Medical and Pharmaceutical Packaging, Primary Films and Flexible Packaging Materials Q&A
Fluid barrier surgical gowns are made of nonwoven materials, which are usually based on polyethylene, such as DuPont Tyvek, or on polypropylene as offered by Kimberly Clark, Molnlycke and many others. A comprehensive list of possible suppliers can be found on Medical Device Link.
The accepted wisdom regarding medical paper and Tyvek as a sterile barrier is that harmful microbes are prevented from entering the packs because they get caught up in the “tortuous pathways” created by the random nature of fibre orientation. It is also considered that a hole with a diameter less than 0.5 µm will prevent a microbe from passing through. Although the pore size in paper is often larger than this critical dimension, the pathways protect the sterile barrier and keep it intact.
As extruded films do not have any form of resin or fibre orientation, they offer a short pathway that will not “capture” bacteria trying to pass through a possible pinhole. It is also likely that holes, where they do occur, will have a diameter greater than the critical size.
Further research into this area was started at Michigan State University by Dr Laura Bix and Dr Jane Severin in 2003. I am not aware that any firm conclusions were reached, as elements such as pressure differential during transport were also being assessed, but in the interests of patient safety, I recommend zero tolerance on pinholes in film used to make a sterile barrier.
Foil pouches are often used for moisture-sensitive products, as they have the highest barrier properties available today. One possible disadvantage to the user is that they are opaque.
In some cases, clear polymer-based structures can replace foil, but the moisture vapour transmission rate (MVTR), until recently, has been worse by a factor of 1000-approximately 1g/m2 versus 0.001g/m2 for foil. Aclar is the only material that has been able to offer levels of MVTR anywhere near this at 0.4g/m2 down to 0.04g/m2, depending on gauge. However, it is not as popular because of its high price.
Advances in EVOH and PVdC processing have resulted in extruded materials that attain MVTR levels down to 0.5g/m2. Some of these materials can also be engineered to filter out UV light, which can affect the efficacy of some devices. Finally, there are coated materials using aluminium or silicone oxide that offer similar barrier properties.
The choice of alternatives is slowly growing, and the most suitable choice for you will depend on the exact demands that your packaging must meet.
All medical packaging comes under the scope of ISO 11607:2006 parts 1 and 2 and European norm EN 868 parts 2 to 10. In addition, many device manufacturers refer to technical report TIR22. This document was published in March 2007 by the Association for Advancement of Medical Instrumentation and is designed to help medical device manufacturers comply with the standards within the regulatory framework of US FDA.
One segment that is not addressed in TIR22 involves healthcare facilities, i.e. hospitals, clinics and other locations where devices may be packaged, particularly for resterilisation in central sterile supply departments. That gap is now being closed with the creation of an Annex J for these facilities and the inclusion of hospital users in the task force that is writing the document. An interesting twist here is that hospital professionals from both North America and Europe are being included to make sure both regions are covered, as working practices and definitions seem to be very different.
The next review of ISO 11607 will start in 2010 and should be completed in 2011; the revised TIR22 will be published soon after. Potential changes or additions to the standard could include tougher environmental challenges to packaging or new measures involving resin interchangeability within a flexible film structure.
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