New demands shaping medical polymer developments

Resin variations help fill gaps for medical processors.

Many of the technical trends in medical and pharmaceutical devices that visitors to next month''s Medtech show (organized by MPW''s parent company, Canon Communications LLC) will see revolve around new or improved resin grades.

One such application set to come onto the market later this year from drug manufacturer Pfizer is the Exubera noninvasive device to allow inhalation of rapid-acting, dry-powder insulin for certain patients. According to Pfizer, diabetes has reached epidemic proportions with roughly 17 million people suffering from it in the U.S. alone. Ten percent of all Germans are reportedly also suffering.

Developed by Nektar Therapeutics (San Carlos, CA), the device is injection molded from a variety of undisclosed plastics and allows the macromolecules of the therapeutic protein-based drug to be delivered to the alveoli of the deep lung, where it is rapidly absorbed into the bloodstream. Nektar cofounder John Patton sees such injection molded pulmonary delivery devices as offering optimal treatment of not only diabetes, asthma, and multiple sclerosis, but also cardiovascular seizures, anaphylaxis, chronic pain, as well as vaccine delivery.

Tilo Vaahs, director of marketing development-industrial at engineering thermoplastics supplier Ticona (Kelsterbach, Germany), says, "The potential of new medicine dosing systems is very big. In the last five years the average annual growth [of this section] in both the European and North American markets was between 18% and 20%."

Still, concern continues among medical OEMs about extraction of plasticizers, additives, and other chemicals, says Ernst A. Poppe, manager healthcare engineering polymers, DuPont (Meyrin, Switzerland). He points to a new grade of polyacetal copolymer, Delrin SC662NC010, developed by his company. It has very low volatiles emission, and in particular, low levels of formaldehyde, which is a concern with acetal because formaldehyde is classified as a carcinogen by the EPA. His company is also pushing its Hytrel polyester elastomer as a plasticizer-free PVC replacement.

Another major concern today is sterilization of plastics medical products, says Clare Frissora, market director healthcare at GE Plastics (Pittsfield, MA). Recent bouts of BSE (commonly known as mad-cow disease) have spurred a renaissance in autoclave sterilization, which bring new demands on plastics.

"Many people believe autoclave is more effective than gamma radiation since units can be small and there is no need for special radiation licenses to own or operate units," Frissora says. This, however, can put extra stress on plastics parts since autoclave users tend to sterilize at higher temperatures (134°C for 20 minutes) today compared to the previous use of 120°C for 30 minutes. "They''re doing this to reduce time and increase the number of loads which can be handled during a work day," explains Frissora. Many of these devices need to withstand up to 2500 sterilization cycles.

GE Plastics has introduced two new biocompatible polycarbonate grades, Lexan HPX4 and HPX8R, which meet autoclave demands but also have improved flow and release capabilities. Another continuing trend is lightweighting devices, such as in a new unit that replaces a series of metal rods and screws with a much smaller unit made of lighter polycarbonate and polyetherimide for patients who have suffered Colles bone breakage, a fracture of the wrist joint due to falling on an outstretched hand.

Polyolefins supplier Borealis (Kongens Lyngby, Denmark) has developed a range of radiation-resistant, transparent, and chemically inert Bormed polyolefin products for syringes, needle hubs, and catheters that can be sterilized at 121°C without suffering from environmental stress cracking.

Processors make plea for less bureaucracyRegulations are putting a brake on innovation in the medical processing field-or at least that is the way one insider, Steve Lovatt, director of regulatory compliance at medical parts processor Bespak (Kings Lynn, England), sees it. If a specific polymer has been designated during development of a medical device and important research into the security, biocompatibility, and effectiveness reveals concerns, any change is usually so expensive that it effectively makes an alteration totally impossible, he says.

"Changes, also when they mean product improvements, are possibly not welcome since each change requires [a time consuming] checking process and also means new approvals from various health service authorities," Lovatt says. "These result in product delays and added costs."

Another sticking point among processors is when medical resins are withdrawn from the market by a producer, meaning that an alternative, if available, has to be found, followed by re-specifying an application with the other material(s), a costly process. Ernst Poppe, manager healthcare engineering polymers at DuPont (Meyrin, Switzerland), says companies like his are often at the mercy of additives suppliers. If an approved additive is pulled from the market it can have a domino effect down the plastics supply chain.

"Processors would like to have us guarantee that certain grades will remain in our portfolio for up to 10 years," Poppe says. "This isn''t always possible." Generally materials will be assured of delivery for up to four years, he says.

Pump it up, baby!Dwarf-sized injection molded pumps are finding increased application in modern medicine, as was evident at this year''s ComPaMed show in Düsseldorf in November. ThinXXS (Zweibrücken, Germany), which last year (February 2004 MPW, p. 54) launched its four-component micropump, has extended the family with model MDP2205 that features better back pressure and suction height in a footprint of 1 inch diameter and a height of 0.20 inch. Maximum back pressure is more than 50 kPa (approximately 8 psi), which is matched by a suction height of 1.5m (about 5 ft). Flow rates range from 9 ml/min for water to 12 ml/min for methanol. Thomas Stange, marketing manager at thinXXS, says the cyclic olefin copolymer (COC) self-priming diaphragm pump, also usable for gases, is finding demand in diagnostics, analytics, miniaturized fuel cells, and chip cooling, as well as some consumer goods.

Competitor Bartels Mikrotechnik (Dortmund, Germany) has a pump that is even smaller. The four-component injection molded unit includes an actuator consisting of a piezoceramic placed on a plastics membrane. This covers the pump chamber, which is fed by two double valves controlling the flow. Flow rate is from 50 nanoliters/min to 5 ml/min for liquids, and 50 µl/min to 15 ml/min for gasses. Feed pressure is up to 500 mbar for liquids and 60 mbar for gases. Ulrike Michelsen, marketing/sales, says the company selected polyphenylene sulphon and polyimide for the unit because these materials offer better chemical resistance than polyetheretherketone (PEEK).

Schwarzer Precision (Essen, Germany) has come out with a new linear pump, SP3600LI, measuring 56 by 120 by 128 mm, and possessing a maximum pressure of 300 mbar and a flow rate of 16 liters/min. It features vibration-damping suspension for low-noise generation. KNF Flodos (Sursee, Switzerland) debuted its Liquiport liquid diaphragm pump for flow rates from 0.2-3 liters/min. It is produced from polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, and rubber. RC

Robert Colvin [email protected]

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