“We've made syringes that looked fine, but after irradiating, the tip would easily snap off,” says Parente. The solution includes how the material is processed, molded, and the amount of regrind in the feedstock. Look at the sterilization process and optimize its cycle. “Designers often don't check the material properties,” he says. “They usually rely on the material vendor to say this stuff is fine. Then, surprise. It becomes a critical issue.”

But if radiation sterilization causes such problems, why bother with it? Two reasons. It's the fastest, and dose strips can be examined right away, on site, as the product comes off line. Dose strips tell how much radiation was received at its location. The usual seven-day wait required by bioindicators is not needed.

If not sure whether a material tolerates radiation sterilization, a quick and simple way to check exposes the material in question a large dose, in the area of 50 kGy (kiloGray. 10 kGy = 1 M rad). “Then look for what fails,” says Parente.

The design suggestion for gamma is to select several materials that might work and evaluate their tolerances. “Then choose the one that shows the least effects of radiation,” says Parente.

Know the path of the gas. “This is critical with EtO because it has to penetrate the packaging and device,” says Sparks. “If you have a device with a long lumen, consider how the gas will get in there. A complex design means setting the process parameters correctly to allow the EtO to penetrate the entire device.”

Problem areas could be a stop-cock in a syringe or inside a plastic barrel. “One way to check puts a spore strip in the secluded space, closes it down, and places the carton with the strip in the middle of the pallet to really challenge the process,” suggests Jack Fitzpatrick, director of business development, Sterigenics, Chicago (sterigenics.com). Spore strips are removed after the cycle, placed in Petri dishes, and examined after seven days to make sure all spores have died.

Parente says the tight fitting needle and sheath were still sterilized with EtO, but at a longer cycle than originally planned. “We made sure we pulled a deep vacuum and lengthened the cycle to five hours of dwell, which means it took nearly an entire shift to process.” One way around the problem sheath, he suggests, would be to design ribs on its inside to create a narrow space between the sheath and needle to lets gas penetrate.

Define packaging during design. Packaging has to tolerate the sterilization method. A product will fail sterilization if packaged incorrectly. Standards dictate what to test on finished products and final packages. The product has to be in the final package before you can validate it. An inappropriate package won't maintain sterilization for long. The critical issue is how long the package can be stored and remain sterile,” she says.

Consider the packaging density. Is the product in a rigid tray and then a pouch, subpack, and another carton? Cardboard cartons absorb EtO. “You must be sure during validation that several layers of packaging are not preventing the EtO from penetrating,”says Sparks. “The most important aspect of packaging is that routine production units supplied to your contract sterilizer duplicate the design, materials, and packaging that was validated. Don't send the product for validtion in a single pouch if it's to be double pouched.

“Start with the anticipated packaging. A foil pack will effectively seal gas out. Gas can penetrate through plastic, but it takes time.

When test sterilizing is necessary, do so to the final product, not just the material. “Don't test a block of plastic that will be made into a product and say ‘it passes’,” says Sparks. “You have not taken into account the process for making it. It may have been handled quite differently in manufacturing making the sterilization process more difficult and possibly increase the bioburden,” she says.

Reexamine the cycle

“As a contract sterilization firm, we document that we followed FDA regulations,” says Fitzpatrick. “But sometimes it's useful to ask component manufacturers for permission to examine the sterilization cycle for the dose the product is hit with because it may be possible to shorten it and still meet FDA guidelines.” This is not to challenge the standards, he says.

A way to take time out of a sterilization cycle is with parametric release. “It's when sterility is confirmed, not by reading bio-indicators, but by establishing process specs for the key parameters and monitoring activity in the EtO chamber to verify each condition has been met.” If the spec says maintain a chamber temperature of 2°F, recording data in the chamber should verify that the chamber was at the temperature. Similarly for humidity and gas concentration at dwell. If a cycle calls for a dwell of five hours, instrumentation should verify that period, and that the process does not need a bio indicator.” (Bio indicators are usually a million spores in a packet placed in the load to be sterilized. Afterward, spores go into a Petri dish for several days to see if any are still alive.) Fitzpatrick says parametric release is approved by the FDA and accepted by AAMI.

“In the end, you are trying to prove your sterilization process is in control, it's reproducible, and it's a way to sterilize the product that will make it safe,” says Howard.

How the Sterilization Methods stack up

Sterilization Method	Advantages
Ethylene oxide	•Economical for high and low volume operations •Can sterilize plastics whose physical properties may degrade with irradiation •Accelerated preconditioning decreases processing time •Will not degrade packaging materials
Gamma radiation	•Economical for high and low-volume operations. •Fast •Does not require a quarantine or post-sterilization treatment •Is easily validated •No residuals •Can be quantitatively monitored •Used in many single-use medical supplies such as syringes, catheters, IV sets, gloves, and face masks
E-beam radiation	•Good for high-volume, low-value products such as syringes or low-volume, high-value products such as cardiothoracic devices •Shorter exposure time often leads to less oxidation on materials •Dosimetric release lets some products forgo sterility testing

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