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Öğe EVALUATION OF MECHANOBIOLOGICAL POTENTIAL OF 3D-PRINTED PLA BONE TISSUE SCAFFOLDS WITH DIFFERENT PORE ARCHITECTURES AND POROSITY RATIOS(2024) Senaysoy, Safa; Lekesız, HüseyınLattice structures are widely used in bone tissue scaffold designs due to interconnected porous structures that mimic the natural extracellular matrix (ECM) to treat large bone defects. This study investigated the mechanical behavior of scaffolds with different pore architectures and porosity ratios using experimental and numerical methods. In addition, mechanobiological potentials of scaffolds were evaluated in terms of the specific energy absorption and the specific surface area. Three different geometries were created by varying the combination of vertical, horizontal, and diagonal struts to evaluate the geometric factor and 50%, 62.5, and 75% porosity ratios are examined as potential permeabilities. Compression tests were performed to calculate stiffness values and energy absorptions of the scaffolds. Finite element simulations were used to obtain stiffness values of scaffolds. The specific energy absorptions of scaffolds were calculated under 4 N compressive load as a representative of potential body loads. According to the results, it was found that pore architectures and porosity ratios had crucial effects on stiffness values, energy absorption levels, specific energy absorption, and specific surface area which may lead to significant differences in bone remodeling. The highest specific energy absorption was observed in the scaffolds designed with only diagonal struts with 75% porosity. The highest specific surface area was observed in the scaffolds designed with the combination of vertical, horizontal, and diagonal struts with 75% porosity.Öğe Mechanical deviation in 3D-Printed PLA bone scaffolds during biodegradation(Elsevier Ltd, 2024) Senaysoy, Safa; İLhan, Recep; Lekesiz, HuseyinLarge 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 LtdÖğe Tensile behavior of C/GFRP-steel hybrid rebars: Effect of volume fraction and helical angle with a proposed analytical model(Elsevier, 2026) Senaysoy, Safa; Yilmaz, Ayten Nur Yuksel; Bedeloglu, Ayse; Altin, Yasin; Sakcali, Gokhan BarisThis study examines the tensile properties of hybrid rebars consisting of a steel core wrapped with layers of Carbon Fiber-Reinforced Polymer (CFRP) or Glass Fiber-Reinforced Polymer (GFRP). The mechanical performance of the Steel-FRP composite bars (SFCBs) was evaluated through axial tensile tests considering two primary parameters: (i) the longitudinal FRP volume fractions (33 %, 40 %, and 47 %) and (ii) the helical wrapping angles (0 degrees, 30 degrees, and 60 degrees). Although SFCBs have gained increasing attention as an alternative to fully FRP or conventional steel reinforcement, the combined influence of fiber volume fraction and helical orientation on their tensile response has not been clearly established. Experimental findings demonstrated the influence of fiber volume fraction and helical angle on the tensile properties of SFCBs. Specimens coated with carbon exhibited greater strength than those coated with glass, especially at larger wrapping angles, while the glass-coated SFCB specimens demonstrated a wider range of deformation capability. The specimen with a 47 % volumetric fraction and a 60 degrees helical wrap exhibited a 21.8 % increase in yield stress compared with that of the steel bar, whereas its glass-fiber counterpart exhibited a 15.9 % increase. Maximum strength was significantly higher in carbon-SFCB rebars than in glass-SFCB ones. In contrast, glass-SFCB rebars showed 59 % higher ultimate strain. As the volume fraction increased, the influence of the helical angle on ultimate strength decreased. Increasing the helical angle from 0 degrees to 60 degrees enhanced the ultimate strength by up to 32 % in carbon-SFCBs and approximately 12 % in glass-SFCBs at a 33 % volume fraction. An analytical model was proposed to predict a five-zone stress-strain behavior, taking into account the effects of volumetric fraction and helical angle. The proposed model effectively replicated the stress-strain patterns of hybrid rebars in every zone with a satisfactory level of accuracy. Generally, the calculated mean absolute percentage errors for key mechanical parameters such as initial stiffness, yield stress, and fiber-contributed stiffness were below 15 %. This study offers a practical framework for designing SFCBs with customised mechanical properties for sophisticated RC applications.Öğe THE EFFECT OF NOZZLE DIAMETER AND LAYER THICKNESS ON MECHANICAL BEHAVİOUR OF 3D PRINTED PLA LATTICE STRUCTURES UNDER QUASI-STATIC LOADING(2023) Demirci, Emre; Senaysoy, Safa; Tuğcu, Salih EmreLattice structures are widely preferred because they have good properties such as lightness, high energy absorption capacity and strength. Moreover, these lattice structures can be produced by utilizing 3D printer. Therefore, this study aimed to investigate the effect of the mechanical behavior of the different printing parameters on the lattice structures. Firstly, FBCC and FBCCZ lattice structures were printed with various printing parameters such as nozzle diameter of 0.25 mm-0.4 mm and layer thickness of 0.1 mm–0.15 mm. Then, quasi-static compression tests were carried out to determine the mechanical behavior of lattice structures. Force-displacement behavior, equivalent elastic modulus and energy absorption capabilities of lattice structures printed with different parameters were calculated from the results of quasi-static compression test. According to the results, it was observed that the mechanical behavior was significantly affected when the nozzle diameter and layer thickness were changed. It was determined that the strength and energy absorption of the structures printed with a nozzle diameter of 0.25 mm and a layer thickness of 1.5 mm were decreased. In addition, it was observed that the effect of the printing parameters on the mechanical behavior can be different according to the lattice type and lattice rod diameter.Öğe The Need for the Evaluation of Sport-Specific Skills in Paralympic Goalball with a 3-D Kinematic Analysis: Research Note(Sagamore Publishing Llc, 2024) Esatbeyoglu, Ferhat; Kirkaya, Izzet; Senaysoy, Safa; Bicici-Ulusahin, SedaGoalball is one of the Paralympic sport disciplines designed for athletes with visual impairments (VI), and athletes wear eyeshades while they perform the sport for a fair competition. The game is played with a ball with bells inside allowing its movement to be heard by the players and therefore sport -specific attack and defense foundations needs to be developed for this Paralympic sport discipline. Taking the VI into account, movement phases of attack and defense techniques may be improved by the coach with proper training programs and with this, athletic ability of the athlete with VI may be enhanced. This is especially significant for novice goalball athletes as mastering fundamental skills properly may lead to better performance on the court while minimizing the risk of injury. In contrast, there is a scarce literature on examining the kinematic analysis of Paralympic goalball sport. Limited studies carried out 2-D video observational analysis for goalball -throwing technique and in fact goalball-throwing technique is three dimensional. Moreover, studies conducted kinematic analysis only for throwing technique. For these reasons, 3-D kinematic analysis of throwing and defense techniques is essential. In addition, development of throwing and defense techniques with precise training methods requires taking into account of kinetic chain of body segments, functional movement must be considered and evaluated completely. From this point of view, functional training methods that can contribute defense performance can be recommended as there is no study evaluating the functional performance of goalball athletes. This also can contribute to development of goalball specific test protocols to evaluate foundational goalball skills and novel training approaches can be applied in order to develop physiological and motor skills of goalball sport.
