Abstract
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.
Highlights
THE INTERACTION of coherent light with tissue may result in a variety of effects depending on the laser wavelength, pulse duration, irradiance, tissue thermal and optical properties [1]
Mediated alterations in cartilage biophysical properties during laser irradiation strongly suggest the occurrence of a phase transformation
Conventional reconstructive techniques require the grafting of autologous cartilage and may involve carving, suturing, and/or morselization to recreate the shape of the absent tissue and, as a consequence, abundant normal healthy cartilage tissue is often discarded
Summary
THE INTERACTION of coherent light with tissue may result in a variety of effects depending on the laser wavelength, pulse duration, irradiance, tissue thermal and optical properties [1]. Mediated alterations in cartilage biophysical properties during laser irradiation strongly suggest the occurrence of a phase transformation. Phase transformations are energy dependent changes in the molecular structure of matter which, during laser mediated cartilage reshaping, are manifest by alterations in the biophysical properties of the tissue matrix. The modification of solids during laser radiation proceeds through phase transformations whose progress is governed mainly by heat and mass transfer processes. To illustrate this technique in a model of nasal reconstruction, we characterize the temperature dependence of alterations in cartilage optical, thermal, and mechanical properties accompanying laser mediated reshaping
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