A novel silver-loaded chitosan composite sponge with sustained silver release as a long-lasting antimicrobial dressing

In this study, a new kind of sustained-release silver-loaded chitosan-based sponge was developed by a simple and green method as a long-lasting antimicrobial dressing. The embedded silver nanoparticles (AgNPs) were prepared by catechol-conjugated chitosan (CCS). The CCS-coated AgNPs (CCS-AgNPs) were incorporated into the chitosan (CS) matrix through interactions between the catechol and amino groups of CS. Well-dispersed and unaggregated CCS-AgNPs were observed in the composite sponges. Due to an interconnected multi-porous structure, the composite sponges exhibited excellent flexibility and water absorption capability, which is beneficial to remove excess exudates effectively. In silver release tests, CCS-AgNPs/CS showed sustained release, whereas the control group without catechol exhibited burst release. As a bridge to bind AgNPs into the CS matrix, catechol extended the silver release time from 1 day to at least 4 days. The prolonged silver release endows CCS-AgNPs/CS sponges with long-lasting bacteriostatic effects against both Gram positive and negative bacteria. Bacterial growth was completely inhibited for up to 3 days. Meanwhile, the embedded CCS-AgNPs significantly improved the bactericidal effect. More than 99.99% bacteria could be killed by the composite sponges, which completely satisfies antibacterial requirements for wound healing. As a double-edged sword, an excessively high silver content induced cytotoxicity in MC3T3 cells. In general, the CCS-AgNPs/CS sponge with appropriate silver content (0.63 wt%) is considered as a potential candidate for wound healing dressings due to its long-lasting bacteriostatic effect, powerful bactericidal activity, and excellent biocompatibility.