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Experimental study of artificial articular cartilage friction
Kulíšek, Vlastimil ; Ranuša, Matúš (referee) ; Rebenda, David (advisor)
Many conventional materials are used to replace damaged articular cartilage, which are beginning to be replaced by innovative biomimetic materials that mimic cartilage properties. One of these materials are poly(vinyl alcohol) (PVA) hydrogels crosslinked by freeze-thawing and cast-drying method. These hydrogels possess similar mechanical as articular cartilage. In order to clarify the effect of kinematic conditions on the friction of hydrogels, three levels of sliding speed and load and a uniform lubricant – PBS were chosen. The coefficient of friction of the FT hydrogel decreased with increasing load. The dependence of the sliding speed did not show a uniform trend and corresponded to the adsorption-repellent model for PVA gels. The coefficient of friction of the CD hydrogel increased with increasing sliding speed according to the repulsion-adsorption model for PVA gels. The increase in load at low sliding speeds of CD hydrogel caused a slight decrease in the coefficient of friction. At the highest speed, there was an optimal load at which a low coefficient of friction was achieved. The CD hydrogel showed a lower coefficient of friction than cartilage. The FT hydrogel achieved a lower coefficient of friction than cartilage only at 5 N and 10 mm s- 1. This work contributes to the understanding of the tribological properties of PVA hydrogels.
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An investigation of friction and lubrication in eye/lens contact
Kulíšek, Vlastimil ; Daniel, Matej (referee) ; Nečas, David (advisor)
Millions of contact lens wearers suffer from eye irritation due to dry eye disease (DED), which is most often treated with the application of artificial tears. As the primary source of irritation and discomfort is mutual rubbing of the eye, lens and lid surface, contact lens tribology research has the potential to bring new insights into the field of DED therapy. The aim of this diploma thesis was to clarify the influence of the properties of the contact lens and the properties of the lubricant on the friction and formation of the lubricating film in the simulated contact between the contact lens and the lid. The experiments were carried out using a pin-on-plate tribometer, which can simultaneously record the coefficient of friction while simultaneously observing the lubricating film. The contact was lubricated with twelve types of lubricants differing in mucin content, buffer type, and molecular weight (MW) of hyaluronic acid (HA). The effect of lubricant type was studied on two types of contact lenses. The results showed that for lenses containing an active wetting agent, the presence of mucin in the lubricant is essential for increasing the tribological performance, while MW of HA does not play a significant role. A closer analysis of the individual tested solutions showed that the highest performance for both types of lenses was achieved by HA with an average MW of 337 kDa. However, the type of buffer played a significant role in this case. In general, it can be stated that suitable artificial tears for DED therapy should be chosen based on the type (material) of contact lenses used and the mucin content in the tear film of a particular patient.
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Experimental study of artificial articular cartilage friction
Kulíšek, Vlastimil ; Ranuša, Matúš (referee) ; Rebenda, David (advisor)
Many conventional materials are used to replace damaged articular cartilage, which are beginning to be replaced by innovative biomimetic materials that mimic cartilage properties. One of these materials are poly(vinyl alcohol) (PVA) hydrogels crosslinked by freeze-thawing and cast-drying method. These hydrogels possess similar mechanical as articular cartilage. In order to clarify the effect of kinematic conditions on the friction of hydrogels, three levels of sliding speed and load and a uniform lubricant – PBS were chosen. The coefficient of friction of the FT hydrogel decreased with increasing load. The dependence of the sliding speed did not show a uniform trend and corresponded to the adsorption-repellent model for PVA gels. The coefficient of friction of the CD hydrogel increased with increasing sliding speed according to the repulsion-adsorption model for PVA gels. The increase in load at low sliding speeds of CD hydrogel caused a slight decrease in the coefficient of friction. At the highest speed, there was an optimal load at which a low coefficient of friction was achieved. The CD hydrogel showed a lower coefficient of friction than cartilage. The FT hydrogel achieved a lower coefficient of friction than cartilage only at 5 N and 10 mm s- 1. This work contributes to the understanding of the tribological properties of PVA hydrogels.
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