Key Engineering Materials Vols. 309-311

Abstract: Hydroxyapatite (HA) material, collected from human tooth, was calcined and then separated very easily to enamel HA (EHA) and dentine HA (DHA). The EHA and DHA were plasma sprayed on pre-prepared titanium implants. HeLa (a lineage malignant fibroblast cell) and primary fibroblast cells cell lines were used in this study. The results using fibroblasts from primary culture are interesting since the cells did not die or became apoptotic. However, this does not mean that the present method reveals the complete biocompatibility of the tested HA material. This study aimed to investigate if fibroblasts with fluorescent tests could be used as a secondary evaluation method for biocompatibity fibroblasts cell culture studies prior to osteoblasts cell culture.

Abstract: The purpose of this study was to develop a biologically derived fluor rich hydroxyapatite (HA) for plasma spraying purposes by a simple way. HA was derived from human teeth and processed in laboratory conditions as plasma coating material. For manufacturing data HALL flowability, shear stress, SEM, metallography, X-ray diffraction and ion analyzing tests were performed. Implant prototypes were prepared from titanium rods, which were coated with HA powder with a plasma coating unit. Statistical studies were also done to test the performance for plasma coatings. All results showed that this production method enables the manufacturing of HA powders with biological origin for plasma spraying purposes compared with other time consuming and delicate methods. Powder morphology developed by selective grinding process was a key parameter to start such a production line in industry.

Abstract: In order to overcome the fragility and to improve the physical stability of hydroxyapatite (HA) on the implant, 5, 10, and 15 % yttria stabilized zirconia (YTZP) was added to the starting plasma spraying HA powder Metco XPT-D-703. From the recent literature it is already known that HA coatings tend to dissolve in body fluid environment. To decrease the dissolution effect many additives like zirconia (Zr) could be added to HA powder. In this study, prepared HA composite powders were sprayed onto titanium (Ti) surfaces with a Metco plasma gun. As a control group, pure HA powder was sprayed onto other Ti samples. All samples were subjected to tensile tests according to the ASTM C-633-79. SEM images were taken using back-scattering from prepared cross-sections. X-ray diffraction images were taken from the surface. It was seen that with the increase of the Zr content, the tensile test values increased. Pure HA showed also that the addition of Zr had improved the tensile bond strenght (TBS) values.

Abstract: Nano-sized HA (nHA) was applied to the surface of glass and titanium substrates using electrostatic atomisation spray (EAS) deposition. The phase purity of nHA was confirmed by X-ray diffraction. The nHA suspension consisted of rod–like particles 20-30nm in width and 50-100nm in length. The viscosity and conductivity of nHA suspension were 321 mPa s and 5.6 x 10-4 S/m, respectively. EAS of nHA in cone-jet mode was achieved at flow rate of 10-9 m3s-1 with the applied voltage between the needle and the ring-shaped ground electrode of ~6 kV. Micrometer- to submicrometerscaled nHA islands were successfully deposited on the substrate surface. Image analysis showed that the area percentage of nHA increased with deposition time, it covered 50% of the surface area after 10s of spraying. Partial dissolution of nHA was observed after immersion in deionised water for 1 month, particularly on the submicrometer sized nHA islands. Formation of a bone-like apatite layer was found after incubation in simulated body fluid (SBF K9) for 5 days, indicating the high bioactivity of the nHA deposits. In vitro culture with human osteoblast cells showed that the nHA islands were able to support the growth of HOB cells during 7 days of culture; the HOB cell activity increased with culture time as well as EAS deposition time. Immunofluorescence study showed that HOB cells expressed well-organised actin stress fibres on nHA deposited surfaces after 3 days of culture. The result indicated that nHA deposition provided more favourable surfaces for cell attachment. Therefore, electrostatic atomization spray deposition of nHA offers great potential for the creation of bioactive surfaces on bioinert implant surface to provide improved interfacial bonding with host tissues.

