Reusable antimicrobial antibiotic-free dressings obtained by photopolymerization.

In recent years significant efforts have been made to develop new materials for wound dressing with improved healing properties. However, the synthesis methods usually employed to this end are often complex or require several steps. We describe here the synthesis and characterization of antimicrobial reusable dermatological wound dressings based on N-isopropylacrylamide co-polymerized with [2-(Methacryloyloxy) ethyl] trimethylammonium chloride hydrogels (NIPAM-co-METAC). The dressings were obtained with a very efficient single-step synthesis procedure based on visible light (455 nm) by photopolymerization. To this end, F8BT nanoparticles of the conjugated polymer (poly(9,9-dioctylfluorene-alt-benzothiadiazole) - F8BT) were used as macro-photoinitiators, and a modified silsesquioxane was employed as crosslinker. Dressings obtained by this simple and gentle method show antimicrobial and wound healing properties, without the incorporation of antibiotics or any other additives. The physical and mechanical properties of these hydrogel-based dressings were evaluated, as well as their microbiological properties, through in vitro experiments. Results show that dressings with a molar ratio of METAC of 0.5 or higher exhibit high swelling capacity, appropriate water vapor transmission rate values, stability and thermal response, high ductility and adhesiveness. In addition, biological tests showed that the dressings have significant antimicrobial capacity. The best inactivation performance was found for hydrogels synthesized with the highest METAC content. The dressings were tested several times with fresh bacterial cultures, showing a bacterial kill efficiency of 99.99 % even after three repetitions in a row, employing the same dressing, demonstrating the intrinsic bactericidal property of the materials and their reusability. In addition, the gels show low hemolytic effect, high dermal biocompatibility and noticeable wound healing effects. Overall results demonstrate that some specific hydrogel formulations have potential application as dermatological dressings for wound healing and disinfection.

Schiff base crosslinked gelatin-Spirulina platensis protein concentrate films with enhanced antioxidant activity.

The aim of this work is to produce bioactive films suitable for aerobic packaging applications by combining the bioactivity of Spirulina platensis protein concentrate (PC; 1% and 2% w/w), the sustainable nature of bovine gelatin (Ge), and sodium alginate dialdehyde (ADA, 5% w/w) as Schiff base crosslinking agent. PC was obtained by an optimized acid-base extraction process and characterized. PC showed a dose-dependent radical scavenging activity (RSA; IC50  = 24.3 mg/L) related to its high content of C-phycocyanin and total phenolic compounds (32.44 ± 1.37 mg gallic acid equivalents per gram of PC). As a general trend, crosslinking decreased the water solubility, improved mechanical properties, and helped improve RSA of Ge-ADA-PC films. Ge-5ADA-2PC film recorded best compromise between solubility (only 33.6%), high UV barrier (0.134% transmittance at 400 nm), reasonable extensibility (217.00 ± 2.34%), tensile strength (3.50 ± 0.43 MPa), water vapor permeability (2.00 ± 0.17 × 10-12  kg·m/m2 ·Pa·s), and RSA (44.70 ± 2.19%). Wrapping hake fillets in this filmdelayed lipid oxidation during storage under refrigerated conditions for 11 days, maintaining the thiobarbituric acid index below 0.5 mg malonaldehyde/kg muscle. Results suggest that Ge-ADA-PC films have potential as aerobic packaging materials for oxidation-sensitive food. PRACTICAL APPLICATION: The combination of gelatin, alginate dialdehyde and Spirulina platensis protein concentrate gave rise to fully biobased films with reduced water solubility and enhanced antioxidant activity, which were able to delay the secondary lipid oxidation of refrigerated seafood. This study also shows the potential of cyanobacteria as renewable resources of high-value ingredients for the design of active and intelligent aerobic packaging solutions.

Antifungal Soybean Protein Concentrate Adhesive as Binder of Rice Husk Particleboards.

