Abstract
In this study, we attempted to determine the critical temperature [T<SUB>c</SUB>] at which accelerated stress relaxation occurred during laser mediated cartilage reshaping. During laser irradiation, mechanically deformed cartilage tissue undergoes a temperature dependent phase transformation which results in accelerated stress relaxation. When a critical temperature is attained, cartilage becomes malleable and may be molded into complex new shapes that harden as the tissue cools. Clinically, reshaped cartilage tissue can be used to recreate the underlying cartilaginous framework of structures such as the ear, larynx, trachea, and nose. 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. Optimization of the reshaping process requires identification of the temperature dependence of this phase transformation and its relationship to observed changes in cartilage optical, mechanical, and thermodynamic properties. Light scattering, infrared radiometry, and modulated differential scanning calorimetry (MDSC) were used to measure temperature dependent changes in the biophysical properties of cartilage tissue during fast (laser mediated) and slow (conventional calorimetric) heating. Our studies using MDSC and laser probe techniques have identified changes in cartilage thermodynamic and optical properties suggestive of a phase transformation occurring near 60 degrees Celsius.
Highlights
1.1 Cartilage BiologyCartilage is a complex macromolecular tissue composed of 80% water, 13% collagen (Type 11), and 7% protein-polysaccharide
In order to minimize the effect of evaporative cooling and the non-uniform temperature distribution within the cartilage tissue created by laser mediated heating, 1(t) was recorded from cartilage tissue immersed in saline solution and subjected to a slow heating rate
Cartilage undergoes temperature dependent stress relaxation accompanied by changes in its optical, mechanical, and thermal properties
Summary
1.1 Cartilage BiologyCartilage is a complex macromolecular tissue composed of 80% water, 13% collagen (Type 11), and 7% protein-polysaccharide (proteoglycans). The extracellular matrix of cartilage is a fiberreinforced gel formed by a three-dimensional network of proteoglycan molecules (100 -200 MD) which possess negatively charged ion groups (SO3 and COO- moieties) [2] enmeshed in collagen fibers. The negative charge density is only partially balanced by free counter ions (Ca and Na+) in solution. This electrical imbalance results in an intrinsic tissue turgor termed the Donnan osmotic pressure [3,4,5], or at a macroscopic level, internal stress. Compressive mechanical deformation of the cartilage is resisted by the screened Coulomb potential between the negatively charged moieties residing on adjacent proteoglycan units [6]
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