Papers by Keyword: PEEK

Abstract: Background: Knee joint replacement surgery is a widely used procedure for managing severe knee osteoarthritis, rheumatoid arthritis, and traumatic arthritis. The selection of implant materials plays a crucial role in the long-term success of the procedure, influencing biomechanical stability, biocompatibility, and wear resistance. Polyether ether ketone (PEEK), a high-performance thermoplastic polymer, has recently gained attention as a potential alternative to conventional metal and polymer implants due to its closer elastic modulus to human bone, excellent biocompatibility, and radiolucency. However, the intrinsic bio-inertness and wear resistance limitations of PEEK have raised concerns regarding its early osseointegration and long-term durability. Methods: To overcome these challenges, researchers have explored various modifications, including bioactive coatings, composite reinforcement, and porous structuring, to enhance it clinical performance. This review evaluates the current applications of PEEK in knee surgery, comparing its properties with commonly used materials such as ultra-high-molecular-weight polyethylene (UHMWPE), cobalt-chromium (CoCr), and titanium. Results: We analyze its role in procedures such as high tibial osteotomy (HTO) and anterior cruciate ligament reconstruction (ACLR). While PEEK demonstrates promising mechanical and biological advantages, further studies on long-term performance, wear behavior, and improved osseointegration techniques are essential to determine its suitability as a standard implant material in knee surgery. Conclusions: PEEK has the potential to serve as an alternative implant material for knee joint replacement due to its biomechanical compatibility and favorable biological properties. However, addressing its bio-inertness and wear resistance limitations through material modifications remains a key area for future research.

Abstract: PEEK is a thermoplastic polymer widely employed in the orthopedic field for the fabrication of prosthetic devices, owing to its Young’s modulus being comparable to that of cortical human bone. Surface functionalization through biomaterial micropatterning represents an effective strategy to enhance osteointegration. To this end, an innovative vibration-assisted surface embossing process was applied to PEEK samples. The surface patterning was performed using a square punch with a side length of 0.5 [mm], fabricated via CNC milling. The process is enabled by a linear actuator capable of generating controlled vibrations to induce localized sub-Tg heating of the polymer surface. After that, the application of a post-load is required for the embossing stage. This system allows frequency tuning in the range of 1–4 [kHz]. Finally, the patterned surfaces were sonicated through an ultrasound cleaner and characterized through contact angle measurements and white-light interferometry, confirming the feasibility of the process and demonstrating an increase in both the polar component of the surface free energy and the hydrophilicity compared with merely polished specimens. Enhancing the polar component of surface free energy is an effective strategy to improve biomaterial biocompatibility, confirming the relevance of the proposed surface modifications. Slightly hydrophilic surfaces promote preferential osteoblast adhesion and stable cytoskeletal organization, demonstrating the complementary roles of surface topography in shaping cellular responses.

Abstract: Complex geometry components fabricated through Fused Filament Fabrication in polyether ether ketone exhibit very interesting performances, but they are very difficult to predict. Non-standard mechanical tests allow for estimating a global structural response and do not provide local information about the failure evolution. This work investigates the integration of a Digital Image Processing method with non-standard mechanical test to improve the knowledge of the component performance through the tracking and the analysis of local failures. This way, a targeted redesign of the component can be provided: in this work the component was modified at manufacturing stage by changing the Fused Filament Fabrication infill, and at optimization stage by employing a stress line approach for locally densifying the interior.

Abstract: The human skull can become fractured or injured through impact and often requires repair through a craniectomy and subsequent cranioplasty, surgery performed to repair defects or damage to the cranium. Challenges related to material choice, which must be biocompatible, and customization for each patient’s anatomy remain. One possible solution is fabrication of patient-specific cranial implants, out of biocompatible polymers, using single point incremental forming (SPIF). In this paper, polyetheretherketone (PEEK) and ultra-high molecular weight polyethylene (UHMWPE) are formed using SPIF at room temperature to manufacture a cranial implant. The SPIF process is used to produce formed parts from which test specimens were extracted to evaluate the tensile performance and thermal properties. Formed cranial implants were impacted using a drop weight to evaluate their suitability under relevant conditions. The geometric conformance of the SPIF process was studied to compare the material behavior for the specified polymers after forming. The results validate that SPIF can be conducted at room temperature with PEEK and UHMWPE biocompatible polymers to enable custom implant manufacturing. However, PEEK exhibited superior performance in terms of tensile strength, geometric conformance, energy absorption, and melting temperature, and is recommended over UHMWPE for future implant applications.

Abstract: A single pocket cage is the SKF product, which is used in Large Size Bearings for wind industry. The function of a bearing cage is to hold, guide and separate rolling elements, and differently from the conventional cage, the current one consists of segments, which eases the bearing assembly and reduces its weight. The long life challenge (25 years!) requires considering fatigue, and since the single pocket cage is made of PEEK polymer, it is also susceptible to creep (in near room temperature), which enhances fatigue damage. The current work proposes the numerical model capturing non-linear viscoelasticity of PEEK. The mechanical behavior of this material is identified in uniaxial tension test and is modeled in Finite Elements (FE) by means of the Parallel Rheological Framework (this numerical tool has been recently implemented in the commercial software ABAQUS). The current FE model enables to apply cyclic loading, simulating the material response of cage when it operates in running bearing. By applying sub-modeling technique only a small domain is modeled which improves the computational time efficiency. The sub-model domain corresponds to the cage region, where the stress is high resulting to the material yielding, fatigue/creep degradation (due to inelastic cyclic deformation) and initiation of fatigue crack. The FE results were combined with the test data, in attempt to relate the numerically predicted damage to the cage life. The development of irreversible deformation during cyclic loading, shakedown analysis and the stress volume effect, are the main focuses of the current work.

