TESTING THE COBALT ION EMISSION ON THE STAND FOR DIFFERENT ANGLES OF POSITIONING THE COMPONENTS OF THE METAL–METAL HIP JOINT ENDOPROSTHESIS

The paper deals with the subject related to the assessment of the influence of the axis angle of the metal components of the hip joint on the emission of cobalt ions. The tribological tests were carried out with the use of a simulator for the examination of hip joint endoprostheses, the structure of which enables the fixation of endoprosthesis components in accordance with the anatomical structure of the human hip joint. During the tests, the simulator performs flexion and extension movements as well as loads occurring in the human hip joint while walking. Loss-wear tests were carried out for nine variants of the “head–cup” system settings. These settings were determined on the basis of CT images obtained from patients after arthroplasty. After the tribological tests were completed, samples of the lubricating fluid with the wear products suspended in it were collected in order to determine the concentration of cobalt ions, which was carried out using the atomic absorption spectrometry method. As a result, the influence of the head antetorsion angle (α) and the acetabular anteversion angle (β) on the concentration of cobalt ions was analysed.

In Vitro Studies concerning Selected Properties of a Composite Material Blended with Nanofluoroapatite Crystals

The aim of the paper was to determine the potential for fluorine release from an original composite material blended with nanofluoroapatite (FAp). The level of fluoride ion emission into deionized water and saline was studied over a period of 12 weeks. Values were recorded after 1, 3, 24, 48, 72, and 96 h and then weekly for a period of 12 weeks. There were statistically significant differences in the periods of fluoride ion release from 5%FAp and 2%FAp materials into saline solution as well as into deionized water. The highest fluorine release from 5%FAp + polymer was observed in the 10th and 11th week of incubation (for saline solution) and in the 9th, 10th, and 11th week (for deionized water). The highest fluorine release from 2%FAp + polymer was observed in the 9th, 11th, and 12th week of incubation for both environments. Total fluoride ion release from 5%FAp + polymer and mean fluoride release levels were similar in 5%FAp and 2%FAp in both environments. Both tested materials (5%FAp and 2%FAp) show the ability to release fluoride ions over a long time in the experimental environment.

MRI-active inner regions of protoplanetary discs. I. A detailed model of disc structure

ABSTRACT Short-period super-Earth-sized planets are common. Explaining how they form near their present orbits requires understanding the structure of the inner regions of protoplanetary discs. Previous studies have argued that the hot inner protoplanetary disc is unstable to the magnetorotational instability (MRI) due to thermal ionization of potassium, and that a local gas pressure maximum forms at the outer edge of this MRI-active zone. Here we present a steady-state model for inner discs accreting viscously, primarily due to the MRI. The structure and MRI-viscosity of the inner disc are fully coupled in our model; moreover, we account for many processes omitted in previous such models, including disc heating by both accretion and stellar irradiation, vertical energy transport, realistic dust opacities, dust effects on disc ionization, and non-thermal sources of ionization. For a disc around a solar-mass star with a standard gas accretion rate ($\dot{M}\, \sim \, 10^{-8}$ M⊙ yr−1) and small dust grains, we find that the inner disc is optically thick, and the accretion heat is primarily released near the mid-plane. As a result, both the disc mid-plane temperature and the location of the pressure maximum are only marginally affected by stellar irradiation, and the inner disc is also convectively unstable. As previously suggested, the inner disc is primarily ionized through thermionic and potassium ion emission from dust grains, which, at high temperatures, counteract adsorption of free charges on to grains. Our results show that the location of the pressure maximum is determined by the threshold temperature above which thermionic and ion emission become efficient.