Additive manufacturing hardly seems like a new technology anymore, but in fact, it’s still well behind the maturity of the more established techniques with which it is often compared. Even more recent is the use of metal in the process. That said, metal implants that are additively manufactured are gaining regulatory clearances for clinical use and are becoming more prevalent.
Companies that wish to take advantage of this rapidly changing manufacturing segment need to maintain a comprehensive understanding of the latest information involving it. That means staying abreast of technologies, materials, capabilities, considerations, and more associated with metal additive manufacturing.
To offer a more complete view of the current metal additive manufacturing landscape, Gautam Gupta, Ph.D., senior vice president and general manager of Medical Devices at 3D Systems, responded to a number of questions on the topic in the following Q&A. With a focus on direct metal printing (DMP), Dr. Gupta shares his expertise on why this technique is ideal for orthopedics, what to keep in mind when designing devices using the technology, and the limitations that still exist with it.
Sean Fenske: How does the fabrication method for metal orthopedic implants impact the final result?
Dr. Gupta: There are several aspects to this question to consider. First, the way you fabricate the implant can affect the mechanical properties of the device and its function. For example, with additive manufacturing as your fabrication method, you can create porous lattice structures that support bone in-growth. This addresses the functional attributes of the implant, improving osseointegration, implant fixation, and overall performance.1
The fabrication method can also affect the design flexibility the engineer has for creating a complex implant. For example, if you have an oncology patient with significant hip resection, a standard implant made using traditional manufacturing methods will not be functional. Instead, you will need to use additive manufacturing technologies to customize an implant specific to that patient’s anatomy.
A third consideration, which is always a key factor, is the economic aspect of the fabrication method. So long as you can achieve (at minimum) the same baseline performance from a method like additive manufacturing that you can achieve with a more traditional technology like casting, you can try the newer technique. However, if the cost is completely out of line with the more traditional approach, regardless of the benefits, the entire project breaks down. Ultimately, the product or implant needs to be commercialized so using a fabrication method where the economics simply don’t make sense isn’t going to work for the company. With faster, multi-laser direct metal printers, additive manufacturing implants have become more cost-competitive, even in large joint applications.
Fenske: What advantages does DMP offer when compared to more traditional methods like machining or forging?
Dr. Gupta: To start, I’d just like to clarify what DMP is. Direct metal printing is the 3D printing of a metal material using a powder bed fusion technology. You start with a powder and, based on software and hardware integration, you can create an implant or instrument.
Just as 3D printing with plastic offers exceptional design flexibility, the same is true when using metal powder. So, an engineer can optimize the design of an implant with more complex geometries using DMP as compared to forging or machining. Currently, triflanges are machined out of large titanium bar stocks and subsequently plasma spray-coated to get a bone in-growth interface. This adds significant cost and limits the overall design and functional flexibility of the final device. Instead, using additive manufacturing, we can produce patient-specific triflanges with integrated lattice structures.
DMP also impacts the supply chain flexibility for manufacturing implants. The number of units you need to buy to make it economically viable may be significantly less than with other methods. For example, if you have to use traditional processes like castings or forgings using molds, you will need to order a minimum quantity to cover your original investment. However, with additive manufacturing, there are no such limitations. You can customize each device and manufacture only the quantities you need on demand.
Finally, repeatability is a huge benefit. There is less human error with DMP since the machine is doing all the work. This also translates to less waste and scrap, further reducing costs. So you get design flexibility, customization, and repeatability while reducing post-processing and the amount of stock that needs to be ordered.
Fenske: Are there limitations on the materials available when DMP is used versus other fabrication methods?
Dr. Gupta: Of course there are material limitations, but no more than with another fabrication method. If the metal has been proven to be successful for orthopedic implants, then that material can generally be printed using DMP.
The situation where material becomes a potential concern is in its availability in powder form. You can find plenty of suppliers selling ingots or bar stock of a material to be used for forging or casting. Since metal 3D printing, however, is still relatively new in comparison, finding a quality supplier of powder metal is not always so easy. In addition to availability, the cost of the powder may also be a limiting factor.
Fenske: What types of implants are most commonly being manufactured using DMP? Is there a reason why these are most common at the moment?
Dr. Gupta: The most common type of orthopedic implant being fabricated with DMP is titanium spine cages. That’s true whether we are producing them or the device manufacturer is producing them using technology from us or another company. Without naming names, eight of the top 10 spine implant companies today have their titanium spine cages produced on our DMP platforms. We are well established as a market leader for supporting that innovation and commercialization of those types of implants.
As far as why, printing with titanium is a well-understood technique—from both a regulatory and biological safety point of view. As a result, we can use titanium with DMP to achieve porosities that are very close to bone; much easier to accomplish when compared to cobalt chrome or stainless, which is much harder. That’s why we’re using titanium with DMP for spine cages.
Fenske: As we see smart implants gaining interest, does DMP better facilitate the inclusion of the necessary technology for these types of products?
Dr. Gupta: While we can’t print in the electronics or necessary components required for smart implants, additive manufacturing with DMP does offer customization capabilities that could make it much easier to position the sensors and other electronics needed to make the smart implant function. This goes back to that design flexibility point I was making earlier. With the freedom in design AM provides, custom pockets can be fabricated to allow for optimal placement of the chip, sensor, battery, and any other required circuitry. But at the moment, while it is possible, this isn’t really happening anywhere yet at a commercial level.
Fenske: What are the most important considerations for using DMP versus a more traditional manufacturing technique engineers should keep in mind?
Dr. Gupta: We’ve discussed many of the major items already. Again, that design freedom is a critical benefit when compared to other, more traditional methods. With new engineers coming into the fold, their exposure to 3D printing has been different. They are much more open to the process than the more established engineers who have a greater familiarity with machining.
As such, it’s also important to be aware of the limitations of additive manufacturing. For example, as far as I know, no one is using AM for a titanium hip stem. Unfortunately, the required strength is simply not there in the final component using additive manufacturing, and the implant wouldn’t pass all fatigue testing.
Also, the cost of manufacturing always needs to be a consideration. This doesn’t just mean the cost of manufacturing an implant, but rather, the total cost from concept through to having the finished implant in hand. How do all the costs compare whether using additive manufacturing, machining, casting, forging, etc.? Are there secondary processes required to fabricate the porous structures? What are the essential cleaning processes? Is blasting necessary? The engineer needs to take into account the entire workflow for the implant, not just the cost of producing the implant itself.
The material is another important consideration. While titanium is very popular for additively manufactured orthopedic implants and cobalt chrome is generating growing interest as well, they aren’t the only options. PEEK is a material being used for many types of implants and primarily gaining interest from orthopedic surgeons for pediatric cases. We’ve had surgeons approach us because they have a procedure for which they need to resect a significant part of a child’s pelvis to eliminate all cancerous tissue. Replacing that with a large chunk of metal can greatly reduce that child’s mobility. Additionally, the weight of the implant would also be a concern for that age. A patient-specific implant made from PEEK in that type of situation may present the best material option.
Ultimately, there are numerous considerations with additive manufacturing and DMP, but I think those three—design freedom and flexibility, cost of manufacturing, and material selection—are at the top of the list of the most important.
Reference
1 Wu Y, Liu J, Kang L, et al. An overview of 3D printed metal implants in orthopedic applications: Present and future perspectives. Heliyon. 2023 Jun 29;9(7):e17718.
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