Quaternized chitosan (nano)fibers: A journey from preparation to high performance applications.

The industrial production of chitosan, initiated over 50 years ago, has transformed its application across diverse industries, agriculture, and medicine. To enhance its properties, numerous chitosan derivatives have been synthesized. The quaternization of chitosan has proven beneficial, as it not only enhances its properties but also imparts water solubility, expanding its potential for a wider range of applications. Specifically, the utilization of quaternized chitosan-based nanofibers has leveraged the synergistic benefits of quaternized chitosan (including hydrophilicity, bioadhesiveness, antimicrobial, antioxidant, hemostatic, and antiviral activities, as well as ionic conductivity) in combination with the distinctive characteristics of nanofibers (such as a high aspect ratio and 3D architecture). This combination has permitted numerous possibilities, spanning from wound dressings, air and water filters, drug delivery scaffolds, antimicrobial textiles, to energy storage systems and alkaline fuel cells. In this comprehensive review, we examine the preparation methods, properties, and applications of various composite fibers containing quaternized chitosan. The advantages and disadvantages of each method and composition are meticulously summarized, while relevant diagrams and figures illustrate the key findings.

A Slot-Die Technique for the Preparation of Continuous, High-Area, Chitosan-Based Thin Films.

Chitosan-based films have a diverse range of potential applications but are currently limited in terms of commercial use due to a lack of methods specifically designed to produce thin films in high volumes. To address this limitation directly, hydrogels prepared from chitosan, chitosan-tetraethoxy silane, also known as tetraethyl orthosilicate (TEOS) and chitosan-glutaraldehyde have been used to prepare continuous thin films using a slot-die technique which is described in detail. By way of preliminary analysis of the resulting films for comparison purposes with films made by other methods, the mechanical strength of the films produced was assessed. It was found that as expected, the hybrid films made with TEOS and glutaraldehyde both show a higher yield strength than the films made with chitosan alone. In all cases, the mechanical properties of the films were found to compare very favorably with similar measurements reported in the literature. In order to assess the possible influence of the direction in which the hydrogel passes through the slot-die on the mechanical properties of the films, testing was performed on plain chitosan samples cut in a direction parallel to the direction of travel and perpendicular to this direction. It was found that there was no evidence of any mechanical anisotropy induced by the slot die process. The examples presented here serve to illustrate how the slot-die approach may be used to create high-volume, high-area chitosan-based films cheaply and rapidly. It is suggested that an approach of the type described here may facilitate the use of chitosan-based films for a wide range of important applications.

Synthesis and characterisation of cross-linked chitosan composites functionalised with silver and gold nanoparticles for antimicrobial applications.

We present a study of a range of cross-linked chitosan composites with potential antimicrobial applications. They were formed by cross-linking chitosan and siloxane networks and by introducing silver and gold nanoparticles (NPs). The aim was to investigate whether adding the metal NPs to the chitosan-siloxane composite would lead to a material with enhanced antimicrobial ability as compared to chitosan itself. The composites were synthesised in hydrogel form with the metal NPs embedded in the cross-linked chitosan network. Spectroscopic and microscopic techniques were employed to investigate the structural properties of the composite and the tensile strength of the structures was measured. It was found that the addition of metal NPs did not influence the mechanical strength of the composite. A crystal violet attachment assay results displayed a significant reduction in the attachment of E. coli to the cross-linked chitosan surfaces. Release profile tests suggest that the metal NPs do not contribute to the overall antimicrobial activity under neutral conditions. The contribution to the mechanical and antimicrobial properties from cross-linking with siloxane is significant, giving rise to a versatile, durable, antimicrobial material suitable for thin film formation, wound dressings or the coating of various surfaces where robustness and antimicrobial control are required.

Large Area 2D and 3D Colloidal Photonic Crystals Fabricated by a Roll-to-Roll Langmuir-Blodgett Method.

We present our results on the fabrication of large area colloidal photonic crystals on flexible poly(ethylene terephthalate) (PET) film using a roll-to-roll Langmuir-Blodgett technique. Two-dimensional (2D) and three-dimensional (3D) colloidal photonic crystals from silica nanospheres (250 and 550 nm diameter) with a total area of up to 340 cm(2) have been fabricated in a continuous manner compatible with high volume manufacturing. In addition, the antireflective properties and structural integrity of the films have been enhanced via the use of a second roll-to-roll process, employing a slot-die coating of an optical adhesive over the photonic crystal films. Scanning electron microscopy images, atomic force microscopy images, and UV-vis optical transmission and reflection spectra of the fabricated photonic crystals are analyzed. This analysis confirms the high quality of the 2D and 3D photonic crystals fabricated by the roll-to-roll LB technique. Potential device applications of the large area 2D and 3D colloidal photonic crystals on flexible PET film are briefly reviewed.

The langmuir-blodgett approach to making colloidal photonic crystals from silica spheres.

The area of colloidal photonic crystal research has attracted enormous attention in recent years as a result of the potential of such materials to provide the means of fabricating new or improved photonic devices. As an area where chemistry still predominates over engineering the field is still in its infancy in terms of finding real applications being limited by ease of fabrication, reproducibility and 'quality'- for example the extent to which ordered structures may be prepared over large areas. It is our contention that the Langmuir-Blodgett assembly method when applied to colloidal particles of silica and perhaps other materials, offers a way of overcoming these issues. To this end the assembly of silica and other particles into colloidal photonic crystals using the Langmuir-Blodgett (LB) method is described and some of the numerous papers on this topic, which have been published, are reviewed. It is shown that the layer-by-layer control of photonic crystal growth afforded by the LB method allows for the fabrication of a range of novel, layered photonic crystals that may not be easily assembled using any other approach. Some of the more interesting of these structures, including so-called heterostructured photonic crystals comprising of layers of spheres having different diameters are presented and their optical properties described. Finally, we offer our comments as to future applications of this interesting technology.

Langmuir-Blodgett assembly of colloidal photonic crystals using silica particles prepared without the use of surfactant molecules.

This short communication reports the observation that in contrast to most previously reported procedures, it is possible to prepare 3D photonic crystal structures from silica particles that have not been deliberately treated with surfactant molecules, using the Langmuir-Blodgett method. We find that colloidal particles prepared simply via the Stöber method with diameters in the range 180-360 nm and dispersed in ethanol, may be effectively floated at the air/water interface and compressed into close packed layers prior to depositing the layers on a substrate. We also find, by comparing structures made with both particles treated with the surfactants 3-(trimethoxysilyl) propyl methacrylate or (3-aminopropyl)triethoxysilane and particles which have not been treated with any surfactant species, that the position of the Bragg peak and the reflectivity of the sample does not appear to be influenced by the presence of the surfactant molecules.