ICG-doped albumin protein solders for improved tissue repair

An in vitro study was performed using an 808 nm-diode laser in conjunction with indocyanine green (ICG) - doped albumin protein solders to repair bovine aorta specimens. Investigations were conducted to determine optimal solder and laser parameters for tissue repair in terms of tensile strength, temperature rise and damage and the microscopic nature of the bonds formed. Liquid and solid protein solders prepared from 25% and 60% bovine serum albumin (BSA), respectively, were compared. The tensile strengths of the repairs were greatly improved with an increase in BSA concentration from 25% to 60% and a reduction in ICG dye concentration from 2.5 mg/ml to 0.25 mg/ml. Increasing the laser irradiance and thus surface temperature resulted in an increased severity of histological injury. Thermal denaturation of the tissue substrate increased laterally and in depth with higher temperatures. Optimal repairs in terms of bond strength and thermal damage were achieved by denaturing a solid protein solder composed of 60% BSA and 0.25 mg/ml ICG with an irradiance of 6.4 W/cm². Using this combination of solder and laser parameters, surface temperatures were observed to reach 85±5 °C with an average temperature difference across the solder strips of 15 °C across a thickness of 150 μm. Histological examination of the repairs formed using these parameters showed negligible evidence of collateral thermal damage to the underlying tissue. Scanning electron microscopy suggested albumin intertwining within the tissue collagen matrix and subsequent fusion with the collagen as the mechanism for laser tissue soldering.