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We have been developing the novel short-term heating angioplasty in which sufficient artery lumen-dilatation was
attained with thermal softening of collagen fiber in artery wall. In the present study, we investigated on the relation
between the mechanical properties of heated artery and thermal denaturation fractures of arterial collagen in ex vivo. We
employed Lumry-Eyring model to estimate temperature- and
time-dependent thermal denaturation fractures of arterial
collagen fiber during heating. We made a kinetic model of arterial collagen thermal denaturation by adjustment of K
and k in this model, those were the equilibrium constant of reversible denaturation and the rate constant of irreversible
denaturation. Meanwhile we demonstrated that the change of reduced scattering coefficient of whole artery wall during
heating reflected the reversible denaturation of the collagen in artery wall. Based on this phenomenon, the K was
determined experimentally by backscattered light intensity measurement (at 633nm) of extracted porcine carotid artery
during temperature elevation and descending (25°C→80°C→25°C). We employed the value of according to our earlier
report in which the time-and temperature- dependent irreversible denaturation amount of the artery collagen fiber that
was assessed by the artery birefringence. Then, the time- and temperature- dependent reversible (irreversible)
denaturation fraction defined as the reversible ((irreversible) denatured collagen amount) / (total collagen amount) was
calculated by the model. Thermo-mechanical analysis of artery wall was performed to compare the arterial mechanical
behaviors (softening, shrinkage) during heating with the calculated denaturation fraction with the model. In any artery
temperature condition in 70-80°, the irreversible denaturation fraction at which the artery thermal shrinkage started was
estimated to be around 20%. On the other hand, the calculated irreversible denaturation fraction remained below 5% and
reversible denaturation fraction reached up to 20% while the artery softening occurred without shrinkage. We think that
our model of arterial collagen thermal denaturation might be reasonable to estimate the artery mechanical properties
during heating.
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