Mechanical behavior of cartilage during laser irradiation

Internal stress sigma (t), diffuse transmitted light intensity I(t) from a He-Ne probe laser (lambda = 632.8 nm), and radiometric surface temperature T-s(t) were measured during the photothermal heating of porcine septal cartilage using a pulsed Nd:YAG laser (lambda = 1.32 mum). Rectangular specimens, 1-4 mm thick, were secured to a tensile force testing rig and laser irradiated. Force measurements during heating showed significant variations in the rate of deformation, which were found to be strongly dependent on tissue orientation; revealing the anisotropic nature of its thereto-mechanical properties. These findings suggests that the collagen and proteoglycan networks lie in a preferential orientation within the extracellular matrix, which must be addressed before this procedure can be used on a wider basis.