Laser tissue welding analyzed using fluorescence, Stokes shift spectroscopy, and Huang-Rhys parameter

Near infrared (NIR) continuous wave laser radiation at the 1,450 nm wavelength was used to weld porcine aorta and skin samples via the absorption of combitional vibrational modes of native water in the tissues. The fluorescence spectra were measured from the key native molecules of welded and non-welded tissues at specific excitation and emission wavelengths from collagen, elastin, and tryptophan. The changes in the fluorescence intensities and differences in Stokes shift (Δν(ss) ) of key native fluorophores were measured to differentiate the Huang-Rhys parameter values (S) of the chromophores. The strength of coupling depends on the local electron-vibration intra-tissue molecular environment and the amount of polar solvent water surrounding the net charges on collagen, elastin, and tryptophan. The S values for both non-welded and welded tissues were almost the same and less than 3, suggesting minimal changes in the local molecular environment as a result of welding.