The aim of this research was to prepare an antifungal soybean protein concentrate (SPC) adhesive containing carvacrol (CRV) as a bioactive agent able to delay the attack of molds and yeast during storage of SPC adhesive at 4 °C as water-based systems. CRV was incorporated in SPC slurry at 0.5% v/v (~10 times its minimum inhibitory concentration against Aspergillus terreus, used as model fungus), to ensure its long-term action. CRV scarcely altered the thermal properties, structure and apparent viscosity of SPC adhesive. Active SPC aqueous dispersion was microbiologically stable for at least 30 days at 4 °C where the colonization begins, while control SPC was visually colonized from the second day. Rice husk (RH) particleboards of density ~900 kg/m3 were manufactured using the active SPC stored for 0, 10, 20, and 30 days as a binder. Modulus of elasticity, modulus of rupture and internal bond of RH-control SPC (without CRV) panels were 12.3 MPa, 2.65 GPa and 0.27 MPa, respectively, and were statistically unaltered compared with those obtained with fresh SPC, regardless of the presence of CRV or the storage time. This last implies that active SPC should not necessarily have to be prepared daily and/or be used immediately after its preparation. Since it is microbiologically stabilized, it can be store at least for 30 days, ensuring the stability of the protein. The quality of the adhesive was evidenced by the consistent properties of the adhesive, expanding its potential use and commercialization.

The Effect of Gelatine Packaging Film Containing a Spirulina platensis Protein Concentrate on Atlantic Mackerel Shelf Life.

The use of packaging films containing natural preservative compounds attracts great attention for the quality improvement of seafood. Microalga spirulina (Spirulina platensis) represents a potential source of high added-value and preservative biocompounds. The goal of this study was to enhance the quality of refrigerated Atlantic mackerel (Scomber scombrus) by including a protein concentrate (PC) of spirulina in a gelatine-based film. Quality changes in fish muscle were monitored by microbial and chemical analyses throughout an 11-day refrigerated storage (4 °C). As a result of the presence of spirulina PC in the film, an antimicrobial effect (p < 0.05) was concluded as determined by comparative evolution of aerobes and psychrotrophs, while no effect (p > 0.05) was concluded for Enterobacteriaceae, proteolytics and lipolytics counts. Furthermore, a lower (p < 0.05) formation of trimethylamine and free fatty acids was detected. Lipid oxidation, measured by fluorescent compounds formation, also exhibited lower average values in fish corresponding to the batch containing spirulina concentrate. The preservative effects observed can be explained on the basis of the presence of antimicrobial and antioxidant compounds in the microalga concentrate. It is proposed that the current packaging system may constitute a novel and promising strategy to enhance the quality of commercial refrigerated fatty fish.

Functional properties and in vitro antioxidant and antibacterial effectiveness of pigskin gelatin films incorporated with hydrolysable chestnut tannin.

The impact of the incorporation of 10% w/w of hydrolyzable chestnut tannin into pigskin gelatin (G) films plasticized with glycerol (Gly) on the physicochemical properties as well as the in vitro antioxidant and antibacterial effectiveness against food-borne pathogens such as Escherichia coli and Streptococcus aureus was investigated. A higher tendency to both redness (a*) and yellowness (b*) coloration characterized gelatin films incorporated with chestnut tannin. The reduced lightness (L) and transparency of gelatin-chestnut tannin films plasticized with 30% w/w Gly might be associated with certain degree of phase separation which provoked the migration of the plasticizer to the film surface. The incorporation of chestnut tannin and glycerol affected the chemical structure of the resultant films due to the establishment of hydrogen interactions between components as revealed by Fourier transform infrared spectroscopy. These interactions reduced gelatin crystallinity and seemed to be involved in the substantial decrease of the water uptake of films with tannin, irrespective of the glycerol level. Such interactions had minor effect on tensile properties being similar to those of the control films (without chestnut tannin) at the same glycerol level. Films modified with 10% w/w chestnut tannin showed significant (P < 0.05) 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity, ca. from 0 ± 0.033 to 87.1 ± 0.002% for chestnut tannin-free and chestnut tannin-containing gelatin films. The limited inhibitory activity of films incorporated with 10% w/w chestnut tannin against the selected bacteria evidenced by disk diffusion method probably resulted from the interactions within the film restricting the diffusion of the active agent into the agar medium. The more modest protective effect observed against a Gram-positive bacterium (S. aureus) was also discussed.