  We consider a statistical mechanics model for biopolymers. Sophisticated
polymer chains, such as DNA, have stiffness when they stretch chains. The
Laplacian interaction is used to describe the stiffness. Also, the surface
between two media has an attraction force, and the force will pull the chain
back to the surface. In this paper, we deal with the random potentials when the
monomers interact with the random media. Although these models are different
from the pinning models studied before, the result about the gap between the
annealed critical point and the quenched critical point stays the same.
