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Medical plastics.

Plastics for the health-care market meet head-on all the pressures that are expected in other major markets, and they respond to the additional imperatives to satisfy increasingly stringent government-regulated biomedical requirements. As expressed by Susan Banovic, senior materials/environmental engineer at Nalge Co. (a producer of laboratory ware, and industrial and packaging products for the diagnostics, pharmaceutical, biotechnical, and life sciences markets), "Cost consciousness; improved performance; solid-waste management through source reduction; recyclability and waste-to-energy conversion; growing demands for single-use products; and ability to withstand various sterilization processes all affect our daily design and manufacturing operations.

"On the regulation front, we also see a trend towards a global standard, with the increasing need to unify the specifications of the Food and Drug Administration (FDA), the International Standards Organization (ISO), and the North American, European, and Japanese regulations. Medical plastics must meet ever-tougher standards, and the technology is working hard at reconciling the many business and functional pressures."


Himont's application of its Catalloy process resins for the medical/personal hygiene market achieves a "soft feel" without the use of plasticizers. The high heat resistance of the resins allows autoclaving, and improved puncture resistance is compatible with the functional needs of biohazard medical waste disposal bags and a range of other medical products. The resins are thus a new entry in an arena noted for its tight competitiveness.


Polyvinyl chloride (PVC) compounds, available in durometers ranging from very flexible 40 Shore A to rigid 90 Shore D, have for many years provided design versatility, processing ease, clarity, sterilizability by all available methods, radio frequency weldability, and cost performance to the medical devices industry. Among the latest-generation radiation-stable grades, for example, is Alpha Chemical & Plastics' 2222RX Series, which marketing manager Robert Schettek says provides significantly improved color stability at 5 megarads exposure. Schettek expects continued growth for PVC in medical applications, notwithstanding environmental pressures regarding the use of di(2-ethylhexyl) phthalate (DEHP) as a plasticizer--it is currently controversial as a possible carcinogen--as well as PVC's frequent labeling as a source of chlorine emissions. In citing the Freedonia Group's projection of a total medical applications market of 2.7 billion lbs by 1996, Schettek notes that PVC is the largest single resin within the group of medical-grade materials. Current estimates put PVC annual growth in the medical field at 5.4% to 750 million lbs in 1996; polypropylene is expected to reach 455 million lbs; polystyrene, 430 million lbs; HDPE, 330 million lbs; LDPE, 180 million lbs; and all other materials, 555 million lbs.

Schettek's optimism for PVC stems in part from "the fact that there are many very good FDA-sanctioned alternatives to DEHP, both phthalates and phthalate-free versions, if these ever prove to be fully mandated." (California Proposition 65 already requires device manufacturers to notify their workers if they could potentially be exposed to levels of "cancer-causing agents" above a "no significant risk" threshold. This includes DEHP.) Alpha Chemical offers a citrate-based plasticizer system in its SuperKleen Series compounds, an alternative to phthalates in medical and other regulated consumer and food packaging uses.

"PVC has a long history as a major factor not only in the the medical market, but across the board in the plastics industry," Schettek affirms. "Vinyl technology is adapting to the needs of the customer. The versatility of vinyl compounds affords, if necessary, the ability to choose the most appropriate plasticizer system for the application and thus addresses the issue of drug interaction/absorption." He mentions Alpha's recently introduced 2235L Series as one of a class of nonmigratory or permanent plasticizer systems with reduced potential for interaction with any component transferred through a device.


Aclar 22A high moisture- and oxygen-barrier, 1.5-mil fluoropolymer copolymer pharmaceutical packaging film has been an AlliedSignal premium product for years. Subsequent commercialization of Aclar 33C, in 0.75-mil- and 2.0-mil-thick terpolymer grades, then broadened the product's use and price range. With the introduction of Aclar |R.sub.x~ 160, a 0.6-mil-thick homopolymer, AlliedSignal now provides a lower-cost alternative. Market development specialist Frank Bieganowsky says that, through new chemistry and upgraded processing, the |R.sub.x~ 160 grade provides excellent barrier per unit thickness. While it has about 20% to 25% less moisture barrier capability, which would be adequate for many products, it is only half the price of the premium 22A grade. Used for blister packaging of pharmaceutical products, the thermoformed film is adhesive-laminated to a 7-1/2-mil to 12-mil PVC, PETG, or polypropylene substrate, and top-sealed with aluminum foil.

