Medical Sterilization Material Compatibility
Electron beam processing of plastics materials may,
in some cases, have a noticeable effect upon the polymers comprising
the plastic. As a polymer is processed, radicals are formed throughout
the polymer. The interactions of the radicals with reactants in plastic
products can be classified as follows:
• Recombination - which creates no change in the property of the polymer
• Cross-linkage - which results in an increase in strength and a decrease in elongation of the polymer
• Chain scission - which results in a loss of strength and elongation
The amount of oxidation which occurs as a result of electron beam processing is a large determining factor in which of the above reactions creates the most dramatic effect upon the material. Because the time of energy application is so short in electron beam processing, the effect of oxidative reaction on materials is limited and more often than not results in recombination or cross-linking rather than chain scission. In gamma radiation, the longer time period spent in exposure to the irradiation source allows for oxygen and other reactants to permeate back into the product, thus allowing for more frequent occurrences of chain scission and termination.
Most medical-grade plastics currently utilized for healthcare products are constructed of plastics which have been stabilized by the raw material manufacturer in order to be radiation compatible. The demand for radiation stable plastic has caused plastics providers to offer radiation stable products at very little, if any, increased cost over non-stable compounds.
In the September, 1995, issue of "Medical Device Technology", it was reported by Sash Pearson Research that the following materials constitute the top ten plastics/polymers used in medical device manufacturing:
1. Polypropylene
2. Polyethylene
3. Silicone
4. Poly (vinyl chloride)
5. High-density polyethylene
6. Polycarbonate
7. Low-density polyethylene
8. Polystyrene
9. Poly (tetrafluoroethylene)
10. Nylon
A separate and unrelated report published by Ageless Processing Technologies of Solana Beach, CA, lists the top 13 "Preferred" Radiation-Resistant Polymers as the following:
1. Polystyrene
2. Polyethylene
3. Polyesters
4. Polysulfone
5. Polycarbonate
6. Polyurethane
7. PVC
8. "High End" Engineering Resins
9. Thermosets (polyesters, polyurethane)
10. Elastomers (silicone)
11. Polyamides (nylon)
12. Polypropylene
13. Flouoroplastics
Nine of the ten most widely used plastics in healthcare products are highly radiation tolerant and recommended for irradiation sterilization. Only PTFE from the top ten list may react less than favorably in some cases to irradiation processing.
AAMI/ANSI/ISO11137 lists several materials in its "General Guide to Radiation Stability of Materials" and grades several materials as "Excellent", "Good" or "Poor" with regard to their irradiation stability.
BeamOne is able to perform feasibility testing on specific polymers to determine their reactivity to irradiation sterilization. Please contact the Customer Service Manager at the respective facility to arrange for feasibility testing.