Antibacterial polylactic acid fabricated via Pickering emulsion approach with polyethyleneimine and polydopamine modified cellulose nanocrystals as emulsion stabilizers.

Antibacterial biodegradable plastics are highly demanded for food package and disposable medical plastic consumables. Incorporating antibacterial nanoagents into polymer matrices is an effective method to endow polymers with antibacterial activity. However, synthesis of sustainable antibacterial nanoagents with high antibacterial activity via facile approach and well dispersion of them in polymer matrices are still challenging. In this study, polyethyleneimine (PEI) was grafted on surface of cellulose nanocrystals (CNCs) via the oxidation self-polymerization of dopamine (DA) and the Michael addition/Schiff base reaction between DA and PEI. The resulted PEI and polydopamine modified CNCs (PPCs) showed substantially enhanced antibacterial activity and reduced cytotoxicity for NIH3T3 than PEI due to increased local concentration and anchoring of PEI. The minimum concentration of PPCs to achieve antibacterial rate of 99.99 % against S. aureus and E. coli were about 50 and 20 µg/mL, respectively. PPCs displayed outstanding emulsifying ability, and PPC coated polylactic acid (PLA) microspheres were obtained by drying PPC stabilized PLA Pickering emulsion, leading to a well dispersion of PPCs in PLA. PPC/PLA film prepared by hot-pressing displayed great antibacterial performance and enhanced mechanical properties. Therefore, this study proposed a facile approach to fabricate biocompatible antibacterial nanoagents and plastics.

Tannic acid-coated cellulose nanocrystals with enhanced mucoadhesive properties for aquaculture.

Mucoadhesion can be exploited as a strategy to target drug and nutrient delivery to the outer mucosal layers of fish in aquaculture farms. Cellulose nanocrystals (CNC) derived from cellulose pulp fibers can interact with the mucosal membranes via hydrogen bonding, however, their mucoadhesive properties are weak and should be enhanced. In this study, CNC were coated with tannic acid (TA), a plant polyphenol with excellent wet-resistant bioadhesive properties, to strengthen their mucoadhesive capability. The optimal CNC:TA mass ratio was determined to be 20:1. The modified CNCs were 190 ± 40 nm in length and 21 ± 4 nm wide and displayed excellent colloidal stability, with a zeta potential of -35 mV. Turbidity titrations and rheological measurements revealed that the modified CNC possessed superior mucoadhesive properties compared to pristine CNC. Modification with tannic acid introduced additional functional groups for stronger hydrogen bond formation and hydrophobic interactions with mucin, which was confirmed by a large reduction in viscosity enhancement values in the presence of chemical blockers (urea and Tween80). The enhanced mucoadhesion of the modified CNC could be utilized for the fabrication of a mucoadhesive drug delivery system to promote sustainable aquaculture practices.

Electroconductive cellulose nanocrystals - Synthesis, properties and applications: A review.

There is a growing interest in the synthesis of electrically conductive cellulose nanocrystal (CNC) for advanced applications, such as supercapacitor, batteries, sensor, and printed electronics. CNC is recognized as an attractive template for the fabrication of functional nanomaterials. Since CNC possesses many attractive properties, it is a sustainable template to prepare conductive nanomaterials, by either coating it with a conductive material or transforming it into carbon nanorods. This review summarizes the utilization of a sustainable and low-cost CNC to produce conductive nanocomposites via an environmentally friendly process. Electroconductive CNCs with enhanced electrical properties, lower electrical percolation threshold, and better mechanical properties can be produced and are attractive systems for many new applications.

Emulsions undergoing phase transition: Effect of emulsifier type and concentration.

