Enhancing Printing Resolution on Hydrophobic Polymer Surfaces Using Patterned Coatings of Cellulose Nanocrystals.

High-resolution inkjet printing of a hydrophobic polymer surface (polystyrene, PS) was accomplished using a patterned coating of cellulose nanocrystals (CNCs) that prevents the ink from bleeding. A periodically crack-free, wrinkled (wavelength of around 850 nm) stamp was prepared by surface oxidation of an uniaxially stretched poly(dimethylsiloxane) elastomeric substrate and was used as a template to transfer aligned patterns of cellulose nanocrystals (CNCs) onto PS surfaces by wet stamping. The morphology of the aligned CNC coatings on PS was then compared with randomly deposited CNCs on PS using atomic force microscopy. The wettability of the CNCs and polymer surfaces with water and ink was measured and analyzed in the context of inkjet printing. This biomaterial coating technique enables high-resolution printing of modern water-based inks onto hydrophobic surfaces for applications in renewable packaging and printing of biomolecules for high throughput diagnostics. Further, with suitable modifications, the technology is scalable to roll-to-roll manufacturing for industrial flexo printing.

Advances in biomaterials based food packaging systems: Current status and the way forward.

World hunger is getting worse, while one-third of food produced around the globe is wasted and never consumed. It is vital to reduce food waste to promote the sustainability of food systems, and improved food packaging solutions can augment this effort. The utilization of biomaterials in smart food packaging not only enhances food preservation and safety but also aligns with current demands for eco-friendly technologies to mitigate the impacts of climate change. This review provides a comprehensive overview of the developments in the field of food packaging based on the innovative use of biomaterials. It emphasizes the potential use of biomaterials derived from nature including cellulose, chitosan, keratin, etc. for this purpose. Various smart food packaging technologies such as active and intelligent packaging are discussed in detail including scavenging additives, colour-changing environment indicators, sensors, RFID tags, etc. The article also delves into the utilization of edible films and coatings, nanoparticle fillers and 2D materials in food packaging systems. Furthermore, it outlines the challenges and opportunities in this dynamic domain, emphasizing the ongoing need for research and innovation to shape the future of sustainable and smart food packaging solutions to enhance and monitor the shelf-life of food products.

Recent Progress in Cellulose Nanocrystal Alignment and Its Applications.

Cellulose nanocrystal (CNC) research has addressed increased attention in the bioprocessing community, especially the utility of these materials in different fields, including biomedical and materials applications. In this review, the different preparation methods and properties of CNC materials will be initially briefly discussed. The latter focuses special attention on the alignment of CNCs and its applications. Different methods to induce CNC alignment, including self-assembly, shear-based alignment, magnetic and electric field alignment, spin-coating, dip-coating, etc., are reviewed in detail, followed by the different characterization techniques to quantify the alignments of CNCs. The current and potential applications of aligned CNCs, such as fillers to enhance the mechanical and thermal properties of biocomposites, photonic materials to deal with structural colors and enhancement in optical properties of iridescent films, and reduced wettability for high-resolution printing, are further discussed to provide more insights into this promising research direction. We hope that this review will shine light on CNC alignment and also open the door to different types of applications.

In Situ Alignment of Bacterial Cellulose Using Wrinkling.

A scalable method for the assembly of oriented bacterial cellulose (BC) films is presented based on using wrinkled thin silicone substrates of meter-square size as templates during biotechnological syntheses of BC. Control samples, including flat templated and template-free bacterial cellulose, along with the oriented BC, are morphologically characterized using scanning electron microscopy (SEM). Multiple functional properties including wettability, birefringence, mechanical strength, crystallinity, water retention, thermal stability, etc., are being characterized for the BC samples, where the wrinkling-induced in situ BC alignment not only significantly improved material mechanical properties (both strength and toughness) but also endowed unique material surface characteristics such as wettability, crystallinity, and thermal stability. Owing to the enhanced properties observed, potential applications of wrinkle templated BC in printing and cell culture are being demonstrated as a proof of concept, which renders their approach promising for various biomedical and packaging applications.

Surface Engineering of Transparent Cellulose Nanocrystal Coatings for Biomedical Applications.

