Stainless Steel Vs Titanium Medical Devices

As, we all know that an implant is a device helping to replace a biological structure that has been damaged due to trauma or bone or cartilage disorders (e.g hip prosthesis). Medical implants may also be used for cosmetic purposes such as breast implants. This blog is all about metal surgical implants and their application.

The most common metals used for surgical implants include:

Stainless steel

The application of stainless steel has stainless steel implant continued in surgical practice since the early twentieth century. There are many forms of stainless steel starting with the introduction of the type 302 for use in orthopedic surgeries. 316L stainless steel type is commonly used in surgical procedures to replace biological tissue or help stabilize a biological structure, such as bone tissue to help the healing process.

316L stainless steel is very popular for surgical practices because it is the most resistant to corrosion when in contact with biological fluid. It is important that a surgical implant is not susceptible to corrosion when placed within the human body to prevent the chances of infection occur. In the case of an infected implant, the device is removed to prevent any additional trauma to the surrounding biological tissue. This type of stainless steel is particularly effective as surgical implant when in cold worked condition. What makes the Type 316L is ideal as an implant device is the lack of inclusion in this material. Including materials also contain sulfur and this is a key component to promote corrosion of metals.

Stainless steel is a metal alloy. By adding the element chromium (16%) stainless steel, the metal becomes resistant to corrosion. The addition of carbon and nickel (7%) for stainless steel help stabilize the austenite in the steel. The 316L stainless steel selected for the purpose of surgical implants contains about 17 to 19% chromium and 14% nickel. As mentioned, it is essential that the metal implants are not susceptible to corrosion. With surgical implants, molybdenum is added to the stainless steel alloy which forms a protective layer that insulates the metal despite exposure to an acidic environment. The corrosion resistance can also be achieved with the element carbon, but only when the carbon is in solid solution state.

Note : It has to be noted that the ferrite element should not be built in stainless steel as this gives the metal a magnetic property, which is never used for surgical implants because it could interfere with equipment of magnetic resonance imaging (MRI). One of the most obvious problems with the use of magnetic implants is their susceptibility to heating that could change the shape or the structural position of the metal implant.

Titanium Alloy

Compared to stainless steel alloys that have been used in medical practice since the early 1900s, Titanium is relatively new in its application as a medical implant for replacement of a biological tissue. One of the biggest advantages is its strength titanium - titanium retains as strong as steel and is exceptionally light weight (lighter approximately 50%), so this material is ideal for use in surgical implants.

Unfortunately, titanium is easily contaminated when exposed to hydrogen, nitrogen and oxygen, which may influence the corrosion process in this metal and may compromise its use in certain medical procedures. In the 1960s a change was experienced in the selection of metals of best fit for titanium surgical implants becoming a popular choice. The following video compares the strength of pure titanium with titanium alloy.

The structural composition of titanium alloys is divided into three distinct categories: alloys A, aleaciones and alloys. Elements including aluminum, oxygen, tin and zirconium all become vital for stabilizing A. Magnesium alloys, molybdenum, iron and chromium become favorable as stabilizers for  alloys. The most common forms of titanium and vanadium are aluminum or combination of aluminum and niobium that is typically applied to manufacture rods and clamps the spine. High tensile strength and light weight characteristic of titanium makes this ideal metal for reconstructive surgery.

Stainless Steel vs. Titanium       

·        Titanium has a high resistance to repeated loading so it is ideal for use as an implant.

·        Titanium is stronger and lighter in weight compared to stainless steel.

·        A lower modulus of elasticity than stainless steel, titanium is less rigid limiting the amount of tension on bone structures.

·        Titanium is less prone to the generation of an immune reaction based on the fact that this material is more resistant to corrosion compared to stainless steel implants.

·        Titanium has a higher resistance under repeated loading stresses, making this metal able to withstand the tension during the internal fixation.