Design News for Mechanical and Design Engineers

“Our new grade not only can deliver a surface finish on par with painted metal, but also maintains the stiffness, strength and chemical resistance necessary for medical instruments and devices,” says Shawn Horrock, healthcare global market manager for Solvay Advanced polymers, Alpharetta, GA.

The new compound is a 50 percent glass-reinforced Ixef polyarylamide that comes in eight colors, all approved for gamma radiation sterilization. The company hopes to replace stainless steel and titanium for applications such as hemostats and forceps.

“There are two advantages,” says Brian Baleno, medical market manager of the Americas. “The first is that it reduces throughput and there is less stress on the hospital in terms of cleaning and disinfecting the instruments. And the second is disease transfer. You don’t take any chance of having bacteria on the instrument. It’s possible after a sterilization process that instruments weren’t cleaned completely.”

The economics strongly favor plastics if both types of instruments (metal and plastic) are used only once. A stainless steel hemostat may cost $12 to $15 per part, while a version made from Ixef costs $2 to $3. Exact costs depend on part geometry and size of the production run.

Baleno recommends device manufacturers conduct mold flow and finite element analysis on the new plastic design before completing a conversion, to make sure the plastic can withstand the loads. “Most of the field testing is done by the surgeons so they can make sure it has the feel and strength of a metal instrument, while at the same time being lighter,” he says.

Single-use medical instruments are irradiated with gamma rays to make sure they are sterile following the molding process. Other plastics that are candidates for devices, such as polycarbonate compounded with ABS, cannot withstand irradiation via gamma rays, according to Baleno. Most plastics discolor following gamma irradiation. Another issue with other plastics is a potential for fiber residue on the device surface. Because Ixef has enhanced flow properties, surfaces are resin-rich, says Baleno.

Solvay Advanced Polymers is competing against polycarbonate for another medical application, reservoirs that hold medications for delivery to hospital patients. Baleno says PC is susceptible to stress cracking after being washed with cleansers typically used in hospitals.

The new Ixef is available in eight stock colors so surgeons can easily differentiate sizes or types of instruments. Parts can also be color coordinated for different wings or wards. The pigments are also gamma stable and biocompatible.

	New polymer comes in eight stock colors.