Ryan Roeder from the University of Notre Dame has reviewed the techniques of incorporating HA and porosity into PEEK for orthopedic and spinal applications. Bioactivity has been conferred to PEEK by the incorporation of calcium phosphate, typically hydroxyapatite (HA) but also Bioglass and tricalcium phosphate, as a coating or filler. Coatings have been applied directly using plasma spray or indirectly using surface treatment to induce apatite deposition in simulated body fluid. A larger number of investigations have studied the use of calcium phosphate fillers to reinforce PEEK. PEEK biomaterials offer a wide variety of opportunities for basic research and product development, which span across materials processing, nano- and microstructural characterization, surface engineering, mechanical behavior, implant design and osteointegration.

PEEK the structural strength and stiffness to provide a stable implant-bone interface.  Thus, it is a good candidate for an all-polymer cervical disc replacement. Initial pin-on-plate wear of PEEK-PEEK pairings has been surprisingly low. The purpose of the present study was to further explore the wear behavior of various PEEK-PEEK pairings, looking for governing principles and tribological limits in order to assess the risk of gross surface damage and/or wear particle-induced osteolysis. Although an all-polymer PEEK implant for cervical disc arthroplasty would be advantageous in terms of medical imaging, the present study suggests that it might also have some tribological risks that need to be addressed in future simulator studies.

Few details have been reported on the mechanical properties of Ti- and Hydroxyapatite-coated medical grade PEEK. In this study from the University of Trento, researchers investigated the influence of plasma spraying on the tensile and flexural properties of PEEK and CFR-PEEK. In order to distinguish the effects induced by sandblasting, representing the first step of plasma spray coating process, mechanical characterization has been carried out also on a set of sandblasted PEEK and CFR-PEEK specimens. Scanning electron microscope (SEM) analysis and adhesion measurements of the coatings were carried out in order to characterize the coatings.

Characterizing the crystallinity in PEEK is critical, since it dictates the mechanical behavior of the polymer. Wide angle X-ray scattering (WAXS) has been typically employed for this purpose; yet, it is impractical for the measurement of some composite materials. Differential scanning calorimetry (DSC) has also been used but with limited accuracy. By comparing FTIR, WAXS and DSC for a range of medical PEEK grades, researchers from Drexel University demonstrate that FTIR can detect changes in crystallinity due to annealing treatments and incorporation of carbon fibers or radiopaque compounds.

The objective of this study was to investigate the tensile fatigue behavior of PEEK with stress concentrations of varying severity and to determine the relative time spent in crack initiation vs crack growth. PEEK OPTIMA LT1™ material was used. Three geometries of circumferentially grooved dogbone specimens were machined and tested. Prior to testing, specimens were pre-conditioned in a 37°C PBS bath for 8 weeks. Fatigue testing to failure (fracture) was performed in a PBS bath at 37°C on an Instron 8511 load frame. This work found that crack propagation lifetime was a minor part of the total lifetime for the moderate and deep notch geometry conditions.