Sterilization

There are several methods of sterilization commonly used in the medical field, including autoclaving, Ethylene Oxide (EtO), Hydrogen Peroxide, Gamma, and Electron Beam (E-beam). Each has a different effect on the materials used in the development of a custom medical device, therefore, determining the type of sterilization that the device will be subjected to is a critical design issue.

Since Gamma sterilization is being used more frequently due to the reduced, post-sterile release cycle time, the product development team at Teleflex Medical OEM has developed a table that contains many common materials and the effects that can be expected when the material is exposed to Gamma sterilization.

GAMMA STERILIZATION OF THERMOPLASTICS*

Material	Stability	Comments
Acrylonitrile/Butadiene/Styrene (ABS)	Excellent
Aromatic Polyesters (PET, PETG)	Excellent	No discoloration
Cellulosics	Fair	Esters better than cellulose acetate.
- Esters and Ethers	Fair
- Cellulose Acetate	Fair
Fluoropolymers	Poor	TFE and PCTFE are significantly damaged at low doses.
- Tetrafluoroethylene (TFE)	Poor
- Polyvinyl fluoride	Good	Tends to cross link.
- Polyvinylidene fluoride	Good	Tends to cross link.
- Ethylene-Tetrafluoroethylene (ETFE)	Good	Tends to cross link.
- Fluorinated ethylene propylene (FEP)	Fair	OK for some applications.
Polyacetals (Deirin, Celcon)	Poor	Irradiation causes severe embrittlement, discoloration, and cracking over time.
Polyacrylics	Fair	Yellow discoloration tends to fade with time. Stabilized and tinted materials available.
- Polymethylmethacrylate	Fair
- Polyacrylonitrile	Fair
- Polyacrylate	Fair
- Polyhydroxacrylate	Fair
- Polycyanoacrylate	Fair
Polyallomers	Good	Copolymer of polyethylene and polypropylene reduces oxidation embrittlement of polypropylene
Polyamides (Nylons)
- Alphatic	Good	Slight discoloration possible. Tends to cross link increasing tensile strength.
- Aromatic	Excellent
Polycarbonate	Excellent	Yellows slightly. Mechanical properties not much affected. Tints stabilizers available.
Polyethylene	Excellent	Cross links, tensile strength increases, and modulus of elasticity decreases.
Poly (ethylene-acrylate)	Good
Polyimides	Excellent	Doses exceeding 1000 Mrads are OK.
Polymethylpentene	Good
Polyphenylene Sulfide	Excellent	Doses exceeding 5000 Mrads are OK.
Polypropylene	Good-poor	Stabilization required to prevent embrittlement. Exercise caution because effects may increase with time – months after irradiation.
Polystyrene	Excellent	Slight yellow discoloration possible.
Polysulfone	Excellent	Natural material is yellow.
Polyvinyl formal	Good	Less stable than PVC.
Polyvinylbutyral	Good	Less stable than PVC.
Polyvinylchloride (PVC)	Good	Can discolor but stabilizers available to prevent yellowing.
Polyvinylidene Chloride	Good	Less stable than PVC.
Styrene/Acrylonitrile (SAN)	Excellent	Less stable than styrene alone.
Allyl digylcol carbonate (polyester)	Excellent	Maintains excellent optical properties.
Epoxies	Excellent	Aromatic curing agents are recommended.
Phenolics	Excellent	Mineral fillers increase stability
Polyesters	Excellent	The use of mineral fillers or glass fibers further increases stability.
Polyurethanes	Excellent	Discoloration is normal.

GAMMA STERILIZATION OF ELASTOMERS*

Material	Stability	Comments
Butyl	Fair
Ethylene-Polyproylene Oiene	Excellent
Fluoro	Good
Natural	Excellent
Nitrile	Fair	Discoloration is normal.
Polyacrylic	Good
Polychloroprene (Neoprene)	Good	Some discoloration. Aaromatic plasticizers improve stability.
Silicones	Good	Phenyl substituted materials are more stable than methyl silicones.
Styrene-Butadiene	Excellent
Urethane	Excellent

Guide to Ratings

Excellent: Doses of more than 100 Mrads may not cause significant damage.
Good: Doses in range of 20 to 100 Mrads may cause significant damage.
Fair: Doses in range of 5 to 20 Mrads may cause significant damage.
Poor: Significant damage may occur at doses of 2 Mrads or less.

"Damage" refers to significant changes that affect the physical properties; other effects like discoloration may occur at lower doses.

*Please note: Information is for reference only. The suitability of a material for use in your project must be determined as part of the product development process.

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