friction and mechanical properties
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This study investigates a tribological performance of diamond like carbon (DLC) coated micro dimpled prosthesis heads against ceramic cups in a novel pendulum hip joint simulator. The simulator enables determining friction coefficient and viscous effects of a concave shaped specimen interface (conformal contact). Two types of DLC such as hydrogenated amorphous carbon (a-C:H) and tetrahedral amorphous carbon (Ta-C) and one set of micro dimple (diameter of 300µm, depth of 70µm, and pitch of 900µm) were fabricated on metallic prosthesis heads. The experiment results reveal a significant friction coefficient reduction to the 'dimpled a-C:H/ceramic' prosthesis compared to a 'Metal (CoCr)/ceramic' prosthesis because of their improved material and surface properties and viscous effect. The post-experiment surface analysis displays that the dimpled a-C:H yielded a minor change in the surface roughness, and generated a larger sizes of wear debris (40-200nm sized, equivalent diameter), a size which could be certainly stored in the dimple, thus likely to reducing their possible third body abrasive wear rate. Thus, dimpled a:C-H can be used as a 'metal on ceramic hip joint interface', whereas the simulator can be utilized as an advanced bio-tribometer.
An advanced surface engineering process combining micro-texture with a plasma carburising process was produced on CoCrMo femoral head, and their tribological properties were evaluated by the cutting-edge pendulum hip joint simulator coupled with thin film colorimetric interferometry. FESEM and GDOES showed that precipitation-free C S-phase with a uniform case depth of 10μm was formed across the micro-textures after duplex treatment. Hip simulator tests showed that the friction coefficient was reduced by 20% for micro-metre sized texture, and the long-term tribological property of microtexture was enhanced by the C-supersaturated crystalline microstructure formed on the surface of duplex treated CoCrMo, thereby enhancing biotribological durability significantly. In-situ colorimetric interferometry confirmed that the maximum film thickness around texture area was 530nm, indicating that the additional lubricant during sliding motion might provide exceptional bearing life.
STATEMENT OF PROBLEM: Fatigue failure of implant components is a common clinical problem. Plasma nitriding, an in situ surface-strengthening method, may improve fatigue properties of dental implants. PURPOSE: The purpose of this in vitro study was to evaluate the effect of plasma nitriding on the fatigue behavior of implant systems. MATERIAL AND METHODS: The preload and friction coefficient of plasma nitrided abutment screws, as well as settlement of the implant-abutment interface, were measured. Then, the reverse torque values and pullout force were evaluated after cyclic loading. Finally, the fatigue properties of the implant system were investigated with static fracture and dynamic fatigue life tests, and the morphology of the fracture on the surface of the implant system was observed. RESULTS: The plasma nitriding treatment reduced the friction coefficient; increased the preload, settlement value, reverse torque values, pullout force, and static fracture load; and prolonged fatigue life. Furthermore, abutment screws with plasma nitriding treatment showed a different fatigue fracture mode. CONCLUSIONS: Plasma nitriding improved mechanical performance and may be a suitable way to optimize the fatigue behavior of dental implants.
This aim of this study is to determine the elastoplastic properties of Ni-free Al3FeSi2 intermetallic coatings grown on medical stainless steel under different experimental conditions. Elastoplastic properties are defined by the plasticity index (PI), which correlates the hardness and the Young's modulus. Special emphasis is devoted to correlate the PI with the wear resistance under sliding contact, determined by scratch testing, and fracture toughness, determined by using a novel method based on successive impacts with small loads. With regard to the substrate, the developed coatings are harder and exhibit a lower Young's reduced modulus, irrespective of the experimental conditions. It has been shown that preheating of the samples prior to hot dipping and immersion influences the type and volume fraction of precipitates, which in turn also affect the nanomechanical properties. The higher the preheating temperature is, the greater the Young's reduced modulus is. For a given preheating condition, an increase of the immersion time yields a decrease in hardness. Although apparent friction coefficients of coated specimens are smaller than those obtained on AISI 316 LVM, they increase when using preheating or higher immersion times during processing, which correlates with the PI. The presence of precipitates produces an increase in fracture toughness, with values greater than those presented by samples processed on melted AlSi alloys with lower Si content (12 wt%). Therefore, these intermetallic coatings could be considered "hard but tough", suitable to enhance the wear resistance, especially when using short periods of immersion.
The use of protective coatings in biomedical field is an ongoing scientific challenge. Among different materials, carbon-based coatings are considered a potential surface treatment for orthopaedic implants. In this study, the effect of Zr incorporation in amorphous carbon coatings on the wear behaviour under protein containing lubrication was investigated. The coatings were deposited by dc unbalanced magnetron sputtering in Ar (non-hydrogenated) and Ar+CH4 (hydrogenated) discharges onto Ti based biomedical substrate. To improve the adhesion between the film and substrate a functional gradient Ti based layer was deposited (~550 nm). The surface wettability was evaluated to assess the effect of the Zr and hydrogen content. The films with Zr were found to be hydrophobic enhancing the protein adsorption onto the surface; no significant differences were found when H was incorporated in the films. The adsorption layer characterized by X-ray photoelectron spectroscopy showed a well defined nitrogen peak originating from the organic layer. The tribological properties of the film were evaluated by unidirectional pin-on-disc testing with diluted bovine serum lubrication and physiological solution at 37 ± 3C°. The friction and the wear of the coatings were very low compared to uncoated substrates in both lubrication conditions. The ability of the surfaces to adsorb proteins was considered as the driving force for wear resistance acting as a protecting layer. In addition, the incorporation of Zr decreased the wear of the counterbody (Ti alloy) due to higher albumin adsorption.
