ABSTRACT
In fused deposition modelling (FDM) based on the selected raster pattern, the developed internal thermal residual stresses can vary considerably affecting the mechanical properties and leading to distinct part distortions. This phenomenon is more pronounced in semi-crystalline than amorphous polymers due to crystallisation. Hence, this study focuses on the simulation of the FDM process of a semi-crystalline polymer (polypropylene) with raster patterns such as line (90°/90°), line (0°/90°), zigzag (45°/45°), zigzag (45°/-45°), and concentric from Cura (slicing software). The simulation provides visualisation and prediction of the internally developed thermal residual stresses and resulting warpage with printing time and temperature. The sample with a line (90°/90°) raster pattern is considered as the reference sample in order to compare the relative levels of residual stress and warpage in the other printed/simulated samples. Among the considered raster patterns, the concentric pattern displays the lowest amount of warpage (5.5% decrease) along with a significant drop in residual stress of 21%. While the sample with a zigzag (45°/-45°) pattern showed the highest increase of 37% in warpage along with a decrease of 9.8% in residual stresses. The sample with a zigzag (45°/45°) pattern, exhibited a considerable increase of 16.2% in warpage with a significant increase of 31% in residual stresses. Finally, the sample with a line (0°/90°) raster pattern displayed an increase of 24% increase in warpage with an increase of 6.6% in residual stresses.
ABSTRACT
In this study, Strontium (Sr) and Zinc (Zn) doped-HA nanoparticles were synthesized and incorporated into polyetheretherketone (PEEK) up to 30 wt.% and processed by a novel approach i.e., fused deposition modelling (FDM) 3D printing for the production of patient specific cranial implants with improved bioactivity and the required mechanical performance. Filaments were produced via extrusion and subsequently 3D-printed using FDM. To further improve the bioactivity of the 3D-printed parts, the samples were dip-coated in polyethylene glycol-DOPA (PEG-DOPA) solution. The printing quality was influenced by filler loading, but was not significantly influenced by the nature of doped-HA. Hence, the printing conditions were optimized for each sample. Micro-CT and Scanning Electron Microscopy (SEM) showed a uniform distribution of bioceramic particles in PEEK. Although agglomeration of particles increased with increase in filler loadings. Differential Scanning Calorimetry (DSC) showed that the melting point and crystallinity of PEEK increased with an increase in doped-HA loading from 343 °C to 355 °C and 27.7% to 34.6%, respectively. Apatite formation was confirmed on the 3D-printed samples after immersion in simulated body fluid (SBF) for 7, 14 and 28 days via SEM, X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). The tensile strength and impact strength decreased from 75 MPa to 51 MPa and 14 kJ/m2 to 4 kJ/m2, respectively, while Young's modulus increased with increasing doped-HA content from 2.8 GPa to 4.2 GPa. However, the tensile strengths of composites remained in the range of human cortical bone i.e., ≥50 MPa. In addition, there was a slight increase in mechanical strength after 28 days immersion which was attributed to apatite formation. Water contact angle showed that the hydrophilicity of the samples improved after coating the 3D-printed samples with PEG-DOPA. Hence, based on the results, the 3D-printed PEEK nanocomposites with 20 wt.% doped-HA is selected as the best candidate for the 3D-printing of craniomaxillofacial implants.
ABSTRACT
Semi-crystalline polymers develop higher amounts of residual stress and part distortion (warpage) compared to amorphous polymers due to their crystalline nature. Additionally, the FDM processing parameters such as ambient temperature play an important role in the resulting residual stresses and part distortion of the printed part. Hence, in this study, the effect of ambient temperature on the in-built residual stresses and warpage of amorphous acrylonitrile-butadiene-styrene (ABS) and semi-crystalline polypropylene (PP) polymers was investigated. From the results, it was observed that increasing the ambient temperature from 50 °C to 75 °C and further to 120 °C resulted in 0.22-KPa and 0.37-KPa decreases in residual stress of ABS, but no significant change in the amount of warpage. For PP, increasing ambient temperature from 50 °C to 75 °C led to a more considerable decrease in residual stress (0.5 MPa) and about 3% increase in warpage. Further increasing to 120 °C resulted in a noticeable 2 MPa decrease in residual stress and a 3.4% increase in warpage. Reduction in residual stress in both ABS and PP as a result of increasing ambient temperature was due to the reduced thermal gradients. The enhanced warpage in PP with increase in ambient temperature, despite the reduction in residual stress, was ascribed to crystallization and shrinkage.
ABSTRACT
Polyetheretherketone (PEEK) is a biocompatible polymer widely used for biomedical applications. Because it is biologically inert, bioactive phases, such as nano-hydroxyapatite (HA), have been added to PEEK in order to improve its bioactivity. 3D printing (3DP) technologies are being increasingly used today to manufacture patient specific devices and implants. However, processing of PEEK is challenging due to its high melting point which is above 340 °C. In this study, PEEK-based filaments containing 10 wt% of pure nano-HA, strontium (Sr)- doped nano-HA and Zinc (Zn)-doped nano-HA were produced via hot-melt extrusion and subsequently 3D printed via fused deposition modelling (FDM), following an initial optimization process. The raw materials, extruded filaments and 3D printed samples were characterized in terms of physicochemical, thermal and morphological analysis. Moreover, the mechanical performance of 3D printed specimens was assessed via tensile tensing. Although an increase in the melting point and a reduction in crystallization temperature was observed with the addition of HA and doped HA to pure PEEK, there was no noticeable increase in the degree of crystallinity. Regarding the mechanical behavior, no significant differences were detected following the addition of the inorganic phases to the polymeric matrix, although a small reduction in the ultimate tensile strength (~14%) and Young's modulus (~5%) in PEEK/HA was observed in comparison to pure PEEK. Moreover, in vitro bioactivity of 3D printed samples was evaluated via a simulated body fluid immersion test for up to 28 days; the formation of apatite was observed on the surfaces of sample surfaces containing HA, SrHA and ZnHA. These results indicate the potential to produce bioactive, 3DP PEEK composites for challenging applications such as in craniofacial bone repair.
