Fracture characteristics of PEEK at various stress triaxialities

Mechanical behaviour of prosthodontic CAD/CAM polymer composites aged in three food-simulating liquids

OBJECTIVES

This study investigated the effect of ageing in three food-simulating liquids (FSLs) on mechanical properties of three prosthodontic CAD/CAM polymer composites intended for construction of implant-supported frameworks.

METHODS

Materials investigated were: (i) a carbon fibre-reinforced composite (CarboCAD 3D dream frame; CC), (ii) a glass fibre-reinforced composite (TRINIA; TR), and (iii) a reinforced PEEK (DentoKeep; PK). Filler contents and microstructural arrangements were determined by thermo-gravimetry and tomography (µ-CT), respectively. Flexural properties (FS and E_f) were measured by 3-point bending (3PB) of 1 mm and 2 mm thick beam specimens. Fracture toughness (K_IC) was measured by single-edge-notched-bending (SENB). All measurements were made at baseline (dry) and after 1-day and 7-day storage at 37 ℃ in either water, 70 % ethanol/water (70 % E/W) or methyl ethyl ketone (MEK). Failed specimens were examined microscopically. Statistical analyses included four-way ANOVA, two-way ANOVA and multiple Tukey comparison tests (α = 0.05). Multiple independent t-tests were performed regarding thickness effects on FS and E_f (α = 0.05).

RESULTS

At baseline, the mechanical properties increased in the sequence: PK< TR< CC (p < 0.001). FS ranged from 192.9 to 501.5 MPa; E_f from 4.2 to 18.1 GPa; and K_{IC f}rom 4.9-12.4 MPa.m^0.5. Fibre-reinforced composites (CC and TR) were significantly stronger than PK. However, all properties of CC and TR reduced after 1 d storage in 70 % E/W and MEK with FS ranging from 58.6 to 408 MPa; E_f from 1 to 15.4 GPa; K_IC from 6.87 to 10.17 MPa.m^0.5. Greater reductions occurred after 7 d storage. MEK was more detrimental than 70 % E/W and water on fibre-reinforced composites.

SIGNIFICANCE

Mechanical properties of each CAD/CAM composite were strongly dependent upon media and ageing. Although the mechanical properties of PK were initially inferior, it was relatively stable in all FSLs. All three materials exhibited sufficient mechanical properties at 1 mm thickness, but thicker specimens were more tolerant to ageing.

Deformation of polyetheretherketone, PEEK, with different thicknesses

In order to determine a suitable thickness of polyetheretherketone (PEEK) for manufacturing of surgical membranes, the purpose was to evaluate how different thicknesses of PEEK influence the mechanical properties under flexure and tension. In total 20 specimens in PEEK with two different thicknesses, 0.5 mm and 1.0 mm were fabricated and tested in a three-point flexural strength test and tensile strength test (n = 5 specimens). Statistical analysis was done with non-parametric Mann-Whitney test with level of significance α = 0.05, for both material tests, respectively. The 1.0 mm-thick samples resulted in higher values in elastic limit and conventional deflection (S_c-value) in the flexural strength test compared to 0.5 mm-thick samples. In the tensile strength test, the results did not show any significant difference in elastic limit depending on the thickness evaluated. However, PEEK with thickness of 1.0 mm received significantly higher maximum value at fracture. Within the limitations of this study, PEEK with a thickness of 0.5 mm-1.0 mm shows mechanical properties that are appropriate thickness and can meet the complex demands for dimensioning of surgical membranes.

Mechanical property characterization of partially crystalline Poly-Ether-Ether-Ketone

The present study investigates the mechanical properties of partially crystalline Poly-Ether-Ether-Ketone between the glass transition and the cold crystallization. Biaxial tension, uniaxial tension, and DMA experiments were conducted to investigate the influence of temperature-induced crystallization on mechanical properties, and three stiffening behaviors are observed. Firstly, a 'U' type mechanical property is observed for all three experiments with first softening and then significant stiffening behavior with increasing temperature. Secondly, stiffening also occurs during low strain rate tests but not in higher strain rate tests. Thirdly, the stiffening behavior of the anisotropic film shows orientation dependence. Crystallinity evolution is predicted by the Nakaruma non-isothermal crystallization kinetics with optimized parameters, with which we demonstrate and explain that the stiffening behaviors are connected to the onset of crystallization. Therefore, the conclusion provides a new tool to approach and distinguish extrinsic and intrinsic properties during characterization, promoting future implementation for constitutive modeling and corresponding simulation that could replicate the influence of temperature-induced crystallization.

