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    Biocompatibility of polymers
    (Elsevier, 2023) Sanli, Abdulkadir; Elibol, Cagatay; Aydınoğlu, Aysu
    Biocompatibility is defined as the ability of a material to perform with an appropriate host response in a specific application. Biocompatible polymers have gained significant importance during the past decades due to their capability to meet specific requirements for various applications such as tissue engineering, genetic disease treatment, and drug delivery. Biocompatibility testing of polymer-based medical devices is an essential requirement for regulatory approval. “EN ISO 10993 Biological evaluation of medical devices” includes several substandards prepared to manage biological risk and evaluate the biocompatibility of medical devices. The source of the polymeric biomaterial is determined by which biocompatibility test methods should be applied to the material itself. In this chapter, we present biocompatibility test methods and the main requirements of some common biocompatible polymers. In addition, we introduce some typical biomedical applications of these polymers after a detailed explanation of common natural and synthetic polymers. © 2023 Elsevier Ltd. All rights reserved.
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    Effect of equal-channel angular pressing on microstructure, aging kinetics and impact behavior in a 7075 aluminum alloy
    (Elsevier, 2024) Elibol, Cagatay; Sagir, Kadir; Dogan, Mert
    Among the precipitation hardenable 7xxx series aluminum alloys, AA7075 alloys (one of the most important engineering alloys) due to their low density (lightweight), high toughness and strength, and enhanced fatigue behavior have been used over the years in aerospace, aircraft, automotive, construction and marine applications. In the present study, the influence of the artificial aging through conventional heat treatment (i.e., precipitation hardening) and the thermomechanical treatment (equal-channel angular pressing (ECAP) + post-ECAP aging) on the quasi-static tensile, impact toughness and precipitation behavior as well as on the microstructure of an AA7075 alloy is investigated systematically. The results indicate that the ECAP process as well as post-ECAP aging result in considerably increased strength and hardness of the AA7075 alloys because of the superimposed effects of grain boundary strengthening (Hall-Petch relation), strain hardening (by means of the increased dislocation density) and precipitation hardening (due to the fine precipitates formed in Al matrix). Multi-pass ECAP processing has been found to result in a considerable decrease of the impact toughness (from 15.3 Jcm(-2) to 7.6 Jcm(-2)) associated with the failure mode (i.e., ductile-to-brittle transition) of the AA7075 alloys, whereas the artificial peak aging leads to a marked improvement (similar to 67 %) in the impact toughness in ECAPed conditions. Moreover, the ECAP process noticeably accelerates the precipitation kinetics of AA7075 alloys: The peak aging time in the ECAPed alloy is reduced significantly - from 30 h to 4 h. The results of the present study provide a deeper understanding of the combination of ECAP and heat treatment, and their effect on the fracture mode and toughness under impact loading, the aging kinetics and the microstructural evolution of an AA7075 alloy.
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    Öğe
    Effect of extruded low-density polyethylene on the microstructural and mechanical properties of hot-press produced 3105 aluminum composites
    (Walter De Gruyter Gmbh, 2021) Wapande, Sadam Hamis; Elibol, Cagatay; Konar, Murat
    This study was conducted to investigate the effect of low-density polyethylene on the microstructural and mechanical properties of 3105 aluminum composites produced by the continuous hot-press method. This production method ensures superior flatness to the composite and excellent peel strength between the composite plies. To this end, the bond between AA3105 and low-density polyethylene was initially characterized using a T-Peel stripping test. Tensile tests were performed on AA3105, low-density polyethylene and 3105 aluminum composites for determining mechanical behavior. A scanning electron microscope was used to characterize the cross-sectional cuts of the 3105 aluminum composite specimens obtained from the tensile tests. The microstructural analysis shows that low-density polyethylene and AA3105 exhibit a good interfacial adhesion bond before the fracture of the first AA3105 sheet. The results of the tensile tests clearly show that the uniform elongation at maximum load (Ag) of the 3105 aluminum composite is higher than that of AA3105. Furthermore, AA3105 exhibits negative strain rate sensitivity due to dynamic strain aging while 3105 aluminum composite exhibits a higher strain-hardening exponent than AA3105. Due to the higher strain rate sensitivity and strain hardening exponent, the 3105 aluminum composite exhibits higher formability than AA3105. This is of crucial importance for the manufacturing process.
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    Öğe
    Processing and characterization of polymeric biomaterials
    (Elsevier, 2023) Elibol, Cagatay; Güner, Mehmet Buğra; Sagir, Kadir
    Polymeric biomaterials feature a wide range of medical applications due to their high biological suitability (noncytotoxicity, biodegradability, and biocompatibility), enhanced mechanical behavior, and good processability. Besides these characteristics, chemical, electrical, and physical properties can be improved by regulating the structural and morphological parameters during processing of polymeric biomaterials. Because of the high clinical expectations, scientists focus on advanced processing techniques. Furthermore, due to the extremely hard-working conditions of polymeric biomaterials, many studies deal with numerous precise characterization techniques, in order to determine how properly polymeric biomaterials were processed, before being used in clinical applications. Therefore, this chapter is focused on gaining a deeper understanding of processing methods and characterization techniques of polymeric biomaterials for providing an extensive overview and a guide for developing polymeric biomaterials within the scope of clinical framework. © 2023 Elsevier Ltd. All rights reserved.