While machined PEEK interbody fusion devices have been used for spinal fusion treatments with positive results since the early 2000's (Kurtz, 2012), interest in PEEK for total joint arthroplasty (TJA) has recently been growing (Du et al., 2018 de Ruiter et al., 2017 Cowie et al., 2016). PEEK has a modulus of elasticity similar to bone, high yield strength and fatigue resistance, and natural radiolucency, making it an attractive biomaterial for implantable medical devices (Panayotov et al., 2016 Honigmann et al., 2018). While FFF has thus far been suitable only for low temperature plastics, recent innovations in FFF have allowed for the printing of high temperature, implantable polymers such as polyetheretherketone (PEEK), opening the door for more advanced osteoconductive surfaces. Even the dominant method for creating AM osteoconductive scaffolds, laser-based metal sintering, comes with significant cost and safety considerations, unlike the extrusion-based fused filament fabrication (FFF) method already being used in-hospital to create custom non-implantable instruments. However, there are reported drawbacks to many of these materials, including dimensional inaccuracy and inadequate mechanical properties (Bobbert et al., 2017 Yang et al., 2019 Lin et al., 2019). AM methods already have a history of use for creating synthetic osteoconductive materials that, in addition to avoiding morbidities related to auto- or allografts, can be bio-functionalized and highly customized (Bobbert et al., 2017 Yang et al., 2019 Lin et al., 2019). This is especially true for osteoconductive surfaces used for orthopaedic implant surfaces or bone defect repair, which benefit from complex trabecular-like morphology not achievable by traditional manufacturing.

In recent years, clinical interest in additive manufacturing (AM), or 3D printing, of biomaterials has been rapidly growing. SEM imaging revealed cells attaching to and bridging micro-topological features of the porous constructs, and cell activity was significantly greater for the porous PEEK compared to solid at multiple time points. Average compressive properties ranged from 210 to 268 MPa for elastic modulus and 6.6–17.1 MPa for yield strength, with strength being greatest for TPMS constructs. μCT imaging showed the porous networks to be open and interconnected, with porous sizes similar (p > 0.05) to the as-designed size of 600 μm. The samples were then imaged via scanning electron microscopy (SEM) to observe cell morphology. The porous PEEK, along with 3D printed solid PEEK, was then seeded with MC3T3-E1 preosteoblast cells for evaluation of cell proliferation and alkaline phosphatase (ALP) activity. The material characteristics, including porosity, yield strength, and roughness, were evaluated using μCT, static compression testing, and optical profilometry. The designs of the porous structures were based on a simple rectilinear pattern as well as triply periodic minimal surfaces (TPMS), specifically gyroid and diamond types. In this study, we created porous PEEK via clinically-available fused filament fabrication (FFF, 3D printing) and assessed the pore structure morphology, mechanical properties, and biologic response.

Though concerns exist regarding PEEK for orthopaedic implants due to its bioinertness, the creation of porous networks has shown promising results for interaction with surrounding tissue.

Vestakeep Fusion is to be offered as both a granulate and a semifinished stock-shape product, which can be milled, compression-moulded and extruded.Due to its unique and advantageous material properties, polyetheretherketone (PEEK) is an attractive biomaterial for implantable devices. It instead provides a natural shadow for accurate placement and observation of the fusion process, the supplier explained. One grade of the biomaterial, 'Vestakeep iC4800', is said to offer mechanical characteristics similar to human bones while avoiding artifacts in imaging processes such as X-ray or MRI. It promotes the faster adhesion of bone cells to implants to positively influence fusion at the boundary between the two, which in turn accelerates convalescence, Evonik said. The osteoconductive properties were achieved with the additive biphasic calcium phosphate. It plans to target such applications with its 'Vestakeep Fusion' brand products, which are scheduled to be unveiled at the virtual 'Eurospine' conference on 6-9 October 2020. German chemicals company Evonik Industries (Essen has announced the development of a new osteoconductive polyether ether ketone (PEEK) that improves the fusion between bones and implants.

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