Copy to clipboard 
Orthopedic device manufacturers that want to remain on the cutting edge of surgical care are embracing new materials used to produce implants and instruments. The following suppliers are meeting that demand with advances in additive manufacturing, cementless implants and next-generation stainless steel.
This is part two of a three-part series where we ask companies throughout the supply chain about how they’re helping orthopedic device companies problem solve. Part one focuses on proficiency and efficiency gains in orthopedic manufacturing and part three presents solutions in R&D and operations.
Reviving Pure Titanium Thanks to Additive Manufacturing
Amnovis with CEO & Co-Founder Ruben Wauthle, Ph.D.
Additive manufacturing of titanium medical devices usually requires Laser Powder Bed Fusion (L-PBF) of Ti-6Al-4V Grade 5 or Grade 23. Despite the lower strength, pure titanium (CP Ti, Commercially Pure Titanium) has some interesting properties that can be beneficial for certain applications when it is processed through additive manufacturing. The required post-processing is a heat treatment, such as annealing or hot isostatic pressing (HIP), that’s required to obtain certain mechanical properties compliant with industry standards.
Supply chain issues and increasing costs are a global problem. Additive manufacturing enables innovation in medical device design, such as integrating porous structures. However, the often-required HIP heat treatment of additively manufactured Ti-6Al-4V ELI adds significant costs and lead times. The proprietary process we developed and validated to 3D print pure titanium requires no heat treatment to meet the applicable ASTM standards. This results in significant lead time reduction at a lower cost.
Our pure titanium exhibits extremely high elongation (>24%) while having the chemical purity of grade 1 titanium and almost matching the strength of grade 4 titanium. This creates many unique possibilities for applications in which alloying components could be an issue or for applications requiring a high ductility or deformability. One such example is deformable implants that are printed as a standard and oversized shape, but are deformable according to the patient’s anatomy or the shape of the bone defect.
Coatings Play a Significant Role in Cementless Implants
Orchid Orthopedic Solutions with Vice President of Business Development Scott Reese
Cementless implants require bone in-growth technologies, and increasing numbers of implants are trending toward cementless options. Cementless hips have long been the standard of care, and more than 90% of hip implants are cementless. Knee implants are increasing adoption rates of cementless technology. In 2012, only about 3% of knees were cementless. In 2022, that rate is closer to 20%, and we will continue to see this trend grow.
A few factors are driving the cementless trend:
- O.R. time – Bone cement takes time to prepare and set in the O.R. Cementless knee (femur and tibia) procedures are approximately 20 minutes faster than cemented procedures. This can help improve O.R. efficiency, which is top of mind for hospitals and ASCs.
- Natural bone growth – Large joint replacement is no longer a treatment reserved for patients 70 years and older, and we need to think longer term and consider the activity level of the person receiving these devices. Surgeons don’t want to sacrifice viable bone stock that may be needed later in life, should a complication arise. The best way to preserve bone is to limit the amount resected or preserve as much as possible.
- Robotic procedures – Cementless implants are a good match for robotic procedures, due to the precise bone cuts the technology affords. To get the best results with a cementless device, you must start with a good resection that allows the native bone and implant in-growth surface to be in direct contact. The next evolution of resection accuracy lies in robotics or navigated procedures.
Cementless implants require bone in-growth surfaces, which can be achieved by application of a coating onto the implant or printing it directly onto the implant through additive manufacturing. Considerations of the anatomical performance requirements are important when selecting a bone in-growth surface type and application method. Some applied coatings simply meet the industry requirements, while others exceed the standards. For example, Orchid’s HA was developed for high-demand situations like today’s anterior first hips. These devices are implanted with a broach-only technique resulting in a tight “line-to-line” fitment. Some OEMs have recognized that this could pose a risk to keeping the HA in place through impaction. For this product, the coating must be very strongly adhered to the device and thin enough to not fill in the in-growth surface or impede impaction. This is a classic example of designing the implant to complement the procedure.
