Chronic wounds (CW) have numerous entry ways for pathogen invasion and prosperity, damaging host tissue and hindering tissue remodelling. Essential oils (EOs) exert quick and efficient antimicrobial (AM) action, unlikely to induce bacterial resistance. Cajeput oil (CJO) has strong AM properties, namely against Staphylococcus aureus and Pseudomonas aeruginosa, as previously established by the team (DOI: 10.3390/antibiotics9060314). Chitosan (CS) is a natural and biodegradable cationic polysaccharide, widely known for its AM features. CS (100-300 kDa; DA of 9.6±1.4%) and PVA (72 kDa, 88% hydrolyzed) films (ratio 30/70; 9%wt) were prepared by solvent casting and phase inversion method (similarly as in DOI: 10.1002/app.48626). CJO was added to CS solution before blending it with PVA, with loading amount of 1 and 10 wt% in relation to total polymeric mass. Loaded films with 0.89 ± 0.05 and 1.14 ± 0.10 mm in thickness were obtained, respectively, 23 and 57% thicker than the unloaded films. Degree of swelling (%) and porosity also increased. Films chemical composition and thermal stability reinforce the achievement of loaded blended films. AM activity was evaluated through the agar diffusion assay and time kill kinetics, with the biomaterials incubated with S. aureus and P. aeruginosa. Thin inhibitory zones were observed with films placed in direct contact each of the bacterium. CS films alone showed an outstanding AM activity against both bacteria, with 1h being sufficient to eradicate all P. aeruginosa colony traces. Still, CS/PVA blended films carrying 1/10% CJO, having improved mechanical properties than CS films alone, resulted in 2/3 (S. aureus) or 3/4 (P. aeruginosa) log reduction in 24h of contact. This study is a first proof of concept that CJO can be dispersed into CS/PVA films and show bactericidal effects, notably when combined with CS, and particularly against P. aeruginosa, this way opening new avenues for CW therapeutics.

Cellulose, the main constituent of paper-based food packages, is a favorable substrate for fungal growth. Gamma irradiation is a well-established low-cost treatment used for decontamination of paper objects. The dose rate plays an important role in the efficacy of the radiation treatment, but further chemical treatment is also important for imparting specific properties for food packaging applications. The aim of this study is to evaluate the influence of γ-radiation dose and bioactive compounds grafting on appearance, structure and properties of two cellulosic substrates: unbleached and bleached Kraft cellulose paper. In this sense, Kraft paper has been activated using gamma irradiation treatment and grafted with two bioactive compounds, namely clove oil and rosehip seed oil. The experimental results showed that: (a) no significant changes of the irradiated samples took place, which prove a good durability; (b) the morphological and structural changes took place after modification with bioactive compounds, imprinting antimicrobial and antioxidant properties to modified substrates; (c) the modified materials extended the shelf-life of tested aliments, indicating that the new obtained materials are suitable for food packaging applications.

The electrospinning, a facile, ecological and efficient technique from production cost view, was applied to yield chitosan (CS) nanofibers with sub-micrometric diameter which preserved the intrinsic properties of chitosan such as biocompatibility, lack of toxicity and good therapeutics activity (anti-microbial, anti-fungus, anti-tumor, anti-viral and anti-cholesterolemic activity) with potential for a large variety of applications [1-6].

The aim of this study was to prepare chitosan-based nanofibers functionalized with 2-formylfenilboronic acid by the imination reaction in heterogenous medium, in order to obtain biodegradable, biocompatible and antimicrobial bandages for burn wound healing applications. The aldehyde has been chosen due to its antifungal and antibiofilm properties demonstrated when it was combined with chitosan [7].

The preparation of the proposed fibers was realized in 3 steps. First, CS/PEO fibers were electrospun form a blend solution of CS/PEO (weight ratio of 2/1) in 80% acetic acid using an Inovenso electrospinning apparatus with a rotary collector, when applied the following parameters: voltage equal with 7 kV, tip to collector distance 10 cm, flow rate 0.4 ml/h, collector rotation speed 800 RPM, the process being realized at room conditions. The obtained material was neutralized using an aqueous solution of 5% NaOH to remove the residual acetic acid and then it was washed with ultra-pure water to remove the PEO, in order to obtain pure chitosan nanofibers. Further, the chitosan nanofibers were reacted with 2-folmylphenylboronic acid in different conditions to obtain a series of materials with different substitution degrees. The as obtained imine functionalized fibers were morphologically characterized by scanning electron microscopy and polarized optical microscopy. The imination reaction and the substitution degree were monitored by FT-IR and ¹H-RMN spectroscopy. The presence of the imine units was also evidenced by thermo-gravimetrical analysis, by variation of the degradation temperature. The water adsorption capacity was investigated by dynamic vapor sorption (DVS) technique and the antimicrobial activity was screened against different bacterial and fungal strains. It was established that the substitution degree influences the water sorption capacity of the fibers and the antimicrobial activity, the best results being obtained against staphylococcus aureus, candida albicans and aspergillus brasiliensis. It was concluded that as prepared materials keep a high potential for wound healing applications.

