A comprehensive analysis of high-temperature material extrusion 3D printing parameters on fracture patterns and strength of polyetheretherketone cranial implants

Abstract

A polyetheretherketone (PEEK) cranial implant is one of the most well-known polymeric implants used in cranioplasty. However, most off-the-shelf PEEK cranial implants are developed by molding and then sized into the patient's defect anatomy by machining, which is time-consuming and capital-intensive. On the contrary, 3D printing, specifically material extrusion, can develop patient-specific cranial implants that precisely fit the defect anatomy, ensuring stable fixation and restoring esthetic cranial symmetry. However, 3D printing high-quality, mechanically robust PEEK implants are challenging due to the high thermal processing conditions required for PEEK printing, its high melt viscosity, and its susceptibility to incomplete crystallization. If appropriately attuned, an optimized set of 3D printing conditions can yield high-quality patient-specific PEEK cranial implants with clinically relevant mechanical properties. Hence, in this study, we comprehensively analyzed the effect of essential 3D printing conditions on cranial implants' material and mechanical properties. Specifically, we varied critical 3D printing material extrusion parameters, such as build orientation, nozzle, bedplate, chamber temperature, and print speed, and analyzed their effect on the implants' impact strength. We also used microscopy and Finite Element Analysis to understand the implants' fracture patterns with the impact indentor's impact. Based on our research, we determined an optimized set of 3D printing conditions to yield cranial implants with appropriate impact strength. Our results revealed that specimens printed at 0° build orientation, i.e., parallel to the bedplate, with optimum printing parameters, such as nozzle, bedplate, chamber temperature, and print speed, sustained a peak force of 2034 N. We envision that this study will help implant manufacturers utilize high-temperature material extrusion 3D printing to develop patient-specific PEEK cranial implants with clinically viable mechanical properties.