Nanofibrils as a Chronic Wound Environment Modulator

There is currently a huge need for new, improved therapeutic approaches for the treatment of chronic wounds. One promising strategy is to develop wound dressings capable of modulating the chronic wound environment (e.g., by controlling the high levels of reactive oxygen species (ROS) and proteases). Here, we selected the thiol-containing amino acid cysteine to endow wood-derived cellulose nanofibrils (CNF) with bioactivity toward the modulation of ROS levels and protease activity. Cysteine was covalently incorporated into CNF and the functionalized material, herein referred as cys-CNF, was characterized in terms of chemical structure, degree of substitution, radical scavenging capacity, and inhibition of protease activity. The stability of the thiol groups was evaluated over time, and an in vitro cytotoxicity study with human dermal fibroblasts was performed to evaluate the safety profile of cys-CNF. Results showed that cys-CNF was able to efficiently control the activity of the metalloprotease collagenase and to inhibit the free radical DPPH (1,1-Diphenyl-2-picrylhydrazyl radical), activities that were correlated with the presence of free thiol groups on the nanofibers. The stability study showed that the reactivity of the thiol groups challenged the bioactivity over time. Nevertheless, preparing the material as an aerogel and storing it in an inert atmosphere were shown to be valid approaches to increase the stability of the thiol groups in cys-CNF. No signs of toxicity were observed on the dermal fibroblasts when exposed to cys-CNF (concentration range 0.1-0.5 mg/mL). The present work highlights cys-CNF as a promising novel material for the development of bioactive wound dressings for the treatment of chronic wounds.

Nanocellulose Bio-Based Composites for Food Packaging

The food industry is increasingly demanding advanced and eco-friendly sustainable packaging materials with improved physical, mechanical and barrier properties. The currently used materials are synthetic and non-degradable, therefore raising environmental concerns. Consequently, research efforts have been made in recent years towards the development of bio-based sustainable packaging materials. In this review, the potential of nanocelluloses as nanofillers or as coatings for the development of bio-based nanocomposites is discussed, namely: (i) the physico-chemical interaction of nanocellulose with the adjacent polymeric phase, (ii) the effect of nanocellulose modification/functionalization on the final properties of the composites, (iii) the production methods for such composites, and (iv) the effect of nanocellulose on the overall migration, toxicity, and the potential risk to human health. Lastly, the technology readiness level of nanocellulose and nanocellulose based composites for the market of food packaging is discussed.