The concept of blood typing diagnostics using blood drops dried onto transparent cellulose nanocrystal thin film (∼35 nm) coatings has been demonstrated. The substrate onto which the blood drops are dried plays an important role in such tests, depending on surface composition, roughness, and wettability. The drying profile of three different fluid dispersions: model latex particles, reagent blood cells, and whole human blood was studied on a range of different surfaces, including cellulose nanocrystals (CNCs), regenerated cellulose, and several hydrophobic polymers, in order to understand the role of surface chemistry, roughness, and fluid dispersion properties. The morphology of these surfaces was investigated using atomic force microscopy, roughness was calculated, and wettability was explored via contact angle measurement. The morphology of dried drops of human blood on different cellulosic surfaces was compared in order to understand the importance of cellulose crystallinity. Well-defined dried blood drops were observed on random and aligned CNC surfaces, facilitating visualization of individual cells. A simple antibody-antigen test was used to demonstrate the effectiveness of the CNC substrate for blood testing, showing high and reproducible selectivity.

Pickering Emulsions Electrostatically Stabilized by Cellulose Nanocrystals.

Cellulose Nanocrystals (CNC) are explored to stabilize oil/water emulsions for their ability to adsorb at the oil/water interface. In this work, the role of electrostatic forces in the CNC ability to stabilize oil/water emulsions is explored using canola oil/water and hexadecane/water as model systems. Canola oil/water and Hexadecane/ water (20/80, v/v) emulsions were stabilized with the addition of CNCs using ultrasonication. Emulsion droplet sizes range from 1 to 4 µm as measured by optical microscopy. It is found that CNC can stabilize oil/water emulsions regardless of their charge density. However, reducing the surface charge density, by adding salts and varying pH, can reduce the amount of CNC's required to form a stable emulsion. Just by adding 3 mM Na+ or 1 mM or less Ca+2 to a CNC suspension, the amount of CNC reduced by 30% to stabilized 2 mL of Canola oil. On the other hand, adding salt increases the emulsion volume. The addition of 100 mM Na+ or the reduction of pH below 2 leads to the aggregation of CNC; emulsions formed under these conditions showed gel-like behavior. This work shows the potential of nanocellulose crystal in stabilizing food and industrial emulsions. This is of interest for applications where biodegradability, biocompatibility, and food grade requirements are needed.

Bismuth Vanadate with Electrostatically Anchored 3D Carbon Nitride Nano-networks as Efficient Photoanodes for Water Oxidation.

In this study, we report a photoanode consisting of a polymeric/inorganic nanojunction between novel nanostructured 3D C3 N4 nano-networks and BiVO4 substrate. This nanojunction is formed such that 3D C3 N4 nano-networks with a positively charged surface are efficiently anchored on the BiVO4 photoanode with a negatively charged surface. This electrostatic self-assembly can initiate and contribute to an intimate contact at the interfaces, leading to an enhanced photoelectrochemical activity and stability compared with that fabricated by non-electrostatic assembly. The C3 N4 nano-network/BiVO4 photoanode achieved a remarkable photocurrent density of 4.87 mA cm-2 for water oxidation at 1.23 V (vs. reversible hydrogen electrode) after depositing FeOOH/NiOOH as oxygen-evolution co-catalyst, which is among the highest photocurrent densities reported so far for BiVO4 -based photoanodes.

Decreasing the Wettability of Cellulose Nanocrystal Surfaces Using Wrinkle-Based Alignment.

Cellulose nanocrystals (CNCs) are a particularly appealing format of the natural biopolymer due to their exceptional strength, nanoscale dimensions, and needle-like shape anisotropy. However, CNCs are hydrophilic and hence their wettability makes them impractical for many coating applications, with various approaches using chemical functionalization to overcome this. Here we show that CNC-coated surfaces can be rendered hydrophobic by alignment of the native CNCs using a wrinkled template-mediated printing process. We present a novel and simple method allowing full release of the CNCs from the template and their permanent adsorption into fine patterns onto the surface, thus preventing CNC repositioning during wetting. The aligned CNCs induce strong pinning effects that capture and retain water droplets with high contact angle and large roll-off angles, without becoming susceptible to oil contamination. The fabrication process for these coatings could be achieved by large-scale printing, making them a practical and cost-effective solution to hydrophobic coatings from raw cellulosic materials.