Radiation Sterilization of Plastics "The sterilization process must be taken into account as early as the product's design phase."

Plastics are an indispensable part of medical technology. Catheters, syringes, implants, and all kinds of single-use products: this material has long been the standard. What often doesn’t come into focus until later is the question of how a plastic behaves when exposed to radiation. In this interview, Annett Heilmann, Key Account Manager for Radiation Sterilization at BGS Beta-Gamma-Service, explains what medical device manufacturers need to keep in mind.

In this interview, Annett Heilmann of BGS Beta-Gamma-Service explains the effects of radiation sterilization on plastics used in medical technology. She explains why the choice of materials and the sterilization process must be coordinated early on, what challenges this poses for product development, and what manufacturers should keep in mind to ensure that functionality and material properties are maintained even after sterilization.

Ms. Heilmann, how do plastics react when exposed to radiation?

Annett Heilmann: There is no one-size-fits-all answer to this question, because the behavior depends heavily on the specific polymer, the product’s structural design, and the applied radiation dose. In general, when exposed to beta or gamma rays, two competing chemical reactions take place: cross-linking and degradation. During cross-linking, the radiation energy generates free radicals that form new bonds between the polymer chains. The result is a three-dimensional network that increases the material’s mechanical strength and abrasion resistance.

On the other hand, radiation can also trigger degradation reactions in plastics: polymer chains are broken, causing the material to lose strength, elasticity, or transparency. Which of these mechanisms predominates depends on the specific material. In addition, visible effects such as discoloration or yellowing may occur, which can happen in some polymers even at low doses.

Which plastic is suitable for which sterilization method?

Heilmann: In general, some polymers can be sterilized with beta or gamma rays without significant changes, others only to a limited extent, and some are simply unsuitable—and that is precisely what determines whether validation of radiation sterilization can be successful at all. Materials that are well-suited include polyethylene (PE), polyethylene terephthalate (PET), as well as cycloolefin copolymers (COC) and cycloolefin polymers (COP). Since material changes often correlate with the applied dose, greater caution is required with plastics that are only conditionally suitable, such as polypropylene (PP). Additives and stabilizers can counteract undesirable effects in these cases.

Polytetrafluoroethylene (PTFE) and polyacetals such as polyoxymethylene (POM), on the other hand, pose problems. Both are prone to discoloration and degradation reactions when exposed to radiation, which can impair their mechanical properties. Alternative sterilization technologies are used for products made from these materials, as well as for products with integrated microelectronic components that could be damaged or destroyed by ionizing radiation.

As a general rule: The simpler a product’s design and the fewer different materials used, the better the conditions for successful product validation.

What factors should medical device manufacturers consider when selecting plastics?

Heilmann: The most important recommendation is this: The sterilization process must be taken into account as early as the product’s design phase, not just shortly before market launch. Those who address this issue too late risk costly product modifications or, in the worst case, having to revise the entire material concept.

In addition to the choice of materials, other criteria play an important role. The structural design and geometry of the product must be evaluated just as carefully as its functionality. Because the entire product is irradiated during radiation sterilization, the process is generally suitable even for complex geometries. With electron beam irradiation, however, limitations regarding penetration depth must be considered depending on the product’s density and structure. Gamma rays, on the other hand, can penetrate even entire pallets or containers with high packing density.

Another relevant consideration is whether the product is a single item or part of a product family. Items that can be irradiated under the same conditions can be assigned to a common processing class, which saves considerable effort when qualifying additional products. Logistical aspects must also be considered: the product’s size, delivery format, and storage conditions must be factored into the planning. Finally, the dose range required for sterilization must be determined, as the irradiation dose directly influences the material changes that may occur.

How can BGS Beta-Gamma-Service help with that?

Heilmann: Ideally, BGS works with manufacturers as early as the development phase—that is, long before a product is scheduled for routine irradiation. Our application development experts advise on the selection of suitable materials for the product and packaging and help determine the optimal packaging scheme for subsequent radiation sterilization. Based on empirical data regarding commonly used polymers, we can provide an initial assessment of radiation resistance. However, individual material tests are essential for a reliable assessment; these allow us to quantify dose-dependent material changes and determine the maximum acceptable dose for the irradiation parameters.

In the next step, we assist the manufacturer in creating the validation plan. The validation of radiation sterilization is divided into three parts: microbiological, dosimetric, and application-specific validation. In microbiological validation, the initial microbial load of the product is determined, and based on this result, the manufacturer establishes the required sterilization dose. Dosimetric validation determines the dose distribution within the product. This is not only product-specific but also configuration-specific and depends on the specific arrangement of the products within the packaging. Finally, application-specific validation provides evidence that the irradiated product functions in accordance with its defined properties and functions within the specified shelf life (expiration date) and when irradiated with the maximum dose.

Once all parameters have been defined and documented, the result is fully reproducible. Provided the product has received the required approval from the notified body, routine irradiation can begin. After irradiation, the products can be placed on the market immediately upon approval by our quality assurance department, without any waiting periods or other downstream process steps.

This article was first published on our sister site www.devicemed.de