Butyl rubber as a macro-cross-linker in the preparation of a shape-memory and self-healing polymer

Recently, a simple strategy was developed for preparing interconnected interpenetrating polymer networks (IPNs) based on butyl rubber (IIR) and poly(n-octadecyl acrylate) (PC18A). Solvent-free UV polymerization of n-octadecyl acrylate (C18A) monomer in the melt of IIR at ambient temperature resulted in IPNs with self-healing and shape-memory functions. Here, we demonstrate that the use of IIR grafted with acrylic acid, methacrylic acid, and 10-undecenoic acid instead of unmodified IIR provides a significant improvement in the mechanical properties of IPNs. Differential scanning calorimetry, small-angle x-ray scattering, and wide-angle x-ray scattering analysis reveal side-by-side packing of C18 side chains of PC18A to form lamellar crystals with a melting temperature Tm between 46 and 52 °C. Transmission electron microscopy analysis indicates the existence of quasispherical nanoparticles composed of crystalline domains, which are dispersed in a continuous interpenetrating rubber-PC18A matrix. This microstructure provides them a complete self-recovery behavior induced by heating and an efficient shape-memory function. IPNs exhibit around tenfold higher chemical cross-link density as compared to those prepared from the native IIR, reflecting the effect of pendant vinyl groups on the extent of covalent interconnections between the IIR and PC18A components. The type of the grafted monomers significantly affects the mechanical performance of IPNs, which can be explained with the individual contributions of chemical and physical cross-links to the total cross-link density. The amount of the grafted rubbers in IPN could be further increased up to 80 wt. % by the incorporation of toluene into the reaction system, resulting in IPNs with a wide range of tunable thermal and mechanical properties

Embedded 3D printing of cryogel-based scaffolds

Cryogel-based scaffolds have attracted great attention in tissue engineering due to their interconnected macroporous structures. However, three-dimensional (3D) printing of cryogels with a high degree of precision and complexity is a challenge, since the synthesis of cryogels occurs under cryogenic conditions. In this study, we demonstrated the fabrication of cryogel-based scaffolds for the first time by using an embedded printing technique. A photo-cross-linkable gelatin methacryloyl (GelMA)-based ink composition, including alginate and photoinitiator, was printed into a nanoclay-based support bath. The layer-by-layer extruded ink was held in complex and overhanging structures with the help of pre-cross-linking of alginate with Ca2+ present in the support bath. The printed 3D structures in the support bath were frozen, and then GelMA was cross-linked at a subzero temperature under UV light. The printed and cross-linked structures were successfully recovered from the support bath with an integrated shape complexity. SEM images showed the formation of a 3D printed scaffold where porous GelMA cryogel was integrated between the cross-linked alginate hydrogels. In addition, they showed excellent shape recovery under uniaxial compression cycles of up to 80% strain. In vitro studies showed that the human fibroblast cells attached to the 3D printed scaffold and displayed spread morphology with a high proliferation rate. The results revealed that the embedded 3D printing technique enables the fabrication of cytocompatible cryogel based scaffolds with desired morphology and mechanical behavior using photo-cross-linkable bioink composition. The properties of the cryogels can be modified by varying the GelMA concentration, whereby various shapes of scaffolds can be fabricated to meet the specific requirements of tissue engineering applications

Bisulfite-initiated crosslinking of gelatin methacryloyl hydrogels for embedded 3D bioprinting

Recent studies on three-dimensional (3D) bioprinting of cell-laden gelatin methacryloyl (GelMA) hydrogels have provided promising outcomes for tissue engineering applications. However, the reliance on the use of photo-induced gelation processes for the bioprinting of GelMA and the lack of an alternative crosslinking process remain major challenges for the fabrication of cell-laden structures. Here, we present a novel crosslinking approach to form cell-laden GelMA hydrogel constructs through 3D embedded bioprinting without using any external irradiation that could drastically affect cell viability and functionality. This approach consists of a one-step type of crosslinking via bisulfite-initiated radical polymerization, which is combined with embedded bioprinting technology to improve the structural complexity of printed structures. By this means, complex-shaped hydrogel bio-structures with cell viability higher than 90% were successfully printed within a support bath including sodium bisulfite. This study offers an important alternative to other photo-induced gelation processes to improve the bio-fabrication of GelMA hydrogel with high cell viability

