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    Biodegradable Nanocomposite Filament Based on PLA/PCL/CNCs for FDM 3D Printing: Production, Characterization and Printability
    (Wiley, 2025) Ilhan, Recep; Gumus, Omer Yunus; Lekesiz, Huseyin
    Additive manufacturing (AM) is a widening technique for the processing of polymers that is not only used by personal users but also by some industries. The development of biodegradable and bio-based composites for AM attracts great interest with respect to various aspects such as environmental issues, user health, and biomedical applications. Polylactic acid (PLA) is a good candidate for bio-based materials. However, its brittleness needs to be improved. In this study, PLA-based filaments with improved toughness by adding polycaprolactone (PCL) (10% and 20% by weight) and cellulose nanocrystals (CNCs) (5% by weight) were produced for the fused deposition modeling (FDM) technique. The physical, thermal, morphological, and mechanical properties of the produced filaments were comprehensively characterized. All filament diameters were found to be within the suitable range for FDM applications (1.75 +/- 0.05 mm). TGA analyses showed that the filaments could maintain their thermal stability up to approximately 256 degrees C and that the CNCs enhanced their thermal stability. The addition of PCL and CNCs did not cause significant changes in T g and T m of the neat PLA (T g = 58.14 degrees C and T m = 175.93 degrees C). The tensile test results indicated that the PCL and CNCs reinforcement increased the elongation at break from 6.76% to 40.25% and the toughness from 2.94 to 14.48 MJ/m3. In the last part, the three-dimensional (3D) printability was demonstrated by producing auxetic sheets with optimized printing parameters based on MFI, TGA, and DSC data, and good dimensional stability was obtained.
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    Innovative reinforcement method for metal foam cell wall using CNTs
    (Iop Publishing Ltd, 2024) Cilsal, Onur Ozan; Lekesiz, Huseyin; Cakir, M. Cemal
    Carbon nanotubes (CNTs) and their composites are gaining popularity due to their exceptional strength qualities. It is well known that adding CNTs to metal foam composites boosts compressive strength. On the other hand CNT addition is still a costly process due to high cost of the CNTs. This study presents a novel and cost-effective solution by selectively adding CNTs to the structurally weakest regions of aluminum foam materials produced via powder metallurgy, employing a newly developed focused multi-step additive method. The cell borders of aluminum foam are strengthened with multiple spherical layers of CNTs, using a transfer method by initially coating the space holders used at the foaming process. The strength increase effect of this CNT addition method was compared with the widely known aluminum foam production parameters via a 4-parameter design of experiment (DOE) study. Compressive strength values of the samples were evaluated using a constant speed compression test acc. to ISO13314. The compacting pressure, CNT concentration, sintering temperature, and sintering period were chosen as DOE parameters, and 78% of the interactions effecting on final compressive strength could be explained with the model. As a result, it was established that, compared to the other parameters, sintering duration had the highest influence on compressive strength. But besides It has also been shown that adding 0.53% CNT by weight only to the cell border regions increases overall strength by 9%. This weight-strength increase ratio is compared with similar studies in the literature and found to be providing a production cost advantage due to the lower amount of CNT addition requirement for the comparable weight relative strength increase. Focused strength increase method has potential to enable controlled failure of foam materials by selectively strengthening strength critical areas of a component.
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    Mechanical deviation in 3D-Printed PLA bone scaffolds during biodegradation
    (Elsevier Ltd, 2024) Senaysoy, Safa; İLhan, Recep; Lekesiz, Huseyin
    Large or carcinogenic bone defects may require a challenging bone tissue scaffold design ensuring a proper mechanobiological setting. Porosity and biodegradation rate are the key parameters controlling the bone-remodeling process. PLA presents a great potential for geometrically flexible 3-D scaffold design. This study aims to investigate the mechanical variation throughout the biodegradation process for lattice-type PLA scaffolds using both experimental observations and simulations. Three different unit-cell geometries are used for creating the scaffolds: basic cube (BC), body-centered structure (BCS), and body-centered cube (BCC). Three different porosity ratios, 50 %, 62.5 %, and 75 %, are assigned to all three structures by altering their strut dimensions. 3-D printed scaffolds are soaked in PBS solution at 37 °C for 15, 30, 60, 90, and 120 days both unloaded and under dead load. Water absorption, weight loss, and compression stiffness are measured to characterize the first-stage degradation and investigate the possible influences of these parameters on the whole biodegradation process. The strength reduction stage of biodegradation is simulated by solving pseudo-first-order kinetics-based molecular weight change equation using FEA with equisized cubic (voxel-like) elements. For the first stage, mechanical load does not have a statistically significant effect on biodegradation. BCC with 62.5 % porosity shows a maximum water absorption rate of around 25 % by the 60th day which brings an advantage in creating an aquatic environment for cell growth. Results indicate a significant water deposition inside almost all scaffolds and water content is determined to be the main reason for the retained or increased compression stiffness. A distinguishable stiffness increase in the initial degradation process occurs for 75 % porous BC and 50 % porous BCC scaffolds. Following the quasi-stable stage of biodegradation, almost all scaffolds lost their rigidity by around 44–48 % within 120 days based on numerical results. Therefore, initial stiffness increase in the quasi-stable stage of biodegradation can be advantageous and BCC geometry with a porosity between 50% and 62 % is the optimum solution for the whole biodegradation process. © 2024 Elsevier Ltd