Worm-like Chain Model
Realistic force-extension curves of protein molecules are based on a Worm-like Chain model (WLC) of entropic elasticity. The constitutive law of the organic interface is derived using a fiber bundle model, wherein the force-extension behavior of each of the fibers is described by a Worm-like Chain model. An unfolding event is characterized by a change in the contour length of the biopolymer fiber.
The mechanical response of a single biopolymer fiber response is obtained using an atomic force microscope (AFM). The Worm-like Chain model describes the corresponding experimental response of a single protein fiber, including the unfolding of the modules (sawtooth pattern).The equation below is used to describe a Worm-like Chain model for a single protein fiber:
where kB is the Boltzmann constant, T is the absolute temperature, A is the persistence length added to the fibers after each module unfolds, L is the contour (total) length of the fibers, and z is the extension (displacement) length