The long-term mechanical integrity of non-reinforced PEEK-OPTIMA polymer for demanding spinal applications: experimental and finite-element analysis

Abstract

Polyetheretherketone (PEEK) is a novel polymer with potential advantages for its use in demanding orthopaedic applications (e.g. intervertebral cages). However, the influence of a physiological environment on the mechanical stability of PEEK has not been reported. Furthermore, the suitability of the polymer for use in highly stressed spinal implants such as intervertebral cages has not been investigated. Therefore, a combined experimental and analytical study was performed to address these open questions. A quasi-static mechanical compression test was performed to compare the initial mechanical properties of PEEK-OPTIMA polymer in a dry, room-temperature and in an aqueous, 37 degrees C environment (n=10 per group). The creep behaviour of cylindrical PEEK polymer specimens (n=6) was measured in a simulated physiological environment at an applied stress level of 10 MPa for a loading duration of 2000 hours (12 weeks). To compare the biomechanical performance of different intervertebral cage types made from PEEK and titanium under complex loading conditions, a three-dimensional finite element model of a functional spinal unit was created. The elastic modulus of PEEK polymer specimens in a physiological environment was 1.8% lower than that of specimens tested at dry, room temperature conditions (P<0.001). The results from the creep test showed an average creep strain of less than 0.1% after 2000 hours of loading. The finite element analysis demonstrated high strain and stress concentrations at the bone/implant interface, emphasizing the importance of cage geometry for load distribution. The stress and strain maxima in the implants were well below the material strength limits of PEEK. In summary, the experimental results verified the mechanical stability of the PEEK-OPTIMA polymer in a simulated physiological environment, and over extended loading periods. Finite element analysis supported the use of PEEK-OPTIMA for load-bearing intervertebral implants.

Do Surface Porosity and Pore Size Influence Mechanical Properties and Cellular Response to PEEK?

“…However, further work is needed to understand the compressive properties of the surface porous layer. Additionally, all mechanical tests were performed in air at room temperature; however, we expect the behavior to be comparable in a more physiologic environment [11]. Third, we have not exclusively singled out pore size as a factor because other parameters also change with pore size (such as layer thickness) ( Table 1).…”

PEEK biomaterials in trauma, orthopedic, and spinal implants

“…Although many papers describe the use of CFR-PEEK for spine implants, the majority of implants involve the use of neat PEEK for both cervical and lumbar spinal cages [11,[140][141][142][143][144][145][146][147]. Because the use of neat PEEK for spine is a relatively recent development, the published literature is generally limited to in vitro biomechanical studies [145][146][147], or shortterm outcomes in animal studies or human clinical trials [11,[140][141][142][143].…”

“…Because the use of neat PEEK for spine is a relatively recent development, the published literature is generally limited to in vitro biomechanical studies [145][146][147], or shortterm outcomes in animal studies or human clinical trials [11,[140][141][142][143]. Recent studies with PEEK cages have looked to improve or accelerate fusion performance by combining the devices with the use of hydroxylapatite [143], 40% β-tricalcium phosphate/60% hydroxylapatite [141], or rhBMP-2 on a collagen sponge [11].…”

The influence of metal artifacts on navigation and the reduction of artifacts by the use of polyether-ether-ketone

“…Polyether-ether-ketone (PEEK OPTIMA Õ ) is a key component in a number of implants [16][17][18] because of the several advantages it offers, including adaptability to sterilization, radiolucency, and superior mechanical properties. The use of PEEKbased instruments in our experiments resulted in improved precision of anatomic pair-point registration as compared to steel or titanium implants.…”