Effects of Ultraviolet-A Radiation on Enzymatically Degraded Tunica Adventitia of the Porcine Abdominal Aorta

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In a previous study, it was demonstrated that mechanical stiffness and strength of tunica adventitia of the porcine abdominal aortic wall were significantly increased following irradiation of the tissue with ultraviolet-A (UV-A) rays, due to photochemically induced crosslinking of adventitial collagen. We have suggested that by applying the process to a dilated aortic region caused by abdominal aortic aneurysm (AAA), the mechanically enhanced adventitial layer might delay or prevent the aneurysmal rupture in human patients. Here, we extended our investigation to adventitial tissue that was subjected to in vitro collagenolysis, such mimicking a step in the aneurysmal pathomechanism. We used tissue isolated from the abdominal region of healthy porcine aortas. The adventitia was separated from the vessel wall and subjected to enzymatic degradation and exposed to UV-A radiation (365 nm) in the presence of a riboflavin derivative as the photo-initiator. Collagenolysis was carried out in buffered medium at two different durations (8 and 20 h). Three sets, each of 30 adventitial specimens (degraded only, irradiated prior to degradation, and irradiated after degradation), were evaluated in a mechanical tester. Mechanical testing of the irradiated specimens indicated an increase in both stiffness (Young’s modulus) and strength (ultimate stress) when compared to those degraded but not irradiated. The specimens first irradiated and then degraded displayed the highest gain in both stiffness and strength. In the tissue irradiated after degradation, the longer the duration of collagenolysis, the less significant was the enhancement of mechanical characteristics. Irradiation with UV-A rays of enzymatically degraded aortic adventitial tissue induced the enhancement of its mechanical characteristics (stiffness, strength). The earlier the irradiation, the more significant the enhancement.