A Tiered Experimental Approach for Characterization and Silver Release of Silver-Containing Wound Dressings

Silver-containing dressings are widely used for wound care owing to their broad-spectrum microbicidal activity. However, the potential adverse effects on human health emerging from exposure to their active ingredients (silver ions or nanoparticles) have resulted in widespread concerns about their use. The release profiles of various chemical forms of silver (Ag) from silver-containing dressing are closely related to their bioavailability and potential adverse effects on the body. In this research, we demonstrated a tiered experimental approach for systematic characterization and assessment of silver-containing wound dressing, which provides information for risk assessments. The combination of scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray, X-ray photoelectron spectroscopy, and X-ray diffraction allowed for systematic characterization of silver-containing dressings including their morphology, size, composition, valence state, and crystal forms, which have a close relationship with their silver release profile, antimicrobial activity, and potential toxicity. We developed an Ag release experiment using a reciprocating holder method and an ultrafiltration membrane column to separate the silver nanoparticles (AgNPs) and silver ions released from the dressing. Furthermore, by adjusting the Ag-ion concentration in the release media (simulated body fluid) we could effectively eliminate the interference from AgCl particles, which have a similar size to the AgNPs. We used our method to analyze the release profiles and the chemical form of the Ag present in three commercial silver-containing dressings. A large variation in the total Ag content, amount of released Ag-ions, and amount of released AgNPs was observed in the three dressings that were tested. The silver release profiles were highly dependent on the crystal structures, surface coating process, and binding modes. The cytotoxicity assays were consistent with the characterization data. This tiered approach provides valuable information of optimized AgNPs usage and proper manufacturing process for further safe applications. This study establishes a systematic characterization methodology for better understanding of risk assessment of nano-embeded consumer products.