Fen Bilgisi Öğretmen Adaylarının Astronomiye Yönelik Tutumlarının ve Astronomi Öğretimi Özyeterlik İnançlarının İncelenmesi: Çevrim İçi Astronomi Eğitimi

Fen bilimleri öğretmen adaylarının astronomiye yönelik tutumları ve astronomi öğretimine yönelik özyeterlik inançları, astronomi öğretim sürecini etkilemektedir. Olumlu tutuma sahip ve özyeterlik inançları yüksek olan bireyler derslere aktif olarak katılmakta ve olumlu davranışlar sergilemektedirler. Bu bağlamda öğretmen adaylarının astronomiye yönelik olumlu tutuma sahip olmaları ve özyeterlik inançlarının yüksek olmasının onların gelecekteki astronomi öğretim sürecinde olumlu etki oluşturacağı ifade edilebilir. Bununla birlikte alanyazında astronomi konularının öğretimi, kavram yanılgılarının belirlenmesi, tutum ve özyeterlilik alanındaki çalışmaların ortaokul, lise düzeylerinde olduğu görülmektedir. Yapılan çalışmalarda fen bilimleri öğretmen adaylarının astronomiye yönelik tutumları ve astronomi öğretimine yönelik özyeterlik inançlarını geliştirmeye yönelik çalışmaların sınırlı olduğu dikkati çekmektedir. Ayrıca COVID-19 pandemisi nedeniyle çevrim içi düzenlenen eğitimlere daha çok ihtiyaç duyulmuştur. Bu bağlamda bu çalışmada çevrim içi düzenlenen astronomi öğretim yöntem ve materyal eğitiminin fen bilimleri öğretmen adaylarının astronomiye yönelik tutumları ve astronomi öğretimine yönelik özyeterlik inançları üzerine etkisi irdelenmiştir. Araştırmada kontrol grupsuz ön-test son-test yarı deneysel desen kullanılmıştır. Araştırmanın çalışma grubunu 35 (erkek=1, kız=34) fen bilimleri öğretmen adayı oluşturmaktadır. Fen bilimleri öğretmen adayları çevrim içi ortamda beş gün boyunca astronomi öğretim yöntem ve materyal eğitimi ile ilgili 23 farklı etkinliğe katılmışlardır. Araştırmada veriler fen bilimleri öğretmen adaylarına uygulama öncesi ve sonrasında çevrim içi olarak uygulanan “Astronomi Tutum Ölçeği (ATÖ)” ve “Astronomi Konularının Öğretimi Öz-yeterlik İnanç Ölçeği (AKÖÖYİÖ)”nden elde edilmiştir. ATÖ ve AKÖÖYİÖ’den elde edilen ön ve son-test verilerinin analizinde tekrarlanan ölçümler için çok değişkenli varyans (MANOVA) analizi kullanılmıştır. Sonuç olarak çevrim içi eğitim şeklinde gerçekleştirilen astronomi öğretim yöntem ve materyal eğitiminin astronomiye yönelik tutum ve astronomi öğretimine yönelik özyeterlik inanç değişkeninin astronomi öğretiminde zorlanma alt boyutu hariç diğer alt boyutlarının gelişiminde yüksek düzeyde etki büyüklüğüne sahip olduğu ortaya çıkmıştır. Bu doğrultuda çevrim içi eğitim uygulamalarının farklı teknolojilerle zenginleştirilerek, öğretmen adaylarının teknolojinin astronomi eğitiminde kullanımına ilişkin bilgi ve deneyim kazanmalarına da fırsat sağlayacak şekilde tasarlanması önerilmektedir

