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This paper considers some issues pertinent to laser welding of elastin-based biomaterials to tissues using a pulsed diode laser (lO-is pulse) and indocyanine green (ICG) as an absorbing chromophore to localize laser heating to the "weld surface", the elastin/tissue interface where welding occurs. Experiments involved laser welding of elastin heterographs to the intimal surface of the carotid artery (in vitro, porcine) as a '-4x5 spotweld, then determining the breaking strength when the two tissues were pulled in a direction parallel to the plane of the spot weld while submerged in water. The questions answered are: . WHAT IS THE PEAK TEMPERATURE REQUIRED FOR WELDING ELASTIN HETEROGRAPH TO THE INTIMAL SURFACE OF CAROTID ARTERY? ANSWER: 3OO °C threshold, -6OO °C for maximum strength. This estimate is based on optical measurements of dye accumulation in stain layer and measurements of thickness of stain layer via fluorescence microscope examination. . WHATIS THE DEPENDENCE OF WELD STRENGTH ON THE LASER EXPOSURE? ANSWER: Breaking force (g) = Max*(1 exp(-(E Eth)/U67)), where Max is the maximum strength achievable by laser welding, expressed as the breaking force in g when elastin heterograph and tissue are pulled. E is the laser pulse energy. Eth is the apparent threshold laser pulse energy that will break the weld. Uth is the laser energy above threshold which achieves 67% of Max. Max was about 15 g for the -2O --2weld area of our experiments. Eth was 0.8 J. U67 was 1 .44 J. . DOES WELD STRENGTH DEPEND ON HYDRATION CONDITIONS? ANSWER: Not on the amount of excess unbound water. There was no significant difference in weld strength between welding dripping wet tissues vs well blotted tissues. S WHAT DIFFERENCE IS THERE BETWEEN IRRADIATING THE WELD SURFACE THROUGH THE BIOMATERIAL VS THROUGH THE TISSUE, WHEN THE BIOMATERIAL IS PARTIALLY STAINED WITH ICG? ANSWER: There is a difference if the stain layer is heavily stained. Irradiation through the tissue allows direct irradiation on the weld surface which achieves the highest peak temperatures for the least laser pulse energy. Irradiation through the elastin heterograph causes direct irradiation of the rear surface of the stain layer, within the biomaterial and away from the weld surface, and thermal diffusion must bring the heat to the weld surface. This difference occurs only when the absorption by the stain layer is sufficiently high that little laser energy directly reaches the weld surface.
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