Molding Bioabsorbable Implants
Used in its contract molding operations, the Sesame™ injection molding machine is designed to provide fast, controlled injection and short material residence time. It uses a pneumatically driven vertical plunger for plasticating, and injects with a tiny horizontal plunger (1- to 2.5-mm diameter) driven by a linear servo motor. Total injection time can be as short as 0.02 seconds. The Sesame’s features include very low melted volume, controlled high speed, and high pressure injection. This allow for the molding of sub micro-sized parts with complex geometric features from materials such as bioabsorbable polymers that would otherwise degrade in standard equipment. Medical Murray has developed processes and designs for creating miniature hinges in molded devices for bioabsorbable fasteners that are activated during placement. Parts have been produced on the Sesame measuring just 0.10 mm and weighing only 2.5 mg, or one-twentieth of a single pellet. Conventional screw plasticizing machines commonly require sprue and runner systems that consume 75 percent or more of the volume needed to produce one part. Medical grades of bioabsorbable resins can sell for upwards of $13 per gram, therefore scrap material must be tightly controlled to minimize the effect on the bottom line.