Figen Kaya

Antileishmanial effect of silver nanoparticles and their enhanced antiparasitic activity under ultraviolet light

Leishmaniasis is a protozoan vector-borne disease and is one of the biggest health problems of the world. Antileishmanial drugs have disadvantages such as toxicity and the recent development of resistance. One of the best-known mechanisms of the antibacterial effects of silver nanoparticles (Ag-NPs) is the production of reactive oxygen species to which Leishmania parasites are very sensitive. So far no information about the effects of Ag-NPs on Leishmania tropica parasites, the causative agent of leishmaniasis, exists in the literature. The aim of this study was to investigate the effects of Ag-NPs on biological parameters of L. tropica such as morphology, metabolic activity, proliferation, infectivity, and survival in host cells, in vitro. Consequently, parasite morphology and infectivity were impaired in comparison with the control. Also, enhanced effects of Ag-NPs were demonstrated on the morphology and infectivity of parasites under ultraviolet (UV) light. Ag-NPs demonstrated significant antileishmanial effects by inhibiting the proliferation and metabolic activity of promastigotes by 1.5- to threefold, respectively, in the dark, and 2- to 6.5-fold, respectively, under UV light. Of note, Ag-NPs inhibited the survival of amastigotes in host cells, and this effect was more significant in the presence of UV light. Thus, for the first time the antileishmanial effects of Ag-NPs on L. tropica parasites were demonstrated along with the enhanced antimicrobial activity of Ag-NPs under UV light. Determination of the antileishmanial effects of Ag-NPs is very important for the further development of new compounds containing nanoparticles in leishmaniasis treatment.

Fabrication and characterisation of Ni-coated carbon fibre-reinforced alumina ceramic matrix composites using electrophoretic deposition

The present study explores the feasibility of fabricating Ni-coated carbon fibre-reinforced alumina ceramic matrix composites via a single-infiltration electrophoretic deposition (EPD) process performed in vacuum. The nano-size boehmite sol was seeded using nano-size δ-alumina powder in order to control the final sintered microstructure and then characterised using transmission electron microscopy, differential thermal and thermogravimetric analysis (DTA/TG) and X-ray disc centrifuge system (BI-XDC) in order to determine the sol microstructure, phase transformation temperatures and particle size (also degree of agglomeration), respectively. An EPD manufacturing cell for fabrication of Ni-coated carbon fibre reinforced alumina matrix composites was designed and experiments were conducted under vacuum (first time to date), resulting in full deposition of the sol material throughout the voids within/between the fibre tows. Composites with high green density (67% theoretical density) were produced using an applied voltage of 15 V d.c. and deposition time of 400 s. The sintered density after pressureless sintering at 1250°C for 2 h was 91% theoretical density. Crack path propagation test showed that the metallic Ni coating was able to provide a weak interface, as an indenter induced crack within the alumina matrix was deflected and arrested at the Ni interface.

Investigation of antileishmanial activities of Tio2@Ag nanoparticles on biological properties of L. tropica and L. infantum parasites, in vitro.

Leishmaniasis is a public health problem which is caused by protozoon parasites belonging to Leishmania species. The disease threatens approximately 350 million people in 98 countries all over the world. Cutaneous Leishmaniasis (CL) and Visceral Leishmaniasis (VL) are the mostly commonly seen forms of the disease. Treatment of the disease has remained insufficient since current antileishmanial drugs have several disadvantages such as toxicity, costliness and drug-resistance. Therefore, there is an immediate need to search for new antileishmanial compounds. TiO2@Ag nanoparticles (TiAg-Nps) have been demonstrated as promising antimicrobial agents since they provide inhibition of several types of bacteria. The basic antimicrobial mechanism of TiAg-Nps is the generation of reactive oxygen species (ROS). Even though Leishmania parasites are sensitive to ROS, there is no study in literature indicating antileishmanial activities of TiAg-Nps. Herein, in this study, TiAg-Nps are shown to possess antileishmanial effects on Leishmania tropica and Leishmania infantum parasites by inhibiting their biological properties such as viability, metabolic activity, and survival within host cells both in the dark and under visible light. The results indicate that TiAg-Nps decreased viability values of L. tropica, and L. infantum promastigotes 3- and 10-fold, respectively, in the dark, while these rates diminished approximately 20-fold for each species in the presence of visible light, in contrast to control. On the other hand, non-visible light-exposed TiAg-Nps inhibited survival of amastigotes nearly 2- and 2.5-fold; while visible light-exposed TiAg-Nps inhibited 4- and 4.5-fold for L. tropica and L. infantum parasites, respectively. Consequently, it was determined that non-visible light-exposed TiAg-Nps were more effective against L. infantum parasites while visible light-exposed TiAg-Nps exhibited nearly the same antileishmanial effect against both species. Therefore, we think that a combination of TiAg-Nps and visible light can be further used for treatment of CL, while application of TiAg-Nps alone can be a promising alternative in VL treatment.

