Evaluation of the degree of cross-linking in UV irradiated porcine valves

A porcine heart valve was irradiated by Ultraviolet (UV) rays (10 W, 254 nm ) for 2, 4, 8 and 24 hours at 4 degrees C to cross-link the structural coll agen matrix. The degree of cross-linking was evaluated by assaying the rele ased amount of hydroxyproline (Hyp) from the matrix, and comparing it with the positive controls of valves treated by glutaraldehyde (GA) solution (0. 625 wt%) and the negative controls of non-treated fresh valves. The undiges ted weight ratio of the specimens increased Ly increasing the UV irradiatio n time. The undigested weight of the leaflets, tunica interna and tunica ex terna of the fresh, GA-treated and UV-irradiated specimens after collagenas e digestion was compared. As UV irradiation increased, the amount of releas ed hydroxyproline was gradually decreased until 8 hours of irradiation, alt er which the released hydroxyproline-reduction occurred slightly until 24 h ours of irradiation time in this system. A total 47.68% of the hydroxyproli ne in the valve was cross-linked by UV irradiation after 24 hours, while 73 .74% of the hydroxyproline in the positive control was crossed-linked. Ligh t microscopic observation revealed that the typical crimp pattern of collag en fibers decreased and was rearranged into a dense flattened pattern as th e UV irradiation induced interfibrilar cross-linking. GA-treated valves dem onstrated a denser matrix pattern than the UV-irradiated specimens. Cross-l inked collagenous tissue prepared by UV irradiation would be useful for imp roving durability and reducing the disadvantages related to using a chemica l cross-linking agent.