Acknowledgements

This work was supported by the Romanian National Authority for Scientific Research MEN – UEFISCDI (grant number PN-III-P1-1.2-PCCDI2017-0569, no. 10PCCDI/2018).

References:

1. Ohkawa, K., Cha, D., Kim, H., Nishida, A., & Yamamoto, H. (2004). Electrospinning of Chitosan. Macromolecular Rapid Communications 25(18): 1600–1605.
2. Jeon, Y. J., Kim, S. K. (2000). Production of chitooligosaccharides using ultrafiltration membrane reactor and their antibacterial activity. Carbohydrate Polymers 41: 133–141.
3. Jeon, Y. J., Kim, S. K. (2002) Antitumor activity of chisan oligosaccharides produced in an ultra-filtration membrane reactor system. Journal of Microbiology and Biotechnology 12: 503–507.
4. Hirano, S., Nagao, N. (1989). Effects of chitosan, pectic acid, lysozyme and chitinase on the growth of several phytopathogens. Agricultural and Biological Chemistry 53: 3065–3066.
5. Chirkov, S. N. (2002). The Antiviral Activity of Chitosan (Review). Applied Biochemistry and Microbiology 38(1): 1–8.
6. Sugano, M., Yoshida, K., Hashimoto, M., Enomoto, K., Hirano, S. (1992). Hypocholesterolemic activity of partially hydrolyzed chitosan in rats. In: Brine, C. J., Sandford, P. A., Zikakis, J. P. (Ed.) Advances in chitin and chitosan. Elsevier, London, pp. 472–478
7. Ailincai D., Marin L., Morariu S., Mares M., Bostanaru A. C., Pinteala M., Simionescu B. C., M. Barboiu (2016). Dual crosslinked iminoboronate-chitosan hydrogels with strong antifungal activity against Candida planktonic yeasts and biofilms, Carbohydrate Polymers 152: 306-316.

The addition of silver nanoparticles (AgNPs) to biomedical textiles can be of great interest to protect the materials against microorganisms, providing higher durability, and also to prevent the spread of microorganisms by contact or release of active antimicrobial silver ions. Textiles can act as a containing or drug release system to prevent healthcare-associated infections and facilitate the wound healing process. However, the human and environmental over-exposure to AgNPs during manufacturing, handling and disposal is leading to numerous concerns due to the AgNPs toxicity that may comprise DNA perturbation and metabolism damage in healthy cells. Thus, improve the AgNPs deposition onto textiles and control their release is crucial to minimize or prevent the AgNPs side effects. Atmospheric dielectric barrier discharge (DBD) plasma treatment is a dry environmental-friendly and cost-competitive method allowing continuous and uniform processing of fibres surfaces without the use of any chemicals or costly gases. In this work, AgNPs were stabilized onto polyamide 6,6 fabrics (PA66) through DBD plasma treatment and the use of chitosan (Ch) layers. The different formulations were obtained by spray where one first layer of Ch was applied, followed by a second layer of nanoparticles dispersed in ethanol (Ch+AgNPs). A final chitosan protective layer was also considered (Ch+AgNPs+Ch) and samples with just AgNPs were used as control. The combination of DBD plasma treatment and different layers of Ch makes it possible to control the amount and oxidation state of nanoparticles in the composites and consequently, manage the antimicrobial performance of the fabrics. DBD plasma treatment revealed a crucial role in AgNPs adhesion (4.8 and 6.3 At%) by the increase of the surface roughness and the introduction of new functional groups onto fabrics surface. The first layer of Ch decreased the AgNPs adhesion in both untreated and DBD plasma-treated samples but treated samples showed higher concentration (1.7 and 4.1 At%). The antibacterial activity was evaluated against Staphylococcus aureus and Escherichia coli after 2 and 24h, showing a superior action in all samples with DBD plasma-treated samples after 24h. The Ch in the first layers of the composite delayed the antimicrobial action of the samples. However, the use of Ch in some cases enhance the antimicrobial action of the composites. The obtained coatings will allow the development of novel and safe wound dressings able to control the antimicrobial action.

This paper provides an overview of the recent progress in research and development dealing with polymers derived from plant oils. It highlights the widening interest in novel approaches to the synthesis, characterization and properties of these materials from renewable resources and emphasizes their growing impact in sustainable macromolecular science and technology. The monomers used include unmodified triglycerides, their fatty acids or the corresponding esters, and chemically modified triglycerides and fatty acid esters. Comonomers include styrene, divinylbenzene, acrylics, furan derivatives, epoxides, etc. Blends and composites are also discussed. The synthetic pathways adopted for the preparation of these materials are very varied, going from traditional free radical and cationic polymerizations to polycondensation reactions, as well as metatheses and Diels-Alder syntheses.

In addition to this general appraisal, the specific topic of the use of tung oil as a source of original polymers, copolymers and nanocomposites is discussed in greater details in terms of mechanisms, structures, properties and possible applications.