Electrophoretic deposition infiltration of 2-D metal fibre-reinforced cordierite matrix composites of tubular shape

Stainless steel (316L) fibre mats shaped into tubular geometry were used to reinforce cordierite. The ductile phase-reinforced cordierite matrix composites were manufactured by using electrophoretic deposition (EPD) and pressureless sintering. An EPD cell suitable for the fabrication of tubular composites was designed. The relevant process parameters required to infiltrate the fibre mats with nanosized cordierite powders and to obtain homogeneous electrophoretic cordierite deposits on the inner and outer surfaces of the fibrous substrate were optimised. EPD experiments were conducted under constant voltage conditions (5 V dc) with varying deposition times. The sintered composites having internal and external deposit thickness of about 1 mm were free of surface cracks when a deposition time of 2.5 min was used. The developed metal fibre reinforced cordierite composites may constitute a promising alternative for manufacturing damage-tolerant tubular components for applications at intermediate-temperatures (up to ∼900°C).

Electrophoretic deposition of ceramic coatings on ceramic composite substrates

Abstract The applicability of electrophoretic deposition (EPD) for the fabrication of single layer and multilayer ceramic coatings on dense ceramic composite materials has been examined. Al2O3/Y-tetragonal zirconia polycrystal (TZP) functionally graded composites of tubular shape were successfully coated with a two layer coating comprising porous alumina and dense reaction bonded mullite layers. The dual layer coating structure was designed to eliminate the numerous cracks caused by volume shrinkage during sintering of the individual EPD formed layers. In another example, mullite fibre reinforced mullite matrix composites were coated with a thin layer of nanosized silica particles using EPD. The aim was to achieve a compressive residual stress field in the silica layer on cooling from sintering temperature, in order to increase composite fracture strength and toughness. The EPD technique proved to be a reliable method for rapid preparation of single layer and multilayer ceramic coatings with reproducible thickness and microstructure on ceramic composite substrates.

Carbon Nanotube-Reinforced Hydroxyapatite Coatings on Metallic Implants Using Electrophoretic Deposition

Electrophoretic deposition (EPD) has been demonstrated to be a convenient processing technique to fabricate composite ceramic coatings containing ordered arrays of carbon nanotubes. In this investigation, EPD was used to coat Ti6Al4V medical implants with hydroxyapatite (HA) layers reinforced with surface functionalized multi-walled carbon nanotubes (MWCNTs). The functionalization of MWCNTs by treating them with an acid mixture was successfully achieved in order to create functional groups on the MWCNT surfaces enabling them to be homogeneously dispersed in water. The surface treatment was also used to induce the adsorption of HA nanoparticles on MWCNT surfaces. Some critical issues, such as microcracking and peeling of HA layers after EPD, were effectively solved by the use of MWCNTs.

On the toughening mechanisms of SiC platelet-reinforced Al2O3/Y-TZP nano-ceramic matrix composites

Abstract Al 2 O 3 ceramic matrix composites toughened with 3Y-TZP (yttria-containing tetragonal zirconia polycrystals) and oriented hexagonal shape α-SiC platelets were fabricated using slip casting and cold isostatic pressing. The effect of platelet aspect ratio and volume fraction on fracture toughness, and mode and microstructure of the final composite was examined. The fracture toughness of the reinforced-composites was evaluated using indentation in four-point bending test. Scanning electron microscopy and transmission electron microscopy were used to determine the microstructural details and dominant toughening mechanisms which occurred. Toughness measurement tests and detailed observations of microstructures and fracture surface profiles have led to the conclusion that multiple-toughening behaviour via transformation toughening, microcracking, crack deflection, load transfer and platelet debonding and pull-out, as well as thermal residual stresses have a significant contribution in improving the fracture toughness. A fracture toughness value as high as 11.2 MPa m 1/2 was achieved for the specimens sintered at 1600°C for 3 h with a platelet addition of 30 vol%.

