Highly effective and sustainable antibacterial membranes synthesized using biodegradable polymers

Biodegradable antimicrobial films prepared in a continuous way by melt extrusion using plant extracts as effective components

Packaging plays an important role in delaying food spoilage. However, conventional packaging films do not have antimicrobial properties. Films with antimicrobial components are receiving growing research interest. However, many of the reported studies use conventional non-degradable polymers during film preparation, posing a significant threat to the environment and sustainable development. Furthermore, conventional inorganic antibacterial agents are commonly used during film preparation, posing a risk to food safety. In this study, antibacterial compounds were extracted from diverse plants, and then biodegradable antimicrobial films were prepared in a continuous way via the melt extrusion method. Especially, films prepared using Vernicia fordii and Phyllanthus urinaria extracts showed effective antibacterial activities against common foodborne pathogens. This study is the first to prepare antibacterial films in a continuous way using natural plant extracts as the effective components, and may shed new light on future research in preparing green antibacterial films via environment-friendly approaches.

Biomimetic Nanozyme-Decorated Smart Hydrogel for Promoting Chronic Refractory Wound Healing

Chronic refractory wounds have become a serious threat to human health and are characterized by prolonged inflammation, recurrent bacterial infections, and elevated ROS levels. However, current therapeutic strategies usually target a unilateral healing function and are unable to tackle the complexity and sensitivity of chronic refractory wound healing. This study fabricated a biomimetic nanozyme based on rhein (Cu-rhein NSs), which effectively mimics the activity of superoxide dismutase (SOD) for scavenging various free radicals. Additionally, zinc oxide microspheres (ZnO MSs) were prepared to enhance the antibacterial activity and mechanical properties of the modified hydrogel. Cu-rhein NSs and ZnO MSs were comodified onto an extracellular matrix-mimetic dual-network smart hydrogel constructed from oxidized sodium alginate, gelatin, and borax via dynamic borate and Schiff base bonds. The smart hydrogel presented the good biocompatibility and targeted the unique acidic microenvironment with high oxidative stress of chronic refractory wounds, intelligently releasing bionic nanozymes to effectively eliminate bacteria, reduce inflammatory responses, and scavenge multiple free radicals for reducing ROS. In vivo experiments on the rat model based on diabetic infection showed that the smart hydrogel could effectively eliminate bacteria, promote vascular regeneration and collagen deposition, reduce inflammatory response, and accelerate the healing of diabetic-infected wounds (almost complete healing within 14 days). The advantages of an intelligent, biomimetic tissue regeneration cascade management strategy against diabetic infected wound healing are highlighted.

Fabrication and characterization of sodium alginate/blueberry anthocyanins/hinokitiol loaded ZIF-8 nanoparticles composite films with antibacterial activity for monitoring pork freshness

A smart film was developed to detect the freshness of pork by incorporating blueberry anthocyanins (BAs) and hinokitiol (HIN) loaded zeolite-imidazolium framework (HIN@ZIF-8) with into a sodium alginate matrix, and its microstructure and physicochemical properties were studied. The SA matrix was doped with BAs and HIN@ZIF-8 nanoparticles (SA-BAs/HIN@ZIF-8) to increase its tensile strength and reduce its water vapor permeability. HIN@ZIF-8 has low cytotoxicity, and SA-BAs/HIN@ZIF-8 membranes have long-lasting antimicrobial and highly sensitive color development properties against Escherichia coli and Staphylococcus aureus. The results of pork preservation experiments showed that SA-BA/HIN@ZIF-8 could extend the shelf life of pork to 6 days at 4 ℃. E-nose evaluation experiments showed that SA-BAs/HIN@ZIF-8 could inhibit compounds that cause unpleasant and irritating odours. Therefore, SA-BAs/HIN@ZIF-8 was considered to be an effective method to improve the freshness of pork, and the results showed that it has a promising application in food preservation.

