This bond is a film and if damaged, will self-heal. This is critical for applications in healthcare, as damage in the form of fissures present a breeding ground for bioload bacteria. Stainless steels are also easy to clean and nonporous, which helps maintain a hygienic environment. Chemically inert, stainless steel can also be safely sterilised without suffering corrosion or degradation.
The application of stainless steel is widespread in healthcare. Stainless steel in medical devices are also common, but not all stainless steels are suitable for the medical industry. Grades of stainless steel vary. You can learn more about this in Understanding stainless-steel grades.
There is no formal definition of what constitutes medical-grade stainless steels. So then what is it? Is surgical steel the same as stainless steel? No.
The difference between surgical steel and stainless steel comes down to the level of corrosion resistance. Surgical steel has the higher resistance. These steels contain a minimum of 13% chromium. Surgical steel is cured and contains at least 0.2% carbon. Nickel reduces brittleness.
Stainless steel surgical instruments should be curable and ductile. Then there are implant stainless steels, which should not be hardenable.
Surgical stainless steels are used for non-permanent implant devices. The nickel content can be a concern. Although generally considered hypoallergenic for most people, the issue is corrosion and wear, which releases nickel ions or fretting debris into the body. Note, stainless steels are vulnerable to crevice corrosion. This refers to oxidation between parts, such as plates and screws, which are common in implant devices.
Nickel, like chromium, are carcinogens. According to the science of toxicology, a material’s impact on our bodies depends on several points:
The risk from nickel derives from exposure in its raw form, but once alloyed with steel, the risk is minimal. Likewise, the amount of chromium encountered by patients is also considered non-hazardous.
Still, nickel-free surgical grade stainless steel, such as BioDur® 108, is available to offset any potential risks. If the implant device you’re designing is permanent, look at plastics, which offer many excellent choices. You can learn about them in What are medical-grade plastics?
Let’s look at the most common surgical grade steels and stainless steels used in healthcare. SAE is the Society of Automotive Engineers who developed the stainless-steel specifications, or grades, that we talk about.
Stainless steel 304 is considered a medical stainless steel. This grade is similar to grade 316. The difference between 304 and 316 stainless steel is that 316 contains molybdenum, which enhances corrosion resistance, while 304 does not. Still, 304 stainless steel corrosion resistance is high, which is why 304 stainless steel tubing is common in healthcare.
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