This work describes the synthesis and characterization of noncytotoxic nanocomposites either colloidal or as films exhibiting high antibacterial activity. The biocompatible and biodegradable polymer chitosan was used as reducing and stabilizing agent for the synthesis of gold nanoparticles embedded in it. Herein, for the first time, three different chitosan grades varying in the average molecular weight and deacetylation degree (DD) were used with an optimized gold precursor concentration. Several factors were analyzed in order to obtain antimicrobial but not cytotoxic nanocomposite materials. Films based on chitosan with medium molecular weight and the highest DD exhibited the highest antibacterial activity against biofilm forming strains of Staphylococcus aureus and Pseudomonas aeruginosa. The resulting nanocomposites did not show any cytotoxicity against mammalian somatic and tumoral cells. They produced a disruptive effect on the bacteria wall while their internalization was hindered on the eukaryotic cells. This selectivity and safety make them potentially applicable as antimicrobial coatings in the biomedical field.

In this work different variables have been analyzed in order to optimize the bactericidal properties of chitosan films loaded with silver nanoparticles. The goal was to achieve complete elimination of antibiotic resistant and biofilm forming strains of Staphylococcus aureus after short contact times. The films were produced by solution casting using chitosan as both a stabilizing and reducing agent for the in situ synthesis of embedded silver nanoparticles. We have applied an innovative approach: the influence of the chitosan molecular weight and its deacetylation degree (DD) were analyzed together with the influence of the bacterial concentration and contact time. The best results were obtained with high DD chitosan where a fast reduction was favored; leading to smaller nanoparticles (nucleation is promoted), and a sufficiently high polymer viscosity prevented the resulting nanoparticles from undesired agglomeration. In addition, for the first time, potential detachment of the silver nanoparticles from the films was evaluated and neglected, demonstrating that uncontrolled release of silver nanoparticles from the chitosan films is prevented. The influence of the ionic silver released from the films, silver loading, nanoparticle sizes, contact, and initial number of bacteria was also analyzed to elucidate the mechanism responsible for the strong bactericidal action observed.

Severe bacterial and fungal infections have become a major clinical and public health concern. Nowadays, additional efforts are needed to develop effective antimicrobial materials that are not harmful to human cells. This work describes the synthesis and characterization of chitosan–ascorbic acid–silver nanocomposites as films exhibiting high antimicrobial activity and non-cytotoxicity towards human cells. The reductive and stabilizing activity of both the biocompatible polymer chitosan and ascorbic acid were used in the synthesis of silver nanoparticles (AgNPs). Herein, we propose an improved composite synthesis based on medium average molecular weight chitosan with a high deacetylation degree, that together with ascorbic acid gave films with a uniform distribution of small AgNPs (<10 nm) exhibiting high antimicrobial activity against biofilm forming bacterial and fungal strains of Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli and Candida albicans. At the same time, the resulting solid nanocomposites showed, at the same doses, reduced or totally excluded cytotoxicity on mammalian somatic and tumoral cells. Data obtained in the present study suggest that adequately designed chitosan–silver nanocomposites are powerful and promising materials for reducing pathogenic microorganism-associated infections without harmful effects towards mammalian cells.