Development and characterization of chitosan and silver based nanoparticles antimicrobial materials for coating applications on medical devices

Abstract

Resumo: Medical devices, such as catheters, probes, and wound dressings, are particularly vulnerable to microbial contamination and biofilm formation, especially by multidrug-resistant bacteria. In this way, nanomaterials with antimicrobial activity hold a promising solution to overcome this problem. Among these nanomaterials, nanoparticles (NPs) derived from natural sources, such as chitosan (CS), and metal-based nanoparticles, such as silver (Ag), are gaining significant attention in nanomedicine. CS can offer great potential as coating and antimicrobial agent, while AgNPs possess antimicrobial effects against different pathogens. Together, these materials can result in a powerful nanocomposite suitable for antimicrobial coatings with enhanced antimicrobial properties due to the combination of the unique properties of both components. This project focused on the development of new antimicrobial materials based on CS-Ag NPs and composite with high antimicrobial properties to be applied as coating in medical devices and it was divided into three parts. The first part investigated the use of various reducing agents, including CS, combined with different AgNO3 proportions in the synthesis of AgNPs. The second part presented a facile and practical approach to preparing potent antimicrobial coatings based on CS-Ag composites, by simply stirring a CS solution with different amounts of AgNO3. The third part presented a two-step synthesis of AgNPs using CS and nanochitosan (NCS) as reducing agents, with varying AgNO3 concentrations. The results showed significant differences in nanoparticle morphology and antimicrobial activity based on the choice of reducing agent and the AgNO3 concentration, revealing CS as the best choice due to its dual role as a reducing and stabilizing agent. The CS-Ag composite demonstrated excellent photocatalytic and antimicrobial activity against E. coli, especially in the presence of light, with a bacterial reduction rate ranging from 75% to 100%. Morphological characterizations revealed the presence of Ag rods formed AgNPs embedded into a CS film. Ag+ ions were reduced to Ag0 during the coating process due to the electron-rich oxygen atoms in the polar hydroxyl and ether groups in the CS. Both CS and NCS effectively reduced Ag? to Ag0, enabling the formation of small, spherical, and potentially semicrystalline AgNPs. Antimicrobial testing revealed that AgNPs synthesized with CS showed a larger inhibition zone against S. aureus, while no significant differences were observed among samples tested against E. coli. The use of CS and NCS appeared to influence the stabilization and size regulation of AgNPs, with no direct relation. Additionally, both CS and NCS based AgNP coatings demonstrated antibiofilm activity, suggesting their great potential as antimicrobial coatings for medical device surfaces. The findings of this study offer promising solutions to combat biofilm formation, highlighting synthesized materials as potential alternatives for applications in the biomedical field

