Optimal parameters for laser tissue soldering: II. Premixed versus separate dye-solder techniques

Background and Objective: Laser tissue soldering by using an indocyanine gr een (ICG)-doped protein solder applied topically to the tissue surface and denatured with a diode laser was investigated in Part I of this study. The depth of light absorption was predominantly determined by the concentration of the ICG dye added to the solder. This study builds on that work with an in vitro investigation of the effects of limiting the zone of heat generat ion to the solder-tissue interface to determine whether more stable solder- tissue fusion can be achieved. Study Design/Materials and Methods: An alternative laser tissue soldering t echnique was investigated, which increased light absorption at the vital so lder-tissue interface. A thin layer of ICG dye was smeared over the surface to be treated, the protein solder was then placed directly on top of the d ye, and the solder was denatured with an 808-nm diode laser. Because laser light at similar to 800 nm is absorbed primarily by the ICG dye, this thin layer of ICG solution restricted the heat source to the space between the s older and the tissue surfaces. A tensile strength analysis was conducted to compare the separate dye-solder technique with conventional techniques of laser tissue soldering for which a premixed dye-solder is applied directly to the tissue surface. The effect of hydration on bond stability of repairs formed by using both techniques was also investigated using tensile streng th and scanning electron microscopy analysis. Results: Equivalent results in terms of tensile strength were obtained for the premixed dye-solder technique using protein solders containing 0.25 mg/ ml ICG (liquid solder, 220 +/- 35 N/cm(2); solid solder, 602 +/- 32 N/cm(2) ) and for the separate dye-solder technique (liquid solder, 228 +/- 41 N/cm (2); solid solder, 578 +/- 29 N/cm(2)). The tensile strength of native bovi ne thoracic aorta was 596 +/- 31 N/cm(2). Repairs created by using the sepa rate dye-solder technique were more stable during hydration than their prem ixed dye-solder counterparts. The conventional premixed dye-solder was simp ler and approximately twice as fast to apply. The separate dye-solder techn ique, however, increased the shelf-life of the solder, because the dye was mixed at the time of the experiment, thus conserving its spectral absorbenc y properties. Conclusion: Two laser-assisted tissue soldering techniques have been evalua ted for repairing aorta incisions in vitro. The advantages and disadvantage s of each of these techniques are discussed. Lasers Surg. Med. 26:346-356, 2000. (C) 2000 Wiley-Liss, Inc.