Structural Reinforcement of Ex-Vivo Aorta by Photocrosslinking of Collagen: The Role of Bunsen–Roscoe Law in Identifying the Optimal Irradiation Strategy

This study aimed to develop an irradiation strategy that would be able to maintain the validity of the Bunsen–Roscoe reciprocity law when exposing the aorta to ultraviolet A (UVA) radiation as a procedure to mechanically reinforce the blood vessels. Furthermore, it aimed to establish a research-based criterion for recommending optimal irradiance levels in a potential clinical setting. Aorta specimens were harvested postmortem from goat eyelids and exposed to UVA radiation (365 nm) in the specified conditions. Thermographic infrared analysis was carried out in order to determine the photothermal response. By performing irradiation in the presence of a photosensitizer (a riboflavin compound), which resulted in the crosslinking of vascular collagen, a photochemomechanical response was also determined based on the changes in mechanical properties as evaluated in a mechanical tester. Based on these radiation-induced photoresponses, a graphical method was employed to define the failure zones when applying the reciprocity law. Loss of the law’s validity was confirmed by the descending values of Schwarzschild’s p-coefficients. Both photoresponses showed that the law’s failure zone begins at an irradiance in the region of 70–75 mW/cm2 for radiant exposures between 6 and 18 J/cm2. Consequently, a higher irradiance is not beneficial when exposing vascular tissue to UVA radiation.