Natural antibacterial membranes prepared using Schisandra chinensis extracts and polyvinyl alcohol in an environment-friendly manner

Foodborne pathogens can cause food spoilage and lead to food safety issues. In recent years, food packaging has received a lot of attention. Traditional packaging membranes are non-biodegradable and remain in the environment for a long time. In this study, natural antimicrobial substances were extracted from Schisandra chinensis by a green extraction process using distilled water as the solvent, and the effects of different treatment on the antimicrobial activity of the extract were compared. At the same time, four types of Schisandra chinensis antimicrobial membranes were prepared using polyvinyl alcohol (PVA) as the substrate. The whole extraction and membrane preparation process did not involve organic solvents, making the process green and environment friendly. Material characterization included inverted biological microscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), tensile strength test, pore size measurement, water uptake test, etc. Among them, no extract particles were observed with the naked eye on the surfaces of MⅡ and MⅣ. MⅡ has a uniformly transparent, nearly colorless morphology and is the most tensile. MⅣ surface is flat and smooth, the microstructure is dense and uniform. At the same time, the four types of membranes were tested against common pathogenic bacteria for 12 h, and the OD600 trend revealed the excellent antimicrobial activity of the membranes against S. aureus, MRSA, E. coli, and L. monocytogenes. The membranes could also be reused at least once. This study provides a new idea for preparing natural plant-based antimicrobial membranes.

Antifouling and antibacterial performance evaluation of polyethersulfone membranes modified with AZ63 alloy

Antibacterial membranes have attracted researchers' interest in recent years as a possible approach for dealing with biofouling on the membrane surface. This research aims to see if blending AZ63 Mg alloy into a polyethersulphone (PES) membrane can improve antifouling and separation properties. The composite membranes' pure water flux continued to increase from pristine PES to PES/AZ63 2.00 wt%. The results showed that PES/AZ63 2.00 wt% membrane supplied the highest permeate flux of E. coli. The steady-state fluxes of AZ63 composite membranes were 113.24, 104.38 and 44.79 L/m²h for PES/AZ63 2.00 wt%, 1.00 wt%, and 0.50 wt%, respectively. The enhanced biological activity of AZ63 was studied based on antioxidant activity, DNA cleavage, antimicrobial, anti-biofilm, bacterial viability inhibition and photodynamic antimicrobial therapy studies. The maximum DPPH scavenging activity was determined as 81.25% with AZ63. AZ63 indicated good chemical nuclease activity and also showed moderate antimicrobial activity against studied strains. The highest biofilm inhibition of AZ63 was 83.25% and 71.63% towards P. aeruginosa and S. aureus, respectively. The cell viability inhibition activity of AZ63 was found as 96.34% against E. coli. The photodynamic antimicrobial therapy results displayed that AZ63 demonstrated 100% bacterial inhibition when using E. coli.

Construction of compostable packaging with antibacterial property and improved performance using sprayed coatings of modified cellulose nanocrystals

Increasing concerns about food safety and the environment have facilitated the development of eco-friendly antibacterial packaging. This study aimed to demonstrate a facile way to fabricate active packaging materials with modified cellulose nanocrystals (CNCs) and compare the effects of different modified CNCs on the performance of compostable materials. Polylactic acid (PLA) film was selected as a model, and CNCs were modified with methacrylamide, cetyltrimethylammonium bromide, and zinc oxide, respectively, and then applied on the surface of PLA films by spray-coating. All modified CNCs showed excellent antibacterial activity against S. aureus and E. coli (>99.999 %). The effects of different CNC modifications on the performance of PLA films were investigated. Compared to neat PLA films, PLA/CNC films exhibited improved mechanical strength with maintained flexibility, lower gas permeability, and faster compost disintegration rate, and extended the shelf life of wrapped pork samples from 3 days to >10 days. Therefore, this work will also facilitate the applications of PLA materials in eco-friendly packaging.

Visible-Light-Driven Zinc Oxide Quantum Dots for the Management of Bacterial Fruit Blotch Disease and the Improvement of Melon Seedlings Growth

Bacterial fruit blotch is one of the most destructing diseases of melon producing-regions. Here, zinc oxide quantum dots (ZnO QDs) were synthesized, and their antibacterial activity against Acidovorax citrulli was investigated. The results indicated that the obtained ZnO QDs displayed 5.7-fold higher antibacterial activity than a commercial Zn-based bactericide (zinc thiazole). Interestingly, the antibacterial activity of ZnO QDs irradiated with light was 1.8 times higher than that of the dark-treated group. It was because ZnO QDs could induce the generation of hydroxyl radicals and then up-regulate the expression of oxidative stress-related genes, finally leading to the loss of cell membrane integrity. A pot experiment demonstrated that foliar application of ZnO QDs significantly reduced the bacterial fruit blotch disease incidence (32.0%). Furthermore, the supply of ZnO QDs could improve the growth of infected melon seedlings by activating the antioxidant defense system. This work provides a promising light-activated quantum-bactericide for the management of pathogenic bacterial infections in melon crop protection.

