Bifurcation of elastic curves with modulated stiffness

We investigate the equilibrium configurations of closed planar elastic curves of fixed length, whose
stiffness, also known as the bending rigidity, depends on an additional density variable. The underlying
variational model relies on the minimisation of a bending energy with respect to shape and
density and can be considered as a one-dimensional analogue of the Canham-Helfrich model for
heterogeneous biological membranes. We present a generalised Euler-Bernoulli elastica functional
featuring a density-dependent stiffness coefficient. In order to treat the inherent nonconvexity of the
problem, we introduce an additional length scale in the model by means of a density gradient term.
We derive the system of Euler-Lagrange equations and study the bifurcation structure of solutions
with respect to the model parameters. Both analytical and numerical results are presented.