In Europe, about 80% of the pharmaceuticals are dispensed in blister packaging, while in Japan, plastic pouches are the predominant packaging method. By contrast, about 80% of U.S. pharmaceutical companies now dispense their products in bottles and vials.

However, Bieganowsky notes a growing interest in the U.S. in marketing both prescription and over-the-counter drugs in blister packages, pointing out that they involve less handling, are inherently tamper-evident, and not least, facilitate proper individual dosages. Some states now require, in nursing homes, "unidose" packaging for convenience and safety.


Under pressure of facility limitations, costs, and efforts to innovate treatment methods, the health-care industry is inching its way to more emphasis on domestically oriented point-of-care (POC) techniques. Jill Fancher, market manager, Medical Group, Dow Plastics, says a number of diagnostic procedures are transferring from hospital labs to the patient's bedside through POC testing. POC testing reduces the need for specimens to be transported from patients to a central laboratory and virtually eliminates the possibility of inaccurate specimen identification. Plastics plays a key role by facilitating design of lightweight, portable, and easily maintained test kits.

The effort to make medical products more passively safe, thus requiring no conscious protective action on the part of the health-care worker or the patient, is a major trend. As an example, the Centers for Disease Control in Atlanta estimates that more than 600,000 accidental needle sticks occur each year in the U.S. One innovative design with plastic to eliminate needle sticks, the Protector Syringe Safety Cap System, manufactured by InjectiMed, Inc., is a disposable syringe accessory that retracts during the injection procedure and then automatically covers and locks over the needle after withdrawal. Using a spring-loaded retractable plastic sheath, the passive system is compatible with existing male luers and avoids the need to consciously prevent needle contact. Dow's Calibre MegaRad 2081 clear polycarbonate resin for the hub component provides the rigidity and precision tolerances for securing the needle while preventing leakage of air or medication at the needle/hub interface.

Fancher also sees a trend toward home and other alternative-site application of a range of lightweight, thermoplastic medical techniques and devices, such as drug therapy with infusion pumps that must avoid interaction with the particular medications.


A recent study by Dow Plastics indicates that thermoplastic resins that undergo sterilization by electron beam or gamma radiation exhibit similar physical and visual property changes, reports Nancy Hermanson, senior development engineer with Dow's Medical Group. The company's customers requested the research in the interest of exploring possible alternative sterilization methods.

The study results can be significant for manufacturers of disposable medical devices that come in contact with the body or body fluids and therefore must be sterilized before use. Ethylene oxide (EtO) and gamma radiation have been the most commonly used sterilization methods. However, EtO, now subject to OSHA and environmental regulations and requiring special safety, health, and handling precautions, is under pressure. Gamma radiation, for its part, although highly effective because of its deep penetration capability, requires a radioactive source, usually cobalt 60 or cesium 137. For those seeking a possible alternative method, E-beam sterilization offers much faster turnaround times--especially important for high-volume production--and high energy benefits without need for a radioactive source. However, the E-beam method's more limited penetration capability could leave areas of a thick part, or "shadow" areas of a complex part, unsterilized. Hermanson notes that recent developments in E-beam technology "have increased its sterilization capability and fueled interest in its use."

In the Dow study, when they were exposed at similar dosages of E-beam or gamma radiation, all the selected thermoplastics exhibited similar physical and visual effects, except for thermoplastic polyurethane, which showed a greater color change with gamma exposure. Hermanson says all the resins tested manifested some degree of discoloration after either form of high energy sterilization. "Within eight weeks, however," she adds, "five of the resins--general-purpose polystyrene (GPPS), high-impact polystyrene (HIPS), styrene acrylonitrile (SAN), acrylonitrile-butadiene-styrene (ABS), and high-density polyethylene (HDPE)--exposed to a standard dosage of 2.5 megarad gamma or to E-beam radiation returned to their initial colors."

