Plastic medical tubing is essential in healthcare, seeing use for the delivery of blood, nutrients and gases to the patient, and for the execution of minimally invasive surgical procedures such as cardiac angioplasty. But the rules of the game are in flux, still.
Medical device manufacturers have to adhere to increasingly stringent rules and regulations, which don’t make it easy to master the many challenges in the manufacture of critical components. While the most common plastic used for medical tubing remains polyvinyl chloride (PVC), there remains a perception of biocompatibility risk despite the existence of certified Class VI for PVC resins. Also gaining momentum, at least in the legislative realm, are potential new manufacturing standards that list certain ingredients of plasticized PVC, such as DEHP (diethylhexyl phthalate), as toxic. In October 2008, the European Chemicals Agency (ECHA) for the first time published its Candidate List of Substances of Very High Concern (SVHC), with the phthalate plasticizers DEHP, DBP and BBP identified as toxic for reproduction.
In view of the harmful substances list and Europe’s pending labeling requirements (Medical Device Directive 2007/47/EC adopted in December 2008, going into effect March 2010) for tubing containing the DEHP plasticizer, and recently legislated U.S. State regulations against phthalates in children’s toys, more and more companies are looking for DEHP alternatives or are moving away from PVC altogether. “Cost performance polymer alternatives to PVC in medical tubing have yet to fare well,” says Peter Galland, industry manager at compounder Teknor Apex, “although PVC blends that contain no liquid plasticizers would obviously generate a lot of interest if they met the basic requirements.”
His firm recently announced it would seek to assuage customer concerns by physically separating its compounding lines for medical-grade PVC compounds containing DEHP and other phthalate plasticizers from those of compounds plasticized with non-phthalate alternatives. The change already has taken place at two Teknor Apex compounding plants in the U.S. and could be carried out at the company’s facility in Singapore if demand warrants, according to Galland. The compounder is not moving away from phthalates, but it recognizes that most medical device manufacturers are in the process or early stages of evaluating phthalate alternatives for plasticized PVC compounds, he says. “There is no valid reason for movement away from PVC in medical applications such as tubing,” he explains. “But it’s hard to convince the public, who has thrived on safe medical treatment with DEHP-plasticized PVC for 50 years, that liver tumors in rodents force-fed high doses of DEHP are irrelevant to humans because humans metabolize DEHP differently than rodents do.” Galland adds that there certainly are a number of high-performing plasticizers for PVC that have a much better track record in rodent toxicology than do the phthalates, but there is not much of a human track record for these alternatives.
Alternatives may be more difficult to find, says Dan Lazas, VP marketing and sales at tubing processor Putnam Plastics Company (Dayville, CT). He has noticed that an increasing number of plastics suppliers are in fact either exiting the medical industry or working only by large-scale contract. “This is probably due to liability or limited volume of material required for certain medical applications,” says Lazas, whose firm extrudes a broad array of materials including PVC, and including for medical applications on four extrusion lines housed in a cleanroom.
Seeking the total package
In order to remain competitive, processors need not only know their materials, but also keep developing their own processing technology. At the PolyMedex Discovery Group, which in February acquired Putnam Plastics, that means ongoing work on its second generation Total Intermittent Extrusion (TIE) capability. “That will be a major step forward in that market,” says Lazas. “This will allow us to target existing applications that utilize welding of a series of thin-walled extrusions to achieve variable durometer assemblies, such as neurovascular devices.” The current TIE process, which produces variable durometer tubing without secondary bonding, is applicable in wall thickness greater than 0.010 inch. —[email protected]