In-vitro bioassay of electrophoretically deposited hydroxyapatite–zirconia nanocomposite coating on Ti–6Al–7Nb implant

Hydroxyapatite–zirconia (HA–ZrO₂) nanocomposite coatings were prepared on Ti–6Al–7Nb implant by electrophoretic deposition at constant voltage of 50?V. The influence of zirconia content on the phase transition, morphological evolution, wettability and in vitro cyto-compatibility, together with the bioactivity of the nanostructured coatings was examined. From the X-ray diffractometer patterns, a tangible increase and decrease in the peak intensity and width of the characteristic peaks were observed after subsequent sintering at 1000°C for 1?h under a constant flow of argon gas. The sintered HA and HA–ZrO₂ composite coatings showed higher hydrophilicity than the bare substrate. From the in vitro bioassays, surface treatment of Ti67 implant by HA–ZrO₂ nanocomposite coating increased the cell response as well as the apatite formability, in simulated body fluid within 5 days of incubation.     

Wet chemistry approach to the preparation of tantalum-doped hydroxyapatite: Dopant content effects

Tantalum-doped hydroxyapatite (Ta-doped HA) nanopowders with different Ta contents were synthesized by a wet-chemical precipitation route. The structure modification and charge compensation mechanism were investigated by various characterization techniques. Due to the smaller size of tantalum ions compared to the Ca²⁺ size, it was assumed that the tantalum ions occupy either the Ca²⁺ and/or the interstitial positions in the HA lattice, where the charge imbalance from to this substitution was compensated by the Ca²⁺ vacancies. From the XRD patterns, the as-synthesized nanopowders were poorly crystalline apatite in the absence and presence of different dopant contents. The hexagonal HA and tricalcium phosphate (β-TCP) phases as biphasic calcium phosphate mixtures were formed after heating at 900 °C. In addition to the β-TCP phase, minor extra phases such as calcium oxide (CaO) and calcium pyrophosphate (Ca₂P₂O₇) were identified from the HA decomposition. The FTIR results indicated that the decrease of structural hydroxyl groups depended on both tantalum oxyanions and carbonate contents. In the XPS profile, the Ta 4 f peak of the doped sample could be decomposed into four main components, which showed different oxidation states for tantalum (TaO₂ oxide). According to the TEM observations, the doped calcined powder at 900 °C was composed of uniform nanoneedles with an average length and width of 120 ± 50 and 10 ± 5 nm, respectively.     

Second-order H∞ optimal LMS and NLMS algorithmsbased on a second-order Markov model

It is shown that two algorithms obtained by simplifying a Kalman filter considered for a second-order Markov model are H^∞ suboptimal. Similar to least mean squares (LMS) and normalised LMS (NLMS) algorithms, these second order algorithms can be thought of as approximate solutions to stochastic or deterministic least squares minimisation. It is proved that second-order LMS and NLMS are exact solutions causing the maximum energy gain from the disturbances to the predicted and filtered errors to be less than one, respectively. These algorithms are implemented in two steps. Operation of the first step is like conventional LMS/NLMS algorithms and the second step consists of the estimation of the weight increment vector and prediction of weights for the next iteration. This step applies simple smoothing on the increment of the estimated weights to estimate the speed of the weights. Also they are cost-effective, robust and attractive for improving the tracking performance of smoothly time-varying models