Elongational flow studies on the molecular properties of collagen and its thermal denaturation

An elongational flow method established in polymer physics was applied to study dynamic structure and properties of biopolymers in solution. Type I collagen solutions in the dilute to semidilute region are studied in elongational flow fields, generated in a Taylor four‐roll mill, for temperatures from 20°C through the melting temperature to 60°C. A nonlocalized birefringent signal, characteristic of stiff molecules, is observed at all temperatures. The conformational changes as a function of temperature can be divided into two separate temperature dependent stages. In stage I, at lower temperatures, the collagen molecule behaves as a rigid rod and the birefringent signal Δ n rises as a function of increasing strain rate ε. Throughout this stage the type of molecular interaction in semidilute solution does not change but the rate of interaction is increased by thermal excitation. In stage II, a characteristic criticality in the Δ n vs. ϵ plot is observed. For strain rates up to a characteristic value, ϵ 0 , the birefringence remains zero and for ϵ>ϵ 0 whole field bright birefringence is observed. The plateau values of birefringence, Δ n p , at high strain rates in the Δ n vs. ϵ curve decreased with rising temperature in stage II. This criticality in behavior and the decreasing tendency in Δ n p with temperature are explained by the collagen molecule changing to a hinged‐rod conformation. Thus the untwining of collagen as a function of temperature initiates at several places simultaneously, probably at specific amino acid sequences, within the collagen rodlike molecule.