Pickering emulsion stabilized by cellulose nanocrystals (CNCs) during the phase transition of the dispersed oil is poorly understood. We investigated the capability of CNC in stabilizing Pickering emulsions during the temperature-induced phase transition. Paraffin wax emulsions stabilized by sodium dodecyl sulfate (SDS) were less stable than CNC stabilized emulsions. The relationship between droplet size and emulsifier content was examined, and a new model describing this relationship is proposed. The droplet size of CNC-based systems was not affected by temperature variation, even at low CNC concentrations. The minimum CNC content required to stabilize the paraffin wax emulsion was lower than SDS. DSC results indicated that higher droplet surface coverage with emulsifiers enhanced the deformation resistance of the crystallized droplets, which enhanced the emulsion stability. Temperature sweep viscosity measurements showed that the stability of CNC-based systems was not significantly impacted by the phase transition of the paraffin wax. Rheological amplitude sweep analysis indicated that emulsions above the melting point of paraffin wax were more stable at all strain levels. However, the SDS-based systems displayed substantial heterogeneity after the liquid-solid transition. Frequency sweep tests revealed that CNC-stabilized emulsions were more stable than SDS-stabilized emulsions.

Bile Acid Sequestrants for Hypercholesterolemia Treatment Using Sustainable Biopolymers: Recent Advances and Future Perspectives.

Bile acids, the endogenous steroid nucleus containing signaling molecules, are responsible for the regulation of multiple metabolic processes, including lipoprotein and glucose metabolism to maintain homeostasis. Within our body, they are directly produced from their immediate precursors, cholesterol C (low-density lipoprotein C, LDL-C), through the enzymatic catabolic process mediated by 7-α-hydroxylase (CYP7A1). Bile acid sequestrants (BASs) or amphiphilic resins that are nonabsorbable to the human body (being complex high molecular weight polymers/electrolytes) are one of the classes of drugs used to treat hypercholesterolemia (a high plasma cholesterol level) or dyslipidemia (lipid abnormalities in the body); thus, they have been used clinically for more than 50 years with strong safety profiles as demonstrated by the Lipid Research Council-Cardiovascular Primary Prevention Trial (LRC-CPPT). They reduce plasma LDL-C and can slightly increase high-density lipoprotein C (HDL-C) levels, whereas many of the recent clinical studies have demonstrated that they can reduce glucose levels in patients with type 2 diabetes mellitus (T2DM). However, due to higher daily dosage requirements, lower efficacy in LDL-C reduction, and concomitant drug malabsorption, research to develop an "ideal" BAS from sustainable or natural sources with better LDL-C lowering efficacy and glucose regulations and lower side effects is being pursued. This Review discusses some recent developments and their corresponding efficacies as bile removal or LDL-C reduction of natural biopolymer (polysaccharide)-based compounds.

Effect of Oil Phase Transition on the Stability of Pickering Emulsions Stabilized by Cellulose Nanocrystals.

Emulsifier design is one of the key strategies in interfacial engineering for emulsion stability. In this study, cellulose nanocrystals (CNCs) were used as an interfacial stabilizer to improve the stability of coconut oil (CO)-in-water emulsions. A Pickering emulsion consisting of CO and water was optimized based on four parameters using the response surface methodology and the central composite design. The droplet coverage remained stable during the crystallization of the oil phase when the temperature was reduced below the melting temperature of CO. Fluorescent-labeled CNCs were used to monitor the partitioning of CNC at the O/W interface during the crystallization of CO. The Generation 6 polyamidoamine (G6 PAMAM) dendrimer covalently grafted on the surface of CNC was used as an intrinsic fluorescent dye. Since it displayed similar properties as the emulsifier, it could be used to monitor the CNC coverage on the oil droplets at various temperatures. The fluorescence micrographs showed that the emission of PAMAM CNCs at the O/W interface remained on both the liquid and solid CO droplets, confirming that oil crystallization did not affect the fluorescent CNC coverage on the oil droplets.

Fishing for the right probiotic: host-microbe interactions at the interface of effective aquaculture strategies.

