The influence of manganese content on the formation of martensite structure and the final properties of a quaternary Cu-Al-Mn-Ag shape memory alloy (SMA) was investigated. Two alloys with designed ...compositions, Cu- 9%wt. Al- 16%wt. Mn- 2%wt. Ag and Cu- 9%wt. Al- 7%wt. Mn- 2%wt. Ag, were prepared in an electric arc furnace by melting of high-purity metals. As-cast and quenched microstructures were determined by optical microscopy and scanning electron microscopy equipped with EDS. Phases were confirmed by high-energy synchrotron radiation and electron backscatter diffractions. Austenite and martensite transformations were followed by differential scanning calorimetry and hardness was determined using the Vickers hardness test. It was found that the addition of silver contributes to the formation of the martensite structure in the Cu-Al-Mn-SMA. In the alloy with 7%wt. of manganese, stable martensite is formed even in the as-cast state without additional heat treatment, while the alloy with 16%wt. of manganese martensite transforms only after thermal stabilization and quenching. Two types of martensite, β1′ and γ1′, are confirmed in the Cu-9Al-7Mn-2Ag specimen. The as-cast SMA with 7%wt. Mn showed significantly lower martensite transformation temperatures, Ms and Mf, in relation to the quenched alloy. With increasing manganese content, the Ms and Mf temperatures are shifted to higher values and the microhardness is lower.
Since only few reported studies propose anti-vascular endothelial growth factor (anti-VEGF) delivery through electrospun scaffolds, this study greatly contributes to the potential prevention of ...patient's vision loss, as it explores electrospun polycaprolactone (PCL) coated with anti-VEGF for the blockage of abnormal cornea vascularization. In terms of physicochemical properties, the biological component increased the PCL scaffold fiber diameter (by ~24%) and pore area (by ~82%), while ut slightly reduced its total porosity as the anti-VEGF solution filled the voids of the microfibrous structure. The addition of the anti-VEGF increased the scaffold stiffness almost three-fold at both strains of 5 and 10%, as well as its biodegradation rate (~36% after 60 days) with a sustained release profile after Day 4 of phosphate buffered saline incubation. In terms of scaffold application function, the PCL/Anti-VEGF scaffold proved to be more favorable for the adhesion of cultured limbal stem cells (LSCs); this was confirmed by the SEM images, where the cells showed flat and elongated conformations. Further support of the LSC growth and proliferation was confirmed by the identified p63 and CK3 markers after cell staining. These results demonstrate the advantageous effect of the surface-adsorbed anti-VEGF to stop vision loss and help damaged corneal tissue repair.
This study reports the results of microstructure and thermal analysis of low-melting Bi–In alloys with potential for commercial application in the field of phase change materials. Three eutectic ...alloys Bi–47.44In, Bi–66.33In, Bi–77.92In (all in at.%) were prepared and investigated by means of scanning electron microscopy (SEM) with energy-dispersive X-ray spectrometry (EDS) and differential scanning calorimetry (DSC). Microstructure of the prepared eutectic alloys was analysed using SEM–EDS, and identification of co-existing phases was done. Melting temperatures and latent heats of eutectic melting were measured using DSC technique. Experimentally obtained results were compared with the results of thermodynamic calculation according to CALPHAD (calculation of phase diagram) method, and good mutual agreement was noticed.
This paper discusses the effect of different heat treatment procedures on the microstructural characteristics, damping capacities, and mechanical properties of CuAlNi shape memory alloys (SMA). The ...investigation was performed on samples in the as-cast state and heat treated states (solution annealing at 885 °C/60'/H
O and after tempering at 300 °C/60'/H
O). The microstructure of the samples was examined by light microscopy (LM) and scanning electron microscopy (SEM) equipped with a device for energy dispersive spectrometry (EDS) analysis. Light and scanning electron microscopy showed martensitic microstructure in all investigated samples. However, the changes in microstructure due to heat treatment by the presence of two types of martensite phases (β
and γ
) influenced alloy damping and mechanical properties by enhancing alloy damping characteristics. Heat treatment procedure reduced the alloys' mechanical properties and increased hardness of the alloy. Fractographic analysis of the alloy showed a transgranular type of fracture in samples after casting. After solution annealing, two types of fracture mechanisms can be noticed, transgranular and intergranular, while in tempered samples, mostly an intergranular type of fracture exists.
Limbal Stem Cell Deficiency (LSCD) is a very serious and painful disease that often results in impaired vision. Cultivation of limbal stem cells for clinical application is usually performed on ...carriers such as amniotic membrane or surgical fibrin gel. Transplantation of these grafts is associated with the risk of local postoperative infection that can destroy the graft and devoid therapeutic benefit. For this reason, electrospun scaffolds are good alternatives, as proven to mimic the natural cells surroundings, while their fabrication technique is versatile with regard to polymer functionalization and scaffolds architecture. This study considers the development of poly(ε-caprolactone) (PCL) immune-compatible and biodegradable electrospun scaffolds, comprising cefuroxime (CF) or titanium dioxide (TiO2) active components, that provide both bactericidal activity against eye infections and support of limbal stem cells growth in vitro. The PCL/CF scaffolds were prepared by blend electrospinning, while functionalization with the TiO2 particles was performed by ultrasonic post-processing treatment. The fabricated scaffolds were evaluated in regard to their physical structure, wetting ability, static and dynamic mechanical behaviour, antimicrobial efficiency and drug release, through scanning electron microscopy, water contact angle measurement, tensile testing and dynamic mechanical analysis, antimicrobial tests and UV-Vis spectroscopy, respectively. Human limbal stem cells, isolated from surgical remains of human cadaveric cornea, were cultured on the PCL/CF and PCL/TiO2 scaffolds and further identified through immunocytochemistry in terms of cell type thus were stained against p63 marker for limbal stem cells, a nuclear transcription factor and cytokeratin 3 (CK3), a corneal epithelial differentiation marker. The electrospun PCL/CF and PCL/TiO2 successfully supported the adhesion, proliferation and differentiation of the cultivated limbal cells and provided the antimicrobial effect against Pseudomonas aeruginosa, Staphylococcus aureus and Candida albicans.
