Medical steel is also known as surgical steel. The general criteria for being medical steel are as follow:-
- Should be ductile and non-magnetic
- Should be corrosion resistive
- Medical tools such as scissors, forceps, etc.
- Implants such as rods, screws, etc.
- Medical equipment such as a blood bag refrigerator.
Types of medical steel
- Austenitic (316, 316L, etc.)
- Martensitic (410, 420, 440, etc.)
The addition of nickel in the stainless steel makes steel austenitic. We know that chromium oxide, molybdenum, and silicon tend to stabilize in the ferritic state. In other words, they like to be in the Body-Centered Cubic (BCC) structure. This will make the steel weaker. So, to overcome this problem nickel is used, which stabilizes the atoms in Face-Centered Cubic (FCC) stage. Nickel also makes the steel non-magnetic. This non-magnetic property is one of the major properties for medical implants such as bolts and screws used in orthopedics.
Let us take an example. If you are going to do MRI in the hospital, medical personals will ask you to remove your belt and keys. This is because, when the MRI machine is operated, it creates a magnetic field. This magnetic field will pull all the magnetic components towards itself. So, if you have a magnetic implant within your body, it will pull your body towards itself. Thus this could be dangerous.
Austenitic Steel (316L)
This might be the most popular steel out of all the available steels in the market.
316L is a type of 300 series austenitic steel where ‘L’ indicates a low level of carbon in the alloy. A decrease in the carbon content makes the steel more ductile. As the steel becomes ductile, it can be easily changed into a thin layer without breaking. This is one of the reasons, why surgical tools such as cautery pencils, forceps, scissors, etc., are generally made up of 316L steel.
The addition of Molybdenum (around 2%), in the austenitic steel, increases the non-corrosive nature of the steel. So, the implants will be more biocompatible to the human body.
Similarly, we know that most stainless steel is brittle at low temperatures. So, they cannot be operated at a low temperature. The only machine I have got to work at a very low temperature is the Ultra-Low Deep Freezer of REMI Company. It can operate at -860C which is useful for storing RBC. I really do not think there is any machine in the health sector which works below this temperature. For those kinds of machines, the best stainless steel will be austenitic steel which can be operated at -150OC to 8700C.
Drawbacks of surgical steels for implantation
- Might be toxic
- Might be allergic
- Chances of being rejected by the human body