Effective aquaculture management strategies are paramount to global food security. Growing demands stimulate the intensification of production and create the need for practices that are both economically viable and environmentally sustainable. Importantly, pathogenic microbes continue to be detrimental to fish growth and survival. In terms of host health, the intestinal mucosa and its associated consortium of microbes have a critical role in modulating fitness and present an attractive opportunity to promote health at this interface. In light of this, the administration of probiotic microorganisms is being considered as a means to restore and sustain health in fish. Current evidence suggests that certain probiotic strains might be able to augment immunity, enhance growth rate and protect against infection in salmonids, the most economically important family of farmed finfish. This review affirms the relevance of host-microbe interactions in salmonids in light of emerging evidence, with an emphasis on intestinal health. In addition, the current understanding of the mode of action of probiotics in salmonid fish is discussed, along with delivery systems that can effectively carry the living microbes.

Encapsulation and controlled release of vitamin C in modified cellulose nanocrystal/chitosan nanocapsules.

Vitamin C (VC), widely used in food, pharmaceutical and cosmetic products, is susceptible to degradation, and new formulations are necessary to maintain its stability. To address this challenge, VC encapsulation was achieved via electrostatic interaction with glycidyltrimethylammonium chloride (GTMAC)-chitosan (GCh) followed by cross-linking with phosphorylated-cellulose nanocrystals (PCNC) to form VC-GCh-PCNC nanocapsules. The particle size, surface charge, degradation, encapsulation efficiency, cumulative release, free-radical scavenging assay, and antibacterial test were quantified. Additionally, a simulated human gastrointestinal environment was used to assess the efficacy of the encapsulated VC under physiological conditions. Both VC loaded, GCh-PCNC, and GCh-Sodium tripolyphosphate (TPP) nanocapsules were spherical with a diameter of 450 â€‹± â€‹8 and 428 â€‹± â€‹6 â€‹nm respectively. VC-GCh-PCNC displayed a higher encapsulation efficiency of 90.3 â€‹± â€‹0.42% and a sustained release over 14 days. The release profiles were fitted to the first-order and Higuchi kinetic models with R2 values greater than 0.95. VC-GCh-PCNC possessed broad-spectrum antibacterial activity with a minimum inhibition concentration (MIC) of 8-16 â€‹µg/mL. These results highlight that modified CNC-based nano-formulations can preserve, protect and control the release of active compounds with improved antioxidant and antibacterial properties for food and nutraceutical applications.

Effect of Molecular Architecture and Composition on the Aggregation Pathways of POEGMA Random Copolymers in Water.

Understanding of the temperature-induced phase transition of poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) random copolymers with varied composition remains largely incomplete. Upon heating they can form either macroscopically phase-separated aggregates or micelles. We examined the effect of polymer architecture by rationally designing and synthesizing various POEGMA copolymer structures via atom transfer radical polymerization using OEGMA monomers of different EO lengths. Micelle formation occurred for copolymers with a small fraction of long side chains counterbalanced by an appropriate number of short side chains, while macroscopic phase separation occurred for other copolymer compositions. In some copolymer compositions and architectures, micelle formation followed by macroscopic phase separation occurred, and the temperature of these phase transitions could be tailored accordingly. This new strategy allows the control over the microstructure and specific transition temperatures enabling, for instance, the preparation of nanocarriers for encapsulating hydrophobic compounds.

Functional cellulose nanocrystals containing cationic and thermo-responsive polymer brushes.

Cationic and thermo-responsive polymer brushes were grafted from the surface of cellulose nanocrystals. Di(ethylene glycol) methyl ether methacrylate (MEO2MA) and poly(oligoethylene glycol) methyl ether acrylate (OEGMA300) and (2-methacryloyloxyethyl) trimethylammonium chloride (DMC) were grafted from cellulose nanocrystals (CNCs) via free radical polymerization. The CNC-g-POEGMA (CP) possessed a tunable lower critical solution temperature (LCST) of about 50 °C, and cloud point measurements confirmed that the LCST of the nanoparticles could be manipulated within the range of 40-47 °C by adjusting the DMC content. The salt effect was also investigated, and the results revealed a typical salting-out effect for the CNC-g-POEGMA after the introduction of KCl. On the other hand, the CNC-g-POEGMA-g-DMC (CPD) copolymers displayed two salt-responsive characteristics; polyelectrolyte effect at lower salt concentrations, followed by the salting-out effect at higher salt concentrations, which is dependent on the DMC content.

