Introduction: The ability to manufacture implants at the point-of-care has become a desire for clinicians wanting to provide efficient patient-specific treatment. While some hospitals have adopted extrusion-based 3D printing (fused filament fabrication; FFF) for creating non-implantable instruments with low-temperature plastics, recent innovations have allowed for the printing of high-temperature polymers such as polyetheretherketone (PEEK). Due to its low modulus of elasticity, high yield strength, and radiolucency, PEEK is an attractive biomaterial for implantable devices. Though concerns exist regarding PEEK for orthopaedic implants due to its bioinertness, the creation of porous networks has shown promising results for bone ingrowth.

In this study, we manufacture porous PEEK constructs via clinically-used FFF. We assess the mechanical characteristics of this novel biomaterial, including the strength, elastic modulus, porosity, and surface roughness. We also examine the effect of porous geometry on preosteoblast viability and proliferation compared to 3D printed solid PEEK. The work represents an innovative approach to advancing point-of-care 3D printing and introduces a potential new porous biomaterial for use in bone ingrowth applications.

Methods: Three porous constructs – a rectilinear pattern and two triply period minimal surface (TPMS; gyroid-type and diamond-type) - were designed to mimic the morphology of trabecular bone with 600 µm pores and variable porosity. The structures, along with solid PEEK samples for use as a control, were manufactured via FFF using PEEK. The samples were imaged via micro-CT (n = 4 each geometry) to determine the resulting pore size and porosity, and surface roughness was assessed using optical profilometry. Surface contact angle measurements were measured through the sessile drop technique. Porous cubes were then tested in static compression, and the stress-strain behavior was plotted to determine the yield strength and elastic modulus of each geometry. The PEEK constructs were seeded with pre-osteoblast cells for 7 and 14 days (n = 6 for each geometry/timepoint). Cell proliferation and alkaline phosphatase activity (ALP) were evaluated at each time point, and the samples were imaged via scanning electron microscopy (SEM).

Results: Micro-CT imaging showed the pores in the PEEK constructs to be open and interconnected (100% average interconnectedness for each geometry). The average pore size was 535 ± 92 µm for the rectilinear, 484 ± 237 µm for the diamond, and 669 ± 216 µm for the gyroid. Porosity was 71% for the rectilinear, 76% for the diamond, and 68% for the gyroid. Average pore size and porosities of the scaffolds showed no significant difference (p \> 0.05) when compared to the as-designed size. Contact angles, an indicator of surface wettability, were greatest for the rectilinear surface (99.9° ± 7) and smallest for the diamond (52.2° ± 5).

Normalized ALP activity of the three porous PEEK samples at 7 days were found to be significantly greater than the solid sample (p \< 0.05 rectilinear, p \< 0.005 gyroid, p \< 0.001 diamond). At 14 days, the same relationships were observed (p \< 0.001 for all three designs). No difference between the three geometries was found. SEM imaging revealed cells with flat, elongated morphology attached to the surface of the PEEK. The 14-day samples appeared to have proliferated well and spread along the PEEK pores. Extensions of filopodia and lamellipodia were observed along with large blankets of cells covering the PEEK surface.

Discussion: We demonstrated the ability of FFF printing to create accurate porous PEEK structures with properties in the range of trabecular bone. We also demonstrated the ability of the PEEK surfaces to support cellular processes necessary for bone-implant fixation, thus establishing a potential new biomaterial for orthopaedic and other bone ingrowth use.


3D Printed Porous Peek Created via Fused Filament Fabrication for Osteoconductive Orthopaedic Surfaces

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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