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Plastics target changing health-care needs
January 9, 1995
10 Min Read
Pick up any newspaper around the globe and the message becomes clear. People want improved health-care services without having to declare bankruptcy. This presents a challenge for those who provide such care, whether it's a government agency or a local doctor.
The dilemma takes on even greater dimensions for those companies that make the medical devices designed to serve those needs. How can they provide the required instruments at a profit, and still fulfill today's pressures for lower-cost, longer-lasting, and safer products?
Enter the plastics producers. The changing needs of the multi-billion dollar health-care industry have resulted in a new wave of plastic materials and products aimed not only at containing costs, but providing enhanced medical care.
Material selection the key. "Health-care industry needs are influencing material selection and product design," says Jesse Singh, medical market manager for GE Plastics. He cites material qualities such as flowability and toughness, as well as thin-wall, material-saving designs, as part of the plastics industry's response.
Producibility is also important, points out Charles Lundy, a group leader at Germany-based Bayer AG's U.S. subsidiary, the Polymers Div. of Miles, Inc. "Materials that can be processed faster and easier can play a big role in holding down costs," he explains. A prime example: a new grade of Makrolon polycarbonate (PC), DP1-1452, with a melt flow rate of 17 gm/10 min and a fast mold release.
"As the number of new and modified material grades increases, material selection practices become even more critical and complex," adds Lundy. The design engineer must know exactly what performance is required: mechanical, safety, regulatory, environmental, monetary, or a combination of these.
Blood pump. To illustrate his point, Lundy attributes polycarbonate's toughness, clarity, and high melt flow in its selection for the design of a centrifugal system and a turbo membrane oxygenator used in open-heart surgery. The 3M Sarnscentrifugal pump system performs the heart's pumping action during the surgery, moving blood through the oxygenator and the perfusion circuit back to the patient.
The oxygenator acts as artificial lungs during the surgery, handling gas exchange functions that normally occur in patients' lungs. Oxygen passes through the oxygenator and diffuses into the blood. The unit also removes excess carbon dioxide from red blood cells and plasma.
The efficient system consists of a disposable pump that features tough impellers made of Makrolon 2658, a polycarbonate noted for its high strength. Makrolon 2558, with its high melt flow, was selected for the pump and oxygenator housings. Permeable membranes for oxygen and carbon dioxide exchange consist of polypropylene or microporous silicone.
3M Health Care's Lynn Tuttle says they selected polycarbonates for the housings because of their clarity, blood compatibility, and chemical resistance to alcohol. The material's moldability, strength, and "superior mechanical properties at a given molecular weight" also weighed heavily in the decision.
Stapler goes on a diet. A new surgical stapler cartridge offers another example of how material selection solved high- flow and strength problems associated with a thin-wall design. This time engineers at 3M's Medical Products Div. searched out Hoechst Celanese's Vectraliquid-crystal polymer (LCP) as a replacement for a glass-reinforced polycarbonate. The material enabled 3M to offer surgeons a less bulky stapler cartridge that provides more working room in the area where the surgical procedures take place.
Made of Vectra A150 LCP, a 50% glass-reinforced grade, the cartridge measures about 25% narrower than its predecessor. Moreover, the material's shrinkage characteristics are similar to those of the material it replaced. Therefore, 3M can use the same molds to manufacture the cartridges merely by modifying existing mold tooling.
"We needed a resin that fit well in the existing mold and was colorable," reports Robert Petrich, senior product control engineer at 3M, "and it still had to allow us to make a narrower part without compromising its strength."
"LCP's combination of stiffness and flexural strength, along with its high-flow capabilities, make it suitable for a number of health-care uses," adds Barbara Canale, marketing manager for Hoechst Celanese's Vectra Healthcare materials. "This includes minimum invasive surgical products," she notes.
Personal medical history. A new preanesthetic system allows patients to complete their own medical histories in minutes. It features primary covers and push buttons made of GE Plastics' Cycoloy C2950 HF ABS and an LCD window of Lexan 121 polycarbonate.
The HEALTHQUIZ(TM) PRESCREEN(TM) from Nellcor, Inc., Pleasanton, CA, lets patients generate their own medical histories by pushing a button to answer "yes," "no," or "not sure" to a series of questions. The battery-powered device has no keyboard or mouse to confuse and intimidate patients. It also creates an electronic record of each patient's medical history, while storing up to 200 patient histories on a small data card.
An office staff member can attach the device to a printer, then select from a menu of reports, including the patient summary. The program flags important issues, presents a risk score, and lists suggested preoperative lab tests.
Rob Clark, mechanical engineer at Nellcor, says the materials selected offer a good compromise between moldability and performance. In the bargain, they did not affect color stability.
Combining three plastics compounds produced an innovative ambulatory intravenous drug infuser from I-Flow Corp., Irvine CA. The materials, all from LNP Engineering Plastics: LubricompDFL, a lubricated glass-reinforced polycarbonate; Lubricomp QFL, a lubricated glass-reinforced nylon 6/10; and Lubricomp DL, a lubricated polycarbonate.
The 7.9-oz SideKick Systemdrug delivery device is intended for home use. I-Flow stresses it is inexpensive enough to be disposable, and durable enough to be used repeatedly.
The Lubricomp materials, says Lee Judge, I-Flow's mechanical engineering manager, "offered us low-static friction, making it easier to use and to process."
