There are multiple myths around the role of stainless steel in surgical instruments and medical equipment.
At least, that’s the conclusion of Daniel Coole, managing director at Surgical Holdings, a company that manufactures surgical instruments and orthopedic implants, supplying National Health Service and the private sector in the U.K.
“I guess the first {Myth} is around stainless steel used for surgical instruments or medical equipment being this sort of superhuman stainless steel that’s very robust and can take anything that’s thrown at it,” says Coole in a recent Beyond Clean podcast.
Another myth that Coole debunks is that good stainless steel can only come from certain European countries. If it is the right composition and ticks the boxes as far as the different chemical elements are concerned, then it is suitable, he says.
“Most stainless steel used in surgical instruments is 420 stainless”, Coole says. “It contains carbon, but it is 70% to 80% iron, extracted from iron ore, so essentially chemically the same as rust. Although we’re describing it as stainless steel, the majority of the composition of the steel itself is very comfortable in a state where it can revert back to rust as quick as possible.”
The thin layer that coats stainless steel is only around 30 microns and is more fragile and easily damaged than many realize. That thin coating is the only thing that protects the steel from deteriorating. Once the passivation layer is compromised, potentially free iron can be released on the surface of the material, which starts corrosion. The application of various acids, including nitric and citric, can initiate a chemical reaction that will help rebuild that protective layer.
How To Know Corrosion When You See It
Technicians on the front line face the enormous challenge of monitoring the high volume of instruments they see go by for blemishes — the kind that might indicate corrosion that could impact patient safety.
To do so, they must be educated to distinguish between different sorts of surface finish changes. Those chemical reactions are like what happens in a home dishwasher when some pieces of cutlery will stain or mark. The type of water used in cleaning and reprocessing devices can impact corrosion. For instance, natural tap water, no matter how pure, contains chloride. “There’s nothing like a bit of chloride, if you’ve got a scratch on an instrument, to initiate some sort of rusting or spotting,” Coole says. Chloride can cause what look like tiny pinpricks but can produce pitting below. The ultimate danger is that the damage eventually will lead to instrument failure.
A Better Stainless Steel
“We’ve been using stainless steel for 100 years in its current format, and it’s a very good steel for surgical instruments, but it hasn’t changed much since, nothing has advanced,” Coole says. With new alloys available and changes in regulations regarding medical devices, there is an opportunity for progress. He cited a 420 stainless steel that contains copper which has natural antimicrobial action and can kill bugs that land on its surface naturally.
That eternal search for better stainless steel led Montreal researchers to discover what they think is a way to change the surface of stainless steel to control bacterial infections in hospitals.
“The beauty of it is its simplicity and capacity to simultaneously improve cellular response and limit bacterial expansion,” said study supervisor, Antonio Nanci, in that 2018 study. The process works just by physical-chemical interaction between the steel and the bacteria, says Nanci, an anatomist in cell biology.
“Everything that’s stainless in a hospital – the doorknobs, the instruments, the operating table – could be treated this way,” the author writes. “With it, bacteria simply don’t propagate.”
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