- MeSH
- adsorpce MeSH
- biokompatibilní materiály MeSH
- biokompatibilní potahované materiály chemie MeSH
- fotoelektronová spektroskopie MeSH
- mechanický stres MeSH
- povrchové vlastnosti MeSH
- proteiny chemie MeSH
- protézy a implantáty MeSH
- sérový albumin hovězí chemie MeSH
- skot MeSH
- slitiny MeSH
- testování materiálů MeSH
- titan chemie MeSH
- tření MeSH
- uhlík chemie MeSH
- vodík chemie MeSH
- zirkonium chemie MeSH
- zvířata MeSH
- Check Tag
- skot MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
In pharmaceutical industry, the use of lubricants is mostly based on historical experiences or trial and error methods even these days. It may be demanding in terms of the material consumption and may result in sub-optimal drug composition. Powder rheology enables more accurate monitoring of the flow properties and because the measurements need only a small sample it is perfectly suitable for the rare or expensive substances. In this work, rheological properties of four common excipients (pregelatinized maize starch, microcrystalline cellulose, croscarmellose sodium and magnesium stearate) were studied by the FT4 Powder Rheometer, which was used for measuring the compressibility index by a piston and flow properties of the powders by a rotational shear cell. After an initial set of measurements, two excipients (pregelatinized maize starch and microcrystalline cellulose) were chosen and mixed, in varying amounts, with anhydrous colloidal silicon dioxide (Aerosil 200) used as a glidant. The bulk (conditioned and compressed densities, compressibility index), dynamic (basic flowability energy) and shear (friction coefficient, flow factor) properties were determined to find an optimum ratio of the glidant. Simultaneously, the particle size data were obtained using a low-angle laser light scattering (LALLS) system and scanning electron microscopy was performed in order to examine the relationship between the rheological properties and the inner structure of the materials. The optimum of flowability for the mixture composition was found, to correspond to empirical findings known from general literature. In addition the mechanism of colloidal silicone dioxide action to improve flowability was suggested and the hypothesis was confirmed by independent test. New findings represent a progress towards future application of determining the optimum concentration of glidant from the basic characteristics of the powder in the pharmaceutical research and development.
Diamond like carbon (DLC) is applied as a thin film onto substrates to obtain desired surface properties such as increased hardness and corrosion resistance, and decreased friction and wear rate. Microdimple is an advanced surface modification technique enhancing the tribological performance. In this study, DLC coated microdimples were fabricated on hip prosthesis heads and their mechanical, material and surface properties were characterized. An Electro discharge machining (EDM) oriented microdrilling was utilized to fabricate a defined microdimple array (diameter of 300 µm, depth of 70 µm, and pitch of 900 µm) on stainless steel (SS) hip prosthesis heads. The dimpled surfaces were then coated by hydrogenated amorphous carbon (a-C:H) and tetrahedral amorphous carbon (Ta-C) layers by using a magnetron sputtering technology. A preliminary tribology test was conducted on these fabricated surfaces against a ceramic ball in simulated hip joint conditions. It was found that the fabricated dimples were perpendicular to the spherical surfaces and no cutting-tools wear debris was detected inside the individual dimples. The a-C:H and Ta-C coatings increased the hardness at both the dimple edges and the nondimpled region. The tribology test showed a significant reduction in friction coefficient for coated surfaces regardless of microdimple arrays: the lowest friction coefficient was found for the a-C:H samples (µ = 0.084), followed by Ta-C (µ = 0.119), as compared to the SS surface (µ = 0.248).
