Appendix 7—table 1. The parameters of the two springs controlling extension and bending, respectively.

The relation between ${\mathrm{\ell }}_B^0$ and ${\mathrm{\ell }}_E^0$ determine the equilibrium configuration of the two connected filaments. When ${\mathrm{\ell }}_B^0\ge {\mathrm{\ell }}_E^0+2d_B$, the straight configuration is the preferred configuration.

Role	spring stiffness constant	free length
Bending	${\kappa }_B$	${\mathrm{\ell }}_B^0$
Extension	${\kappa }_E$	${\mathrm{\ell }}_E^0$