Polyvinyl alcohol improves resistance of epoxy-treated bovine pericardium to calcification in vitro

Abstract

Background. Around half of bioprosthetic heart valves become dysfunctional 15 years postimplantation because of structural valve deterioration notable for the degradation and calcification of the prosthetic tissue. Protection of bioprosthetic heart valves from structural valve deterioration requires innovative materials, science approaches including enveloping of the bioprosthetic heart valves into the polymer sheath.Aim. To develop a polyvinyl alcohol sheath for improving resistance of bioprosthetic heart valves to calcification.Material and methods. Bovine pericardium fixed with ethylene glycol diglycidyl ether was incubated with distinct concentrations of polyvinyl alcohol (5, 10, 12, or 15%) with the following freezing and thawing to perform cryotropic gelation. Surface and structure of unmodified and polyvinyl alcohol-modified bovine pericardium have been investigated by fluorescence microscopy and scanning electron microscopy, whilst tensile testing was carried out by uniaxial tension test. Haemocompatibility was assessed through the measurements of haemolysis and platelet aggregation/adhesion upon the contact of donor blood with the samples. Resistance to calcification was tested by incubation of the samples in calcium and phosphate supersaturated (10 µmol/L) cell culture medium for 3 and 6 weeks with the following tissue lysis and colorimetric measurement of Ca2+ ions.Results. Using cryotropic gelation, we obtained a polyvinyl alcohol-coated and filled bovine pericardium matrix. Out of all polyvinyl alcohol concentrations, 12% polyvinyl alcohol solution sealed pores and hollows within the bovine pericardium (what was not achieved using 5% or 10% polyvinyl alcohol solutions) and demonstrated the best processability as compared to 15% polyvinyl alcohol solution. Cryotropic gelation did not deteriorate durability, elasticity, or haemocompatibility of bovine pericardium. After 3 and 6 weeks of the incubation in calcium-supersaturated solution, polyvinyl alcoholmodified bovine pericardium contained 5- and 3-fold reduced amount of calcium compared to unmodified bovine pericardium.Conclusions. Enveloping of bovine pericardium into polyvinyl alcohol increases its calcification resistance, retains its tensile properties and haemocompatibility, and can be considered as a promising approach for the modification of bovine pericardium during the manufacturing of bioprosthetic heart valves.