Silver-and metal-containing polyurethanes

Silver- and metal-containing polyurethanes Metal- and silver ion-containing polyurethanes... 

Immersions of polymer microtensile specimens in solutions of metal ions or lipid emulsions at elevated temperatures for 16 weeks have been reported [32]. Temperatures of 37, 70, and 90°C are recommended with sampling monthly to establish trends. For pacemaker leads, the solutions should include all the metals found within the device, a base, and an acid. For example, aqueous solutions of 1 M AgNOs or 0.1 M C0CI2 (acetylacetanoate) can assess oxidation. Immersion in 1 N acetic acid. Ringer s solution, and 1.0 N HCl can assess hydrolytic resistance. Immersion in 20% intralipid (soybean) emulsion can assess the propensity to absorb lipids. However, in our experience, none of the above in vitro tests appear to be reliably predictive of performance in pacemaker lead insulation. Why The in vivo environment cannot be duplicated in vitro. For example, the oxidation state of an ion varies as a function of what it is dissolved in. Distilled water containing a metal ion does not represent the environment within a lead. This accelerated test predicts that Ag+ will oxidize and degrade polyether polyurethanes while Co will not. Multiple in vivo studies clearly demonstrate exactly the opposite [14, 33]. Traces of cobalt will degrade the polymer in vivo whereas silver will not. 

It is absolutely necessary to consider all the materials used in the device so that interactions can be evaluated. For example, modern cardiac and neurological leads may be insulated with silicone rubber or polyether polyurethane. They also contain metallic conductors (typically MP35N, and sometimes also platinum or silver). The individual conductor wires may be covered with a redundant insulation such as eTFE. The conductors and insulation are connected to stainless steel connector pins and platinum electrodes. 

---