Shape memory alloys (SMAs) represent an exceptional class of smart materials as they are able to recover their shape after mechanical deformation, making them suitable for use in actuators, sensors ...and smart devices. These unique properties are due to the thermoelastic martensitic transformation that can occur during both thermal and mechanical deformation. Cu-based SMAs, especially those incorporating Al and Ag, are attracting much attention due to their facile production and cost-effectiveness. Among them, Cu-Al-Ag SMAs stand out due to their notably high temperature range for martensitic transformation. In this study, a Cu-based SMA with a new ternary composition of Cu-10Al-7Ag wt.% was prepared by arc melting and the samples cut from this casting alloy were quenched in water. Subsequently, the phase composition and the development of the microstructure were investigated. In addition, the morphology of the martensite was studied using advanced techniques such as electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The analyzes confirmed the presence of martensitic structures in both samples; mainly 18R (β1′) martensite was present but a small volume fraction of (γ1′) martensite also was noticed in the as-quenched sample. The observation of fine, twinned martensite plates in the SMA alloy with symmetrically occurring basal plane traces between the twin variants underlines the inherent correlation between microstructural symmetry and the properties of the material and provides valuable insights into its behavior. The hardness of the quenched sample was found to be lower than the as-cast counterpart, which can be linked to the solutioning of Ag particles during the heat treatment.
Cells grown on bioactive matrices have immensely advanced many aspects of biomedical research related to drug delivery and tissue engineering. Our main objective was to perform simple evaluation of ...the structural and biotic qualities of cell scaffolds made of affordable biomaterials for liver cell line (HepG2) cultivation in vitro. In this work the electrospun matrix made of synthetic polyester poly(ε-caprolactone) (PCL) was compared with the natural protein-based extracellular matrix isolated from porcine liver (ECM). Mechanical and structural analysis showed that ECM was about 12 times less resistant to tensile stress while it had significantly larger pore size and twice smaller water contact angle than PCL. Bioactivity assessment included comparison of cell growth and transfection efficiency on cell-seeded scaffolds. Despite the differences in composition and structure between the two respective matrices, the rate of cell spreading and the percentage of transfected cells on both scaffolds were fairly comparable. These results suggest that in an attempt to produce simple, cell carrying structures that adequately simulate the natural scaffold, one can rely on PCL electrospun mats.
Aluminium alloys possess excellent mechanical, physically chemical and technological properties which have found an extensive application in the automotive industry. Alloy AlSi11 belongs to a group ...of eutectic alloys characterized by high fluidity, low pouring temperature and narrow solidification interval which comprehend to the uniformly distributed eutectic microstructure indicating superior mechanical and technological properties. Study of AlSi11 alloy solidification sequence has been accompanied by calculation of equilibrium phase diagram, and simultaneous thermal analysis, all in correlation with microstructure development. Thermodynamic calculation revealed solidification sequence with corresponding temperatures in equilibrium state. Differential scanning calorimetry enables determination of exact temperatures of phases’ transformations correlated at different cooling rates. Dilatometer thermal analysis defined dimensional changes of AlSi11 alloy. Microstructural examination revealed development of following constituents: primary aluminium (α
Al
), high-temperature intermetallic phases on the iron base (Al
5
FeSi and/or Al
15
(Fe,Mn)
3
Si
2
), binary eutectic (α
Al
+ β
Si
) and secondary eutectic (Mg
2
Si and Al
5
Mg
8
FeSi
6
) as a last solidifying phases. Synergy of performed phase diagram calculation, thermodynamic and microstructural investigation enables determination of thermodynamic stability of AlSi11 alloy exposed to different cooling conditions, with respect to phase’s evolution.
Beside their technological importance in soldering, the low melting eutectic alloys based on bismuth and indium have potential for commercial application in the field of phase-change materials ...(PCMs). In this respect, the knowledge of their microstructure and thermal properties such as melting temperature, latent heat of melting, supercooling tendency, thermal conductivity, etc. is of large importance. In this study, two ternary eutectic Bi-In-Sn alloys were investigated by means of scanning electron microscopy (SEM) with energy dispersive X-ray spectrometry (EDS) and differential scanning calorimetry (DSC). Microstructure of the prepared eutectic alloys was analyzed using SEM-EDS and identification of co-existing phases was done. Melting temperatures and latent heats of eutectic melting were measured using DSC technique. Experimentally obtained results were compared with the results of thermodynamic calculation according to CALPHAD (calculation of phase diagram) approach and good mutual agreement was obtained.
In this paper, the effect of different collector geometry on the PCL scaffold architecture and cell viability was investigated. PCL scaffolds with antibiotic Cefuroxim
®
, 15%wt. and 20%wt., were ...electrospun and characterized by ATR-FTIR, while thermal stability were observed by DSC and TG. PCL/15%CFU
®
scaffolds were electrospun on six 3D printed collectors, three ribbed and three mesh geometries, to produce the most favourable structure for cells adhesion and proliferation. SEM study and MTT assay revealed that collectors with the widest slot in both ribbed and mesh geometries exhibited the most favourable structure to enhance cells adhesion. In general, cells spreading on the surface and cells viability proved to be better for the ribbed collectors. The study showed that by controlling the collector geometry and the scaffold three-dimensional structure, it is possible to control cell attachment and differentiation and, consequently, to adjust them for the special tissue demands in the regeneration process.
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