Implantable PEEK materials can be processed into different forms using a variety of manufacturing methods. Extruded thin-walled tubing is one such example.

For well over a decade, poly-ether-ether-ketone, better known as PEEK, has been used as an effective biomaterial for implantable medical device applications. During this relatively short period of time, specific grade offerings have greatly expanded and the the variety of implantable devices utilizing PEEK materials has experienced a steady growth in the marketplace. Spinal cages, bone fixation screws, cardiac and neurological leads, and dental implants are a few examples of how PEEK has been successfully implemented into implant designs. What makes PEEK the favored material choice for so many new applications, and what makes it such a viable biomaterial? PEEK's biocompatibility, physical properties, and versatility all play a part. This article will highlight the characteristics of PEEK and examine specific areas where it has been used successfully. It also will identify the attributes that differentiate PEEK from other legacy biomaterials.

Biocompatibility and biostability
PEEK has a number of intrinsic properties well-suited to an implantable device. As is the case for any biomaterial, the key attribute is biocompatibility. If a material has not proven its ability to be readily accepted by the body, or breaks down in the body over time (save materials that purposefully break down, such as bio-absorbable materials), it would obviously be considered a poor material choice. However PEEK, when properly manufactured and processed, has displayed neither of these deficiencies. In fact, numerous independent studies have shown the long-term compatibility of PEEK in the human body1, 2, 3, 13, 15. Furthermore, the excellent chemical resistance of PEEK has allowed it to be utilized anywhere in the human body, and over the patient’s lifetime, no relevant degradation in physical properties has been observed4, 5, 13, 15. Additional research has shown that, even after a patient is deceased, the soft tissues and bones of the patient are likely to decompose long before a PEEK implant would degrade. As a result, PEEK reduces significant risks a medical device company must face when choosing an implantable material.

Medical submarkets including spinal, orthopedic, cardiac, and neuroscience have successfully implemented PEEK into device designs.

Mechanical properties
The mechanical properties of PEEK also help make it a desirable biomaterial choice. In the realm of polymers, it is universally recognized for its strength and stiffness. Since PEEK’s inception, it has been used in numerous applications as a replacement for historically utilized metals, such as titanium and stainless steel. As a frame of reference, a typical unfilled PEEK material has a tensile strength around 100MPa, with a modulus around 4 GPa. Chopped carbon-filled PEEK materials can have tensile strengths above 200MPa, and moduli over 20GPa. This makes it a great choice for many structural applications, as evidenced by the fact that the largest market for PEEK materials today is in the spinal fusion market. Recent statistics show that spinal fusion applications represent as much as 75% of PEEK’s usage, as expressed in revenue6.

A review of the data reveals that PEEK’s modulus, or stiffness, is very similar to that of bone. In fact, PEEK can be tailored using structural additives to match the modulus of both cortical and cancellous bone density7. This match in modulus makes it a logical choice for many bone replacement applications. PEEK’s use helps avoid potential issues such as stress shielding and bone resorption, which are often seen with stiffer materials such as stainless steel and titanium14, 15. This is one of the key reasons for the increased use of PEEK materials in the spinal, dental, and trauma markets today.

Other desirable mechanical properties of PEEK include favorable fatigue, creep, and wear performance. There are numerous studies that have reviewed PEEK’s performance in these areas. Test results per ASTM and ISO are generally available, as well as specific test information in a number of application areas such as in joints, the spine, and other orthopedic areas of interest. Many of these studies are publicly available or can be accessed by contacting implantable PEEK material suppliers directly. In any regard, PEEK’s performance when compared to other materials choices tend to be excellent, adding to the list of inherent characteristics that make PEEK such a favorable material choice8, 9, 13, 14, 15.