The infuser's design features a cylinder with a screw-top lid. Inside the lid rests a spring-loaded pressure plate that applies 6 psi of pressure to deliver medication through IV tubing at a controlled rate. Pressure is applied as the lid is screwed down on 50- or l00-ml bags of medication.
The top half of the system consists of nylon, the bottom half of reinforced polycarbonate. The spring retainer and pressure-plate cover are composed of the polycarbonate compound.
It's in the bag. Draka Polva B.V., Amsterdam, The Netherlands, has developed a sophisticated lay-flat tubing for critical-care medical bags. For this application, Draka extrudes Ecdel(TM), a copolyester ether elastomer from Eastman Chemical Co., in tubular form. Major advantages: a substantial reduction in the length of the weld and improved interior cleanliness.
The inert SOLMED PCCE Medipaks do not contain plasticizers. This makes the material suitable for packaging amino acids, lipids, and low- and high-pH solutions. It also exhibits cold temperature resistance for the storage of blood at temperatures to -80 degrees C. Heat sealable and fully collapsible, Medipaks also remain clear after autoclaving at 121 degrees C, a procedure that can be done once the bags are empty.
Sharper images. A new imaging coil promises clearer pictures in less time from non-invasive techniques that show tissue contrast in medical and biological examinations. One of its key ingredients: DuPont's TeflonPTFE fluoropolymer.
The coil, a joint development of Polyfon Co. of New York and researchers at the University of Queensland, Brisbane, Australia, performs equally well in equipment for magnetic resonance imaging (MRI) and image-directed spectroscopy (IDS). The copper conductors, electroplated to the Teflon dielectric, eliminate the need for adhesive bonding or lamination.
"Electroplated Teflon gives vastly superior image quality," says William J. LaRusso, Polyflon president. "Plating reduces the potential for gaps."
Picture sharpness fostered by the new coil speeds image processing by reducing the need for time-consuming computations, LaRusso explains. In use, the coil transmits radio-frequency energy to a sample tissue, then picks up faint signals emitted by the tissue. It conforms to a typical MRI bird-cage resonator configuration.
Concerns over allergies caused by reactions to medical drain tubing made of latex rubber led Mentor Urology, Inc., Santa Barbara, CA, to switch to an alternative tubing material. The new Tygon LR-40tubing, a product of Norton Performance Plastics Corp., not only is non-toxic, but is non-pyrogenic, non-cytoxic, and compatible with blood.
The proprietary, modified PVC tubing features smooth inner walls that facilitate flow. As a result, Mentor uses the tubing for its male disposable urinary leg-bag kits. In Mentor's case, the tubing comes in 18-inch lengths with 5/16-inch ID and 7/16-inch OD.
"We selected the tubing as a replacement for the traditional latex-rubber tubes that may cause discomforts such as itching and rashes," says Mark Ewald, Mentor product manager. The Tygon LR-40 also features flexibility, cutability, and clarity.
Niche markets. "The intensity of worldwide competition, coupled with more frequent product changes, is fostering development of 'niche' markets," says Sam Snyder, president of Polymer Design, Rockland, MA. "This results in the production of low-volume items and frequent design changes."
A non-invasive ultrasound device for treatment of benign prostatic hyperplasia typifies this trend. The image-guided device, the Sonablate 200 from Focus Surgery, Milpitas, CA, enables doctors to reach past healthy tissue and treat only the targeted tumor area.
Polymer Design turned to LRCliquid-resin casting to produce the system's custom rectal probe. Making the probe requires casting of six separate parts--front and rear housings, a collar, a neckpiece probe-tip, a probe-tip button, and a thimble.
The hour-glass-shaped neckpiece required an extremely smooth surface to minimize patient discomfort. Another objective: achieve the tightest possible seal.
To accomplish this, Polymer developed a special technique for casting the neckpiece with a single parting line. This, in turn, created a better sealing surface. Two grooves also were cast to secure a latex sheath. The grooves, which have a 5-degree taper, induce a camming action when O-rings are fitted, producing a water-tight seal.
The rear housing assembly presented another challenge. At each end of the assembly, passageways surround cavities critical to the unit's function. To allow the casting of undercuts and easy part fallout, Polymer made the molds out of soft RTV silicone. For the probe material, the firm employed a thermoset polyurethane with a Shore D-85 hardness rating.
Snyder says that liquid-resin casting can produce complex parts in volumes not suited for such processes as injection molding. And, to address niche markets, he adds, it allows more frequent and rapid design changes.
Cracked casings. Behring Diagnostics, Westwood, MA, faced another problem--chipping and cracking of casings that house blood serum analyzing machines. The solution: a switch from ABS foam to polyurethane.
The Opus Plus machine's new two-part housing is reaction injected molded (RIM) of Miles' Baydur 726 IBS polyurethane. The structural foam system offers repeatability, good strength, fire retardancy, moldability, and excellent surface finish, according to Behring designers.
Previous housings were made by pouring ABS pellets and a blowing agent into male and female tooling, which was shaken and then baked. This process resulted in cracking and chipping problems and the need for numerous secondary operations. With the Baydur system, the base, which includes about 20 brass inserts, is molded in seven to eight minutes. The top, with its complex side action, undercuts, and five inserts, takes about the same time to mold.
What's ahead. The future for plastics in the medical industry continues to be promising--at least for the next few years. Strongest growth is expected to be among the engineering plastics, or so says market researcher, the Freedonia Group, Cleveland.
The study confirms what many in the plastics industry already know and continue to address. Changing medical-care trends will push them to provide an even wider array of cost-effective materials that will meet tomorrow's needs.
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