Sterilization and Medical Packaging
Before designing packaging for medical devices, engineers must consider the effects that available methods of sterilization have on materials.
by Daphne Allen, Managing Editor
Prior to designing a medical device package, packaging engineers should first consider the method by which the packaged product will be sterilized. Sterilization is a rigorous process, which can subject the device—and its package—to extreme temperatures, gases, radiation, and other elements that can alter certain materials. Engineers, therefore, need to fully understand the chosen sterilization method and its effects on packaging materials.
Packaged products are being conveyed to an in-line electron-beam sterilization system. Photo courtesy of RPC Technologies Inc.
Packaging engineers don't have to go it alone, though. Many suppliers and service providers are making the packaging engineer's job easier with new materials and equipment. Engineers can also use sterilization to complement a package's design.
Packaging engineers do not usually have the luxury of specifying a particular sterilization method. Mike Scholla, medical packaging segment leader for DuPont Nonwovens (Wilmington, DE), says that companies tend to use the sterilization method they have previously been using or have in-house. Bill Wetzel, marketing manager—rollstock for Perfecseal (Philadelphia), agrees, adding that the "medical product itself also determines the sterilization method." Once informed of the particular method and product, engineers must then choose the appropriate packaging materials, adhesives, and configuration.
But there is more to package design than simply choosing materials that withstand the rigors of sterilization. Spiro Apostolou, president of Poly-Focus (Clayton, MO), a consultancy focusing on polymers, radiation sterilization, and healthcare technology assessment, calls packaging "both a science and an art. Radiation may not harm a particular material, but it could discolor it." Packaging engineers therefore need to balance concerns about material performance with those about aesthetics.
When considering materials, engineers must understand the conditions that packaging materials encounter during sterilization and during the product and package life cycle. (Packaging engineers must also handle cost, weight, space, and environmental concerns.) John Bleecker, packaging engineering manager for C.R. Bard Urological Products Div. (Covington, GA), describes these conditions as "temperature, moisture, positive and negative pressure, time, and exposure." To measure the effects of sterilization, Bleecker says that packaging engineers routinely test materials both before and after sterilization and perform simulated transit testing. For instance, one such test his department performs is a pull test, which involves dissecting sections of a package and placing the top and the bottom web materials each into two separate jaws and then measuring the amount of force needed to pull the two webs apart. (For more information on package testing, see Package Testing: Is Standardization on the Horizon?, PMP News, March 1998.)
Perfecseal's Wetzel explains that ISO 11607 does "put the onus on producers of materials to determine a material's compatibility with particular sterilization methods." He explains that the standard urges producers to make sure that newly developed materials are tested for compatibility with various sterilization methods that are being used in the marketplace.
But, even with material producers performing such testing, packaging engineers must still perform their own evaluations. As Tim Early, marketing specialist for the sterile packaging team for DuPont's Tyvek spunbonded olefin, puts it, "packaging engineers must assume the responsibility and coordination of materials qualification for sterilization."
NEW PACKAGING MATERIALS
When choosing packaging materials for a particular sterilization method, engineers tend to turn toward materials they know. "You don't want to select materials you don't have confidence in or that don't have an anticipated history," C.R. Bard's Bleecker explains.
Using long-established materials can help engineers reduce time spent on material qualification. But they shouldn't close their eyes to new formulations. Many suppliers have developed new packaging options to solve specific needs of packaging engineers. For instance, Beacon Converters (Saddle Brook, NJ) is currently qualifying a special steam-sterilizable film to be used with Tyvek spunbonded olefin to manufacture pouches. "We have known there is a need for a new autoclavable material," says William Daly, Beacon's president and CEO. "In the past, paper usually had to be a component of any autoclavable package. But when you peel open the paper-containing pouches, you create paper fibers that are contaminants." Daly explains that using Tyvek in place of paper eliminates the fibers, but it can't be sealed to itself because the two pieces would just weld together. Instead, another substrate that can withstand the high heat of steam sterilization was needed to be used along with the Tyvek. Beacon expects to market the new pouches in April.
Perfecseal recently introduced its Clean Peel Transfer (CPT) film for use with uncoated Tyvek. The combination is designed to give engineers a packaging option that doesn't generate fibers during peeling and provides a white seal transfer similar to that of adhesive coatings. Because the Tyvek isn't coated, it is more porous. Wetzel explains that during EtO sterilization the greater porosity allows the sterilant to pass through more easily, reducing the stress on seals.
Pouches consisting of Perfecseal's CPT film and uncoated Tyvek spunbonded olefin can be sterilized using EtO.
AlliedSignal Inc. (Morristown, NJ) recently formed a team designed to assist healthcare packaging engineers in selecting materials for medical device and pharmaceutical uses involving sterilization. Allied manufactures Aclar monolayer PCTFE films, whose moisture resistance, color, and clarity are not significantly affected by gamma radiation up to 10 Mrd. Aclar can also withstand E-beam sterilization. Gomar National Industries, a division of AlliedSignal Specialty Films, manufactures metallized materials, laminates, and coated materials that can be engineered to withstand EtO, gamma, E-beam, plasma, and high-energy pulsed light sterilization.
