Collagen denaturation is of fundamental importance for clinical treatment. Conventionally, the denaturation process
is quantified by the shrinkage of collagen fibers, but the underlying molecular origin has not been fully understood.
Since second harmonic generation (SHG) is related to the molecular packing of the triple helix in collagen fibers,
this nonlinear signal provides an insight of molecular dynamics during thermal denaturation. With the aid of SHG
microscopy, we found a new step in collagen thermal denaturation process, de-crimp. During the de-crimp step, the
characteristic crimp pattern of collagen fascicles disappeared due to the breakage of interconnecting bonds between
collagen fibrils, while SHG intensity remained unchanged, suggesting the intactness of the triple helical molecules.
At higher temperature, shrinkage is observed with strongly reduced SHG intensity, indicating denaturation at the