Interaction of artificial carbon pyroceram mitral valve with blood plasma

Abstract

The nanocrystalline material of an artificial carbon pyroceram mitral valve obtained by sintering of 15 wt.% B 4 C with crystals <10 nm that are uniformly distributed in 85 wt.% carbon with particles ~10 nm has exceptionally high chemical stability in blood plasma. The electrochemical interaction resulting from contact with a possible microadditive (for example, iron) on the valve surface is experimentally modeled by polarization induced by an external current source specially to create extreme corrosion conditions. The interaction kinetics is studied at 37°C using anodic polarization curves. Curcumin is used as an analytical reagent for spectrophotometry of boron traces in a solution. Emissive spectroscopy is used to determine iron traces in the spume-like film formed after polarization. It is established that a chemisorbed oxygen film forms when microgalvanic elements appear at 0.4 V and stable passivation of the valve surface is observed at ~1.0 V since a lowconductive nanostructured carbon film forms. It is shown that this film results from the discharge of α-amino acids on the valve surface (amino acid residues of complex peptide chains of plasma proteins) containing heterocyclic rings. The sessile drop method shows that the valve is promptly wetted by blood plasma (wetting angle is 50°), this also promotes the formation of a stable protective film on its surface.The paper examines the interaction of an artificial carbon pyroceram mitral valve ( Fig. 1) with human blood plasma. The ATS mitral valve [1, 2] was made at the Production Scientific Enterprise MedInzh (Penza, Russia). It is widely used in valve replacement operations at the Bakulev Scientific Center for Cardiovascular Surgery, Russian Academy of Medical Sciences (Russia).The material of valve leaflets (carbon pyroceram-2 as a working name) represents a two-phase mechanical mixture of nanocrystalline carbon (85 wt.%) with mean particles ~10 nm in size and uniformly distributed nanocrystals of B 4 C (15 wt.%) with mean particles <10 nm. The nanocrystalline structure of the material after sintering has no matrix and looks like glass [3].Nanocrystalline carbon was obtained [4] in a furnace by the decomposition of methane at 1500°C and boron by the decomposition of liquid boron chloride BCl 3 by the following reaction:with subsequent solid-phase reaction: 4B + C cryst = B 4 C.The porousless material for the mitral valve has excellent mechanical properties: bending strength σ b = 360 MPa and compressive strength σ c = 720-820 MPa while high-grade MPG-7 structural graphite has σ b = 50 MPa and σ c = ~80-100 MPa [5,6].