Can We Develop Polymer Additives That Provide Clear Indications Of A Device’s Sterilisation History?

This question is in response to issues which have been reported to me whereby hospital sterilisation departments put single use plastic devices through more than one sterilisation cycle, often accidentally but sometimes in an effort to save costs.

Explaining one half of the problem, one source told me: “Some hospitals have unofficial lists of devices intended for single use that they actually re-sterilise or clean for repeated use. For instance, it was reported to me that in Brazil dialysis sets would often be cleaned and reused after contact with more than one patient, which obviously creates a major risks related to recontamination and the spread of blood transferred diseases. We know that unoffical lists for the reuse of single use devices also exist in Europe.”

Sometimes, hospitals may accidentally repeat sterilise devices using more than one method, so for example steam and gamma radiation. So detecting the possible combinations is difficult.

In an attempt to curb this practice, some device manufacturers are using materials which degrade upon a second sterilisation cycle. But this may present a further risk if the actual polymer degradation is not obvious to the eye, as it may cause the device to fail when in use.

Having an additive technology which provides an indication of the number of sterilisation cycles that a material has been exposed to, by changing colour, would be desirable for device makers and the industry as a whole.

The ideal solution would be to develop a range of indicators, which could be in the form of an additive to allow it to be integrated directly into a moulding or tube, without it affecting the mechanical performance of the base material. The solution would involve indicators which were sensitive to the main forms of sterilisation—EtO, steam and gamma raditation. It would also be able to indicate the level of sterilisation that a material has been subjected to—or in other words the number of each type of sterilisation cycle it has been through.

I asked Dr David Opie, senior vice president for R&D at US developer of nitrogen dioxide sterilisation technology Noxilizer to comment. He said: “There are many Class 1 chemical indicators which indicate that the chemical indicator has been exposed to the target process. This class of indicator does not indicate the sufficiency of the process. An example of this is common autoclave tape. Beyond autoclave tape, such indicators also exist for nitrogen dioxide, ethylene oxide and hydrogen peroxide sterilisation processes.”

Dr Opie goes on to say: “Better control of the sterilisation processing of devices may result from two improvements. The first would be the implementation of practices that result in better control of products. For example, requiring that any product exposed to a sterilisation process has a new, unexposed chemical indicator. Products that cannot be exposed to more than one sterilisation cycle should be controlled in this manner.” 

Dr Opie added: “The second improvement could be, as you describe, integration of the chemical indicator chemistry with the product. One could consider that the chemical indicator chemistry could be printed directly on the medical device. Additionally, and theoretically, the chemical indicator chemistry could be integrated into the polymers used in the product. So long as the application of the chemical indicator chemistry into the medical device does not change the function or safety of the device, this is feasible. We must be mindful that this improvement requires that the package has a transparent window so that the hospital staff is able to see the indicator portion of the product within the package. Furthermore, hospital procedures must dictate that these critical products are inspected prior to sterilisation to ensure that the product has not been exposed.”

If we look at other sectors, there are examples of colour changing compounds around. Thermochronic (temperature senstive) pigments have been integrated into plastics and epoxy resins by a number of researchers, although I am not aware of any evidence of any biocompatibility testing of these pigments.

Other colour changing technologies include water absorption and levels of carbon monoxide and carbon dioxide levels in the air.

Dr Opie closes with: “For products where the control of repeat sterilisation processing is critical, coordination between product designers and sterilisation personnel is necessary. Designers need to design the medical device and packaging so that reasonably simple control procedures are possible. This coordination with hospital personnel will then lead to the best implementation of the best chemical indicator solution.”