Medical Device Link.

Metallocenes, Siloxane
Safety Discussed at Medical Plastics Conference

With the goal of providing a comprehensive overview of current plastics technology in the medical device industry, the "Medical Plastics '96" 10th International Conference and Exhibition was held September 24­26 at the Due Torri Hotel Baglioni in Verona, Italy. During the three days of the conference, 20 speakers from Europe, Canada, and the United States explored both proven and emerging polymer technologies and offered pragmatic solutions to some of the challenges facing suppliers of medical materials and manufacturers of finished devices. The program included presentations in the areas of materials, processing and sterilization, surface treatment, biocompatibility and testing, and regulatory compliance.

Befitting its status as the hottest topic in polymer chemistry, the subject of metallocene-catalyzed materials led off the sessions in a talk by Robert Brookman of Colorite Polymers Co. (Ridgefield, NJ, USA). Comparing metallocene polyolefins and PVC, Brookman conceded that the former represent a real technological advance but maintained that questions regarding the sealability, elastic recovery, sterilizability, and cost of the new materials will pre- vent them from replacing flexible PVCs on any widespread basis, at least in the near future. Metallocenes can be recommended, according to Brookman, when an application calls for very low densities or an absolute lack of extractables, and as metallocene chemistry evolves, both properties and economics of the materials are likely to improve.

The medical industry's increased use of so-called engineering plastics for structural components and packaging was reflected in presentations on styrenic blends and on polyetherimide (PEI) and PEI blends. Marc Heerbrant of Phillips Petroleum Co. (Overijse, Belgium) discussed recent modifications to the molecular-weight architecture of transparent styrene-butadiene (SB) copolymers that have resulted in improved spiral-flow properties and impact toughness. Combining these new grades with styrene methylmethacrylate copolymers has produced resins whose enhanced stiffness, surface hardness, and resistance to heat and warpage make them potential replacements for polycarbonate at approximately half the price. Other blends of SB copolymers with polystyrene or styrene-butadiene rubber, along with a reformulated antioxidant system, offer promise for flexible packaging products.

The development of an impact-modified PEI polymer was described by François de Bie of General Electric Plastics (Bergen op Zoom, The Netherlands). The material is of particular interest to the medical market in that it outperforms standard PEI grades in impact strength and property retention following repeated autoclaving.

The program for "Medical Plastics '96" included several studies devoted to the critical arena of medical material biocompatibility. Maarten van Geffen of Dow Corning Medical (Sophia Antipolis, France) outlined the most extensive: a $30-million, five-to seven-year research project that analyzes the toxicology, pharmacokinetics, and clinical effects of common ingredients, known as siloxanes, that are found in silicone elastomers as well as in various consumer products. The Dow Siloxane Research Programme--which van Geffen called "the largest single voluntary study by any company of its raw materials"--comprises descriptive animal studies, fundamental in vitro and in vivo research, human clinical studies, and human exposure assessments. The project's main goal is to provide an unprecedented amount of information about the safety of siloxanes. The work will also serve as an example of the feasibility of the kind of procedures recommended in the current draft standard of ISO 10993-16, which describes a dose-dependent toxicological analysis for the toxicokinetic evaluation of medical materials.

Polyurethane biocompatibility was the subject of a presentation by Robert Carson of CardioTech International Ltd. (Tarvin, Cheshire, UK), who reviewed the resistance of different formulations to environmental stress cracking, a characteristic type of implant degradation. In vitro testing was conducted on materials fashioned into vascular grafts, representing another step in the quest to identify an effective small-diameter vascular-graft material.

"Medical Plastics '96" was sponsored by the Society of Plastics Engineers (SPE) Scandinavia, the European Confederation of Medical Suppliers Associations (EUCOMED), the department of polymer materials at Chalmers University of Technology, the faculty of technology of the Brno Technical University, the Finnish Plastics Association (Muoviyhdistys), and the Association of Processors and Distributors of Plastics in Europe (APPLE).