Optimal parameters for laser tissue soldering. Part I: Tensile strength and scanning electron microscopy analysis

Background and Objectives: The use of liquid and solid albumin protein sold ers to enhance laser tissue repairs has been shown to significantly improve postoperative results. The published results of laser-solder tissue repair studies have, however, indicated inconsistent success rates. This can be a ttributed to variations in laser irradiance, exposure time, solder composit ion, chromophore type, and concentration. An in vitro study was performed u sing indocyanine green-doped albumin protein solders in conjunction with an 808 nm diode laser to determine optimal laser and solder parameters for ti ssue repair in terms of tensile strength and stability during hydration. Study Design/Materials and Methods: Twenty-five different combinations of l aser irradiance (6.4, 12.7, 19.1, 25.5, 31.8 W/cm(2)) and exposure time (20 , 30, 40, 50, 100 or 40, 60, 80, 100, 200 seconds) were used. The effect of changing bovine serum albumin (BSA) concentration (25% and 60%) and indocy anine green (ICG) dye concentration (2.5 mg/ml and 0.25 mg/ml) of the prote in solder on the tensile strength of the resulting bonds was investigated. The effect of hydration on bond stability was also investigated using both tensile strength and scanning electron microscopy analysis. Results: Tensile strength was observed to decrease significantly with incre asing irradiance. An optimum exposure time was found to exist where further irradiation did not improve the tensile strength of the bond. Tensile stre ngth was found to be greatly improved by increasing the BSA concentration. Finally, the lower ICG dye concentration increased the penetration depth of the laser light in the protein solder leading to higher tensile strengths. The strongest repairs were formed by using 6.4 W/cm(2) irradiation for 50 seconds with a protein solder composed of 60% BSA and 0.25mg/ml ICG. In add ition, the solid protein solder provided more stable adhesion to the tissue than did the liquid protein solder when the tissue was submerged in a hydr ated environment. Conclusions: This study greatly enhances the current understanding of the v arious factors affecting the soldering process. It provides a strong basis for optimization of the laser light delivery parameters and the solder cons tituents to achieve strong and reliable laser tissue repairs. Lasers Surg. Med. 24:319-331, 1999. (C) 1999 Wiley-Liss, Inc.