No abstract

No abstract

Internal stress σ(t), diffuse transmitted light intensity I(t) from a He-Ne probe laser (λ = 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 (λ = 1.32 µm). 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 thermo-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.

Cartilage laser thermoforming, also known as laser reshaping, is a new surgical procedure that allows in-situ treatment of deformities in the head and neck with less morbidity than traditional approaches. During laser irradiation, cartilage becomes sufficiently subtle or deformable for stretching and shaping into new stable configurations. This study describes the experimental and theoretical characterization of the thermal response of porcine cartilage to laser irradiation (Nd:YAG). The surface temperature history of cartilage specimens was monitored during heating and thermal relaxation; using laser exposure times ranging between 1 and 15 s and laser powers of 1 to 10 W. The experimental results were then used to validate a finite element model, which accounts for heat diffusion, light propagation in tissue, and heat loss due to water evaporation. The simultaneous solution of the energy and mass diffusion equations resulted in predictions of temperature distribution in cartilage that were in good agreement with experiments. The model simulations will provide insights to the relationship between the laser treatment parameters (exposure time, laser beam diameter, and power) and the onset of new molecular arrangements and cell thermal injury in the material, thus conceiving basic guidelines of laser thermoforming.