Crosslink formation in porcine valves stabilized by dye-mediated photooxidation

Bovine pericardial and porcine valve materials stabilized by dye-mediated photooxidation have shown potential for bioprosthetic valve use. Previously, in vitro and in vivo stability of these materials was demonstrated through enzymatic, chemical, extraction, rat subcutaneous, and functional challenges. Here, we examine the stability of photooxidized porcine aortic valves through amino acid, crosslink, and hydrothermal isometric tension analysis. Photooxidation reduced intact histidine residues from 17.0 to 0 residues per 1000, indicating the photooxidative alteration of this amino acid. Diphenyl borinic acid-derivitized hydrolyzates of proteins were separated by high-performance liquid chromatography, which identified several amino acid crosslinks that appeared with photooxidation that were absent in untreated controls. Thermal relaxation analysis indicated a significantly higher (p < 0.0002) thermal stability for photooxidized porcine cusps than that of untreated controls, with mean relaxation times for untreated cusps of 14,000 +/- 4650 versus 22,900 +/- 2480 s for photooxidized cusps. In summary, porcine aortic valve tissue treated by dye-mediated photooxidation contains new chemical species and exhibits properties consistent with intermolecular crosslink formation, which explain the increased biostability of this material and its potential for use in bioprosthetic devices.