In order to assist with the prognosis of wear processes in low profile disc heart valves, an approximate haemodynamic theory has been used for the determination of opening and closing dynamics of these valves, together with the most developed theory to date of frictional fatigue. The heart valve element wear was defined by solving the contact problem, which takes account of changes to the contact surface form as a consequence of wear. Calculated values are compared with in vivo wear data for artificial heart valves. The proposed model for estimating wear in artificial heart valves allows an optimization to be made of the wear resistance in available designs and to predict the wear resistance of artificial heart valves at the design stage.
The nanocrystalline material of an artificial heart valve sintered from 15 wt.% B 4 C with crystals <10 nm in size uniformly distributed in 85 wt.% carbon with particles about 10 nm in size has exceptionally high chemical stability in human blood plasma. The electrochemical interaction resulting from contact of the valve surface with a potential trace impurity (for example, iron) is experimentally modeled by polarization from an external current source to simulate an extreme corrosion event. The interaction kinetics is studied at 37°C using the method of anodic polarization curves. The elemental composition of interaction products is analyzed by emission spectroscopy using a DFS-13 spectrograph; the composition and thickness of the film layers formed on the valve surface during electrolysis are determined with quantitative Auger electron spectroscopy using a Riber LAS-2000 device. It is established that a nanocrystalline film 350 nm thick forms after 3 h electrolysis on the ceramic surface of the heart valve. The film contains to 94.0 at.% C and to 6.0 at.% N (including to 89.5 at.% C as nanocrystalline graphite and to 4.5 at.% C as nanocrystalline C 3 N 4 , as well as to 6.0 at.% N in C 3 N 4 ) and an insignificant amount of sulfur and inclusions of boron and oxygen atoms. It is shown that the film results from the discharge of anions of corresponding α-amino acids (amino acid remains of complex blood protein chains) containing heterocycle rings.
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