Life Sciences

How Package Engineers Keep Medical Devices Sterile

08 August 2018

It is imperative in the pharmaceutical and medical markets that a sterile environment is maintained. It is the first line of defense, although it is often an afterthought when it comes to medical device package design. In order to ensure devices are sterile, packaging considerations have become a science of their own.

Packaging Considerations

Medical devices including surgical tools, syringes, hypodermic needles and other sterile packaged consumables require a package design that facilitates sterilization, maintains a sterile barrier for the acclaimed shelf life and is presented in a manner that is conducive for its use in the field. The first limitation is the method of sterilization followed by barrier requirements and package design.

The most dominant sterilization methods include the use of ethylene oxide (EO), ionizing radiation and steam sterilization. These methods are typically carried out during the packaging process and the method used is dictated either by the contents to be packaged or the packaging materials.

Ethylene Oxide

EO is a colorless, flammable carcinogen. The gas is primarily used as a precursor and sterilization is carried out in a vacuum. The process can be tailored in a way that is most suitable for the contents to be contained as a range of sterilization temperatures, concentrations and vacuum pressures are utilized.

In EO sterilization bacteria lethality is a function of temperature, concentration and humidity. Process temperatures range from 90° F to 135° F, and EO concentrations range from 400 mg/l to 800 mg/l. Relative humidity also plays a vital role in EO sterilization as levels greater than 30% help improve material porosity and subsequently EO penetration.

Increasing temperature and EO concentration can help drive down sterilization cycle time, although the improper selection of process parameters can affect residual EO concentrations and require longer aeration times.

The International Organization for Standardization (ISO) has developed two standards that collectively govern development, validation, process controls and acceptable limits for residual EO concentrations, ISO 11135:2014 and ISO 10993-7:2008.

Ionizing Radiation

Ionizing radiation is a process by which the device is irradiated either by gamma radiation, x-rays or by an electron beam. After exposure to radiation, some materials may become brittle as radiation can alter material chemistry on a molecular level.

Ionizing radiation is a much simpler form of device sterilization but is slightly more limited in use due to the sensitive nature of some polymers and electronic circuit boards. Cobalt 60 is the most common source of gamma radiation, although Cesium 137 is also used.

Electromagnetic radiation is highly penetrating and an effective method of medical device sterilization. Benefits include time efficiency; the ability to sterilize products that are already fully sealed in their final packaging; it works well with temperature sensitive materials; and there are no residual contaminants.

Steam Sterilization

Steam sterilization is the third most popular method of medical device sterilization. The high-temperature process is performed in a temperature range of 121° C to 134° C with an exposure time that ranges from three to 15 minutes.

Steam sterilization is another effective method of sterilization. so long as the device is presented in a manner where there is a free passage of steam around the device and packaging. There are, however, several limitations in steam sterilization.

Certain materials are not compatible with steam exposure. Steam is most conducive for use with paper-based pouches, woven and non-woven wrapping materials, as well as reusable metal trays. Adhesives particularly may be compromised by steam and care should be taken to ensure the sterile barrier between lids and bond trays joined by adhesives are not compromised.

ISO 17665-1:2006 specifies development, validation and routine control requirements of moist heat sterilization processes for medical devices.

Conclusion

In the medical field, maintaining a sterile environment is paramount. Physicians, surgeons, nurse practitioners and all other healthcare works depend on clean products so that a sterile environment is maintained. The device itself and the packaging need not only be sterile, but also accessible and conducive for its application. The dependable nature of the packaging materials is as important as the device to be used.

To contact the author of this article, email shawn.martin@ieeeglobalspec.com


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