Sterilization - Tough on Germs, Tough on Plastics, too

electing the most appropriate plastic material for a medical device is no easy task. Designers must balance cost-containment pressures that favor using the least-expensive material and S processing techniques against the need to ensure the patients’ safety and wellbeing at any cost. Product liability also is a concern. So for any given application, the designer ends up specifying the most affordable material that delivers the desired function, yet provides maximum assurance against failure during use. Before arriving at that point, the designer must analyze many types of materials data and evaluate them in light of current safety, environmental, and regulatory issues. That process can be very time-consuming because of the many plastic materials used in the medical device industry. “The problem increases each year as the variety of new or modified materials being introduced to the medical device industry increases,” says Charles E. Lundy of Miles, Polymers Division (Pittsburgh, Pennsylvania). But the materials maze is manageable, he says, if the engineer follows established guidelines. Those are provided in “Criteria for Selecting Polymeric Materials in Medical Device Applications,” a paper Lundy Presented in February at the Medical Design &i Manufacturing West conference in Anaheim, California. The first step Lundy cites is to determine the performance requirements for a specific device, based on four attributes: mechanical properties, environmental issues, regulatory issues, and sterilizability. By defining the significance of each attribute, Lundy says, the designer can determine the overall material performance requirements for a particular medical device application. Sterilizability is a particularly important performance attribute, because every reusable medical device destined to contact the body or bodily fluids must be sterilized. But sterilization processes also alter the materials of construction their mechanical properties, clarity, color, bondability, and shelf life. This article examines the various sterilization methods, their effects on commonly used thermoplastics, and new resin formulations that offer more resistance to sterilization processes. It also provides examples of design approaches that can reduce sterilization’s negative impact.