Fig. 2

The initial multiple-ball model and topological structure of deformable structure (filament and surface/membrane). The initial model of a deformable structure is its simplest status. As shown in (a) and (c), all the balls are collinear in filament, while are coplanar in membrane. In our model, all balls in the same structure have the same radius. In order to represent deformable property, the topography of filaments and membranes are no longer similar to the fully connected macromolecule structure. As shown in (b), the balls in a filament is connected to its left and right neighbors in turn, and each ball is constrained by at most two chemical bonds. As shown in (d), balls in a membrane are connected to its surrounding four neighbors and form a mesh-like structure. For the above topology, as long as the bond length of the chemical bond not change, the structure will not stretch. Deformation such as bending can occur, when the bond angle changes elastically