Medical Device Link . Predicting Shelf Life from Accelerated Aging Data: The D&A and Variable Q 10 Techniques With increasing requirements for predicting the longevity of medical devices kept in storage, simple methods for calculating shelf life

Medical Device & Diagnostic Industry The medical device industry has long been interested in techniques for predicting the shelf life of polymer-based devices. This year, that interest will increase substantially. As of June 14, 1998, the European Union is banning the sale of sterile or degradable medical devices that have no expiration dates. Now more than ever, developers of polymer-based medical products need ways to ensure a product shelf life of five or six years. Because real-time testing is impractical, accelerated aging techniques must be used. However, the two best-known techniques for predicting the future properties of polymers using accelerated storage data, the Arrhenius and the Q equations, are not reliable for most medical devices. Fortunately, alternative techniques are available. The two methods described below are relatively easy to use, and have been shown to be more accurate in predicting actual shelf life than the better-known techniques. Many polymers important to the medical device industry are damaged by the radiation required to sterilize them. This damage can involve embrittlement (as in polypropylene), discoloration (as in polycarbonate), or additive blooming (as in polyvinyl chloride). Often the chemical damage is not complete when the radiation stops, but continues in a "dark reaction" for some time, often years. Manufacturers need to know how devices will perform throughout their required shelf lives, often as much as four to five years after irradiation. Storage at high temperatures is used in accelerated aging testing to speed the chemical degradation processes. Test results of these accelerated aging samples are mathematically manipulated to yield a prediction of the performance of products aged at room temperature. The rates of chemical reactions, within the limits of certain restrictions, increase with temperature, as described by the Arrhenius equation. This equation says that log rate (ln ) is proportional to the inverse absolute