[Strong Antibacterial Efficacy of Titanium Surfaces Modified by Nanotubes and Silver Nanoparticles]. / Silné antibakteriální vlastnosti kovového povrchu modifikovaného nanotrubicemi titanu a nanostríbrem.

PURPOSE OF THE STUDY Nano-structuring and nano-silver have been extensively studied for improving the antibacterial ability of implants due to their powerful antibacterial activity; however, there is no clinical application as yet. The aim of the study was to determine the antibacterial, antiadhesive and cytotoxic features of Ti6Al4V modified with nano-texturing and silver nano-particles. MATERIAL AND METHODS The nanoparticles were applied on polished and nano-textured Ti6Al4V using sonoreduction. The surface topography, roughness, friction coefficients, hardness and elastic modulus values for prepared top layers were established. The materials were tested for antibacterial and antiadhesion activity using reference bacterial strains (Staphylococcus epidermidis CCM 7221, Staphylococcus aureus MRSA 4591, Enterococcus faecalis CCM 4224, Escherichia coli CCM 3954) and their cytocompatibility. RESULTS A strong antibacterial activity of samples treated with nano-texture and/or silver nanoparticles compared to all the tested bacterial strains at 24 hours was proven. This antibacterial activity was diminishing in relation to Staphylococcus aureusand Enterococcus faecalisat 48 and 72 hours but remained very effective against Staphylococcus epidermidisand Escherichia coli. We also demonstrated antibiofilm activity for samples treated with silver nanoparticles and nano-tubes in experiments lasting 24 and 72 hours. DISCUSSION Our main findings are in agreement with those reported in recent literature. The implant surfaces treated with nano-texture in combination with silver nanoparticles exhibit strong antibacterial and antibiofilm characteristics. Despite there is conclusive evidence of strong antibacterial functioning, why these implant modifications have not been widely applied in clinical practice remains a question. While many obstacles including legislative procedures required for clinical implementation are more or less known, it should be clearly demonstrated that this surface modification does neither harm the patient nor interfere with the long-term survivorship of the implants before their wide-range clinical application. CONCLUSIONS Surface modification of Ti6Al4V with nano-texturing and silver nanoparticles resulted in strong antibacterial and modest antibiofilm effects. Thus, our results confirmed the technological potential of nano-texturing and silver nanoparticles for the improvement of antibacterial properties of implants. Key words:prosthetic joint infection, anti-infective biomaterials, titanium alloy, silver nanoparticles, nanotubes, prevention of infection.

The mechanism of corrosion of palladium-silver binary alloys in artificial saliva.

Palladium dental casting alloys are alternatives to gold alloys. The aim of this study was to determine the electrochemical behaviour and the corrosion mechanism of binary silver-palladium alloys. Seven binary silver-palladium alloys and pure palladium and silver were tested in a model saliva solution. Electrochemical tests included corrosion potential, polarization resistance, and potentiodynamic polarization measurements. The corrosion products, which may be theoretically formed, were determined by thermodynamic calculation. The behaviour of silver and silver-rich alloys was dominated by the preferential formation of a thiocyanate surface layer, which controlled the free corrosion potential. Palladium dissolved in the form of a thiocyanate complex, but the surface became passivated by either palladium oxide or solid palladium thiocyanate layer, the thermodynamic calculations indicating preference for the oxide. Palladium-rich alloys showed evidence of silver depletion of the surface, resulting in behaviour similar to palladium. Examination of binary silver-palladium alloys has made possible determination of the role of the components of the alloys and model saliva in the corrosion behaviour. The findings are applicable to the more complex commercial dental alloys containing silver and palladium as major components.

[Effect of manifacturing technology on the resistance to corrosion of amalgam fillings and speed of mercury emission]. / A fogászati amalgám gyártástechnológiájának hatása az amalgámtömés korrózióállóságára és a higany kibocsátásának sebességére.

The study investigates the influence of the various manufacturing technological alternatives of a given alloy on the corrosion properties, as well as it evaluates the quantity of mercury release from the amalgam filling having the same alloy. The resistance of dental amalgams to corrosion is the function of their precious metal (mercury and silver) content. The release speed of the mercury depends on the original condition of the alloy. The highest values were given for filing amalgam. When investigating the composition of amalgam mainly in spherical form, a significant decrease could be here determined.

[Changes in Roughness of Exposed Head of POLDI Femoral Component.]. / Zmeny drsnosti exponované hlavice cementované totální endoprotézy kycelního kloubu POLDI.

The authors have examined the roughness of the heads of four exposed all-metal cemented femoral components of Poldi type using Talysurf 6 device. The results achieved were compared with the roughness of the not yet used head of Poldi femoral component. Both in the exposed and not used heads the Ra factor lower than the value reported in production documentation of the manufacturer. Even in a longterm exposition (17 years) there occurred no changes in the roughness of the metal head of the femoral component. Therefore it is possible in revision surgeries due to aseptic loosening of the acetabular component, to replace only the cup and leave the original stem in place. Key words: THR, femoral component, surface roughness.

[Causes of corrosive mechanical defects in isoelastic endoprostheses]. / Príciny korozne mechanických poruch izoelastických endoprotéz.

Within the framework of evaluation of endoprostheses of the hip joint reoperated at the orthopaedic clinic of the Institute for Postgraduate Medical Training, Faculty Hospital Na Bulovce in Prague in the course of six years the authors made a more detailed analysis of the group of isoelastic POLDI endoprostheses which displayed obvious signs of corrosion. The specimens from this group were subjected to evaluation focused on corrosion, metallographic and fractographic evaluation. In impaired wires of isoelastic endoprostheses the fracture surfaces have a fatigue character where a corrosion fatigue mechanism may be assumed as well fracture with a dominant mechanical component of stress. From the analysis of corrosion ensues that the connections of the wire shank with the head of the endoprosthesis are affected by crevice corrosion, the revealed fractures and cracks are most probably associated with corrosion fatigue. The construction of isoelastic prostheses of this type is the cause of corrosion processes which lead to mechanical failure. This should be the reason to refuse them for patients of any age group.