Interfacial Control of the Synthesis of Cellulose Nanocrystal Gold Nanoshells.

Cellulose nanocrystal (CNC) gold nanoshell was prepared using a polymer-coated CNC as a template. A seed-mediated shell growth approach (ex situ) was employed, gold nanoparticles (AuNPs) of two sizes were prepared, and the effect of the size of AuNP on the shell quality (smoothness, evenness, and continuity) was elucidated. Additionally, a novel one-pot synthesis approach (in situ) was evaluated for the preparation of the gold nanoshell, where polymer-coated CNCs with adsorbed ascorbic acid were used to reduce Au ions to form a metallic gold shell on CNC. The surface coverage was manipulated by adding different amounts of plating solutions. The formation and morphology of gold nanoshells were evaluated by zeta potential measurements, dynamic light scattering, UV-vis spectroscopy, and transmission electron microscopy (TEM). The catalytic performance of the CNC-gold nanostructures for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) was governed by the surface area of gold shells.

Functionalized cellulose nanocrystals as the performance regulators of poly(ß-hydroxybutyrate-co-valerate) biocomposites.

To investigate the relationship between functional groups on cellulose nanocrystals (CNC) and the performance of poly(ß-hydroxybutyrate-co-valerate) (PHBV), the surface of CNC was modified by surface graft modification and PHBV/CNC biocomposites were prepared by melt blending. To demonstrate the interfacial adhesion difference between hydrophobic PHBV and hydrophilic CNC, palmitoyl chloride and ε-caprolactone had been used to tailor the oleophilic property of CNC. Results showed that CNC had heterogeneous nucleation effect on the crystallization process of PHBV, while the entanglement of molecular chains weakened the promoting functions of CNC-g-C16 (CNC grafted with palmitoyl chloride) and CNC-g-CL (CNC grafted with ε-caprolactone). Furthermore, CNC-g-CL exhibited better interfacial adhesion with PHBV when compared with CNC-g-C16. And 1 wt% CNC-g-CL improved the tensile strength of PHBV biocomposite to 38.09 MPa, which is 26.25% higher than PHBV.

Double stabilization mechanism of O/W Pickering emulsions using cationic nanofibrillated cellulose.

HYPOTHESIS: Hydrophobic oleic acid/water interfaces are negatively charged. Hence, the use of cationic nanocelluloses as stabilizers of Pickering emulsions could improve the colloidal stability due to the electrostatic complexation at the oil-water interface. EXPERIMENTS: Two cationic nanofibrillated cellulose (cNFCs) with two degrees of substitution were prepared and used as stabilizers of Pickering emulsions. The adsorption of cNFCs at the oil: water interface was evaluated by interfacial tension, atomic force microscopy, and centrifugation measurements. LUMiSizer and optical microscopy techniques were used to analyze the colloidal stability and oil droplets morphology, respectively. Besides, the rheological behavior of the continuous aqueous phase was determined through flow and stress sweep curves. Finally, the dispersion of cNFCs in a diluted emulsion was visualized by cryogenic transmission electron microscopy (cryo-TEM). FINDINGS: Cationic NFCs were more efficient in partitioning to the oil:water interface compared to their anionic analogous, oCNF. The electrostatic attraction between the positively charged trimethylammonium groups and the negatively charged deprotonated oleic acid reduced the interfacial tension and improved the colloidal stability of O/W Pickering emulsions. cNFCs dispersed in the aqueous phase were found to increase the viscosity, decelerating the oil drops coalescence. Therefore, the stabilization of cNFCs Pickering emulsions had a synergistic effect from the electrostatic complexation at the liquid-liquid interface and network formation in the aqueous phase, as visualized by cryo-TEM.