The physical properties of three families of the tested resins (ABS, HDPE, and TPU) were reduced after exposure to high doses of radiation by both methods. Hermanson concludes from the test results that manufacturers can consider the E-beam method an alternative to gamma radiation for the sterilization of disposable devices, but cautioned that the size and flexibility of the packaging, the complexity of the device, the time added to the process for sterilization, and the susceptibility of the various plastics to degradation should be considered.


Dow Corning Corp., with a reorganized company structure, plans to commercialize by 1994 a new, more extensively tested line of Medical Grade silicone materials, including a new Monograph materials category. Medical Grade silicones currently undergo evaluations of local reaction and organ pathology, following 90 days of intramuscular and subcutaneous implantation. Long an internal company standard, the test requirements exceed the 72-hour USP Class VI standard and meet the Tripartite (United States, Canada, and U.K.) guidelines for implant tests. The new Medical Grade materials will be subject to these and additional qualification tests, including those for pyrogenicity (material mediated), hemolysis, and mutagenicity. Upon completion of these tests, the new Medical Grade materials will meet selected testing guidelines set by Tripartite and ISO. The Monograph Grades designation will apply to materials that comply with chemical, physical, and biosafety tests set forth in different international monographs, including European Pharmacopeia, USP/NF, ISO, ASTM, and others. The increased level of new product testing will permit customers to start from an advanced point in their production efforts.

Among Dow Corning's new medical materials business guidelines, the company says it will continue to sell materials for non-implant devices and pharmaceutical applications, and for many, but not all, short-term implants (29 days or less). With very limited exceptions, which will involve detailed contractual agreements, the company will no longer sell materials for long-term implant application (30 days or more), and will not sell materials for any applications related to reproduction, contraception, obstetrics, or cosmetic surgery and procedures.


Medical products have not been immune from the fast maturation of the age of tailorability. About ten years ago, says George Forczek, market development manager, LNP Engineering Plastics, his company saw a limited market for custom-compounded engineered medical products. In the mid-'80s, however, an increasing need emerged for tailored materials to meet specific design requirements in a more competitive market. Where metals had previously been used, for example, applications developed for such products as repeatedly sterilizable dental drill journal bearings molded of lubricated polyetheretherketone (PEEK) or polyphenylene sulfide (PPS). Now, many new products are coming to market, mostly as metal replacements, requiring more compounding sophistication; with close-tolerance control of fillers, and with stricter FDA and other specifications. Another change is a growing affinity in hospitals for the warmer, more colorful reinforced plastics for furniture and cabinetry, as well as to lighter-weight wheelchairs and other portable, more ergonomic products.

Today's emphasis on one-time-use, disposable products and the increasing interest in new techniques, such as minimally invasive surgery, further pressurizes the quest for tailored, functionally precise materials that will also be less costly.

Forczek foresees growth for statically conductive reinforced engineering plastics. LNP is working on developing a clear, conductive plastic composed of a chemical or alloy and another polymer, instead of conductive fibers, as an additive. LNP expects to be commercial this year with diagnostic and surgical products.


Recent research at Miles's Polymer Division shows that addition to polycarbonate resin of a polypropylene glycol derivative in concentrations of less than 1%, in combination with a compound capable of scavenging electrons, produces a synergistic effect that reduces reactions along the material's backbone after exposure to high-energy radiation. Charles Lundy, group leader for Makrolon technical marketing, says the result is a stabilization of the material against yellowing. In tests combining electron- and radical-scavenging compounds in polycarbonate resins, 10-day post-irradiation yellowing index reductions of up to 75%, depending on the exact additives used, were observed, compared with untreated material. Lundy says the combination of these compounds terminates radicals produced in the polymer before they can interact extensively with the host polymer or oxidize into discolorants.

In another Polymers Division development, senior research chemist Douglas G. Powell notes that annealing with infrared radiation (IR), requiring only minutes rather than several hours as in a conventional oven, greatly reduces the residual stresses in molded polycarbonate parts. Powell says that test results also show that IR annealing may be less detrimental to the inherent toughness of polycarbonate than oven annealing.