Mechanical properties of multifunctional hydrogels

Hydrogels are 3D cross-linked polymeric networks with the ability to hold huge amounts of water that are applicable in several industrial and biotechnological research areas. Regarding the defined application, the performance of the hydrogels is strongly influenced by their mechanical properties. Therefore, there has been a great effort in the investigation of mechanical features of the hydrogels, from microscale to macroscale, to create desirable characteristics for any given application. To understand the mechanical behavior, it is important to address the theories for determining the characteristics of hydrogels and models for testing them. This chapter is mainly focused on the theoretical models and experimental methods to identify mechanical behavior of hydrogels. In detail, the models including rubber elasticity and viscoelasticity have been elucidated. In addition, experimental methods including stress-strain tests, creep and stress relaxation, cyclic deformations, and dynamic mechanical analysis have been explained. Besides, network models and strategies to alter the micro and macro structure of hydrogels, and material addition for tunning and controlling the mechanical features, by emphasizing the relationship of structure-activity, have been clarified. Finally, the mechanoresponsive hydrogels for biomedical applications are discussed

3D bioprinting of tyramine modified hydrogels under visible light for osteochondral interface

Recent advancements in tissue engineering have demonstrated a great potential for the fabrication of three-dimensional (3D) tissue structures such as cartilage and bone. However, achieving structural integrity between different tissues and fabricating tissue interfaces are still great challenges. In this study, an in situ crosslinked hybrid, multi-material 3D bioprinting approach was used for the fabrication of hydrogel structures based on an aspiration-extrusion microcapillary method. Different cell-laden hydrogels were aspirated in the same microcapillary glass and deposited in the desired geometrical and volumetric arrangement directly from a computer model. Alginate and carboxymethyl cellulose were modified with tyramine to enhance cell bioactivity and mechanical properties of human bone marrow mesenchymal stem cells-laden bioinks. Hydrogels were prepared for extrusion by gelling in microcapillary glass utilizing an in situ crosslink approach with ruthenium (Ru) and sodium persulfate photo-initiating mechanisms under visible light. The developed bioinks were then bioprinted in precise gradient composition for cartilage-bone tissue interface using microcapillary bioprinting technique. The biofabricated constructs were co-cultured in chondrogenic/osteogenic culture media for three weeks. After cell viability and morphology evaluations of the bioprinted structures, biochemical and histological analyses, and a gene expression analysis for the bioprinted structure were carried out. Analysis of cartilage and bone formation based on cell alignment and histological evaluation indicated that mechanical cues in conjunction with chemical cues successfully induced MSC differentiation into chondrogenic and osteogenic tissues with a controlled interface

THE FREQUENCY OF HLA-A, B AND DRB1 ALLELES IN PATIENTS WITH BETA THALASSEMIA

ObjectiveHLA class I and II alleles are shown to be associated with certain diseases. A restricted numbers of alleles were found to be related to alloimmunisation in thalassemia population. The role of human leucocyte antigens in thalassemia is trend topic. In this study, the aim was to evaluate the differences in HLA frequencies of beta thalassemia patients comparing with healthy controls.MethodologyThe data were collected of 100 patients who were diagnosed with beta thalassemia and 100 healthy controls were included in the study. The low resolution HLA-A, -B, -DRB1, tissue group data were performed Istanbul University, Faculty of Medicine, Medical Biology Department HLA typing laboratory. All data were analyzed retrospectively and their HLA allele frequencies were analyzed by SPSS (v22) program.ResultsWe found an increased frequency of HLA-B*14 (8% versus 2%) and HLA-B*52 (17% versus 2%) compared to the control group (p=0.05, OR=4.26; p<0.01, OR=10.03). On the other hand, HLA-B*13 frequency was decreased in thalassemia patients (5% versus 13%, p=0.04, OR=0.35). Other HLA-A, -B and -DRB1 allele frequency was similar with healthy controls.ConclusionOur results showed that HLA-B*14 and -B*52 allele were associated with beta thalassemia in Turkish population. Several studies found that HLA-DRB1*15 and DRB1*11 were associated with alloimmunisation in thalassemia. Other some studies showed DRB1*07 and chronic infection relation in patients with thalassemia. We found HLA-B certain alleles difference in thalassemia patients which may yield a challenge in finding the matched donor in our population