Quantitative measurements of linear birefringence during heating of native collagen

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Abstract
Linear birefringence is an anisotropic property of rat tail tendon, which is largely composed of collagen. Our goal is to show that the dynamic range and sensitivity of the linear birefringence loss of collagen during heating are sufficient for kinetic modeling of the reaction. Study Design/ Materials and Methods: The linear birefringence loss was quantified for tendon denatured via both a heated-isotonic-saline bath and a heated stage. All measurements were made with a polarizing transmission microscope equipped with a Berek compensator. The data show that the loss of linear birefringence is a first-order kinetic reaction. The native rat tail tendon birefringence, Δn = 3.0 ± 0.6 × 10−3 (mean ± std. err.), is lost after denaturation occurs (Δn = 0). Application of the Arrhenius equation to the linear birefringence data yields the activation energy (Ea = 89 ± 1 kcal/mole), pre-exponential coefficient (A = e130±1 s−1), enthalpy (ΔH = 88 ± 1 kcal/mole) and entropy (ΔS = 197 ± 2 cal/°K·mole). This study shows that dynamic changes in linear birefringence can be used to monitor thermally induced changes in collagen. Lasers Surg. Medicine 20:310–318, 1997.