Medical devices over the years have seen significant development, especially in orthopedics. The material used to create such devices is often as important to the success of the process as much as the device itself. An orthopedic implant is a medical device built to replace a missing joint or bone. They also have the ability to support damaged bones.
The ideal implant material should be biocompatible, not chemically reactive, is strong with good wear resistance, and corrosion-proof. Through trial and error, some of the most effective orthopedic implant materials have been determined, below.
Various metals are often the most commonly used material in orthopedic implants. The main metal used is stainless steel, specifically 316L, as it has an incredibly low-carbon content. Stainless steel is most commonly used in non-permanent implants, due to its low fatigue strength and durability. Other metals and metal alloys used are iron, cobalt, chromium, titanium, and tantalum. Titanium and cobalt-based alloys have been used as replacements for stainless steel devices, as they are more resistant to corrosion and more biocompatible.
In order to form polymers, you must first link them to a large number of monomers through chemical reactions. In orthopedics, the most commonly used polymer is UHMWP, also known as ultra-high molecular-weight polyethylene. UHMWP can be strengthening by Vitamin E stabilization and this process is currently used by many implant manufacturers. Another common polymer is HDP, known as high-density polyethylene. These have been proven to be the most successful polyethylene for articulating with metal or ceramics. Carbon fiber is another common reinforcement for mechanical strength needs. However, polyethylene has raised concerns in the past due to progressive wear.
The most commonly used ceramic material in orthopedic implants includes aluminum oxide and calcium phosphates. These materials have been proven to be resistant to compression, though they can be weak under tension. The use of ceramics is necessary for orthopedic implants to actually form the implants needed. They have also demonstrated their ability to have low wear characteristics, and can even be used to coat metals when necessary.
While these materials will continue to develop over time as more and more medical devices are developed, they have already demonstrated their considerable capabilities in improving the lives of patients who would otherwise have to go without.
Dr. Arnold Peter Weiss is the R. Scot Sellers Scholar of Hand Surgery; Chief of Hand Surgery; Vice Chairman & Professor, Brown University.