Nanocellulose-lysozyme colloidal gels via electrostatic complexation

Low gelatin concentration assisted cellulose nanocrystals stabilized high internal phase emulsion: The key role of interaction

Low concentrations of gelatin (0.02-0.20 wt%) were applied to regulate the surface and interface properties of CNC (0.50 wt%) by forming CNC/G complexes. As gelatin concentration increased from 0 to 0.20 wt%, the potential value of CNC/G gradually changed from -44.50 to -17.93 mV. Additionally, various gelatin concentrations led to micromorphology changes of CNC/G complexes, with the formation of particle interconnection at gelatin concentration of 0.10 wt%, followed by network structure and enhanced aggregation at gelatin concentration of 0.15 and 0.20 wt% respectively. The water contact angle (25.91°-80.23°) and interface adsorption capacity of CNC/G were improved due to hydrophobic group exposure of gelatin. When gelatin concentration exceeded 0.10 % at a fixed oil phase volume fraction (75 %), a high internal phase emulsion (HIPE) stabilized by CNC/G can be formed with a good storage stability. The rheological and microstructure results of HIPE confirmed that low gelatin concentration can assist CNC to form stable emulsion structure. Especially, the auxiliary stabilization mechanism of various gelatin concentration was different. CNC/G-0.10 % and CNC/G-0.15 % stabilized HIPE mainly depended on the enhanced interface adsorption and network structure, while CNC/G-0.20 % stabilized HIPE mainly relied on enhanced interface adsorption/accumulation due to weak electrostatic repulsion and aggregate granular morphology of CNC/G-0.20 %.

2D foam film coating of antimicrobial lysozyme amyloid fibrils onto cellulose nanopapers

Amyloid fibrils made from inexpensive hen egg white lysozyme (HEWL) are bio-based, bio-degradable and bio-compatible colloids with broad-spectrum antimicrobial activity, making them an attractive alternative to existing small-molecule antibiotics. Their surface activity leads to the formation of 2D foam films within a loop, similar to soap films when blowing bubbles. The stability of the foam was optimized by screening concentration and pH, which also revealed that the HEWL amyloid foams were actually stabilized by unconverted peptides unable to undergo amyloid self-assembly rather than the fibrils themselves. The 2D foam film was successfully deposited on different substrates to produce a homogenous coating layer with a thickness of roughly 30 nm. This was thick enough to shield the negative charge of dry cellulose nanopaper substrates, leading to a positively charged HEWL amyloid coating. The coating exhibited a broad-spectrum antimicrobial effect based on the interactions with the negatively charged cell walls and membranes of clinically relevant pathogens (Staphylococcus aureus, Escherichia coli and Candida albicans). The coating method presented here offers an alternative to existing techniques, such as dip and spray coating, in particular when optimized for continuous production. Based on the facile preparation and broad spectrum antimicrobial performance, we anticipate that these biohybrid materials could potentially be used in the biomedical sector as wound dressings.

Nano-SiO2 reinforced alginate-chitosan-gelatin nanocomposite hydrogels with improved physicochemical properties and biological activity

