The use of PEEK (polyetheretherketone) implants in spinal surgery is again gaining momentum, marking a comeback for this proven material. Introduced in the 1990s, PEEK gained traction for its biocompatibility, radiolucency, and mechanical similarity to human bone. The material was FDA-approved in 1998 and, since then, studies have showcased its high fusion rates and positive patient outcomes, solidifying PEEK spinal cages as the gold standard by the 2010s.

By the mid-2010s, advancements in spinal implant design, including porous structures for enhanced osseointegration, challenged traditional PEEK manufacturing methods like machining and molding. These methods struggled with customization and the production of complex geometries, which was becoming more apparent, especially with the rise of patient-specific care. As in many other industries, 3D printing has emerged to respond to these challenges.

Due to the high temperatures and stringent conditions required for printing PEEK, it took time for 3D printing technology to mature to the point where it could reliably process such a high-performance material in complex geometries. Further, it is not just the equipment that is required, but the overall proprietary process to produce high-quality porous PEEK cages had to be perfected. The difference advanced technology brings is striking even to the naked eye, so let’s explore what stands behind the new generation of PEEK spine cages. 

Why PEEK?

First, let’s address why PEEK is being used for spinal applications. PEEK is biocompatible and has an established history of success in spinal surgeries, making it a staple material in implantable medical devices. PEEK can be enhanced with fillers like biphasic calcium phosphate (BCP) or hydroxyapatite (HA), which has been said to promote bone ingrowth for stronger, faster fusions. Its radiolucency allows for unobstructed postoperative imaging. Finally, PEEK’s mechanical properties are remarkably similar to human cortical bone, which has been found to minimize stress shielding and enable natural load-sharing, contributing to successful fusion outcomes.

The New Generation of PEEK Spine Cages

Extensive research and monitoring of clinical outcomes help to identify the ideal profile of spine implants. With that, a new generation of spinal cages are being introduced thanks to 3D printing. The additive manufacturing process allows production without compromise on their design. The new cages will be defined by several factors. 

• Open porous structures that promote bone integration
• Osseointegrative PEEK variants (BCP/HA enhanced) that promote bone growth
• Designs that represent tailored structural solutions with dense areas taking the load only where needed

For the first time, while leveraging 3D printing, we can rethink implant design by choosing from various lattice structures that establish a baseline of mechanical properties for the cage. By strategically adding dense areas, the stiffness and strength of the cage can be precisely tailored to meet specific surgical and patient needs. This allows for unparalleled control over implant properties, ensuring each cage is optimized for load distribution and fusion outcomes. This process enables the production of spinal cages that are not only functionally superior but also more adaptable to evolving clinical requirements. 

Processing PEEK 

Extrusion technology: Most printers that process PEEK leverage extrusion-based 3D printing technology. The printed spine cages have to be compliant with the ASTM 2026 and F2077 standards for PEEK spinal implants, which are critical guidelines for evaluating the quality and performance of implantable medical devices. Thanks to technological advances, there are 3D printing solutions that show above-standard results. These are not only observed with print time (in manufacturing, print time matters; 15 minutes for one cervical spine cage), but also for printing in all three directions (XYZ), which is rare for extrusion technology.

Application development: The excellence of PEEK for clinical application is only comparable to the degree of complexity required to print it. The material behaves differently depending on geometries and part sizes, which is why highly specific printing parameters are required for each application. Full control must be leveraged over the extrusion techniques, temperature management, calibration, etc.

Temperature control: Temperature control is critical for processing implant-grade PEEK types. Due to their rapid crystallization, precise temperature management is essential to achieve strong mechanical properties, particularly interlayer bonding. A sophisticated temperature management system with precise airflow control in the build chamber is required to create the right environment for crystallization. Such a system can not only ensure a homogeneous temperature distribution but also filter the air to maintain a cleanroom environment and prevent contamination in porous structures.

Calibration: With every 3D printer, calibration is a prerequisite for successful, predictable performance. The temperature, which is the crucial aspect of printing with PEEK, should be adjusted to the highest possible degree of tolerance. 

All these factors considered together contribute to a successful manufacturing process. With 3D printing, medical device manufacturers can produce 3D-printed PEEK spinal cages that are not only technologically superior but also economically viable. This democratization of cutting-edge medical technology empowers more surgeons and medical device manufacturers to adopt 3D printing to help improve patient care. 

The Future with 3D Printing 

Compared to traditional manufacturing methods, 3D printing significantly reduces the time required for complex geometries, drastically reducing production and wait times for custom implants without compromising structural integrity or performance. This streamlined production process means healthcare facilities can benefit from faster turnaround times, ultimately providing patients with quicker access to life-enhancing implants.

As the quality of spine cages increases with the development of advanced 3D printing technologies, spinal surgeries are set to benefit from customized implants that can meet individual patients’ needs more precisely. The sheer ability for such spinal cages to be manufactured is setting a new standard for implants and patient care.

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Stefan Leonhardt, Ph.D., is director, Medical Devices, for 3D Systems. In this role, he leads the company’s efforts focused on 3D printing with high-performance medical polymers. Dr. Leonhardt joined 3D Systems in 2022 through the acquisition of Kumovis, a company he co-founded with four colleagues in 2017. While at Kumovis, he and his colleagues developed the first 3D-printing platform specifically designed for medical device production, now known as 3D Systems’ EXT 200 MED. Dr. Leonhardt studied medical engineering at the Technical University of Munich. He holds an MBA with a focus on digital transformation and new business models. Dr. Leonhardt also earned a Ph.D. for his work on material development for resin-based 3D-printing technologies for the development of bioreactors.