3D printed PEEK implants: Spinal fusion and beyond
Mark Brady, programme leader - spine at Invibio, explain why PEEK is gaining in popularity and what is coming next for this technology as 3D printing capabilities improve.
Today people are living and staying active longer and expecting more quality of life than ever before. This has been made possible, in part, by advancements in material sciences - including breakthroughs in implant devices designed to support the human body.
The challenge for device manufacturers has been to develop implants that mimic the inherent properties of the human skeleton. This is particularly critical for spinal implant applications, as the spine carries constant load whilst still allowing flexibility in bending and twisting. Spinal implants must be durable, integrate well and share load with the surrounding bone, and be well-tolerated by the human body.
Two advancements, which have evolved over the past 30 years have dramatically improved the quality and choice of surgical implants: The introduction of PEEK (polyetheretherketone) polymers and the development of additive manufacturing (3D printing) technology.
Advantages of PEEK
Spine cages have historically been machined from solid titanium, due to its strength and biocompatibility. In the early 2000s however, Invibio Biomaterial Solutions recognised the potential of PEEK in the medical device sector where today its PEEK-OPTIMA polymers have been used in more than 15 million implanted devices. Key elements to PEEK’s popularity, in spinal fusion applications, include:
- Strength and stiffness: High strength-to-weight ratio, with a modulus similar to bone that reduces stress shielding and leads to improved physiological loading.
- Biocompatibility: Required to meet the applicable requirements of ISO 10993 and USP for long-term implantation. A metal-free alternative, avoiding hypersensitivity issues associated with some metals.
- Radiolucency: Enables clear imaging on simple X-rays to allow accurate monitoring of fusion progression whilst eliminating the need for more complex and costly CT scans. When CT and MRI scans are required, PEEK also has advantages as metal implants can result in artifacts which can reduce the image quality and make it challenging to obtain clear diagnostic information.
- Sterilisation resistance: PEEK can undergo repeat sterilisation by steam, ethylene oxide or gamma irradiation without degradation in mechanical properties or biocompatibility.
3D printing PEEK
The unique benefits of PEEK have been complemented by more recent innovations in additive manufacturing technologies, providing device manufacturers with greater design freedom. Access to new processing routes and new PEEK forms, including filaments, allows the creation of complex porous architectures that have the potential for improved bone in-growth, or other features that add greater functionality to devices with the potential to improve patient outcomes. It’s also a win for sustainability given that additive manufacturing typically uses less material than conventional subtractive manufacturing routes. That means making high-end products with fewer components, less weight, and less waste.
Invibio offers implantable PEEK filaments to customers with access to their own additive manufacturing technology, wishing to develop devices. Invibio’s parent company Victrex has also invested in BOND3D who have a novel additive manufacturing process, and together they co-develop with device manufacturers to bring their designs to market.
In contrast to similar extrusion-based PEEK additive manufacturing processes, BOND3D’s unique technology utilises a combination of flow- and pressure-controlled printing to deliver parts that are virtually void less and deliver the high isotropic strength required for interbody fusion applications.
Expanding horizons: 3D printed PEEK implants beyond the spine
The versatility of 3D printed PEEK implants extends far beyond spinal fusion applications such as total joint replacement, craniomaxillofacial implants, trauma plates and bone void defects.
With a growing interest in metal-free solutions in various medical applications, including knee replacement and trauma care, the advent of new additive manufacturing techniques ushers in a new era of possibilities. Unlike metals, PEEK can be compounded with other materials to tailor its properties to the application. Combining 3D printing with PEEK incorporating bioceramics offers the potential for complex porous PEEK structures that play an active part in osteoconduction and the healing process. Compounding with carbon fibres can also help tailor strength and stiffness properties to match the needs of the application. Each of these may bring advantages, not just in mass production, but also in patient-specific devices produced by traditional device manufacturers, or at point of care at hospitals.
High-performing polymers are crucial to fulfil these needs and PEEK, on its own or combined with other compounds such as carbon fibre, will play a significant role in the industry. As the field of material sciences continues to advance, innovative surgical implant devices are redefining possibilities. These breakthroughs not only extend and improve the lives of individuals but also empower them to maintain an active and fulfilling lifestyle.