Ridgefield, NJ--In discussions with customers who make medical devices, Unichem Products technical service personnel often heard them express a wish for a vinyl replacement for the more expensive silicone rubber. Although vinyl is widely used in the medical market, it is most often chosen for its excellent properties as a fluids container or conduit used for hoses, bulbs, bags, and tubes, for instance.
However, the material is not noted for its recovery characteristics. Consequently, medical equipment design engineers almost automatically turn to silicone rubber as the preferred material for tubing, pumping devices, bushings, grommets, and the like. This tendency, says Unichem Technical Service Manager Meg Henke, overlooks recent advances in vinyl chemistry, and, as result, "many of today's products may be over-engineered."
That may no longer be the case. Henke advises design engineers to check out Unichem's Flexchem vinyl before making the final material decision. The material exhibits many of the characteristics of silicone rubber, but at about one-half the cost, she explains. And, she adds, design engineers in the medical industry, under intense pressure to reduce costs while maintaining performance, have shown much interest in the potential for Flexchem in their latest designs.
Henke cites peristaltic pump tubing as an example. The tubing is pinched and released repeatedly by a cam wheel. Therefore, it's important that the tube material rebound each time the cam wheel releases. While silicone rubber works perfectly for the application, Flexchem works just as well, but at half the cost, says Henke.
In addition, Henke notes, vinyl also accepts printing better than silicone, and it can be heat-, RF-, or solvent-welded, making it easy to assemble medical devices that are relatively complicated.
Not always best. However, vinyl also has some problems, particularly when it comes to sterilization. The most common way to sterilize polyvinyl chloride (PVC) products used for medical devices has been ETO sterilization, deemed hazardous to our ecosystem. On the other hand, the most efficient form of sterilizaton is radiation, but PVC can't be radiated due to its susceptibility to material degradation--the material turns brittle and yellow during the radiation process.
Enter "eco-packaging" from Alga Plastics (Cranston, RI). Alga engineers have developed enhanced structural design features that allow the use of alternative materials, such as PETG (glycol modified polyethylene terephthalate) and Barex (nitrile barrier resin), to be down-gauged, while maintaining the integrity of the medical package. An added benefit: improved package aesthetics.
The eco-packaging approach also solves another major problem facing today's medical profession. Use of the new material eliminates pinholing of a PVC sheet, which causes contamination of the packaged product, according to Rick Collins, Alga's vice president of engineering.