Miles's new Apec polycarbonate grades are bolstering the material's position where repeated sterilization is required, as in dental trays and other multiple-use products. With chemical sterilization, where ethylene oxide (EtO) faces increasing regulatory pressures, growth of the traditional method of steam autoclaving of medical devices is anticipated.

Today's sharpened sensitivity to contamination in medical treatment environments demands increased built-in security against product breakage. Tougher, more focused regulatory requirements are being expressed in terms of more demanding testing protocols for product validation. As an example, Lundy notes, the Tripartite agreement relative to testing biocompatibility of medical devices now includes the Ames test for the mutagenicity effect, to verify whether a particular plastic material might change the shape of a cell or how it replicates. Reflecting recently adopted Tripartite guidelines, the FDA's existing USP Class VI requirements are now being revised to include the Ames test procedures.

A Miles response to the program to remove chlorofluorocarbons (CFCs) as a blowing agent is cited by Patricia Boyd, marketing manager, Engineering Polymers and Composites. Replacing the CFC while still achieving UL 94V-0 and V-5 ratings has been a challenge. Miles's newly commercial interactive blowing system is claimed to provide an improved high-density skin thickness, compared to a straight water-blown system, although there is still some loss of skin density relative to the traditional CFC systems. Boyd adds that paintability is comparable to the excellent surfaces typically attainable with the CFC-blown formulations.

Boyd says that RIM-processed polyurethane structural foam, for noninvasive medical applications, has shown average annual growth in the medical market of about 16%. Selected for applications including enclosures, cabinetry, testing equipment, grip pads, and protections for bed rails, the material provides the ability to achieve variable wall thicknesses, with close-tolerance reproducibility.


Monsanto Co.'s Advanced Performance Materials Group has announced its new Lexel catalyst deposition technology, which permits plating of thin metal patterns on polymer films. The first commercial products will be based on selectively depositing intricate patterns of copper on polyethylene terephthalate (PET). Potential markets include any signal-carrying circuit; membrane switches for medical devices; computer keyboards; flat antennas; and security tags. Designs could include conductive patterns for carrying sensing signals for human diagnostics and monitoring, and applications requiring physical flexibility, such as bio-engineering devices.

The Lexel coatings technology eliminates the traditional etching process for producing metal patterns on plastic films and reduces conventional manufacturing costs by enabling direct additive metal patterning of wide webs, permitting continuous rolls of PET film up to 45 inches wide. With the proprietary electroless deposition process, metal thickness can range from 0.1 to 1.0 micron on films ranging from 25 to 100 microns thick. Lincoln D. Germain, marketing development manager for Lexel coatings, says the first applications will be in the medical and electronics markets. The Advanced Performance Materials business unit focuses on customer-needs-based technologies that exploit surface chemistries and physics, Germain adds.


As a result of the solid waste disposal concerns at all levels of government, legislators across the U.S. continue to propose legislation that seeks to restrict or regulate plastics, including medical packaging, in a number of ways. Such anti-plastic proposals include bans on certain kinds of packaging, mandated recycled content, and fees or taxes on plastic products.

In 1992, the American Plastics Council (APC) monitored more than 500 bills in the 50 states, many of which would have placed draconian restrictions on plastic packaging and other products. The most wide-reaching and restrictive legislations are the so-called "environmentally acceptable packaging" bills developed by state Public Interest Research Groups, or PIRGs, which would ban any package, including medical packaging, that failed to meet stringent recycling, reuse, or recycled content rates by certain dates. "Although many of these proposals contain exemption language for products or packages regulated by the FDA," according to Roger Bernstein, APC's director of state government affairs, "companies run risks by relying on problematic exemptions that do not comprehend the way FDA actually works."

This year, 20 states, including such bellwether states as New York, Florida, Wisconsin, and California, are expected to consider legislation that can have an adverse impact on plastic packaging. Activities at the federal level, in the 103rd Congress, will also continue.
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Author:Wigotsky, Victor
Publication:Plastics Engineering
Date:Jul 1, 1993
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