Characterization of temperature-dependent biophysical properties during laser mediated cartilage reshaping

Laser radiation can be used to reshape cartilage tissue into new morphologic configurations. When a critical temperature is attained, mechanically deformed cartilage becomes malleable and may be reshaped into new geometric configurations that harden as the tissue cools. This temperature dependent process results in mechanical stress relaxation and is characteristic of a phase transformation. The principal advantages of using laser radiation for the generation of thermal energy in tissue are precise control of both the space-time temperature distribution and time-dependent thermal denaturation kinetics. We illustrate the utility of laser mediated cartilage reshaping in ex vivo porcine model of reconstructive nasal and laryngeal surgery, and attempt to determine the temperature range in which accelerated stress relaxation occurs during laser mediated cartilage reshaping. Optimization of the reshaping process requires identification of the temperature dependence of this phase transformation and its relationship to observed changes in cartilage optical (diffuse scattering), mechanical (internal stress), and thermodynamic properties (heat capacity). Light scattering, infrared radiometry, and modulated differential scanning calorimetry were used to measure temperature-dependent changes in the biophysical properties of cartilage tissue during fast (laser mediated) and slow heating (conventional calorimetric beating). Our studies using MDSC and laser probe techniques have identified changes in tissue thermodynamic and optical properties suggestive of a phase transformation occurring near 60/spl deg/C. Clinically, reshaped cartilage tissue can be used to recreate the underlying cartilaginous framework of structures in the head and neck such as the ear, larynx, trachea, and nose.