Pharmaceuticals and Personal Care Products in the Environment with Emphasis on Horizontal Transfer of Antibiotic Resistance Genes

Pharmaceuticals and personal care products (PPCPs) discharged into environment has several adverse impacts. PPCPs are widely utilised for veterinary as well as cosmetic and personal health reasons. These are members of the expanding class of substances known as Contaminants of Emerging Concern (CECs). Antibiotic resistance in the environment and garbage generated by PPCP endanger life. The World Health Organisation (WHO) now recognises antibiotic resistance as a significant global health problem due to the expected increase in mortality caused by it. In the past ten years, mounting data has led experts to believe that the environment has a significant impact on the development of resistance. For human diseases, the external environment serves as a source of resistance genes. It also serves as a major pathway for the spread of resistant bacteria among various habitats and human populations. Large-scale DNA sequencing methods are employed in this thesis to better comprehend the dangers posed by environmental antibiotic resistance. The quantification of the number is an important step in this process. Metagenomic measurement of the number of antibiotic resistance genes in various contexts is a crucial step in this process. However, it’s also crucial to put this data into a broader context by integrating things like taxonomic information, antibiotic concentrations, and the genomic locations of found resistance genes.

Novel silver-modified carboxymethyl chitosan antibacterial membranes using environment-friendly polymers

The rapid reproduction of foodborne bacteria in food packaging threatens the health of consumers, the massive use and waste of packaging also causes serious environmental pollution. In this study, novel biodegradable antibacterial membranes based on silver-modified carboxymethyl chitosan (Ag-CMCS) were prepared. Polylactic acid (PLA) and polybutylene adipate-co-terephthalate (PBAT) were used as the base membrane materials. Characterization of the prepared membranes was performed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS), water contact angle, and so on. Especially, the silver on the surface of Ag-CMCS was proved to be metallic silver. For the first cycle of zone of inhibition test, the diameter of inhibition zone could reach up to 17 mm while the mass of silver released was negligible. The prepared antibacterial membranes could kill almost 100% of bacteria under certain conditions and inhibition zone still existed after more than 7 cycles of tests, indicating the prepared antibacterial membranes were effective. This study could provide new ideas for preparing efficient and environment-friendly antibacterial food packaging membranes.

Expanding the application of ion exchange resins for the preparation of antimicrobial membranes to control foodborne pathogens

Although ion exchange resins (IERs) have been extensively adopted in water treatment, there are no reports on the application thereof for synthesizing antibacterial materials against pathogenic bacteria. The present study is the first in which the ion exchange characteristic of IERs was utilized to introduce silver ions that possess efficient antibacterial properties. The resulting antibacterial materials were incorporated into polylactic acid (PLA) and/or polybutylene adipate terephthalate (PBAT) to prepare antibacterial membranes. XPS spectra revealed the occurrence of in-situ reduction of silver ions to metallic silver, which was preferable since the stability of silver in the materials was improved. EDS mapping analysis indicated that the distribution of silver was consistent with the distribution of sulfur in the membranes, verifying the ion exchange methodology proposed in the present study. To investigate the antibacterial performance of the prepared membranes, zone of inhibition tests and bacteria-killing tests were performed. The results revealed that neither bare polymeric membranes of PLA and PBAT nor IER-incorporated polymeric membranes exhibited noticeable antibacterial activities. In comparison, the antibacterial membranes demonstrated effective and sustainable antibacterial activities against pathogenic bacteria Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). The prepared antibacterial membranes exhibited potential in food-related applications such as food packaging to delay food spoilage due to microbial growth.

Enhanced Antimicrobial Cellulose/Chitosan/ZnO Biodegradable Composite Membrane

In this study, chitosan and sugarcane cellulose were used as film-forming materials, while the inorganic agent zinc oxide (ZnO) and natural compound phenyllactic acid (PA) were used as the main bacteriostatic components to fabricate biodegradable antimicrobial composite membranes. The water absorption and antimicrobial properties were investigated by adjusting the concentration of PA. The scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) results demonstrated that the components of the composite membrane were successfully integrated. The addition of ZnO improved the mechanical and antimicrobial properties of the composite membrane, while the addition of PA with high crystallinity significantly reduced the water absorption and swelling. Moreover, the addition of 0.5% PA greatly improved the water absorption of the composite membrane. The results of antimicrobial experiments showed that PA improved the antimicrobial activity of the composite membrane against Staphylococcus aureus, Escherichia coli, Aspergillus niger and Penicillium rubens. Among them, 0.3% PA had the best antimicrobial effect against S. aureus, E. coli and A. niger, while 0.7% PA had the best antimicrobial effect against P. rubens.