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Saber-Samandari S.,Swinburne University of Technology | Berndt C.C.,Swinburne University of Technology | Gross K.A.,Innovation and Development Center
Acta Biomaterialia | Year: 2011

Mechanical compatibility between a coating and a substrate is important for the longevity of implant materials. While previous studies have utilized the entire coating for analysis of mechanical compatibility of the surface, this study focuses on the nanoindentation of a uniformly thermally sprayed splat. Hydroxyapatite was thermally sprayed to create a homogeneous deposit density, as confirmed by microRaman spectroscopy, of amorphous calcium phosphate. Substrates were commercially pure Ti, Ti-6Al-4V, Co-Cr alloy and stainless steel. Nanoindentation revealed that splats deposited on the different metals have similar hardness and elastic modulus values of 4.2 ± 0.2 GPa and 80 ± 3 GPa, respectively. The mechanical properties were affected by the substrate type more than residual stresses, which were found to be low. It is recommended that amorphous calcium phosphate is annealed to relieve the quenching stress or that appropriate temperature histories are chosen to relax the stress created in cooling the coating assembly. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Source


Cortazar T.M.,Innovation and Development Center | Guzman-Alonso M.,Innovation and Development Center | Novoa H.,University of Quindio | Riano M.,Innovation and Development Center
Skin Research and Technology | Year: 2015

Background: Researchers have studied the water content at different skin depths. Since skin differs among tissue depth, we sought to determine the depth variability of the water content after moisturizing formulation application. Furthermore, we compared the effects of formulations with different type of manufacturing processes (hot and cold process). Methods: To characterize the variations in the water content at different depths in the skin, measurements were done on the center of the inner forearm middle line of 18 sitting healthy women, before and after 1, 3, and 5 h of the application of two different moisturizing formulations (hot and cold process). Measurements included stratum corneum hydration via capacitance (SC) at 1.25 MHz (30-40 μm), and dermal water via tissue dielectric constant (TDC) at 300 MHz to depths of 500, 1500, and 2500 μm. Results: There were significant differences between the SC mean values at all evaluated time intervals after application of both formulations when compared to baseline before application (T0). The SC mean values at 1 and 3 h are higher than those of the 5 h post application for both formulations. When comparing the formulations, hot formulation shows higher SC levels at 3 and 5 h, than cold formulation. TDC mean values to skin depths of 500 and 1500 μm increased after the application for both formulations. This increase was statistically significant at 1 and 3 h, when compared with T0. At 5 h no increases were seen in the TDC for any of the formulations. When comparing the mean values of each time evaluated, there is no statistically significant difference between the two formulations at depth of neither 500 μm nor 1500 μm. TDC mean value to a depth of 2500 μm does not increase after the application of any of the formulations. Conclusions: Hot and cold formulations are effective moisturizers; however, a distinct profile was obtained for each. When water content averages were compared, the effect of hot formulation in the superficial layers of the skin was greater and longer in time than those of the cold formulation. On the other hand, moisturizing formulations applied to the skin affected the dermis water content until depth of 1500 μm. © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd. Source


Anzabi O.,Istanbul University | Aydin M.M.,Istanbul University | Ozyegin L.S.,Marmara University | Oktar F.N.,Marmara University | And 6 more authors.
Key Engineering Materials | Year: 2012

Splitting problems at HA-coated implants are generally due to biological reasons. Bondcoatings were used to prevent the splitting problem of zirconia ceramics; this method can be widely seen in industrial applications. Two main groups were used; the first group consisted of spraying a bond layer of titania onto commercially pure titanium. This followed by a spray of HA with 5, 10 and 15 % zirconia (8 % yttria doped) as main layer onto the first bond-coating. For the second group, the samples were coated without bond-coating. Firstly, X-ray diffraction patterns of the starting powders were taken. Then x-ray diffraction patterns of the plasma sprayed samples were taken. In literature, it was seen that 20 % zirconia was sufficient for the transformation into a monoclinic structure for the bond-coated samples. For this study it was found that 10 % zirconia was sufficient to transform to the same structure of the desired crystalline phase transformation. The coating kept its crystal structure and relatively small amount of amorphous transformation was detected. A similar structure was produced using less zirconia. It was thought that the use of titanium-oxide bond-coating layer would play an important role as a third variable in the results. To further investigate these phenomena, more detailed researches must be conducted with using titanium-oxide yittria stabilized zirconia (8 wt %) hydroxyapatite bond-coatings with HA main coatings. © (2012) Trans Tech Publications. Source


