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

Laser radiation can be used to reshape cartilage tissue into new morphologi c configurations. When a critical temperature is attained, mechanically def ormed cartilage becomes malleable and may be reshaped into new geometric co nfigurations that harden as the tissue cools. This temperature-dependent pr ocess results in mechanical stress relaxation and is characteristic of a ph ase transformation. The principal advantages of using laser radiation for t he generation of thermal energy in tissue are precise control of both the s pace-time temperature distribution and time-dependent thermal denaturation kinetics, In this study, we illustrate the utility of laser mediated cartil age reshaping in ex vivo porcine model of reconstructive nasal and laryngea l surgery, and attempt to determine the temperature range in which accelera ted stress relaxation occurs during laser mediated cartilage reshaping. Opt imization of the reshaping process requires identification of the temperatu re dependence of this phase transformation and its relationship to observed changes in cartilage optical (diffuse scattering), mechanical (internal st ress), and thermodynamic properties (heat capacity). Light scattering, infr ared radiometry, and modulated differential scanning calorimetry were used to measure temperature-dependent changes in the biophysical properties of c artilage tissue during fast (laser mediated) and slow heating (conventional calorimetric heating). Our studies using MDSC and laser probe techniques h ave identified changes in tissue thermodynamic and optical properties sugge stive of a phase transformation occurring near 60 degrees C, Clinically, re shaped cartilage tissue can be used to recreate the underlying cartilaginou s framework of structures in the head and neck such as the ear, larynx, tra chea, and nose.