Alginate (Alg) hydrogels possess desirable advantages for application in tissue engineering; however, they are limited by their weak mechanical properties, poor chronical stability in phosphate buffered saline, and absence of mammalian cell recognition sites, severely restricting their biomedical applications. To overcome these limitations, we integrated Alg hydrogels with nano-silica (SiO2) to produce nano-SiO2 reinforced Alg-chitosan-gelatin nanocomposite hydrogels (Alg/SiO2-CHI-GA NCH) for biomedical purposes, utilizing Chitosan (CHI) and gelatin (GA) in an alternate electrostatic adsorption. Specifically, we investigated the regulatory and promotional effects of the nano-SiO2 on the morphological structure, mechanical properties, thermal stability, rheological properties, swelling, biodegradability, biomineralization and cytocompatibility of the resultant Alg/SiO2-CHI-GA NCH. The experimental findings demonstrate that the constructed Alg/SiO2-CHI-GA NCH exhibited uniform morphology and a regular structure. Upon freeze-drying, the internal cross-sections of the NCH exhibited a honeycomb porous structure. Furthermore, the physicochemical properties and biological activities of the prepared Alg/SiO2-CHI-GA NCH were regulated to some extent by nano-SiO2 content. Notably, nano-SiO2 inclusion enhanced the attachment and viability of MG63 and MC3T3-E1 cells and induced three-dimensional cell growth in ALG/SiO2-CHI-GA NCH. Among the fabricated NCH, Alg/SiO2-CHI-GA NCH with 0.5% and 1.0% (w/v) nano-SiO2 exhibited significant proliferative activity, which is attributable to their high porosity and uniform cell adhesion. Furthermore, the alkaline phosphatase activity in the cells gradually increased with increasing of nano-SiO2 amount, indicating the favorable effect of nano-SiO2 on the osteogenic differentiation of MG63 and MC3T3-E1 cells. Our study findings provide a comprehensive foundation for the structural- and property-related limitations of Alg hydrogels in biomedicine, thereby expanding their potential applications in tissue engineering.

Novel PVA/carboxylated cellulose antimicrobial hydrogel grafted with curcumin and ε-polylysine for chilled chicken preservation

PVA/CC/CUR/PL composite films containing curcumin (CUR) and ε-polylysine (PL) were prepared by casting and chemical grafting methods to address the threat to food spoilage. Morphological analysis showed that the grafting of CUR and PL resulted in a rough cross-section of the polymer matrix. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis confirmed the grafting of CUR and PL into the polymer matrix via esterification and amidation reactions, respectively. Thermal weight loss analysis showed that grafting process positively improved the thermal stability. The PVA/CC/CUR/PL films exhibited strong bactericidal activity, reaching 99.0% and 99.8% for Pseudomonas lundensis and Shewanella putrefaciens, respectively. After 8 days of storage, the total number of colonies and the TVB-N content in the PVA/CC/CUR/PL group decreased by 1.51 lg CFU/g and 13.77 mg/100 g, respectively. Therefore, PVA/CC/CUR/PL films are considered as a promising bactericidal material with good mechanical properties, functionality, and other excellent characteristics.

The Colloidal Properties of Nanocellulose

Nanocelluloses are anisotropic nanoparticles of semicrystalline assemblies of glucan polymers. They have great potential as renewable building blocks in the materials platform of a more sustainable society. As a result, the research on nanocellulose has grown exponentially over the last decades. To fully utilize the properties of nanocelluloses, a fundamental understanding of their colloidal behavior is necessary. As elongated particles with dimensions in a critical nanosize range, their colloidal properties are complex, with several behaviors not covered by classical theories. In this comprehensive Review, we describe the most prominent colloidal behaviors of nanocellulose by combining experimental data and theoretical descriptions. We discuss the preparation and characterization of nanocellulose dispersions, how they form networks at low concentrations, how classical theories cannot describe their behavior, and how they interact with other colloids. We then show examples of how scientists can use this fundamental knowledge to control the assembly of nanocellulose into new materials with exceptional properties. We hope aspiring and established researchers will use this Review as a guide.

Benchmarking supramolecular adhesive behavior of nanocelluloses, cellulose derivatives and proteins

One of the key steps towards a broader implementation of renewable materials is the development of biodegradable adhesives that can be attained at scale and utilized safely. Recently, cellulose nanocrystals (CNCs) were demonstrated to have remarkable adhesive properties. Herein, we study three classes of naturally synthesized biopolymers as adhesives, namely nanocelluloses (CNFs), cellulose derivatives, and proteins by themselves and when used as additives with CNCs. Among the samples evaluated, the adhesion strength was the highest for bovine serum albumin and hydroxypropyl cellulose (beyond 10 MPa). These were followed by carboxymethylcellulose and CNCs (ca. 5 MPa) and mechanically fibrillated CNFs (ca. 2 MPa), and finally by tempo-oxidized CNFs (0.2 MPa) and lysozyme (1.5 MPa). Remarkably, we find that the anisotropy of adhesion (in plane vs out of plane) falls within a narrow range across the bio-based adhesives studied. Collectively, this study benchmarks bio-based non-covalent adhesives aiming towards their improvement and implementation.

