The effect of polyacid on the physical and biological properties of chitosan based layer-by-layer films

Layer-by-layer assembly of chitosan/alginate thin films containing Salmonella enterica bacteriophages for antibacterial applications

The emergence of antibiotic resistant bacteria and the ineffectiveness of routine treatments inspired development of alternatives to biocides for antibacterial applications. Bacteriophages are natural predators of bacteria and are promising alternatives to antibiotics. This study presents fabrication of a Salmonella enterica bacteriophage containing ultra-thin multilayer film composed of chitosan and alginate and demonstrates its potential as an antibacterial coating for food packaging applications. Chitosan/alginate film was prepared through layer-by-layer (LbL) self-assembly technique. A bacteriophage, which belongs to Siphoviridae morphotype (MET P1-001_43) and infects Salmonella enterica subsp. enterica serovar Enteritidis (Salmonella Enteritidis), was post-loaded into chitosan/alginate film. The LbL growth, stability, and surface morphology of chitosan/alginate film as well as phage deposition into multilayers were analysed through ellipsometry, QCM-D and AFM techniques. The bacteriophage containing multilayers showed antibacterial activity at pH 7.0. In contrast, anti-bacterial activity was not observed at acidic conditions. We showed that wrapping a Salmonella Enteritidis contaminated chicken piece with aluminium foil whose surface was modified with phage loaded chitosan/alginate multilayers decreased the number of colonies on the chicken meat, and it was as effective as treating the meat directly with phage solution.

Layer-by-Layer Assembly of Ag@Ti3C2TX and Chitosan on PLLA Substrate to Enhance Antibacterial and Biocompatibility

Poly L-lactic acid (PLLA) is a non-toxic, biocompatible degradable polymer material with excellent mechanical properties after molding. However, it faces challenges in the use of biomedical materials because of its intolerance to bacteria. Here, we use an easy-to-operate method to prepare a composite multilayer membrane: PLLA membrane was used as substrates to assemble positively charged chitosan and negatively charged Ag@MXene on the surface using the Layer-by-layer (LBL) method. The assembly process was detected by Fluorescein Isothiocyanate (FITC)-labelled chitosan and the thickness of the coating multilayer was also detected as 210.0 ± 12.1 nm for P-M membrane and 460.5 ± 26.5 nm for P-Ag@M membrane. The surface self-assembled multilayers exhibited 91.27% and 96.11% growth inhibition ratio against E. coli and S. aureus strains under 808 nm near-infrared (NIR) laser radiation with a synergistic photothermal antibacterial effect. Furthermore, best biocompatibility of P-M and P-Ag@M membranes compare to PLLA membrane motivated us to further explore its application in biomedical materials.

Chitosan: An Overview of Its Properties and Applications

Chitosan has garnered much interest due to its properties and possible applications. Every year the number of publications and patents based on this polymer increase. Chitosan exhibits poor solubility in neutral and basic media, limiting its use in such conditions. Another serious obstacle is directly related to its natural origin. Chitosan is not a single polymer with a defined structure but a family of molecules with differences in their composition, size, and monomer distribution. These properties have a fundamental effect on the biological and technological performance of the polymer. Moreover, some of the biological properties claimed are discrete. In this review, we discuss how chitosan chemistry can solve the problems related to its poor solubility and can boost the polymer properties. We focus on some of the main biological properties of chitosan and the relationship with the physicochemical properties of the polymer. Then, we review two polymer applications related to green processes: the use of chitosan in the green synthesis of metallic nanoparticles and its use as support for biocatalysts. Finally, we briefly describe how making use of the technological properties of chitosan makes it possible to develop a variety of systems for drug delivery.

Reprogrammable optical metasurfaces by electromechanical reconfiguration

Metasurfaces, with artificially designed ultrathin and compact optical elements, enable versatile manipulation of the amplitude, phase, and polarization of light waves. While most of the metasurfaces are static and passive, here we propose a reprogrammable metasurface based on the state-of-art electromechanical nano-kirigami, which allows for independent manipulation of pixels at visible wavelengths through mechanical deformation of the nanostructures. By incorporating electrostatic forces between the top suspended gold nano-architectures and bottom silicon substrate, out-of-plane deformation of each pixel and the associated phase retardation are independently controlled by applying single voltage to variable pixels or exerting programmable voltage distribution on identical pixels. As a proof-of-concept demonstration, the metasurfaces are digitally controlled and a series of tunable metasurface holograms such as 3D dynamic display and ultrathin planar lenses are achieved at visible wavelengths. The proposed electromechanical metasurface provides a new methodology to explore versatile reconfigurable and programmable functionalities that may lead to advances in a variety of applications such as hologram, 3D displays, data storage, spatial light modulations, and information processing.