How to Balance Rough and Smooth in Orthopedic and Dental Implants
The development of 3D printing technology has had nothing short of a revolutionary impact on the medical device industry, opening up unlimited new possibilities in product design and mass customization. However, there is an interesting twist — the need for polishing metal parts — in some of the most popular applications: namely, the 3D printed metal parts that are especially beloved for orthopedic and dental implants due to the rough finish and inherent porosity of the printed surfaces.
Why 3D printed metal parts for implants?
Whether 3D printed metal parts are created in a special atmosphere (for example, when building titanium parts in an argon atmosphere) and made using direct metal laser sintering (DMLS), selective laser melting (SLM), electron beam melting (EBM), or some other process, the nature of 3D printing is that three variables determine the finish of a part and its density (or porosity):
- The “elevator” layer steps of the printing process
- The laser beam size
- The metal particle size
In fact, in addition to the capacity for mass customization, the benefit of 3D printed metal parts for orthopedic and dental implants is that this combination of metallurgical variables creates a very rough, porous finish that promotes the fusing of bone and other tissue to the implant, which is critical to the success of the procedure.
But what if you need a smooth finish, such as in a joint implant where good wear characteristics are needed? That is when polishing metal parts comes into play.
What is the role of polishing metal parts in 3D printed implants?
For an application such as a 3D printed knee implant, part of the surface needs to be rough and porous in order to allow bone to fuse to the implant. However, on the wear surface of the knee, you need a finish that is as smooth as possible, to reduce friction and ensure that the implant has a reasonably long life and does not cause pain in the recipient. The same principle applies to hips, shoulders, and other types of implants where there is both a wear surface and a surface that must fuse with bone or other tissue.
In the U.S. alone, each year more than a million people undergo hip or knee replacement surgery. In recent years, there have been a number of well-publicized lawsuits related to device failure, pain or injury linked to the these types of implants, or instances where the devices — which are intended to last about 20 years — need to be replaced early due to excessive wear.
Fortunately for implant manufacturers, the proper finishes can be achieved by combining the use of 3D printing and the proper technique for polishing metal parts. This allows certain surfaces of 3D printed metal implants to be made as smooth as possible while other surfaces maintain the roughness and porosity required for effective implant-to-tissue fusion.
What are the concerns when polishing 3D printed metal parts?
There are a number of methods used today for polishing metal parts, ranging from labor-intensive and precise (and therefore, more costly) hand polishing to various automated abrasion methods and polishing by laser or electron beam. The goal of all these techniques is to obtain a surface finish that is smooth and free of porosity.
For polishing metal parts created through very precise 3D printing, the ability to tightly control material removal is vitally important to ensuring that the original form of the part — with all its tight dimensional tolerances — is preserved. In general, that means the polishing technique for 3D printed parts must achieve the specified smoothness while removing the smallest possible amount of material. This is especially true for metal parts having complex geometries, sharp edges, and fine details.
Therefore, when polishing metal parts for 3D printed orthopedic or dental implants and other medical devices, although there may be a need for a highly shiny, even mirror-like finish in some applications, the focus is primarily on maintaining tolerances. This is an area where Metal Cutting can achieve Ra 0.1 µm and below, depending on the type of metal used, while maintaining tight tolerances and minimal material removal. The result is surface finishes that provide the required technical properties for implant use.
As medical technology advances, Metal Cutting will continue to meet the changing needs of the medical device industry. As a precision metal fabricating company, we are experts in very tight tolerance cutting, grinding, lapping, and polishing of all metals for medical device applications. We also provide secondary operations such as bending, angle cutting, and pointing and slotting of small diameter tubes, wires, and rods. In addition, tungsten and molybdenum products, such as wire, ribbon and rod, are available.
To learn more about specifying precision metal tubing for your medical device needs, download a free copy of our comprehensive guide, Metal Tubing in the 21st Century: Who Needs It? The Future of Innovation in Medical Devices.