Thermoplastic elastomers could have a significant future in parenteral closure products if they meet the stringent requirements of the biomedical industry.
Parenteral applications - which involve drug administration via injection, implantation or infusion - include packaging systems, vial stoppers and prefilled syringes. The stoppers and syringe components, such as plungers, tip caps and lined seals, typically are made of compression-molded halobutyl rubber and other blended materials, said Doug Duriez of medical components manufacturer West Pharmaceutical Services Inc.
Duriez, who is responsible for formulation development for the Americas region at West, talked about the benefits of TPEs in parenteral closure applications in a presentation at the ACS Rubber Division's TPE Conference in Akron.
To be considered as a viable material in parenteral products, TPEs must meet the same requirements traditional rubber and plastic compounds do, Duriez said.
TPEs meet general standards for chemical cleanliness, sterilizability and low generation of particulates.
The material also has to be competitive in manufacturing costs and provide reasonable cavitation and cycle times. Again, Duriez said, TPEs have the potential to meet that requirement.
Questions do arise in areas such as barrier properties, however. Butyl rubber is the standard bearer for low gas permeation, and TPEs designed for use as stoppers need to meet those levels for oxygen and moisture vapors, Duriez said.
TPEs also must have specific stopper requirements such as sealability and resealability, Duriez said. Seal integrity is a major issue because the stopper can't allow leakage past the plunger of the lined seal or tip cap on a syringe.
The main drivers behind TPE use in parenteral products are superior cleanliness, shorter cycle times, clean compact processes, automation and comolding. Comolding is a unique property of TPEs, as opposed to other elastomers, which allows materials of different densities to be integrated or joined through the molding process.
This opens up a ``whole new world'' of TPE-based components, Duriez said.
West makes more than 300 million caps per year for various applications, so the possibilities for TPEs are tremendous, he said. The company has made seals for its Blow-Fill-Seal IV bottles from TPE materials and found they meet the requirements of resealability, penetration and pull-out forces, and no leak path between the cap and elastomeric septum.
In fact, a reliable welding bond within this application only can be achieved with a septum made from a TPE material, Duriez said.