  We propose a simple approach, based on the minimization of the total
(entropic plus unfolding) energy of a two-state system, describing the
stretch-induced unfolding of macromolecules (proteins, silks, nanopolymers,
DNA/RNA). The model is fully analytical and enlightens the role of the
different energetic components regulating the unfolding evolution. As an
explicit example of application we compare the analytical results with the
titin Atomic Force Microscopy experiments showing the ability of the model to
quantitatively reproduce the mechanical behavior of macromolecules unfolding.
