Incorporation of copper and zinc nanoparticles and salts into medical-grade silicone as antibacterial candidates for prevention of capsular contracture

Capsular contracture (CC) is one of the most common clinical complications following breast augmentation or reconstruction surgery using implants. The foreign body reactions (FBR) due in parts to the hydrophobicity of the silicone elastomer and bacterial adherence to the implants are problematic and believed to be leading to the development of CC. A common strategy implemented to reduce FBR has been the addition of textures on the surface of the implants. While this approach has led to reduced incidence of fibrous capsule formation around implants, it has also led to an association with anaphylactic large cell lymphomas. Therefore, new strategies are needed to reduce rates of CC [1]. Release of copper and zinc ions (Cu2+ and Zn2+ respectively) have been reported as effective antibacterial agents against gram-positive S. aureus and gram-negative E. coli strains, bacteria believed to be at the source of implant colonization and therefore infection. The incorporation and release of those ions from the medical grade silicones used to manufacture breast implants have not been studied. Here, for the first time, we report the incorporation and release of Cu2+ and Zn2+ from medical implant grade silicone elastomers as a strategy to reduce the risks of CC and implant associated infection. Silicone elastomer films (0.3 cm thick) containing 1–30% w/w copper and zinc nanoparticles or copper and zinc anhydrous salts were prepared from medical grade addition-cure silicone elastomer dispersions (MED 6400 and MED 6600, NuSil). Briefly, silicone parts A and B (1:1) were mixed with drug (1 min, 3000 rpm), left overnight for solvent evaporation, and then post-cured (3 hr, 90oC). Changes in the tensile strength of the materials were measured by elongating 0.5 × 4 × 0.3 cm films until break. 1 × 3 × 0.3 cm films were incubated at 37oC, 60 rpm in a phosphate buffer (PBS) and media was collected every 24 hr over three weeks to measure the amount of ions released using ICP-OES. Antibacterial capacities of the materials against S. aureus (ATCC 6538) were assessed by incubating 1 × 1 × 0.3 cm films with the bacteria in Mueller Hinton Broth (MHB) over 5, 24 and 48 hours and biofilm formation and planktonic concentrations were measured using the Miles and Mesra method. Conclusions: Incorporation of the nanoparticles and anhydrous salts in medical grade silicone samples both showed to have advantages and disadvantages as the NPs did do not affect the physical properties of the materials but proved ineffective as antibacterial agents while the salts significantly decreased the tensile strength of the silicone but released great amounts of Cu2+ and Zn2+ reaching the determined MIC and MBC for a S. aureus strain.