Schematic representation of an interacting kinetic growth model for microtubules with finite width W. The size of an individual microtubule j is described by a constant width W, and segment lengths l_j,k, where the subscripts denote the k^th segment on j^th microtubule in the system. Every microtubule is covered with semicircle at both ends. The dash-dotted line indicates the central axis of microtubule, and the red arrow indicates the plus-end direction. In the cartoon, CMT2 will collide with CMT1 by further polymerization. α_j is the colliding angle of the j^th microtubule with its neighbor. The result depends on the choice of an critical zippering angle α₀. For steep angle with α_j > α₀, the growth of microtubule is blocked and may trigger induced catastrophe; for shallow angle α_j < α₀, such as CMT3, it will zipper and grow along its colliding neighbor’s body axis. CMT4 represents a newly nucleated one in the free space.