Reinforcement of rubber nanocomposite thin sheets by percolation of pristine cellulose nanocrystals.

Research on the use of bio-based material rather than fossil fuel-based synthetic polymers is of considerable value due to the increasing interest in biodegradable and ecofriendly products. This paper describes an in-depth analysis of the effect of cellulose nanocrystals (CNC), a promising nanomaterial filler derived from cellulosic biomass, on the mechanical properties of rubber latex thin sheets. Sheets of styrene butadiene rubber (SBR) and its bio-based alternative, natural rubber (NR) were tested and compared. Percolation of CNC was studied within the rubber matrices, where the tear strength, water permeability, and water absorption increased due to the formation of a continuous network of CNC within the polymer thin sheets. The rubber nanocomposites were resistant to tear propagation, caused by increased tortuosity along the tear path brought about by CNC dispersion and filler network formation. The CNC reinforcement yielded thin sheets that were much stronger and more durable than their non-reinforced counterparts. Additionally, the increased water uptake of the sheets could aid in the biodegradation of the polymer. Thus, CNC is found to be an excellent functional filler in rubber sheets, where its formation of a percolating network significantly improved their properties.

Enantiomeric glycosylated cationic block co-beta-peptides eradicate Staphylococcus aureus biofilms and antibiotic-tolerant persisters.

The treatment of bacterial infections is hindered by the presence of biofilms and metabolically inactive persisters. Here, we report the synthesis of an enantiomeric block co-beta-peptide, poly(amido-D-glucose)-block-poly(beta-L-lysine), with high yield and purity by one-shot one-pot anionic-ring opening (co)polymerization. The co-beta-peptide is bactericidal against methicillin-resistant Staphylococcus aureus (MRSA), including replicating, biofilm and persister bacterial cells, and also disperses biofilm biomass. It is active towards community-acquired and hospital-associated MRSA strains which are resistant to multiple drugs including vancomycin and daptomycin. Its antibacterial activity is superior to that of vancomycin in MRSA mouse and human ex vivo skin infection models, with no acute in vivo toxicity in repeated dosing in mice at above therapeutic levels. The copolymer displays bacteria-activated surfactant-like properties, resulting from contact with the bacterial envelope. Our results indicate that this class of non-toxic molecule, effective against different bacterial sub-populations, has promising potential for the treatment of S. aureus infections.

Polymeric hollow microcapsules (PHM) via cellulose nanocrystal stabilized Pickering emulsion polymerization.

A practical and sustainable method to prepare polymeric hollow microcapsules (PHMs) using cellulose nanocrystal (CNC) stabilized Pickering emulsion polymerization was developed. Pristine CNCs hydrolyzed from wood pulp are hydrophilic and could be employed as emulsifiers to prepare oil-in-water (O/W) Pickering emulsions. The O/W Pickering emulsions were used as templates for the Pickering emulsion polymerization of hydrophobic monomers inside the emulsion droplets. The crosslinked hydrophobic polymers phase separated and partitioned to the interface of the Pickering emulsion, leading to the formation of hydrophobic PHMs. Correspondingly, cinnamate modified CNCs with less surface hydrophilicity were employed as emulsifiers to obtain water-in-oil (W/O) inverse Pickering emulsions, which were then used as templates for inverse Pickering emulsion polymerization of hydrophilic monomers to prepare hydrophilic PHMs. Therefore, both hydrophobic and hydrophilic PHMs could be obtained via this approach. Herein, polystyrene, poly(4-vinylpyridine), and poly(N-isopropyl acrylamide) hollow microcapsules were prepared as models, where the size, crosslinking density, shell structure and stimuli-responsive properties of PHMs could be tuned by varying the synthesis parameters.

CO2-Responsive Cellulose Nanofibers Aerogels for Switchable Oil-Water Separation.

