Inter-Laboratory Study on Measuring the Surface Charge of Electrically Polarized Hydroxyapatite.

Surface charges on implants improve integration into bone and so require a clear protocol for achieving a surface charge and comparable results from different laboratories. This study sintered hydroxyapatite (HAp) at one laboratory to remove the influence of the microstructure on surface charge and then polarized/depolarized the pellets at two different laboratories (in Tokyo and Riga). Surface charges on HAp pellets induced by electric polarization at 400 °C in a 5 kV/cm DC electric field were measured by the thermally stimulated depolarization current (TSDC) method as 6-9 µC/cm2. The surface charge results were comparable between laboratories and also agreed with previously documented values. Recommendations describe conditions for polarization and depolarization to generate a surface charge and repeatedly achieve a comparable outcome. A visual display of the polarization mechanisms and the contribution to surface charge point to further aspects that need further development.

Measurement of ice friction and aerodynamic drag for sliding on ice: Faster sliding in winter sports.

This Method Article is co-submitted with the article Nr. JTRI_106967 in "Tribology International". In the article we investigate the reasons behind a change in friction coefficient at low sliding velocities for a skeleton on ice. To complete the study a numerical model was created with air drag and the coefficient of friction in an equation representing sliding on ice. An experiment with two measurement systems, timing sensors on an ice track and a portable accelerometer at the base of the skeleton, was performed. A numerical model was amended with experimental data. Finally, changes of friction coefficient were analyzed, the difference in results provided by experiment and numerical calculations were illustrated, and conditions at the start when static friction transitioned to kinetic friction highlighted. The main findings about the methods used were as follows: • Portable accelerometer helped to define the speed for transition to smooth sliding; • The numerical model of time and velocity had greater error; • The numerical model of distance and velocity was very close to experimental results.

Visible light to switch-on desorption from goethite.

Switching adsorption-desorption by visible light could provide the possibility for a wide range of applications that require controlled release-on-demand. Here, we demonstrate a visible-light controlled desorption behavior in aqueous suspensions for the first time. We observed cationic dye adsorption on amphoteric goethite α-FeOOH in the dark and release during visible light exposure at a pH value slightly over the isoelectric point of goethite. During this process, the dye does not degrade. Desorption is triggered by local heating due to light absorption in narrow band gap goethite, α-FeOOH.

Crystallized nano-sized alpha-tricalcium phosphate from amorphous calcium phosphate: microstructure, cementation and cell response.

New insight on the conversion of amorphous calcium phosphate (ACP) to nano-sized alpha tricalcium phosphate (α-TCP) provides a faster pathway to calcium phosphate bone cements. In this work, synthesized ACP powders were treated with either water or ethanol, dried, crystallized between 700 and 800 °C, and then cooled at different cooling rates. Particle size was measured in a scanning electron microscope, but crystallite size calculated by Rietveld analysis. Phase composition and bonding in the crystallized powder was assessed by x-ray diffraction and Fourier-transform infrared spectroscopy. Results showed that 50 nm sized α-TCP formed after crystallization of lyophilized powders. Water treated ACP retained an unstable state that may allow ordering to nanoapatite, and further transition to ß-TCP after crystallization and subsequent decomposition. Powders treated with ethanol, favoured the formation of pure α-TCP. Faster cooling limited the growth of ß-TCP. Both the initial contact with water and the cooling rate after crystallization dictated ß-TCP formation. Nano-sized α-TCP reacted faster with water to an apatite bone cement than conventionally prepared α-TCP. Water treated and freeze-dried powders showed faster apatite cement formation compared to ethanol treated powders. Good biocompatibility was found in pure α-TCP nanoparticles made from ethanol treatment and with a larger crystallite size. This is the first report of pure α-TCP nanoparticles with a reactivity that has not required additional milling to cause cementation.