One of the hottest trends in medical molding is use of bioabsorbable polymers in implants. These materials decompose into carbon dioxide and water via hydrolysis, and present no threat to the human body.They provide support until bone, muscle or tissue heals and, eventually, no longer needs an implant's support. Close to 1,600 U.S. patents filed since 1976 include some description of bioabsorbable polymers.
Medical-grade bioabsorbable parts available from a variety of sources include screws, tacks, pins and anchors. Tests show that radiolabelled implants of poly-DL-lactide decomposed in animals after 18 months to five years. Molding these materials, presents a serious challenge, however.Look for processors that have Scientific Injection Molding Principles, Class 100,000 or better clean room manufacturing space, and significant design know-how. “We use dedicated screws and barrels to guard against cross contamination and then shroud the resin in nitrogen fog as it enters the barrel to ensure there is no oxygen present,” comments Dave Thoreson, Medical Molding and Assembly Plant Manager at Phillips Plastics, Menomonie, WI. Bioabsorbable resins typically cost $1600 to $2200/lb and are shipped in vacuum-sealed cans or sealed polybags. Some new generations of implants include bioactive substances such as antibiotics. Bioabsorbables are also being actively investigated for use in drug-eluting stent systems—the biggest medical device market in the world today. Bioabsorbable materials could be used in the polymer coating that releases the drug as well as for the stent structure itself. Stent prototypes have been molded from a blend of polylactide and trimethylene carbonate.