(618ah) Biopolymer/ METAL NANOPARTICLES Composite; Conductivity and Antibacterial Activity Relationship

Nowadays metal–polymer nanocomposites are the subject of increased interest due to their potential to combine the features of polymers with those of inorganic materials. Specifically, the combination of a natural polymer (biopolymer) such as chitosan (CS) and silver nanoparticles (AgnP) is highly appealing because of the individual antibacterial activity of both components, and the possibility to generate a biodegradable and biocompatible composite. The incorporation of AgnP to CS can improve its mechanical properties and enhance its antibacterial activity, which can extend its applications, specifically in those where hygiene is a key factor. In this work, the antibacterial activity of CS/AgnP films against two gram-positive and two gram-negative bacteria is evaluated. The films were obtained by the solvent cast method. The AgnP were incorporated into CS/acetic acid aqueous solutions by ultrasonic dispersion at concentrations varying from 0.5% wt to 20% wt. The contact times between the films and strains were 0. 5. 24 and 48 h with initial inocula of 9.12 UFC/cm². A potential increase in the antibacterial activity of chitosan with the addition of silver nanoparticles was observed; the inhibiting growth of the tested microorganisms clearly increases with increasing AgnP content and it is more effective against gram-positive bacteria, however, at 20% wt, in both, gram-positive and gram-negative this effect decreases in comparison to films with lower AgnP content, this decline is ascribe to the formation of agglomerates generating larger metal particles.

On the other hand, a percolation threshold in the electrical conductivity was observed at 2% wt of AgnP; the same percentage by which the anti-bacterial effect is the highest. This effect is related to the presence of protonated amino groups and the size of metal nanoparticles which strongly influences both the conductivity and the antibacterial effect. Thus, these compounds can be used as antibacterial sensors from conductivity measurements.