Development of novel short-term heating angioplasty: Thermal denaturation dynamics of collagen in artery wall

We have studied to develop the new thermal angioplasty methodology, photo-thermo dynamic balloon angioplasty (PTDBA), which provides artery dilatation with short-term (<15s) and uniform heating through the balloon by the combination of the efficient laser driven heat generation and fluid perfusion. Thermal denaturation degree of the collagen in artery media may be the important factor to attain sufficient artery dilatation for the PTDBA. In order to predict the optimum heating condition i.e. the balloon temperature and heating duration, we investigated the thermal denaturation dynamics of artery collagen in ex vivo. The extracted fresh porcine carotid artery was used. The temperature-dependent light scattering property and mechanical property of the artery specimen were simultaneously measured during artery temperature rising by specially made setup to assess the denaturation of arterial collagen. The change rate of the backscattered light intensity from the artery specimen; I(T)/I₀ with 633nm was measured to evaluate the artery scattering property change with the thermal denaturation. The artery specimen was heated from 25°C to 80°C with constant temperature rising rate of 3°C/min. The measured I(T)/I₀ was suddenly increased over 48°C. This boundary temperature might be the initiation temperature of the arterial collagen denaturation. We defined the variation of the I(T)/I₀ as the collagen denaturation ratio, and calculated the reactive enthalpy by the chemical equilibrium theory. Since the calculated enthalpy was similar to the enthalpy in literature report, the variety of I(T)/I₀ during the temperature rising might be attributed to the collagen conformational change due to the denaturation. In terms of the artery internal force measurement, the artery force was decreased with increasing of the artery temperature up to 65°C (i.e. softening), and increased over 65°C (i.e. shrinkage). We confirmed that the changes of the backscattered light (at 633nm in wavelength) from the artery might represent the artery collagen thermal denaturation degree.