Abstract
Preface. The increasing number of interventions with the application of implanted devices contacted with blood as well as the high demands to the life quality of patients in the postoperative period have raised the task before engineers regarding improvement of the structure and properties of materials used for manufacturing of these devices. Pyrolytic carbon possesses the best properties for using in cardiac surgery. Pyrolytic carbon has been used for manufacturing mechanical prostheses of heart valves for more than 40 years. In Russia this material is known as «uglesitall». The microstructure of pyrocarbon materials contains micro- and nano-measured pores i. e. the porosity is a characteristic of the microstructure. Objective. To evaluate the microstructure porosity of pyrocarbon materials used in manufacturing of implanted devices.
Material and methods. The samples from uglesitall USB used in manufacturing of the Russian prostheses of heart valves and isotropic pyrocarbon bearing the PGI trade-mark have been used for the trials. The samples of the 1st type made of the annular intermediate product outer diameter 28 mm, thickness 5 mm, height 20 mm and samples of the 2nd type in the form of plate with thickness 6 mm, height 25 mm and width 43 mm have been evaluated. In order to evaluate the form, dimension and density of pores distribution the scanning and transmitting electron microscopy have been applied together with the method of focusing ionic beam-tomography. Outcome. After processing of images of sample materials in the studied sections the characteristics of pores have been obtained, their mean values have been determined, the indicators of density and microhardness of materials have been determined. The evaluation has been performed regarding changes in pores characteristics towards uglesitall (USB) formation (growth) compared with those of isotropic pyrocarbon (PGI). In order to verify the received records the digital processing of images of sample sections has been carried out. The characteristics of pores as for the thickness of the sample from pyrocarbon PGI remained practically unchanged towards the growth of material. The pores have differed mainly with tiny (submicron) dimension. The average size of pores sections in pyrocarbon PGI made up about 110 nm. The average dimension of pores in uglesitall reached 300 nm in samples of the 1st type and up to 220 nm in samples of the 2nd type.
Conclusion. It is defined that isotropic pyrocarbon PGI is less porous material than uglesitall USB. The properties of pores in some parts of the material do not characterize it on the whole. It is evident that microhardness and porosity are determined by the same technological factors: velocity of material precipitation and density of structure packaging. In uglesitall samples the greater values of the local drop of microhardness were observed in comparison with porosity. The reverse character of microhardness dependence on porosity of uglesitall has been confirmed. It has been shown that the technology is just that very factor managing of which one can obtain materials with the needed degree of homogeneity of microstructure and properties.
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