The ability to create patient-specific implants (PSI) at the point-of-care has become a desire for clinicians wanting to provide affordable and customized treatment. While some hospitals have already adopted extrusion-based 3D printing (fused filament fabrication; FFF) for creating non-implantable instruments, recent innovations have allowed for the printing of high-temperature implantable polymers including polyetheretherketone (PEEK). With interest in FFF PEEK implants growing, it is important to identify methods for printing favorable implant characteristics such as porosity for osseointegration. In this study, we assess the effect of porous geometry on the cell response and mechanical properties for FFF-printed porous PEEK. We also demonstrate the ability to design and print customized porous implants, specifically for a sheep tibial segmental defect model, based on CT images and using the geometry of triply periodic minimal surfaces (TPMS). Three porous constructs – a rectilinear pattern and gyroid/diamond TPMSs – were designed to mimic trabecular bone morphology and manufactured via PEEK FFF. TPMSs were designed by altering their respective equation approximations to achieve desired porous characteristics, and the meshes were solidified and shaped using a CAD workflow. Printed samples were mCT scanned to determine the resulting pore size and porosity, then seeded with pre-osteoblast cells for 7 and 14 days. Cell proliferation and alkaline phosphatase activity (ALP) were evaluated, and the samples were imaged via SEM. The structures were tested in compression, and stiffness and yield strength values were determined from resulting stress-strain plots. Roughness was determined using optical profilometry. Finally, our process of porous structure design/creation was modified to establish a proof-of-concept workflow for creating PSIs using geometry established from segmented sheep tibia CT images.Introduction
Methods
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 endeavor to manufacture porous PEEK constructs via clinically-used FFF. We assess the effect of porous geometry on cell response and hypothesize that porous PEEK will exhibit greater preosteoblast viability and activity compared to solid PEEK. The work represents an innovative approach to advancing point-of-care 3D printing, cementless fixation for total joint arthroplasty, and additional applications typically reserved for porous metal. Three porous constructs – a rectilinear pattern and two triply period minimal surface (TPMSs) - were designed to mimic the morphology of trabecular bone. The structures, along with solid PEEK samples for use as a control, were manufactured via FFF using PEEK. The samples were mCT scanned to determine the resulting pore size and porosity. The PEEK constructs were then seeded with pre-osteoblast cells for 7 and 14 days. Cell proliferation and alkaline phosphatase activity (ALP) were evaluated at each time point, and the samples were imaged via SEM.Introduction
Methods
Initially, all the femoral canals were prepared with the routine cementless fixation technique modified by the author (rasp-ream-rasp technique). With insertion of the final-size rasp, reliable fixation was not obtained possibly due to poor bone quality or inherent canal geometry. To avoid fracture with insertion of the next-sized stem, bone cement was added as gap-filler to augment fixation of the final-sized stems.
