Characterization and the release kinetics of silver from four different dressings

Introduction: Silver in the ionic form of silver nitrate has been used for the treatment of chronic wounds, ulcers, burns and infections since mediaeval times. Recently the interest in using silver to heal wounds has increased due to the rise of antibiotic resistant bacteria. Currently several different silver dressings have been commercialized and are widely used in burns centres. The dressings are typically composed of a polymeric scaffold and metallic or ionic silver. Even though these medications are used on a large scale worldwide, studies on the effective content of silver and their release of silver into the wound are still unknown. Materials and methods: In this work we have characterized the structure of four silver dressings by scanning electron microscopy (SEM) and have measured the concentration of silver in the dressings by Inductively Coupled Plasma Mass Spectrometry After chemical characterization, we assessed the kinetics of silver release in three different matrices: ultra pure water, normal saline solution (made in house from silver free analytical grade 0.9% m/v NaCl) and a serum substitute (Hit serum substitute, STEMCELL technologies, Vancouver, Canada). The concentration of silver released in ultra pure water represents the simplest matrix for studying silver release. The saline solution chemically simulates the wound environment, in which the available ionic silver will precipitate from solution as insoluble silver chloride. The serum substitute contains human serum albumin, insulin and transferrin and reflects the protein composition and concentration observed in human serum. We used this solution to assess if these proteins, and particularly albumin, could enhance the solubility of silver by shifting the equilibrium towards more silver in solution by actively competing with chloride as a complexing agent. After the silver release experiments, the dressings were re-characterized using the SEM to spot any morphological differences. . Results: Depending on the dressing considered, the silver concentrations ranged from 2.2 to 159 mg/g, our results confirm these levels. In most cases, the greatest release rate was in serum substitute, while saline solution was shown to virtually inactivate the dressings. Conclusions: Our results demonstrate that the current practise of carrying out release experiments in pure water has no chemical basis and should be discouraged.