Damage assessment of alumina fibre-reinforced mullite ceramic matrix composites subjected to cyclic fatigue at ambient and elevated temperatures

Abstract The damage evaluation behaviour of alumina fibre-reinforced mullite ceramic matrix composites subjected to cyclic fatigue was investigated by means of acoustic emission (AE) monitoring and forced resonance techniques. AE technique provided sufficient information about the damage initiation and progression in real time whilst the forced resonance (FR) technique allowed the detection of changes in elastic modulus ( E ) and internal friction ( Q −1 ) that occurred with increasing number of cyclic fatigue at room temperature. From the two non-destructive detection techniques results combined with microstructural observations, it is concluded that the composite cyclic fatigue damage evolution begins with multiple crack formation within the matrix and is followed by delamination (interfacial failure). Final failure of the composite is caused by fibre fracture and extensive cyclic sliding along the fibre/matrix interface. The strong bonding between mullite matrix and alumina fibre caused by the glassy phase within the mullite matrix determined the fatigue performance of the composite at 1350°C. Regions with glassy phase failed catastrophically as a result of early fibre fracture.

Processing, toughness improvement and microstructural analysis of SiC platelet-reinforced Al2O3/Y-TZP nano-ceramic matrix composites

Abstract Hexagonal SiC platelet-reinforced Al 2 O 3 /Y-TZP ceramic matrix composites having sub-micron grains were fabricated. Slip casting was used as a wet colloidal processing route to minimize the processing defects and obtain preferred orientation with platelets. The effect of platelet volume fraction and aspect ratio on fracture toughness, strength, mode and microstructure of the final composite were examined. The fracture toughness and flexural strength of the reinforced-composites were evaluated using indentation in bending and four-point bending tests, respectively. High resolution scanning electron microscopy (HRSEM) and transmission electron microscopy were used to determine the microstructural details and the dominant toughening mechanisms that occurred. Mechanical tests and detailed microstructural results have led to the conclusion that multiple-toughening behavior via transformation toughening, microcracking, crack deflection, load transfer and platelet pull-out as well as thermal residual stresses have a significant contribution to improving the fracture toughness. A fracture toughness value as high as 11.2 MPa m 1/2 was achieved for a specimen sintered at 1600°C for 3 h with a platelet addition of 30 vol.%.

Hydrothermally Mixed Hydroxyapatite–Multiwall Carbon Nanotubes Composite Coatings on Biomedical Alloys by Electrophoretic Deposition

Hydroxyapatite (HA) coatings have been used to improve biological and mechanical fixation of metallic prosthesis. Because of extraordinary features of carbon nanotubes (CNTs), they have a lot of facilities, such as extremely strong nanoreinforcement materials for composites. HA powders were synthesized and mixed with multiwalled carbon nanotubes (MWCNTs) by a hydrothermal process. Calcium acetate (Ca (CH(3)COO)(2)) and phosphoric acid (H(3)PO(4)) were used as starting materials for synthesizing nano-HA powders. HA-MWCNTs were treated together hydrothermally at 200 °C for 2 h to synthesize nano-HA powders mixed homogeneously with MWCNTs. Cathodic deposits were obtained on Ti-based alloys using suspensions containing nano-HA and MWCNTs dispersed in n-butanol solvent. It was shown that MWCNTs interacted with HA powders during hydrothermal processing, and therefore, they can easily be dispersed within aqueous-based suspensions. It was also shown that hydrothermal surface modification of MWCNTs with functional groups was achievable, which was a significant step toward eliminating nonwetting surface behavior of MWCNTs, resulting in obtaining homogeneous dispersion of them in liquids.