Different coating types are optimized for various performance factors and applications. You need to get good initial stability to achieve solid implant interface. It’s not all about who has the greatest pour volume or the deepest matrix. Porosity, roughness and thickness are common considerations, but more of each is not always better. Coating zones and thickness and roughness should be optimized to deliver a device that has been designed to resist micro motion, encourage cell on-growth and minimize the potential for stress shielding down the road.
Adopting Next-Generation Stainless Steel for Medical Devices
Carpenter Technology with Head of Applications Engineering and Business Development Gaurav Lalwani, Ph.D.
Among the various metallic materials used for orthopedic devices, stainless steel (SS) alloys — such as 300 series, 400 series, 17-4PH, C455 and C465 — are some of the most widely used for medical implants and surgical tools due to excellent corrosion resistance, biocompatibility and mechanical properties. However, a need exists for next-generation SS alloys to meet the demanding needs of medical devices due to developments in surgical procedures (robotic-assisted and minimally invasive surgeries), production techniques (additive manufacturing, lights-out production) or changing regulatory frameworks (EU MDR).
As minimally invasive surgeries evolve and robotic surgical platforms continue to be adopted, the need for smaller devices will require both the precision of advanced machining and the characteristics of next-generation materials, where more performance is packed into a smaller unit volume. A great example of this is the BioDur 108 alloy, which takes the performance expectations of an industry standard (vacuum melted 316 stainless) and increases the strength, corrosion resistance, fatigue and biocompatibility (Ni and Co removal for regulatory and allergic concerns).
Next-generation stainless steel alloys meet the demands of the changing orthopedic landscape.
Machining practices are continually evolving, and trends such as lights-out manufacturing and IoT mobile machinists for 24/7 production are being adopted and used routinely. However, to do this effectively, reliably and consistently, the work piece needs to have high consistency from piece to piece along with tight tolerances, dimensional controls and repeatability. Miniaturization requires advancements in both processing and materials, such as Custom 465 stainless, allowing for a drop-in replacement to 17-4PH with increased strength and hardness, while retaining very high levels of ductility and corrosion resistance. We are also developing a minimum residual stress 17-4PH bar stock for unique medical machining applications to ensure consistency from bar to bar. Ultimately, this would ensure minimal deflection during the machining operation and open the door to advanced, hands-off manufacturing of complex and thin-wall geometries.
Changes to EU MDR 2017/745 have been implemented, and medical devices containing more than 0.10 wt% cobalt content require labeling to indicate the presence of cobalt as a potential carcinogenic, mutagenic and reproductive toxin substance. Historical data suggests stainless steel alloys, such as the 300 and 400 families, contain between 0.05 and 0.40 wt% cobalt in a traditional melt, exceeding proposed EU MDR limits. With improved melting cleanliness protocols, effective scrap reuse and recycling controls, we have successfully limited the cobalt levels in several commonly used alloys, per EU MDR requirements. Carpenter can now offer low-cobalt, EU MDR-compliant variations of several commonly used stainless steel alloys for the medical device industry.
Advancing 4D-Printed Nitinol Parts for Orthopedic Applications
Marle Group with Vice President of Sales Frank D. Noone
Nitinol is a shape memory alloy used in medical applications, such as staples and instruments. It can present a shape memory effect (SME) activated by temperature or a superelastic effect with recoverable strains about 10 times higher than conventional alloys. These specific properties are useful to insert and deploy devices during surgery and to provide an active function to the implant.
Conventional shaping of Nitinol is tricky, as it is hard to machine. The achievable geometries are thus derived from tubes, wires or sheets, limiting its extensive use. Limitations can be overcome with 3D printing, allowing geometric complexity and mass customization. Nonetheless, laser powder-bed fusion of Nitinol is challenging, as the alloy is prone to cracking, oxidation and SME behavior shift. We’ve optimized the 3D printing process and post-processing to obtain functional 4D-Nitinol staples. It’s a promising perspective for innovative 4D devices.
What separates good medical device contract manufacturers from the field is passion and the ability to connect with customers. Contract manufacturers need to play to their strengths to win new business. It’s important to build a team that can innovate, collaborate and solve problems.
