A lot of medical equipment cases are made from unstrengthened plastics that are subjected to sanitisation, even though they were not initially designed for patient contact. This repeated action causes environmental stress cracking from repeated wipe-downs with increasingly aggressive disinfectants.

This is a particularly difficult problem and something that has caused huge issues for medical professionals. "I have seen multiple problems with various unconnected medical devices," says Bill Brash, a member of the Institute of Physics and Engineering in Medicine’s Clinical Engineering special interest group, and area technical manager at the Medical Physics Department of University Hospital Crosshouse in Kilmarnock, Scotland.

Brash’s background is in medical physics and medical equipment management, and he can list several examples of where the problems lie, showing that it’s a drain on time and resources, particularly with dialysis machines, tympanic thermometers, endoscopes and ultrasound imagers.

"The problems," he explains, "fall into two main categories: discolouration and damage from high-level disinfectants – mainly oxidising agents such as Sterilox, sodium hypochlorite and chlorine dioxide; and crazing and softening of plastics from low-level disinfectant wipes." It’s the latter, he believes, that is probably the most widespread issue.

New problems

The number of medical device product recalls has been rising steadily over the past 15 years. New devices that incorporate emerging materials such as polymers, hydrogels, biomaterials and nanomaterials are at a higher risk from this wear-and-tear experience due to their more delicate nature. Materials can fail due to routine physical wear and tear, or mechanisms like oxidation, hydrolysis or exposure to chemicals. This is expensive, can increase stay times, and can also create a possibly unsafe environment for patients as products break down after use and begin to fragment.

It appears to be a combination of the detergent and the particular plastic material, and possibly the frequency of cleaning.

Healthcare providers and manufacturers need to have a clear understanding of how the material will degrade under expected and extreme-use cases, and how processes like decontamination will impact the product’s lifespan and durability.

While these advanced materials have enabled innovation such as new drug-delivery mechanisms, surgical care products and implantable devices, it is not always easy to predict how they will respond in different use cases.

Many properties of plastics are dictated by their physical structure and surface chemistry – things that are highly dependent on manufacturing conditions, and the environment they are kept and used in. Small differences in product formulation, especially for plastics and polymers, can lead to unexpected changes in material properties.

For example, in one case, a seemingly insignificant change to a substrate-hydrogel interface used in a medical device caused the gel to phase-separate over time. In another, a manufacturer changed the plasticiser in a component to meet new regulatory requirements and discovered that the change led to earlier failure of the component.

Trends Brash has noticed corroborate this. "Anecdotally, plastics [ABS] containing a high level of recycled materials appear to be more likely to be damaged by clinical wipes," he says, "and manufacturers tend not to be too forthcoming about the constituents of their equipment."

This could be a problem for those handling the product, and especially those cleaning it or using it without being overly familiar with its care procedures. Brash points to the sterilisers and disinfectants being used as the main cause of plastic degradation in medical equipment but is clear that these may not be the only reason.

"It’s never been fully explained. Some clinical wipes have caused superficial and structural damage to plastic cases on items such as dialysis machines and thermometers, but other similarly purposed items, cleaned using the same materials, have no damage evident. It appears to be a combination of the detergent and the particular plastic material, and possibly the frequency of cleaning."

While Brash doesn’t believe things are getting worse in this respect, he doesn’t think they are getting better either. "I’ve not found any significant change; however, the peak of the problem was around five years ago."

So far, some basic solutions have helped – "Changing to a different brand of wipe, often with the same active ingredient, can make a big improvement," Brash notes – his main advice, however, is to keep a close eye on the situation. "I would continue with recommended cleaning and disinfection practice, but closely monitor the effect on the particular material. If damage is noticed, log it and report it to MHRA and suppliers." He also recommends small and large changes if anything does happen: "Consider changing the brand of wipes – or of equipment."

Be vigilant

There is a lack of consensus over whether the situation is being taken seriously enough by medical device manufacturers; Brash remains unconvinced that they are doing all they can, but he is hopeful.

"Some equipment manufacturers only recommend their own-brand disinfectants and will warrant against damage if these are used," he says, though he admits that his may be for commercial reasons rather than a recommendation as an outcome of specific testing.

The use of plastics in medical devices is sure to continue – and increase – as the technology develops and adapts to the proliferation of new ideas, and products will inevitably end up incorporating more compounds and novel materials. So what does Brash foresee for the future of plastics in medical equipment and the way this issue is handled? "Perhaps metallic-loaded polymers with silver or copper that don’t need disinfection," he muses.

More than just a start, this could be a huge stride forward for the industry on an issue that will never go away unless it is completely solved. But would it at least lead to products lasting longer before they need replacing? Products exempt from cleaning seem likely to suffer less wear and tear, after all. Brash, however, isn’t so sure.

"Not generally. There are many variables affecting equipment lifetime; cleaning is only one of these and difficult to separate out," he explains. "It’s not really a longevity issue – if any significant damage is noticed, it would have to be rectified – parts replaced and so forth."

We have had some equipment manufacturers accept responsibility and repair equipment at their own expense; there are others that have been less sympathetic.

It’s often a case-by-case issue, he says. "It doesn’t affect the overall lifetime, but it does cost money to rectify – we have had some equipment manufacturers accept responsibility and repair equipment at their own expense; there are others that have been less sympathetic."

Everything under consideration

Improper care for a product is an issue, and one that hospitals and other places where the plastic equipment is used must address with the staff that handle it regularly. If a patient’s safety is put at risk through lack of expertise in cleaning and maintenance, it is clearly a problem. One of the most publicised cases of this was on the polymer coatings of implants for cardiovascular complaints, an area where wear and tear could lead to breakdowns of the plastic while in the body – something that, in turn, could lead to huge complications.

Some device material failures can be caused by mistakes made by the manufacturer at any point throughout the product development process. Among the most common are selecting the incorrect materials, and not taking into account the full set of criteria of mechanical strength, durability, flexibility, permeability, leechability, surface energy, maximum operating temperature, chemical resistance, electrical conductivity, thermal conductivity and optical requirements.

These considerations are the manufacturer’s area, and a lack of proper due diligence here could lead to problems further down the line, so it is vitally important that device OEMs take steps to mitigate the risks of materials-related product failure.

Whether or not the fast-moving world of medical device manufacturing, and the hospital staff that represent the end users and carers for such equipment, have taken the concerns and warnings to heart is yet to be seen. Information on proper care is increasingly available; it just has to be put into practice – something the industry, right now, is still wising up to.