- MeSH
- biokompatibilní potahované materiály chemie MeSH
- kyčelní protézy * MeSH
- lidé MeSH
- povrchové vlastnosti MeSH
- uhlík chemie MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Nowadays, most of the newly developed active pharmaceutical ingredients (APIs) consist of cohesive particles with a mean particle size of <100μm, a wide particle size distribution (PSD) and a tendency to agglomerate, therefore they are difficult to handle in continuous manufacturing (CM) lines. The current paper focuses on the impact of various glidants on the bulk properties of difficult-to-handle APIs. Three challenging powders were included: two extremely cohesive APIs (acetaminophen micronized (APAPμ) and metoprolol tartrate (MPT)) which previously have shown processing issues during different stages of the continuous direct compression (CDC)-line and a spray dried placebo (SD) powder containing hydroxypropylmethyl cellulose (HPMC), known for its sub-optimal flow with a high specific surface area (SSA) and low density. Four flow-enhancing excipients were used: a hydrophilic (Aerosil® 200) and hydrophobic (Aerosil® R972) fumed silica grade, a mesoporous silica grade (Syloid® 244FP), and a calcium phosphate excipient (TRI-CAFOS® 200-7). The APIs and binary API/glidant blends (varied between 0.5-2.75 w/w%) were characterized for their bulk properties relevant for CDC. The results indicated that optimizing different bulk parameters (e.g., density, flow, compressibility..) of an API required varying weight percentages of the glidant (e.g., different surface area coverage (SAC)) depending on the APIs. Moreover, even at similar SAC, the impact of the glidant on the bulk characteristic of the APIs depended on the glidant type properties. While nano-sized silicon dioxide were effective for improving the flowability of a powder, other glidants (mesoporous silica and tricalcium phosphate (TCP)) showed also promise as alternatives. Additionally, an excess of glidant, referred to as oversilication, negatively impacted some bulk parameters, but other characteristics were unaffected. Finally, to determine the appropriate concentration of the different classes of glidants, SAC calculations, an understanding of the glidant's working mechanism, and knowledge about the API's characteristics (i.e., morphology, compressibility, flowability, aeration, density, and wall friction) are required. This study confirmed the necessity of including various material characterization techniques to assess the impact of glidants on the bulk characteristics of APIs.
- MeSH
- deriváty hypromelózy * chemie MeSH
- farmaceutická chemie metody MeSH
- fosforečnany vápenaté * chemie MeSH
- hydrofobní a hydrofilní interakce MeSH
- metoprolol * chemie MeSH
- nerozplněné léky MeSH
- oxid křemičitý chemie MeSH
- paracetamol * chemie MeSH
- pomocné látky * chemie MeSH
- prášky, zásypy, pudry * MeSH
- příprava léků metody MeSH
- reologie * MeSH
- velikost částic * MeSH
- Publikační typ
- časopisecké články MeSH
Předmět sdělení: Opotřebení zubu je komplexní multifaktoriální fenomén podmíněný interakcí biologických, mechanických, chemických a tribologických faktorů. Povrch tvrdých zubních tkání, stejně jako výplňového materiálu nahrazujícího sklovinu a dentin, je za své funkce mechanicky zatěžován buď otěrem o antagonisty (atrice) nebo o jiný objekt v dutině ústní, například zubní kartáček, pastu atd. (abraze). Tyto procesy vedou ke vzniku povrchových defektů tvrdých zubních tkání, ale i výplní. Ve sdělení jsou popsány možné metody experimentálního ("pin on disc" metoda, tooth brushing machine, počítačem řízený simulátor čelistí, měření tvrdosti a modulu pružnosti materiálů za použití nanoindentorů a vrypové zkoušky atd.) a klinického hodnocení (kritéria podle Ryge a Cvara, FDI kritéria, profilometrie a měření počítačových modelů CAD/CAM skenerem) opotřebení dentálních rekonstrukčních materiálů. Závěr: Znalost jednotlivých vlastností rekonstrukčních materiálů ovlivňujících jejich opotřebení pomůže ošetřujícímu lékaři zvolit vhodný typ materiálu a správně informovat pacienta o životnosti rekonstrukce.
Background: Tooth wear is a complex multifactorial phenomenon conditioned by the interaction of biological, mechanical, chemical and tribological factors. The surface of hard dental tissues as filling material replacing enamel and dentine has mechanical load by antagonist (attrition) or another object in the oral cavity such toothbrush, toothpaste, etc. (abrasion). These processes lead to surface defects of hard dental tissues and fillings. The report describes the possible methods of experimental ("pin on disc" method, tooth brushing machine, computer-controlled jaw simulator, material hardness and elastic modulus measurement using nanoindentation, scratch test, etc.) and clinical evaluation (Ryge and Cvar criteria, FDI criteria, profilometry, measurement of computer models by CAD/CAM scanner) wear of dental reconstruction materials. Conclusion: Knowledge of the individual properties of the reconstruction materials influencing their wear will help the dentist to choose the appropriate type of material and to properly inform the patient about its reconstruction lifespan.
- Klíčová slova
- opotřebení, kritéria Ryge a Cvara, FDI kritéria, tribologie, nanoindentace, profilometrie,
- MeSH
- lidé MeSH
- opotřebení zubů * diagnóza MeSH
- tření MeSH
- zubní materiály * MeSH
- zubní náhrady * MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- přehledy MeSH
... 13 -- 3.1.1 Medial Meniscus 13 -- 3.1.2 Lateral Meniscus 15 -- 3.2 Meniscal Functions 16 -- 3.3 Friction ... ... -- 4.2 Articular Cartilage 64 -- 4.2.1 Histology 64 -- 4.2.2 Nutrition of Cartilage 65 -- 4.2.3 Properties ... ... Etiology of Patellar Chondropathy 72 -- 4.3.1 General Aspects 72 -- 4.3.2 Mechanical Lesions of the Patellar ... ... Increased Patellar Mobility 83 -- Increased Pressure in the Patellofemoral Joint 85 -- 4.3.3 Non-Mechanical ...