Cellulose nanofibers (CNFs) aerogels with controllable surface wettability were prepared by grafting poly( N, N-dimethylamino-2-ethyl methacrylate) (PDMAEMA) polymer brushes via surface-initiated atom-transfer radical polymerization. After grafting PDMAEMA polymer, the surface of the aerogel was hydrophobic. However, in the presence of CO2, the surface of the aerogel gradually changes from hydrophobic to hydrophilic. The porous structure and CO2-responsiveness of PDMAEMA brushes within the CNFs aerogels allowed for the on-off switching of the oil-water mixture separation process. These CNFs aerogels were recyclable and displayed attractive separation efficiency for oil-water mixture and surfactant-stabilized emulsions. Furthermore, the switchable surface wettability holds an advantage of avoiding oil-fouling, which will greatly improve its recyclability.

A comparative study on grafting polymers from cellulose nanocrystals via surface-initiated atom transfer radical polymerization (ATRP) and activator re-generated by electron transfer ATRP.

Both Surface-Initiated Atom Transfer Radical Polymerization (SI-ATRP) and Surface-Initiated Activator Re-Generated by Electron Transfer ATRP (SI-ARGET ATRP) were performed to graft polystyrene and poly(4-vinylpyridine) on the surface of cellulose nanocrystals (CNCs) to evaluate the potential benefits of each method. The polymer grafted CNCs and their corresponding free polymers initiated from sacrificial initiators were characterized by Fourier transform infrared spectroscopy, gel permeation chromatography, dynamic light scattering, differential scanning calorimetry, thermogravimetric analysis, and elemental analysis, respectively. It was found that SI-ARGET ATRP favored the grafting of longer polymer chains with lower grafting density compared with the classical SI-ATRP. The surface initiation efficiency of brominated CNCs in SI-ARGET ATRP is much lower than that in SI-ATRP, which is mainly due to the much lower amount (ppm level) of catalysts and faster propagation rate in SI-ARGET ATRP system.

Cellulose Nanocrystal-ZnO Nanohybrids for Controlling Photocatalytic Activity and UV Protection in Cosmetic Formulation.

A high-performance semiconductor zinc oxide (ZnO) on melamine formaldehyde-coated cellulose nanocrystals (MFCNCs) was synthesized and evaluated for its application in smart cosmetics. These ZnO@MFCNC hybrid nanostructures were evaluated for their in vitro sun protection factor performance and photocatalytic activity under simulated UV and solar radiation. The photodegradation kinetics of a model pigment (methylene blue) was fitted to the Langmuir-Hinshelwood model. A 4-fold increase in the photocatalytic activity of ZnO@MFCNCs was observed when compared to pure ZnO. This is associated with (i) increased specific surface area provided by the MFCNC template, (ii) confined surface energy and controlled growth of ZnO nanoparticles, and (iii) entrapment of photoinduced charge carriers in the pores of the core-shell MFCNC rod, followed by fast promotion of interfacial e-charge transfer to the surface of the catalyst. The present study demonstrates how an increase in photocatalytic activity can be engineered without the introduction of structural defects or band gap tailoring of the semiconductor. The aqueous-based ZnO@MFCNC hybrid system displayed attractive UV-absorption and photocatalytic characteristics, offering the conversion of this renewable and sustainable technology into intelligent cosmetic formulations.

Amphiphilic Cellulose Nanocrystals for Enhanced Pickering Emulsion Stabilization.

Sulfated cellulose nanocrystals (CNC) with high surface charge density are inadequate for stabilizing oil-water emulsions, which limits their applications as interfacial stabilizers. We performed end-group modification by introducing hydrophobic chains (polystyrene) to CNC. Results showed that the modified CNC are more effective in emulsifying toluene and hexadecane than pristine CNC. Various parameters were investigated, such as concentration of particles, electrolytes, and polarity of solvents on the characteristics of the emulsions. This study provides strategies for the modification of cellulose nanocrystals to yield amphiphilic nanoparticles that enhance the stability of emulsions. Such systems, bearing biocompatible and environmentally friendly characteristics, are attractive for use in a wide range of industries spanning food, biomedicine, pharmaceuticals, cosmetics, and petrochemicals.