Sterilization Compatibility for Synthetic Polymers

Synthetic polymers are essential in various medical applications as they are used to make a range of healthcare devices. They replace glass, metal, and other standard materials in single-use and reusable medical devices. Polymers are typically the first choice for medical device makers due to their exceptional attributes, including high strength, low weight, flexibility, and ease of fabrication. 

Sterilization of reusable medical devices made of synthetic polymers is necessary to prevent the spread of pathogens. Essentially, the sterilization process aims at destroying or removing living organisms in the form of fungal or bacterial spores. There are several sterilization techniques, and the right one depends on the device, its intended use, and the type of healthcare facility.

The FDA regulates four forms of sterilization techniques, including steam autoclave, dry heat, ethylene oxide, and irradiation. The effectiveness and suitability of these methods depend on the specific properties of each medical device being sterilized. We will look at the compatibility of synthetic polymers with each of these methods below. 

Dry Heat Sterilization

Dry heat sterilization involves exposing hot air to the product being sterilized. The device is exposed to steady temperatures and held for a specific period depending on the polymer type. Dry heat sterilization is arguably one of the most effective methods as heat reaches all surfaces equally. However, some polymer types may not withstand the ideal temperatures needed and can get discolored as a result. The following polymer types are compatible with this method. 

• Acetals
• Aromatic Polyamide
• Copolyester Thermoplastic (TPC)
• Ethylene Chlorotrifluoroethylene (ECTFE)
• Ethylene Tetrafluoroethylene (ETFE)
• Fluorinated Ethylene Propylene (FEP)
• Polycaprolactone (PCL)
• Polyetheretherketone (PEEK)
• Polyethersulfone (PES)
• Polyglycolic Acid (PGA)Polyphenylene Sulfide (PPS)
• PolyL-lactide (PLLA)
• Polysulfones (PSU)
• Silicone

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Ethylene Oxide

This method is used to sterilize medical devices that are sensitive to moisture or heat. Ethylene oxide has high toxicity levels, and devices should be completely dry before the sterilization. Water can inhibit the gas's effectiveness, and it is imperative to control temperature, humidity, and gas concentration exposure time. Typically, polymers sterilized using this method should withstand exposure to ETO gas and the process's moisture. Devices sterilized using the method require up to 12 hours of aeration to rid of residual gas. All types of polymers are compatible with ETO sterilization.

Steam Autoclave

The steam autoclaving method is one of the most recommended and widely used medical device sterilization techniques. Steam autoclave is not only fast but also reliable and inexpensive. This method uses a combination of moisture and heat to kill microorganisms. The actual cycle time and the ideal temperature levels will be influenced by the type of polymer in the sterilized devices. Standard cycles are between 15 to 30 minutes, with temperatures ranging from 121 to 134 degrees Celsius. The polymers used for reusable medical devices should be chosen carefully as a large number of them may not withstand prolonged, repeated exposure to high temperatures and steam.

Most polymers are compatible with steam autoclave sterilization and can withstand high steam sterilization cycles without significant loss of mechanical properties. The following polymer types are compatible with the steam autoclave sterilization method. 

• Acetals
• All polymers in the fluoropolymer family
• Aromatic Polyamide
• Polyetheretherketone (PEEK)
• Polyethersulfone (PES)
• Polyethylene (PE)
• Polyglycolic Acid (PGA)
• Polyphenylene Sulfide (PPS)
• Polypropylene (PP)
• Polysulfones (PSU)
• Silicone

Irradiation

This method involves using radiation generated by an electron beam or gamma rays to sterilize healthcare devices. Typically, the dosage amount can range from between 2 to 4 Megarads or 20 to 40 kilograys. However, the dosage may vary depending on the packaging density within the sterilization chamber and the polymer type. It is important to note that some polymer types' color and mechanical properties can be affected by radiation. The following polymer types are compatible with both gamma ray and E-beam sterilization. 

• All polymers in the elastomer family
• All high temperature thermoplastic polymers
• All polymers in the polyester family
• All polymers in the polystyrene family
• Aromatic Polyamide
• Cyclo Olefin Copolymers (COC)
• Ethylene Chlorotrifluoroethylene (ECTFE)
• Ethylene Tetrafluoroethylene (ETFE)
• High Density Polyethylene (HDPE)
• Low Density Polyethylene (LDPE)
• Polycaprolactone (PCL)
• Polyethersulfone (PES)
• Polyethylene (PE)
• Polyglycolic Acid (PGA)
• Polyimide (PI)
• Polylactic Acid (PLA)
• PolyL-lactide (PLLA)
• Polyurethane (PU)
• Polyvinyl Chloride (PVC) Plasticized
• Polyvinyl Fluoride (PVF)
• Polyvinylidene Fluoride (PVDF)
• Ultrahigh Molecular Weight Polyethylene (UHMWPE)