Originally Published MDDI September 2002
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PVC. The most commonly used material in the manufacture of flexible medical devices, PVC has come under fire owing to concerns about the use of phthalates as plasticizers and environmental problems with disposal. The softness, flexibility, and low-temperature characteristics of PVC are determined by the type and amount of plasticizer used in the compound. The most widely used plasticizer, di-ethylhexyl phthalate (DEHP), has been linked to toxic effluents produced during manufacturing and to the generation of hydrogen chloride during incineration. Environmentalists have raised concerns that the disposal of PVC by incineration may be a source of dioxin contamination.
PVC devices, such as IV bags and blood bags, typically contain 30–40% DEHP by weight. Other devices, such as medical tubing, may contain as much as 80% DEHP by weight. Because DEHP is not chemically bound to the polymer in a PVC device, it can be released when the device is heated, or it can leach out when the device comes into contact with certain media, such as blood, drugs, saline, or water. As a result, several pharmaceutical manufacturers are providing warning labels that advise against the use of DEHP-plasticized PVC for administration of specific products.6
These findings have encouraged the medical industry to welcome alternatives to PVC that can provide the same or better performance characteristics at comparable costs.
Polyolefin-based systems are being used successfully for barrier covers or sleeves, machine covers, and similar products.
Metallocene polyethylene film is being used as a PVC replacement for medical applications, but it is not suitable for RF welding unless it is blended with other polyolefins or specialty polymers.
Ethylene-vinyl acetate polymer, another alternative to PVC, is RF weldable. Devices made from this material are easily abraded, however. The material also has poor strength and flex-fatigue resistance.
Natural Rubber Latex (NRL). A desire for safer alternatives to NRL arose more than a decade ago, when the number of reported cases of allergic reactions to latex started increasing dramatically. Healthcare personnel, such as nurses and lab technicians, are particularly at risk for latex sensitivity because of their high exposure to the material.7 NRL alternatives include nitrile rubber, synthetic latex, styrenic elastomers, polyurethane, and silicone.
Thermoplastic Polyurethanes. Thermoplastic polyurethanes contain no plasticizer and have a lower density than PVC, producing a higher film yield. The films offer toughness and strength, and high water-vapor permeability. They can be sealed using RF welding. Soft formulations can be dip molded into gloves, although the process is more expensive than welding
Polyurethanes are thermoplastic rubbers made from isocyanates and are designated aromatic or aliphatic on the basis of the chemical nature of the diisocyanate component in their formulation. Aromatic and aliphatic polyurethanes share the following properties that make them suitable for use in medical devices:
- High tensile strength (4000–10,000 psi).
- High ultimate elongation (250–700%).
- Wide range of durometer (72 Shore A to 84 Shore D).
- Good biocompatibility.
- High abrasion resistance.
- Good hydrolytic stability.
- Ability to be sterilized via EtO or gamma irradiation.
- Ability to retain elastomeric properties at low temperature.
- Resistance to chemicals, oil, and UV light.
Newly developed low-durometer, high-elongation formulations of thermoplastic polyurethanes are attractive alternatives to PVC and latex in medical applications.8 Products assembled from polyurethanes have passed toxicological, biological, and physiological testing procedures. They are environmentally sound and can be recycled or safely incinerated.
A thorough understanding of processing conditions is required when working with polyurethane resins, however, due to their hygroscopic nature. Polyurethanes absorb and react with moisture in the air very rapidly. Extreme care must be taken when processing a polyurethane. Otherwise the material can be degraded and defects can result in the finished products.
For example, successful RF welding of polyurethanes requires special die designs, modifications to conventional equipment, and adjustments to the parameters of the welding process. The die determines the width of the seam. A typical die design incorporates an insulated knife that cuts and seals the film in one step. Using conventional RF welding equipment with thin films produces excessive arcing and weak seams. It is a technology that requires high-level skills.
CONCERNS ABOUT PVC
Human exposure to DEHP can occur in the ambient environment and in the medical setting. DEHP exposures occurring in the medical setting are of particular concern because the amount of exposure can be substantial and because those exposed, such as premature infants and adults with life-threatening illnesses, may be particularly vulnerable to the effect of toxic chemicals. Adverse health effects such as respiratory distress, cholestasis, and histoloical abnormalities of the liver have been found in subjects having documented exposure to DEHP.
Researchers have concluded that humans are exposed to substantial levels of DEHP through medical devices.6 Certain populations, such as hemophiliacs, kidney dialysis patients, and high-risk newborns are particularly heavily exposed. Given the human exposure to DEHP from medical uses and the potential for adverse health effects, it is prudent to investigate alternative materials for use in medical environments.
An organization known as Health Care without Harm petitioned FDA to issue a warning to medical professionals, institutions, and consumers about the potential hazards posed by phthalate leaching from PVC medical products. 9
Also, three studies published in 2000 by the European Commission confirmed serious environmental and economic problems with PVC waste disposal, including findings that incineration of 1 kg of PVC leads in most cases to more than 1 kg of hazardous wastes.10 Furthermore, landfilling of PVC releases hazardous phthalate softeners, such as DEHP, and contributes to the formation of dioxins and furans in accidental landfill fires.11
Copyright ©2002 Medical Device & Diagnostic Industry