Abstract: Polyether ether ketone (PEEK) was printed via FDM using gyroid, line, and tri-hexagon infill patterns. Its effect on the mechanical behavior (tensile, flexural and compression) and the investigation of void percentage and orientation angles within the internal structure were studied. The line pattern showed the highest tensile strength at 55.46 MPa due to its internal structure with a higher number of deposited layers oriented along the direction of the stress enabling higher stress absorption, the laminate theory. The angular lines on both tri-hexagon and gyroid patterns provided disadvantage as supported by Timoshenko's theory where the internal structures acted like a beam which is prone to easier deformation. Line pattern also demonstrated the highest flexural strength at 103.67 MPa. The continuity of the pattern along the internal structure perpendicular to the direction of the force provided more effective transfer of stress. However, the highest compressive load was observed in gyroid pattern with 8,266.89 N. The redundancies in the internal structure design of gyroid pattern enabled more compression load absorption. Symmetry and internal angles in gyroid and tri-hexagon patterns allowed more compressive force which are more susceptible to fractures due to higher strains created. Lastly, void percentage showed line pattern with the lowest at 1.53%. In addition, the mean void orientation angle showed that the closer it is to 0^o, the weaker the part.

Abstract: This article presents an experimental investigation of biocompatible Polyether ether ketone (PEEK) polymeric sheet deformed using Single Point Incremental Forming (SPIF) at room temperature, with the objective of manufacturing a cranial medical implant. The investigation was performed in terms of formability and failure within the principal strains space, being the material Forming Limit Diagram (FLD) assessed by means of Nakajima tests. This material characterization allowed to obtain the formability limits at necking and at fracture of PEEK polymeric material. In addition, an experimental work plan in SPIF was performed in terms of spifability (or formability in SPIF) with the aim of determining the effect of the main process parameters on the spifability, modes of failure, and temperature, among others. As a result, an optimum set of parameters along with the established methodology were used for manufacturing a cranial medical implant made of this high-performance and biocompatible polymeric material. The work primarily shows the feasibility of manufacturing PEEK medical prostheses and implants using SPIF.

Abstract: The 3D printing technology is being applied more and more every day, this is a consequence of its applicability and low waste generation, becoming one of the best options to obtain good quality pieces. Sometimes, post machining processes are necessary to fulfil tight tolerances or achieve complex geometries by means of the connection between different pieces printed using this technology. The field of knowledge and studies focused on 3D printing is in constant evolution. There are plenty of materials that can be used to apply 3D printing technology. Among them, PEEK is one of the best options when good mechanical properties are required. Being applied in aeronautic or automobile industry, is also used in biomedical applications, such as prosthesis or mechanical components among others. Within the machining processes, milling, turning, and drilling are the most widespread. Orthogonal cutting is a machining process in which the cutting edge of the tool is perpendicular to the cutting speed, and it is commonly used when a simple and pure study of the mechanism behind a material removal process is required. In this study, tests that analyze the orthogonal cutting on 3D printed PEEK samples using different orientations (0o and ±45o) have been conducted. The influence of cutting speed (30, 60 and 90 m/min) and depth of cut (50, 100 and 150 μm) is studied through the analysis of cutting forces and surface finish quality. As a general approximation, it can be seen that the fiber orientation affects significantly to the forces monitored but unexpectedly, lightly to the surface finish.

Abstract: Start-stop rolling contact fatigue tests of PEEK-PTFE hybrid radial bearings were carried out, to investigate the influence of start-stop heat cycle on the friction coefficient of PEEK-PTFE hybrid radial bearings. It was found in all start-stop tests, the temperature of sample side increased as the friction coefficient increased. RCF cycles to reach 50 °C of the third start-stop phase clearly increased from the second start-stop tests, and then kept constant value.

Abstract: In order to research the relation between fracture and texture conditions of PEEK thrust bearing in water, the rolling contact fatigue, RCF test was carried out. And then, the specimen after test was observed with a laser confocal microscope. Three types of surface damage: single crack, flaking and multiple crack: were ob-served. Arithmetic Average Roughness Height, AARH’s around single crack and no-damaged area were calculated. AARH’s in these two areas have no sig-nificantly different each other. This means the effect of cracks on roughness was negligible, and vice versa. The changing of AARH during the test was also dis-cussed. AARH’s both of failure and non-failure specimens were decreased dur-ing RCF tests. AARH Range of non-failure specimens after test included that of the failure specimen. It indicated AARH was not dominated the condition failure of PEEK bearing in water. On the other hands, the load had a clear threshold. This means the failure of PEEK bearing in water is strongly affected by load.