Physicochemical characterization and in vitro hemolysis evaluation of silver nanoparticles

Silver nanomaterials are increasingly being used as antimicrobial agents in medical devices. This study assessed the in vitro hemolytic potential of unbound silver particles in human blood to determine which physical and chemical particle properties contribute to mechanisms of red blood cell (RBC) damage. Four silver particle powders (two nano-sized and two micron-sized) were dispersed in water and characterized using transmission electron microscopy, dynamic light scattering, surface-enhanced Raman spectroscopy, and zeta potential measurement. Particle size and agglomeration were dependent on the suspension media. Under similar conditions to the hemolysis assay, with the particles added to phosphate buffered saline (PBS) and plasma, the size of the nanoparticles increased compared with particles suspended in water alone due to interaction with chloride ions and plasma proteins. To determine hemolysis response, aqueous particle suspensions were mixed with heparinized human blood diluted in PBS for 3.5 h at 37°C. Both nanoparticle preparations were significantly more hemolytic than micron-sized particles at equivalent mass concentrations > 220 μg/ml and at estimated surface area concentrations > 10 cm(2)/ml. The presence or absence of surface citrate on nanoparticles showed no significant difference in hemolysis. However, the aqueous nanoparticle preparations released significantly more silver ions than micron-sized particles, which correlated with increased hemolysis. Although significant size changes occurred to the silver particles due to interaction with media components, the higher level of in vitro hemolysis observed with nanoparticles compared with micron-sized particles may be related to their greater surface area, increased silver ion release, and direct interaction with RBCs.