Increasingly, permanent and bioresorbable polymers are being enhanced with additives to increase therapeutic effect. These include radiopaque fillers for x-ray visibility, bio-active bone growth additives and other active ingredients.
Custom compounding such materials requires facilities, equipment and processes necessary for implantable applications. All batching and hot-melt extrusion processes must be conducted in a clean environment: ISO 100,000 class cGMP certified clean room at a minimum.
Twin screw extruders are often required to provide optimal distributive and dispersive mixing when melt blending liquid and powdered additives into an implantable polymer matrix. Small scale twin screw extruders are required from an economic standpoint as ingredients for enhanced orthopedic implants are relatively expensive.
Pre and post extrusion equipment are also highly specialized for implantable polymers. Desiccant and vacuum driers are required to prepare active ingredients in fine powder form and pellets of bioresorbable polymers with low melt temperatures. Polymers having dissimilar bulk densities are best fed into the extruder separately using multiple single screw loss-in-weight feeders. Fine powder additives are also fed separately using twin screw or disk type loss-in-weight feeders. Liquid ingredients are injected into the melt blend with peristaltic, gear, piston, or syringe pumps. Post extrusion cooling of the polymer blend is essential for precise sizing and metering. Long term implantable polymers are cooled using water while bioresorbable polymers must be cooled with a dry air supply. In both cases the cooling medium must be clean and maintained at a specific temperature.