Saber-Samandari S.,University of Melbourne | Saber-Samandari S.,Swinburne University of Technology | Gross K.A.,University of Melbourne | Gross K.A.,Innovation and Development Center
Biomaterials | Year: 2010

The objective of this work was to characterize the deposits of calcium phosphate produced by thermal printing in terms of structure, topography and mechanical properties. Hydroxyapatite was molten and directed to (a) a titanium target in relative motion and (b) stationary titanium substrates preheated to 100 °C and 350 °C. Scanning electron microscopy showed round-like deposits, but high resolution profilometry measured the profile. Micro-Raman spectroscopy and X-ray diffraction characterized the surface for structure, while nanoindentation revealed the hardness and elastic modulus. A symmetrical hemispherical deposit was formed on a surface in slow relative motion, but an off-centre shape formed at a higher relative speed. Deposits on preheated surfaces (100 °C and 350 °C) were identified as amorphous calcium phosphate. Nanoindentation revealed no significant difference in hardness between the amorphous deposits (4.0-4.4 ± 0.3 GPa), but the elastic modulus increased from 65 ± 4 GPa (annealed calcium phosphate reference) to 88 ± 3 GPa (100 °C surface) and then to 98 ± 3 GPa (350 °C substrate). The large change in elastic modulus is thought to arise from the dehydroxylation during thermal printing. Production of functional materials through crystallization is discussed to extend the range of possible microstructures. The characterization and testing approach is useful for hemispherical deposits produced by printing, coatings (laser ablation, thermal spraying, simulated body fluid) and melt extrusion elements in scaffolds. © 2010. Source


Gross K.A.,University of Melbourne | Gross K.A.,Swinburne University of Technology | Gross K.A.,Innovation and Development Center | Saber-Samandari S.,Swinburne University of Technology | Heemann K.S.,University of Melbourne
Journal of Biomedical Materials Research - Part B Applied Biomaterials | Year: 2010

The performance of biomedical implants relies on the ability to assess and refine the microstructure of biomaterials. Instrumented nanoindentation was applied to determine the mechanical properties of plasma sprayed hydroxyapatite-coated implants from different commercial vendors. All biomedical devices contained both amorphous and crystalline phases. Nanoindentation of the amorphous phase revealed a hardness of 1.5 ± 0.3 GPa and an elastic modulus of 48 ± 6 GPa. The crystalline phase revealed a range in hardness of 3.0-7.7 GPa. The large range is attributed to the presence of porosity, surrounding amorphous areas, and hydroxyapatite (unmolten particle cores and recrystallized hydroxyapatite). A selection of the powder type (spray-dried or sintered) leads to different mechanical properties within the coating. A spray-dried powder provides a lower hardness and elastic modulus when unmolten particle cores are included in the coating. Meanwhile recrystallized areas are intermediate in hardness. The combination of a polished cross-section and nanoindentation offers the ability to determine a range of quality control tests including hardness, elastic modulus, bond strength, fracture toughness, substrate and coating roughness, crystallinity, and coating thickness. Property maps determined from nanoindentation will provide a graphical representation of the mechanical property distribution within the coating and provide a basis for coating property refinements. The assessment of commercial coatings is used a basis for discussion of future developments for hydroxyapatite coatings. © 2010 Wiley Periodicals, Inc. Source

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