Covalent Surface Modification by Amino Acid Derivatives Improved the Surface Thromboresistance in Glutaraldehyde-Processed Bovine Pericardium for Use as a Heart Valve Leaflet

Subclinical leaflet thrombosis is a major cause of failure in both surgical and transcatheter bioprosthetic heart valves. Thromboresistance is a basic prerequisite for a cardiovascular biomaterial. In this study, bovine pericardium (BP) was decellularized and processed (DCL-BP) with 0.2% glutaraldehyde (GA) and covalently conjugated with amino acid derivatives. Hexylamides of L-Glutamic acid (Glutamyl dihexylamide- GHA ), L-Lysine (Lysinyl hexylamide─ LHA ), and the propargyl derivative of L-Lysine (Lysinyl propargyl amide─ K1 alk ) were investigated. These modifications of BP generate three different scaffolds (DCL- GHA BP, DCL- LHA BP, and DCL- K1 alk BP) of varying surface energies and hydrophilic/phobic properties. The surface modifications altered the water contact angles of glutaraldehyde-processed pericardium from 59.25° to 67.74° in DCL- GHA BP and 79.98° in DCL- LHA BP, while DCL- K1 alk BP became highly hydrophilic such that the measurement of static angle was not feasible. Successful conjugations were confirmed by quenching of acid fuchsin color reaction and confocal Raman chemical mapping. The materials were found to be non-hemolytic and greatly reduced the overall protein adsorption and platelet adhesion, thus markedly improving the surface thromboresistance in vitro as observed by the whole blood clotting assay. The results of the ex vivo study in the sheep model correlated well with the in vitro data, where a marked reduction in protein adsorption from whole blood and platelet adhesion/thrombus deposition was observed, in comparison with the thrombogenic control. There was no activation of coagulation or complement system by any of the three test materials, making them non-thromboinflammatory and suitable candidate materials for use as a bioprosthetic heart valve leaflet.