Mechanical Performance and Microstructural Evaluation of FDM-Manufactured PEEK, CFR-PEEK, and PA12: Implications for Patient-Specific Cranioplasty

The clinical demand for patient-specific cranial implants has driven a transition from traditional autogenous bone grafts to advanced alloplastic materials. In cranioplasty, the selection of materials that balance biocompatibility with precise mechanical performance is critical to ensure brain protection and long-term stability. This study evaluates the mechanical properties and microstructural quality of four high-performance polymers widely used in biomedical applications: Polyamide 12 (PA12), Polyether ether ketone (PEEK), and PEEK reinforced with a 10% of carbon fiber (PEEK-CF10). 

Standardized specimens were fabricated using Fused Deposition Modelling (FDM), a cost-effective additive manufacturing technique ideal for personalized medicine. To assess the influence of process-induced anisotropy, samples were printed in two distinct orientations: horizontal (XY plane) and vertical (YZ plane). Tensile and flexural tests were conducted according to ISO 527 and ISO 178 standards, respectively. Furthermore, Scanning Electron Microscopy (SEM) was employed to characterize the fracture surfaces, evaluating filament adhesion, porosity, and fibre-matrix interaction in the reinforced composite.

Preliminary experimental results revealed that perimeter-dominated specimens with a wider wall thickness achieved optimal flexural performance, reaching higher strength and modulus. Extended filament drying (>6 h) enhanced flexural strength by around a 20%, whereas prolonged inter-layer cooling during multi-part printing significantly compromised mechanical properties.

In a subsequent stage, we integrated these characterization data into a CAD/CAM workflow to design and fabricate a high-fidelity anatomical skull model featuring a custom cranial implant. We validated the structural integrity of the resulting assembly through Finite Element Analysis (FEA) and experimental physical testing, to ensure that the digital predictions aligned with the mechanical behaviour of the 3D-printed prosthesis under physiological loading conditions.

These findings provide essential data for optimizing 3D-printed cranial prostheses to ensure they meet the demanding physiological requirements of craniomaxillofacial reconstruction.