Additive manufacturing is a rapidly expanding technology in many scientific fields like tissue engineering. One of the most essential duties of tissue engineering scaffolds is to provide sufficient mechanical strength for the injured bone tissue. Scaffold architecture plays a significant role in its mechanical properties. Here, six delicate different geometry computer-aided design models with identical porosity were designed. The sets of 0/90, 0/45/135/90, 0/60/120, and their shifted models as the most prevalent scaffold geometries were fabricated by fused deposition modeling printer through the optimized processing parameters and were investigated by the upset test. Their modified models according to printing procedure changes were redesigned, and finite element analysis (FEA) simulations were accomplished through a simplifying strategy. Mechanical performances of the designed scaffolds were evaluated, and a good agreement was observed between the FEA and experiments. The strongest patterns were derived via evaluation of three aspects of scaffold elastic modulus, scaffold yield strength, and a newly defined parameter named ''scaffold geometry rupture resistance factor''. The large difference between Young's modulus of 0/90 (230.44 MPa) and 0/90 shifted (156.56 MPa) indicated the role of scaffold geometry in mechanical properties. The mechanical effect of layer pattern sequence change was also investigated.
Purpose
Fabrication settings such as printing speed and nozzle temperature in fused deposition modeling undeniably influence the quality and strength of fabricated parts. As available market filaments do not contain any exact information report for printing settings, manufacturers are incapable of achieving desirable predefined print accuracy and mechanical properties for the final parts. The purpose of this study is to determine the importance of selecting suitable print parameters by understanding the intrinsic behavior of the material to achieve high-performance parts.
Design/methodology/approach
Two common commercial polylactic acid filaments were selected as the investigated samples. To study the specimens’ printing quality, an appropriate scaffold geometry as a delicate printing sample was printed according to a variety of speeds and nozzle temperatures, selected in the filament manufacturer’s proposed temperature range. Dimensional accuracy and qualitative surface roughness of the specimens made by one of the filaments were evaluated and the best processing parameters were selected. The scaffolds were fabricated again by both filaments according to the selected proper processing parameters. Material characterization tests were accomplished to study the reason for different filament behaviors in the printing process. Moreover, the correlations between the polymer structure, thermo-rheological behavior and printing parameters were denoted.
Findings
Compression tests revealed that precise printing of the characterized filament results in more accurate structure and subsequent improvement of the final printed sample elastic modulus.
Originality/value
The importance of material characterization to achieve desired properties for any purpose was emphasized. Obtained results from the rheological characterizations would help other users to benefit from the highest performance of their specific filament.
Polythioether is an elastomer with proper thermal resistance and elongation at break, which can be used in various high-temperature and high-pressure sealing applications. This research is aimed to determine the suitable thiol/vinyl ratio and the branching agent content to synthesize a novel polythioether and the polythioether/ multiwall carbon nanotube (MWCNT) composite using two monomers, including dimercapto dioxaoctane (DMDO) and triethylene glycol divinylether. For each synthesis process, the gel permeation chromatography (GPC) was used to measure the molecular weight and the polydispersity index of the polymer chains. Fourier transforms infrared spectroscopy and Nuclear Magnetic Resonance were used to study the bond formation, while the glass transition of the polymer was evaluated by differential scanning calorimetry. Tensile and lap adhesion tests were also used to assess the mechanical properties of the samples. Field emission scanning electron microscopy was utilized to observe the dispersion of nanoparticles in polythioether/ MWCNT nanocomposite. GPC results showed that the thiol/vinyl ratio of 0.5 and branching agent molar ratio of 0.2 (relative to vinyl monomer) led to the most suitable average molecular weight (2022 g/mol) which had the highest mechanical properties.The nanocomposite containing 1 wt% MWCNT, showed the highest tensile strength and elongation at break up to 2.12 MPa and 303%, respectively. A considerable increase of 30 C is obtained in maximum degradation temperature of the produced nanocomposite compared to neat polythioether.
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