Protein release from nanocellulose and alginate hydrogels: The study of adsorption and desorption kinetics

This work presents a study of the lysozyme release from crosslinked TEMPO nanocellulose (TOCNF) and alginate (ALG) hydrogels in a medium with different ionic strength and temperature. The main objective is to develop a mathematical model for a detailed study of the concurrent action of diffusion mechanism and adsorption/desorption kinetics. Model fit parameters provide important information about the initial (maximum) adsorption rate and its deceleration with increasing ionic strength of the release medium. Similarly, the initial (minimum) desorption rate and its acceleration with increasing salt concentration can be determined. The model leads us to the conclusion that the initial adsorption rate is higher in the case of TOCNF, but due to fewer electrostatic interactions and morphology as well as topography of the surface, it decreases to a negligible value much faster than in the case of ALG, where the diffusion process becomes dominant.

Biohybrid Nanocellulose-Lysozyme Amyloid Aerogels via Electrostatic Complexation

Modern science is increasingly turning to nature for inspiration to design sustainable biomaterials in a smart and effective way. Herein, we describe biohybrid aerogels based on electrostatic complexation between cellulose and proteins-two of the most abundant natural polymers on Earth. The effects of both particle surface charge and particle size are investigated with respect to aerogel properties including the morphology, surface area, stability, and mechanical strength. Specifically, negatively charged nanocellulose (cellulose nanocrystals and cellulose nanofibers) and positively charged lysozyme amyloid fibers (full-length and shortened via sonication) are investigated in the preparation of fibrillar aerogels, whereby the nanocellulose component was found to have the largest effect on the resulting aerogel properties. Although electrostatic interactions between these two classes of charged nanoparticles allow us to avoid the use of any cross-linking agents, the resulting aerogels demonstrate a simple additive performance as compared to their respective single-component aerogels. This lack of synergy indicates that although electrostatic complexation certainly leads to the formation of local aggregates, these interactions alone may not be strong enough to synergistically improve bulk aerogel properties. Nevertheless, the results reported herein represent a critical step toward a broader understanding of biohybrid materials based on cellulose and proteins.

Chitin-amyloid synergism and their use as sustainable structural adhesives

Structural adhesives are relevant to many engineering applications, especially those requiring load-bearing joints with high lap shear strength. Typical adhesives are synthesized from acrylics, epoxies, or urethanes, which may pose a burden to sustainability and the environment. In nature, the interfacial interactions between chitin and proteins are used for structural purposes and as a bio-cement, resulting in materials with properties unmatched by their man-made counterparts. Herein, we show that related supramolecular interactions can be harnessed to develop high strength green adhesives based on chitin nanocrystals (ChNCs), isolated from shrimp shells, and hen egg white lysozyme (HEWL) used in its monomeric or amyloid forms. Consolidation of the bicomponent suspensions, placed between glass substrates, results in long-range ordered superstructures. The formation of these structures is evaluated by surface energy considerations, followed by scanning electron, atomic force, and polarized microscopies of the consolidated materials. For 0.8 mg of bio-adhesive (lysozyme, ChNCs or their composites), lap shear loads of over 300 N are reached. Such remarkable adhesion reaches maximum values at protein-to-ChNC ratios below 1 : 4, reflecting the synergy established between the components (ca. 25% higher load compared to ChNCs, the strongest single component). We put the observed adhesive performance in perspective by comparing the lap-shear performance with current research on green supramolecular adhesives using natural biopolymers. The results are discussed in the context of current efforts to standardize the measurement of adhesive strength and bond preparation. The latter is key to formalizing the metrology and materials chemistry of bio-based adhesives. The proposed all-green system is expected to expand current developments in the design of bio-based adhesives.

Drug-loading colloidal gels assembled from polymeric nanoparticles as an anti-inflammatory platform

Injectable colloidal gels shed PLA–PEG and CS nanoparticles autonomously under physiological conditions and release aspirin to inhibit inflammation.