Abstract: Commercial hydroxyapatite powders were electrophoretically deposited on titanium substrates. In this study, the effect of deposition durations and applied voltages on deposition yield was investigated. Green and sintered coatings were studied by SEM and XRD. It was observed that by applying low voltages and presedimentation, uniform and smooth hydroxyapatite coating can be prepared. In order to obtain roughened hydroxyapatite coatings, high voltages have to be applied. It was concluded that experimental conditions of powder concentration, applied potential, and presedimentation have a significant effect on the deposited coating morphology.

Abstract: Homogeneous nano-thin layer of hydroxyapatite (HAp) nanocrystals on the gold surface was fabricated by an electrophoretic deposition method (EPD); the HAp nanocrystals were dispersed into ethanol and the applied voltage was varied. The HAp nanocrystals were prepared by a wet method at 4 °C and 80 °C, which were characterized by X-ray diffraction and Fourier-transform infrared spectroscopy. The micro-thin layer of HAp nanocrystals was initially formed, and the ultrasonic treatments can remove the surplus nanocrystals from the surface. The nanostructure of the surface was investigated by atomic force microscopy and contact angle measurement. The thickness of coating layers was approximately 20nm and the root mean square (RMS) roughness was under 6.6 nm, which was clearly depended on the crystal sizes, applied voltages and applied times.

Abstract: A new hydrothermal method is proposed which enables us to prepare thin hydroxyapatite (HA) ceramic coatings on Ti substrates with a curved surface at low temperatures. The method uses double layered capsules in order to produce a suitable hydrothermal condition; the inner capsule encapsulates the coating materials and a Ti substrate, and the outer capsule is subjected to isostatic pressing under the hydrothermal condition. In this study, it is demonstrated that a pure HA ceramic layer with the thickness of 50 µm could be coated to a Ti cylindrical rod at the low temperature as low as 135°C under the confining pressure of 40 MPa. Pull-out tests were conducted to obtain an estimate for the adhesion properties of the HA coating prepared by the double layered capsule method. The shear strength obtained from the pull-out tests was in the range of 4.0-5.5 MPa. It was also shown that the crack propagation occurred within the HA coating layer, not along the HA/Ti interface in the pull-out tests.

Abstract: In order to optimize the dissolution resistance, cell attachment and Ca and P releasing ability of the calcium phosphate coatings, Hydroxyapatite/fluorapatite (HA/FA) biphasic coatings are prepared and characterized. Ultrasonically dispersing of HA powders in the mixed ethanol solution of Ca(NO3)2, P2O5 and HPF6, to form a “colloidal sol” for dip coating. The coatings are prepared on Ti6Al4V substrate by dip coating, 150oC drying and 600oC firing. The coatings are characterized by X-ray Diffractometer for the crystalline phase, X-ray Photoelectron Spectroscopy for chemical composition and Scanning Electron Microscopy for the surface morphology. The results show biphasic HA/FA coatings with homogenous distribution of HA particle in the FA matrix can be obtained. The nominal F content of the coatings decreases with the increasing amount of HA, and the surface morphology is rough. These demonstrate the obtained biphasic HA/FA coatings are suitable to response to cells, accelerating bone formation.

Abstract: Biomimetic apatite coatings are widely used in orthopaedic applications to provide bioinert material surfaces with bioactive behaviour by means of initiating bone growth at the implant surface. In this study we manufactured biomimetic calcium phosphate coatings consisting of a calcium deficient carbonated apatite by immersing activated titanium platelets into simulated body fluid (SBF). The development of the crystal phases was monitored by X-ray diffractometry (XRD) in addition to Fourier-transform infrared (FT-IR) spectroscopy. After annealing in air up to 600 °C luminescence of the biomimetically derived apatite was observed. The photo-induced emission spectra were recorded in the range from 400-750 nm at excitation wavelengths ranging 238 to 450 nm. A blue (437 nm) and a green (556 nm) emission were found between 200 to 600 °C visually appearing white. The results are discussed in terms of chemical and crystallographic changes in the biomimetic calcium phosphate layer during heat treatment.