Yapıncak Göncü

Electrophoretic deposition of hydroxyapatite-hexagonal boron nitride composite coatings on Ti substrate

In this study, commercial pure titanium samples were coated with nano hydroxyapatite-nano hexagonal boron nitride (nano HA-nano hBN) composite by electrophoretic deposition (EPD). The effect of process parameters (applied voltage, deposition time and solid concentration) on the coating morphology, thickness and the adhesion behavior were studied systematically and crack free nano hBN-nano HA composite coating production was achieved for developing bioactive coatings on titanium substrates for orthopedic applications. For the examination of structural and morphological characteristics of the coating surfaces, various complementary analysis methods were performed. For the structural characterization, XRD and Raman Spectroscopy were used while, Scanning Electron Microscopy (SEM) equipped with an energy dispersive spectrometer (EDS) and Transmission Electron Microscopy (TEM) techniques were carried out for revealing the morphological characterization. The results showed that nano HA-nano hBN were successfully deposited on Ti surface with uniform, crack-free coating by EPD. The amounts of hBN in suspension are considered to have no effect on coating thickness. By adding hBN into HA, the morphology of HA did not change and hBN has no significant effect on porous structure. These nanostructured surfaces are expected to be suitable for proliferation of cells and have high potential for bioactive materials.

Wear Characteristics of Traditional Manganese Phosphate and Composite hBN Coatings

In this study, the tribological properties of traditional manganese phosphate coatings and composite hBN coatings composed of nano-hexagonal boron nitride (hBN) in layered manganese phosphate crystals on AISI 1040 steel were investigated. Wear tests were carried out under controlled temperature and humidity using ball-on-disc tribometers for samples that were either submerged in oil or retaining oil on their surfaces at a sliding speed of 2.5 cm/s with loads of 1, 3, 5, and 10 N and sliding distances of 40, 80, 100, and 120 m. The surface profiles before and after the tests were used to characterize the wear. The surfaces of the coated samples were examined using scanning electron microscopy (SEM). The coefficients of friction and wear rates of the coated samples were also measured. The average wear rates of the composite hBN-coated samples were significantly lower than those of the traditional manganese phosphate–coated samples for each of the loading conditions for the oil submersion and retained oil tests. The coefficient of friction (COF) values for the traditional manganese phosphate–coated samples did not change significantly with increasing load. The COF values for the composite hBN coated–samples decreased with increasing load in the oil submersion test.

Effects of hexagonal boron nitride nanoparticles on antimicrobial and antibiofilm activities, cell viability

The objective of this work was to investigate the antimicrobial and antibiofilm activities of hBN nanoparticles against Streptococcus mutans 3.3, Staphylococcus pasteuri M3, Candida sp. M25 and S. mutans ATTC 25175. Minimum Inhibitory Concentration (MIC) of hBN nanoparticles were determined against Streptococcus mutans 3.3, Staphylococcus pasteuri M3, Candida sp. M25 growth. In addition, we aimed to evaluate the cytotoxic effects of hBN nanoparticles on human normal skin fibroblast (CCD-1094Sk, ATCC® CRL 2120 ™) and Madin Darby Canine Kidney (MDCK) cells by using various toxicological endpoints. Cell viability was assessed by MTT, SRB and PicoGreen assays. After experimental analyses, it was revealed that hBN nanoparticles show better MIC results. The MIC values were higher for Streptococcus mutans ATTC 25175 and Staphylococcus pasteuri M3 and lower against Streptococcus mutans 3.3, Candida sp. M25. Surprisingly, hBN nanoparticles showed a high antibiofilm activity on preformed biofilm, which inhibited biofilm growth of S. mutans 3.3, S. mutans ATTC 25175 and Candida sp.M25. These results show that hBN nanoparticles may be an option to control oral biofilms. In cell viability tests, the cells were exposed to 0.025-0.4 mg/mL concentrations of hBN nano particle suspension. The exposure time to the hBN nanoparticle suspensions were 24 h and 48 h. The results indicate that there is no cytotoxic effect on CRL 2120 and MDCK cells at the concentration range of 0.025-0.1 mg/mL. However, on both first and second day, hBN caused mild cytotoxicity on CRL-2120 cells at high hBN concentration (0.2-0.4 mg/mL). Considering all the results of this study, in appropriate concentration (0.1 mg/mL) hBN nanoparticles can be considered a potential safe oral care product.

Structural and chemical analysis of hydroxyapatite (HA)-Boron nitride (BN) nanocomposites sintered under different atmospheric conditions

Calcium phosphate derivatives have been widely employed in medical and dental applications for hard tissue repair, as they are the main inorganic constitution of hard tissue; such as bones and teeth. Owing to their excellent osteoconductive and bioactive properties, hydroxyapatite- (HA) based ceramics are the best candidates of this group for medical, bioscience, and dental applications. However, when replacing a bone or tooth, HA is not able to sustain similar mechanical properties. In this study, to improve the mechanical properties, nanoscale hexagonal boron nitride with different compositional percentages was added to the nano HA to form composites. The effect of compositional changes and sintering parameters on microstructural and morphological properties of the ceramic composites was comparatively investigated. Detailed chemical characterization of the composite materials was carried out using X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, and energy-dispersive X-ray spectroscopy, whereas scanning electron microscopy and atomic force microscopy investigations were employed to monitor morphological and surface features. Additional transmission electron microscopy investigations were carried out to reveal the nanostructure and crystal structure of the composites.