Dynamic mechanical properties of medical grade silicone elastomer stored in simulated body fluids

Medical grade silicone rubber samples were immersed in distilled water and in pseudo-extracellular fluid (PECF) at 37.5 degrees C for up to four months. Periodically, the storage modulus and log decrement of the samples were measured on a torsion pendulum. Up to 20% increases in storage modulus and about 40% decreases in log decrement were found over the four months independent of sample surface area. Similar trends were seen in both distilled water and in PECF. Higher (59 degrees C) storage temperatures accelerated the changes. Small amounts of moisture uptake were detected. However, the presence of water in the samples did not cause the change in mechanical properties.