Abstract: Les dispositifs médicaux, tels que les cathéters, les sondes et les pansements, sont particulièrement vulnérables à la contamination microbienne et à la formation de biofilms, notamment par des bactéries multirésistantes. Dans ce contexte, les nanomatériaux dotés d’une activité antimicrobienne représentent une solution prometteuse pour lutter contre ce problème. Parmi ces nanomatériaux, les nanoparticules (NPs) issues de sources naturelles, comme le chitosane (CS), et les nanoparticules métalliques, telles que celles à base d’argent (Ag), suscitent un intérêt croissant, particulièrement en nanomédecine. Le CS présente un fort potentiel pour la création de revêtements antimicrobiens, tandis que les AgNPs possèdent des propriétés antimicrobiennes efficaces contre divers pathogènes. Ensemble, ces matériaux peuvent former un nanocomposite doté de propriétés antimicrobiennes élevées, idéal pour des revêtements destinés aux dispositifs médicaux. Ce projet visait à développer de nouveaux matériaux antimicrobiens à base de NPs de CS-Ag et de composites aux propriétés antimicrobiennes améliorées, destinés à être appliqués comme revêtements sur des dispositifs médicaux. Il a été divisé en trois parties. La première partie a examiné l’utilisation de divers agents réducteurs, y compris la CS, combinés à différentes proportions de AgNO3 pour la synthèse des AgNPs. La deuxième partie a proposé une méthode simple et pratique pour préparer des revêtements antimicrobiens efficaces à base de composites CS-Ag, en mélangeant simplement une solution de CS avec différentes quantités de AgNO3. La troisième partie a exploré une synthèse en deux étapes des AgNPs, utilisant la CS et la nanochitosane (NCS) comme agents réducteurs, avec des concentrations variables de AgNO3. Les résultats ont montré des différences significatives dans la morphologie des NPs et dans l’activité antimicrobienne en fonction du choix de l’agent réducteur et de la concentration de AgNO3. La CS s’est révélée être le meilleur choix en raison de son double rôle d’agent réducteur et stabilisant. Le composite CS-Ag a démontré une excellente activité photocatalytique et antimicrobienne contre E. coli, notamment en présence de lumière, avec un taux de réduction bactérienne allant de 75 % à 100 %. Les caractérisations morphologiques ont révélé la présence de structures en forme de tiges d’Ag formées par des AgNPs intégrées dans un film de CS. Les ions Ag? ont été réduits en Ag° durant le processus de revêtement, grâce aux atomes d’oxygène riches en électrons des groupes hydroxyles de la CS. La CS et la NCS ont toutes deux efficacement réduit Ag? en Ag°, favorisant la formation de petites AgNPs sphériques et potentiellement semi-cristallines. Les tests antimicrobiens ont révélé que les AgNPs synthétisées avec la CS présentaient une zone d’inhibition plus large contre S. aureus, tandis qu’aucune différence significative n’a été observée entre les échantillons testés contre E. coli. L’utilisation de la CS et de la NCS semble influencer la stabilisation et la régulation de la taille des AgNPs, bien que sans relation directe. De plus, les revêtements d’AgNPs à base de CS et de NCS ont tous deux démontré une activité antibiofilm, ce qui souligne leur fort potentiel en tant que revêtements antimicrobiens pour les surfaces des dispositifs médicaux. Les résultats de cette étude offrent des solutions prometteuses pour combattre la formation de biofilms, positionnant les matériaux synthétisés comme des alternatives potentielles pour des applications dans le domaine biomédical.

Abstract: The rise of bacterial infections, particularly those caused by multidrug-resistant strains, presents a critical challenge to healthcare systems, with millions of hospital-acquired infections annually and substantial economic burdens. In this context, nanotechnology offers a promising solution to develop advanced antimicrobial materials to be used as coating on medical devices. This doctoral thesis investigates the synergistic potential of silver nanoparticles and chitosan for antimicrobial applications. It highlights the advantages of chitosan as a reducing agent over plant-based green synthesis methods, providing superior control over nanoparticle size, stability, and antimicrobial efficacy. The proposed synthesis routes aim to create reproducible and efficient antimicrobial coatings to address this pressing issue. In the first article (Chapter 3), different methods for synthesizing silver nanoparticles were explored, using reducing agents such as sodium borohydride, heparin, glucose, chitosan, and nanochitosan, based on adaptations of methodologies reported in the literature. Among the reducing agents and synthesis methods evaluated, chitosan stood out as the most effective, resulting in nanoparticles with superior antimicrobial properties. Among the synthesis methods using chitosan, two were particularly noteworthy: one conducted without the application of heat during synthesis and another involving heating to 100°C. It was observed that the use of temperature played a crucial role in the reduction of silver ions to metallic silver, leading to the formation of nanoparticles with high antimicrobial activity and significant potential to inhibit biofilm formation. The second article (Chapter 4), based on the previous findings, focused on the synthesis of a silver-chitosan nanocomposite developed through a simple method, without the need for heating, aimed at antimicrobial coatings. Different proportions of silver ions (5%, 10%, 20%, and 50%) relative to the amount of chitosan were tested. The results demonstrated that the formulation containing 20% Ag+ exhibited the most promising antimicrobial activity, eliminating up to 100% of bacteria within just 120 minutes of contact. Furthermore, this formulation effectively inhibited biofilm formation by Escherichia coli and Staphylococcus epidermidis. The third article (Chapter 5) was built on the findings presented in the first article and used chitosan and nanochitosan as reducing agents for the synthesis of silver nanoparticles. Chitosan and nanochitosan were produced from shrimp shells and used in combination with different concentrations of AgNO3 (75 mg, 37.5 mg, and 25 mg). All formulations demonstrated satisfactory antimicrobial activity against Escherichia coli and Staphylococcus aureus. Furthermore, these formulations were applied as coating on the surface of central venous catheters, and subjected to biofilm formation tests, showing promising results in biofilm inhibition. Overall, this thesis demonstrates that the combination of chitosan and silver nanoparticles represents a promising alternative for the development of antimicrobial coatings, with the potential to significantly reduce bacterial infections in patients relying on medical devices.