Three-dimensional finite element analysis of intramedullary nail with different materials in the treatment of intertrochanteric fractures

Intramedullary nails are the common treatment options for femoral intertrochanteric fractures. However, aseptic loosening is considered to be one of the primary forms of failure that can be caused by the stress shielding between the bone and implants. The matching in mechanical properties of implant and bone is a key issue to prevent this failure. Polyetheretherketone (PEEK) and Function-graded (FG) materials are widely used in clinical because of their excellent mechanical properties. In this study, to investigate the biomechanical behaviors of intramedullary nails made of Ti-6Al-4V alloy, Stainless Steel (SS), PEEK and two FG materials, three-dimensional finite element models of intertrochanteric fracture femur with intramedullary nail were constructed with ABAQUS. The maximum von Mises stress on the femoral fracture surface fixed by PEEK intramedullary nail was the largest, followed by FG intramedullary nail, which help stimulate bone growth and subsequently reduce fracture healing time. Compared with traditional metal intramedullary nails, PEEK and FG implants might increase von Mises stress along the same path in the proximal femur. The results showed that PEEK and FG intramedullary nails obviously changed the stress distributions in the bone and reduced stress shielding. This finding indicated that PEEK and FG intramedullary nails have the potential to become alternatives to the conventional metal intramedullary nails.

Photofunctionalization effect and biological ageing of PEEK, TiO2 and ZrO2 abutments material

The aim of this study was to evaluate the effectiveness of UVC photofunctionalization in removing the surface carbon contamination compounds from the most used surfaces utilized in dental implantology: TiO₂, ZrO₂ and PEEK. Machined samples were treated by UVC light in an Ushio Therabeam SuperOsseo® device for 12 min each. Non-treated disks were set as controls. X-Ray photoelectron spectroscopy was used to monitor the changes in surface chemical composition. Photofunctionalization of the PEEK material has been analyzed here for the first time. The removal of hydrocarbons allowed by UVC irradiation was nearly twofold, and irradiation simultaneously led to an increase of H-O-C=O bonds. For TiO₂ and ZrO₂ surfaces, the loss of hydrocarbons detected after UVC irradiation was threefold. The chemical stability of surfaces when left at atmospheric conditions after UVC irradiation was monitored during 10 weeks. After 6 weeks the carbon contamination on TiO₂ surfaces returned to the level before UVC treatment, while for ZrO₂ and PEEK it was 75% and 60% of its initial value, respectively. None of the materials tested displayed any toxicity towards human fibroblasts cultured in direct contact with them, confirming their potential employment for manufacturing of implant abutments. UVC photofunctionalization can be thus regarded as a valid method in order to reverse the detrimental effects of biological ageing of implant surfaces.

Comparison of dynamic response of three TLIF techniques on the fused and adjacent segments under vibration

To explore which TLIF techniques are advantageous in reducing the risk of complications and conducive to bone fusion under the vibration. The L1-L5 finite element lumbar model was modified to simulate three different TLIF techniques (a unilateral standard cage, a crescent-shaped cage, and bilateral standard cages). The results showed that the crescent-shaped cage may reduce the risk of subsidence and provide a more stable and suitable environment for vertebral cell growth under the vibration compared to the other TLIF techniques. Unilateral cage may increase the risk of adjacent segment disease and cage failure including fatigue failure under vibration.

Production of graphene nanoplate/polyetheretherketone composites by semi-industrial melt-compounding

Current studies on nanocomposites have focused on their multifunctional properties and their industrial production. In this work, polyetheretherketone (PEEK)/graphene nanoplate (GNP) composites were produced by a direct semi-industrial process. Different percentages of untreated GNP (1, 5, and 10 wt.%) were added to PEEK by employing melt-compounding followed by injection-moulding. Despite the semi-industrial approach used, the modulus, strength, and Poisson coefficient of the nanocomposites (1 and 5 wt.%) were not significantly affected by the addition of GNP. However, there was a slight decrease in the strength at 10 wt.% GNP. Our study also shows that the thermal conductivities of PEEK/GNP composites are up to 2.5 times higher than that of pure PEEK.

Fracture Assessment of PEEK under Static Loading by Means of the Local Strain Energy Density

Polyetheretherketone (PEEK) has gained interest in many industrial applications due to its high strength-to-weight ratio, excellent heat tolerance and high corrosion resistance. Stress concentrators such as notches and geometrical discontinuities are present in many such components necessitating the reliable assessment of notch sensitivity of PEEK in monotonic tension. Here we evaluate the applicability of the strain energy density (SED) approach for the assessment of the fracture strength of experimentally tested notched geometries subject to corrosion. The fracture behavior of neat, circumferentially razor-grooved dog-bone specimens and circumferentially U-notched specimens with different notch radii can be predicted with a discrepancy lower than ±10%. Reliable predictions are shown on two previously published datasets employing both computed and published mechanical properties as inputs for the SED calculations. This report presents the first successful application of SED for PEEK as well as the successful prediction of tensile behavior in corrosive environments. This opens the road towards future applications of PEEK in fields its compliant use is of growing popularity.