Regulations in the making could spell hard times for PVC in medical devices—or at least for PVC plasticized with phthalates. Or, as in the past, recent news may prove more smoke than fire.
Despite controversy surrounding its use, polyvinyl chloride (PVC) remains the most widely used plastic in single-use medical applications. Fully one third of medical devices contain plasticized PVC, with the most common plasticizer DEHP (diethylhexyl phthalate).
Phthalate plasticizers are added to the typically rigid plastic to make it pliable, but it is exactly these additives that have created the most controversy. Their low molecular weight makes them prone to migration from the plastic to the contained product. Concerns increased after various tests identified phthalate plasticizers as causing health problems in rodents, especially with regard to development of reproductive organs in males. In January 2006 the European Union placed a ban on six types of phthalate softeners in some children’s toys, including DEHP. In the U.S., President Bush signed a bill on August 14 banning the use of six types of phthalates in children’s products (and essentially banning lead from use in all products designed for children under the age of 12). The ban is permanent for the use of children’s toys or childcare articles that contain more than 0.1% of DEHP, dibutyl phthalate (DBP) or benzyl butyl phthalate (BBP). The ban is temporary for the sale of children’s toys or childcare articles with concentrations of more than 0.1% of diisononyl phthalate (DINP), diisodecyl phthalate (DIDP) or di-n-octyl phthalate (DnOP).
The temporary ban may be lifted after a federally approved study is completed, though by then the materials may already have been replaced, permanently, by alternative plastics to PVC or by other plasticizers.
Clearly phthalate use remains a hot topic in the industry, and this was plainly evident in discussions at the Medical Molding & Extrusion Conference in Cologne, Germany early this summer. The subject is fraught with importance, as a new European Union directive will, beginning in December 2008, require medical device manufacturers to label any products containing plasticized PVC. Medical Device Directive 2007/47/EC almost certainly also will have a major impact on how such labeling is handled in other regions. Under the Directive, if those devices are intended for the treatment of children, or pregnant or nursing women, the use of phthalates has to be specifically justified. Catheters, intravenous tubing and bags, dialysis bags and tubing, blood bags, or air tubes are some examples of devices made of DEHP-softened PVC.
Best way forward? Opinions vary
Opinions differ on how the industry should move forward. “DEHP-plasticized PVC is probably the most widely used blood contacting material and it is very difficult to replace,” notes James Courtney, professor of bioengineering at England’s University of Strathclyde and a recognized expert in medical polymers. “It’s a low-cost, high-volume product.” Nevertheless, there are alternatives. Courtney suggests the industry either find a replacement for DEHP, “a similar plasticizer with a higher molecular weight” to limit migration, or develop the means to modify a PVC part’s surface, which can be accomplished by, for instance, ionically bonding heparin—a sulfuric acid ester that prolongs blood clotting-- to its surface. This may improve blood compatibility, reduce DEHP surface concentration, and reduce DEHP extraction in contact with blood.
Rainer Otter, director of regulatory toxicology chemicals at plastics supplier BASF (Ludwigshafen, Germany), foresees a future down either of two paths: either staying with PVC or moving to another polymer. “People generally don’t like the second option too much,” Otter says. “That’s because you would have to discard your production hardware, you would lose your knowledge in the polymer, and you would have to ask yourself ‘what are the concerns with the new polymer?’” To BASF the likely industry answer remains staying with proven PVC, and as a result the supplier has invested steadily in development and capacity of its alternative to DEHP, Hexamoll DINCH, a non-phthalate plasticizer with migration levels eight times lower than that of DEHP. “If you want to change the hazard, you need to change the plasticizer of the polymer,” he states. He stresses that additives have to be evaluated for each application based on availability, technical functionality, hazard, and risk and benefit for intended use. In 2007 BASF raised its Hexamoll capacity from 25,000 to 100,000 tonnes/yr.
Other options remain. For instance, compounder PolyOne Corp. (Avon Lake, OH) this summer entered into an exclusive license arrangement for a series of bio-based plasticizer technology patents owned by Battelle (Columbus, OH), the world’s largest non-profit independent R&D organization. The soybean-based technology is described by PolyOne as a path to commercially viable, renewable plasticizers.
Jim Gray, business development director for PolyOne, told MPW that while soy-based materials are central to the technology, it is not limited to these. PolyOne estimates the global plasticizer market at $11 billion/yr, with 90% going into vinyl formulations. Gray said that Battelle’s patents cover a wide range of chemistries derived from vegetable oils for potential use as plasticizers in PVC formulations, with the ultimate goal being a plasticizer that is 100% biobased. Gray said the biobased plasticizers might compete “favorably” with certain phthalates in specific applications. The company also anticipates usages in non-phthalate markets.
One possible future: more use of TPE
Not surprisingly, others predict a non-PVC future in medical devices. Michiel van den Berg, director of global pharmaceutical packaging development at compounder Tekni-Plex Europe (Erembodegem, Belgium), comments, “There’s a trend towards non-DEHP. So why not go PVC-free?” Van den Berg promotes his firm’s TPE (thermoplastic elastomer) compounds as an alternative. He says Tekni-Plex is working to develop a TPE suitable for IV bags and tubes. But the firm has its bets hedged: it also markets medical-grade PVC compounds, with and without DEHP, and three-layer polypropylene-based sheet as an alternative in medical applications to flexible PVC.
Others also look to TPE as a potential alternative to PVC for medical applications. As reported in last month’s Material Thoughts section of MPW, compounder GLS Corp. (McHenry, IL) has launched a portfolio of specialty Versaflex TPEs for use in gaskets and stoppers. Earlier this year, it launched a TPE line for pouches and bags, with future plans for tubing, the goal being a complete phthalate-free fluid-delivery packaging platform.
As discussion and research about the hazards of phthalates used to soften PVC continues, alternatives will continue to be developed and, almost certainly, new regulations will be passed. With no ban on phthalates’ use in medical devices, processors and their customers must weigh the difficulties of specifying an alternative. Pushing through higher prices for competitive materials, and testing these materials in the applications now processed of PVC, may be difficult but could prove a marketing advantage as label laws take effect.