Popular Sterilization Methods and Their Effects on Medical Packaging
The majority of sterile medical devices are sterilized with either EtO gas or a high-energy radiation such as gamma or electron-beam. Several other emerging techniques are also in use, such as gas plasma or UV light. Because of the wide use of EtO and radiation, there is a great deal of information about their effects on medical device packaging. The following, provided by John Donohue of Sherwood Davis & Geck (Hazelwood, MO), is a list of the widely used methods and their effects on packaging.
ETHYLENE OXIDE GAS
- Packages can burst from the repeated high and low pressures to which they are exposed as EtO penetrates in and evacuates.
- Some materials with a high affinity for EtO (polyurethane or plasticized PVC) may require several evacuation cycles to reduce EtO residuals.
- Large amounts of toxic ethylene chlorohydrin can form from chlorine-containing materials in the sterilized product.
- Excessive temperatures can distort or melt some materials.
GAMMA RADIATION AND ELECTRON-BEAM RADIATION
- Several materials, such as PVC, polyurethane, and polycarbonate, can discolor.
- Rubber can be damaged.
- Several materials can become odorous.
- Silicone lubricants become more viscous.
- Some adhesives lose significant strength.
- Material degradation, which may have been acceptable immediately after irradiation, can continue as the package sits on the shelf. This can become a problem a year or two after irradiation.
- Thin areas of a package are more sensitive to radiation because of oxidation from the air.
STERILIZATION COMPLEMENTS PACKAGE DESIGN
Another element that packaging engineers must consider along with material selection is package design. Products must be configured in certain ways for certain sterilization methods. Ray Calhoun of Titan Scan (San Diego), a supplier of E-beam sterilization systems, explains that "there are significant opportunities to improve sterilization efficiency by designing packaging that presents the product in the most favorable orientation to the electron beam." For instance, Calhoun says that "one key element of packaging for E-beam sterilization is to ensure that products are placed in a uniform arrangement within the package. This can increase production throughput while also meeting maximum dose requirements."
Jim Doyle, senior development engineer at Exactech Inc. (Gainesville, FL), says that packaging engineers can even use sterilization to complement package design.
"Before sterilization, some foams maintain a flexible shape memory, but afterward, deformations caused during the assembly become set," Doyle explains. "It is imperative that packaging engineers be aware of this material property transition so they can take advantage of it without fearing its occurrence. For instance, a square part can be placed into a round die-cut foam hole. Postradiation, the set, squared foam hole aids in stabilizing the product during the rigors of typical shipping."
Radiation sterilization may affect medical packages in other ways. According to Doyle, radiation tends to strengthen the adhesive seal between PETG and spunbonded olefin lid stock used in medical device trays.
Certain sterilization methods are also giving packaging engineers a bit more flexibility in material selection and design. Gray Buetzow, sales manager for RPC Technologies Inc. (Hayward, CA), producer of the Minilac in-line E-beam sterilization system, says that having such a system on the production line has economic and marketing advantages. "Packagers can place sterilized parts into cartons in custom quantities, which allows them to meet specific customer requests," Buetzow says. "Shipping to contract sterilizers makes it difficult to place custom quantities into cartons."
Ray Johnson, vice chairman for Doyen Medipharm (Morris Plains, NJ), is also working with another company that is developing an in-line sterilization system, only this one will use UV light. "If you sterilize something just before packaging, you reduce the amount of bioburden inside the package," Johnson explains. According to Exactech's Doyle, "A presterilization reduction in bioburden usually equates to a poststerilization reduction in pyrogens. Certain types of pyrogens, especially in high quantities, can lead to clinical complications in patients receiving these sterile medical devices."
Ted Mielnik of AbTox Scientific (Mundelein, IL) explains that many "polymeric packaging materials are sensitive to temperature," making them unsuitable for some sterilization methods. AbTox's system uses a low-temperature gas plasma that does not alter many commonly used packaging materials.
The ethylene oxide gas-diffusion sterilization system developed by Andersen Products Inc. (Haw River, NC), designed to control emission and reduce gas use, offers packagers another specific benefit. During the sterilization process, excess air is removed from a plastic film bag, and the bag is given a programmed amount of EtO gas and then sealed. Afterward, the bag is transferred to a temperature-controlled room. As the EtO diffuses out of the package, the bag shrinks around the packaged product, holding the contents firmly in place to prevent them from shifting and providing a visual assurance of sterility.
One new technique that could help save both sterilizers and packagers time is the use of parametric release when sterilizing packaged products with EtO. According to Clark Houghtling of contract sterilizer Cosmed Group Inc. (Queensbury, NY), "With this technology, sterilized products may be shipped to market immediately after aeration while eliminating biological indicator and sterility testing costs."
As James Whitbourne, president of Sterilization Technical Services Div., STS duoTEK (Rush, NY), puts it, "Packaging engineers may wear a lot of hats—they are really doing a variety of tasks." That means that they are balancing many concerns when designing packages, including sterilization. Fortunately, many packaging material and sterilization equipment suppliers are willing to assist these engineers as they design their packages. With a little investigation, packaging engineers should be able to find the most appropriate material and to use sterilization to their advantage.