Polyetheretherketone (PEEK) is a biocompatible high-performance thermoplastic that can be processed through material extrusion (ME) additive manufacturing (AM) for load-bearing implant applications. In this work, density measurements and compression testing were used to investigate the relation between printing temperatures and deposition patterns of PEEK 3D printed samples. Different deposition patterns were tested with different nozzle and zone heater temperatures to observe how the heat input from the printing process influenced the deposition stability with different nozzle paths. Compression test results showed that samples with concentric-based deposition patterns resulted in higher compressive yield strength and modulus than the rectilinear samples. These results were correlated with the samples’ void contents estimated from density measurements. Both the highest 0.2% offset yield strength of 100.3 MPa and the highest modulus of 3.58 GPa were obtained with an interlayer offset deposition which resulted in reductions in estimated void contents between 48 and 72% in relation to concentric deposition. Different printing temperatures and deposition sequences were tested, where higher printing temperatures resulted in lower yield strength and stiffness. Alternating deposition between the outer and inner lines of the concentric pattern resulted in a reduction of about 43% in void contents and increased elastic modulus and yield strength from 3.12 to 3.40 GPa and 94.4 to 95.2 MPa respectively. The results from this work suggest that the relation between printing temperatures and deposition strategy for different print geometries plays a significant role in the ME-AM of PEEK for high-performance applications.

Polyetheretherketone (PEEK) is the leading high-performance thermoplastic biomaterial that can be processed through material extrusion (ME) additive manufacturing (AM), also known as three-dimensional (3D) printing, for patient-specific load-bearing implant manufacture. Considering the importance of cyclic loading for load-bearing implant design, this work addresses the high-cycle fatigue behaviour of 3D-printed PEEK. In this work, printed PEEK specimens are cyclically loaded under stress-controlled tension–tension using different stress levels between 75% and 95% of printed PEEK’s tensile strength. The experimental results are used to document 3D-printed PEEK’s fatigue behaviour using Basquin’s power law, which was compared with previous fatigue research on bulk PEEK and other 3D-printing materials. As a pioneering study on its fatigue behaviour, the results from this work show that 3D-printed PEEK exhibits an above-average fatigue strength of 65 MPa, corresponding to about 75% of its tensile strength. Fracture surface analysis suggests that a transition can occur from ductile to brittle fracture with maximum stresses between 85% and 95% of the tensile strength. Evidence of crack propagation features on fracture surfaces under scanning electron microscope (SEM) observation suggests crack initiation in void defects created by printing deposition that propagates longitudinally through line bonding interfaces along layers. Considering this, 3D-printed PEEK’s fatigue behaviour can be strongly related to printing conditions. Further research on the fatigue behaviour of 3D-printed PEEK is necessary to support its use in load-bearing implant applications.

Additive manufacturing (AM), also known as 3D printing, offers many advantages and, particularly in the medical field, it has stood out for its potential for the manufacture of patient-specific implantable devices. Thus, the unique properties of 3D-printed biocompatible polymers such as Polylactic Acid (PLA) and Polyetheretherketone (PEEK) have made these materials the focus of recent research where new post-processing and joining techniques need to be investigated. This study investigates the weldability of PLA and PEEK 3D-printed plates through stationary shoulder friction stir welding (SS-FSW) with assisted heating. An SS-FSW apparatus was developed to address the challenges of rotating shoulder FSW of thermoplastics, with assisted heating either through the shoulder or through the backing plate, thus minimizing material removal defects in the welds. Successful welds revealed that SS-FSW improves surface quality in both PLA and PEEK welds compared to rotating shoulder tools. Process parameters for PLA welds are investigated using the Taguchi method, emphasizing the importance of lower travel speeds to achieve higher joint efficiencies. In PEEK welds, the heated backing plate proved effective in increasing process heat input and reducing cooldown rates which were associated with higher crystallinity PEEK. Despite these findings, further research is needed to improve the weld strength of SS-FSW with these materials considering aspects like tool design, process stability, and 3D printing parameters. This investigation emphasizes the potential of SS-FSW in the assembly of thermoplastic materials, offering insights into the weldability of additively manufactured biocompatible polymers like PLA and PEEK.

Polyetheretherketone (PEEK) is a high-performance thermoplastic that, when combined with Additive Manufacturing (AM), presents considerable advantages to produce customizable implantable medical devices. Despite this potential, PEEK's use as an implant material still presents challenges imposed by its bioinert nature. This study investigates the biofunctionalization of 3D-printed PEEK implants to enhance fibroblasts' cellular response due to their important role in the healing of connective tissue post-implantation. Different combinations of biofunctional features were investigated by surface modifying solid, porous, and surface-rough 3D-printed PEEK samples with the sulfonation treatment and incorporation of hydroxyapatite (HA) particles. The porous scaffold construct was designed based on a gyroid surface and then analysed using micro-CT and compression tests. Fibroblast culture assays were conducted to assess the effects of different surface morphologies on cellular adhesion and proliferation. Preliminary data of fibroblast metabolic activity on differently modified PEEK samples was also collected. Results from the experiments suggest that solid PEEK samples with rough surfaces and subjected to both sulfonation and HA incorporation procedures exhibit the most favourable environment for maintaining fibroblasts morphology and viability. Conversely, the lower adhesion and proliferation on smooth as-printed surfaces highlight the necessity for surface functionalization of 3D-printed PEEK. Additionally, results for metabolic activity paired with cell morphologies observed under SEM indicate that large-scale porous scaffolds may present less favourable environment for fibroblasts viability compared to solid surfaces. These findings offer valuable insights to 3D-printed PEEK biofunctionalization towards the improvement of fibroblast response, particularly considering their active role on extracellular matrix formation which is critical for connective tissue support and cohesion during the healing process after surgical implantation.