Open Access
This article is

- freely available
- re-usable

*Mathematics*
**2016**,
*4*(1),
6;
https://doi.org/10.3390/math4010006

Article

Microtubules Nonlinear Models Dynamics Investigations through the $\mathrm{exp}(-\mathsf{\Phi}(\xi ))$-Expansion Method Implementation

^{1}

Department of Mathematics, Pabna University of Science & Technology, Pabna 6600, Bangladesh

^{2}

Department of Mathematics, Faculty of Basic Education, PAAET, Al-Ardhiya 92400, Kuwait

^{*}

Author to whom correspondence should be addressed.

Academic Editor:
Reza Abedi

Received: 24 November 2015 / Accepted: 20 January 2016 / Published: 4 February 2016

## Abstract

**:**

In this research article, we present exact solutions with parameters for two nonlinear model partial differential equations(PDEs) describing microtubules, by implementing the $\mathrm{exp}(-\mathsf{\Phi}(\xi ))$-Expansion Method. The considered models, describing highly nonlinear dynamics of microtubules, can be reduced to nonlinear ordinary differential equations. While the first PDE describes the longitudinal model of nonlinear dynamics of microtubules, the second one describes the nonlinear model of dynamics of radial dislocations in microtubules. The acquired solutions are then graphically presented, and their distinct properties are enumerated in respect to the corresponding dynamic behavior of the microtubules they model. Various patterns, including but not limited to regular, singular kink-like, as well as periodicity exhibiting ones, are detected. Being the method of choice herein, the $\mathrm{exp}(-\mathsf{\Phi}(\xi ))$-Expansion Method not disappointing in the least, is found and declared highly efficient.

Keywords:

The exp(−Φ(ξ))-Expansion Method; models of microtubules; exact solutions; periodic solutions; rational solutions; solitary solutions; trigonometric solutions## 1. Introduction

Microtubules (MTs) are major cytoskeletal proteins. MTs are cytoskeletal biopolymers shaped as nanotubes. They are hollow cylinders formed by Proto-Filaments (PFs) representing a series of proteins known as tubulin dimers. Each dimer is an electric dipole. These dimers are in a straight position within the PFs or placed in radial positions pointing out of the cylindrical surface. MTs compriseaninteresting type of protein structure that may be a good candidate for designing and manufacturing electronic nano-devices. MTs dynamical behavior is modeled by nonlinear partial differential equations (NPDEs). These equations are mathematical models of physical circumstances that emerge in various fields of engineering, plasma physics, solid state physics, optical fibers, chemistry, hydrodynamics, biology, fluid mechanics and geochemistry. To date solving NPDEs exactly or approximately, a plethora of methods have been in use. These include, but are not limited to, (G′/G)-expansion [1,2,3,4,5,6], Frobenius decomposition [7], local fractional variation iteration [8], local fractional series expansion [9], multiple exp-function algorithm [10,11], transformed rational function [12], exp-function method [13,14], trigonometric series function [15], inverse scattering [16], homogeneous balance [17,18], first integral [19,20,21,22], F-expansion [23,24,25], Jacobi function [26,27,28,29], Sumudu transform [30,31,32], solitary wave ansatz [33,34,35,36], novel (G′/G) -expansion [37,38,39,40,41,42], modified direct algebraic method [43,44], and last but not least, the $\mathrm{exp}(-\mathsf{\Phi}(\xi ))$-Expansion Method [45,46,47,48,49,50].

The objective of this paper is to apply the latter method, namely the $\mathrm{exp}(-\mathsf{\Phi}(\xi ))$-Expansion Method, to construct the exact solutions for the following two NPDEs modeling MT dynamics, [51,52,53,54,55,56,57,58,59]. In particular, in presenting the questions to be solved, for comparison purposes, we follow the initial set up established by Zayed and Alurrfi [56], solving the extended Riccatti equations (see Equations (1) and (2)). We then depart generically from their development by using an entirely distinct method, albeit we compare our final results with theirs in [56], keeping in focus the developments in [57,58,59], as well.

- (i)
- The model of nonlinear dynamics of microtubules assuming a single longitudinal degree of freedom per tubulin dimer is described by the nonlinear PDE (see [59]),$$m\frac{{\partial}^{2}z(x,\hspace{0.17em}t)}{\partial {t}^{2}}-k{l}^{2}\frac{{\partial}^{2}z(x,\hspace{0.17em}t)}{\partial {x}^{2}}-qE-Az(x\hspace{0.17em},t)+B{z}^{3}(x,t)+\gamma \frac{\partial z(x,\hspace{0.17em}t)}{\partial t}=0$$
- (ii)
- The nonlinear PDE describing the nonlinear dynamics of radially dislocated MTs:$$I\frac{{\partial}^{2}z(x,\hspace{0.17em}t)}{\partial {t}^{2}}-k{l}^{2}\frac{{\partial}^{2}z(x,\hspace{0.17em}t)}{\partial {x}^{2}}+pEz(x\hspace{0.17em},t)-\frac{pE}{6}{z}^{3}(x,t)+\mathrm{\Gamma}\frac{\partial z(x,\hspace{0.17em}t)}{\partial t}=0$$

This paper is organized as follows: In Section 2, we give the description of the $\mathrm{exp}(-\mathsf{\Phi}(\xi ))$-Expansion Method, while in Section 3, we apply the said method to solve the given NPDEs, Equations (1) and (2). In Section 4, physical explanations are given, followed by the conclusion in Section 5. The paper ends with relevant acknowledgments, and a rich list of references for interested readers.

## 2. Description of the $\mathrm{exp}(-\mathsf{\Phi}(\xi ))$-Expansion Method

Following th initial setup in [56], we consider the nonlinear evolution equation in the form,
where, $F$, is a polynomial in, $u(x,t)$, and its partial derivatives, involving nonlinear terms and highest order derivatives. The focal steps of the method are as follows:

$$F(u,{u}_{t},{u}_{x},{u}_{tt},{u}_{xt},{u}_{xx},\cdots \cdots )=0$$

**Step 1.**It is well known that, for a given wave equation, a travelling wave, $u(\xi )$, is a solution which depends upon, $x$, and, $t$, only through a unified variable, $\xi $, such that,

$$u(x,t)=u(\xi ),\xi ={k}_{1}x+\omega t$$

$$\frac{\delta}{\delta t}=\omega \frac{\delta}{\delta \xi},\frac{{\delta}^{2}}{\delta {t}^{2}}={\omega}^{2}\frac{{\delta}^{2}}{\delta {\xi}^{2}},\frac{\delta}{\delta x}={k}_{1}\frac{\delta}{\delta \xi},\text{and},\frac{{\delta}^{2}}{\delta {x}^{2}}={{k}_{1}}^{2}\frac{{\delta}^{2}}{\delta {\xi}^{2}}$$

We reduce Equation (3) to the following ODE:
Here, $Q$ is a polynomial in, $u(\xi )$, and its total derivatives, such that $\prime =\frac{d}{d\xi}$.

$$Q(u,{u}^{\prime},{u}^{\u2033},\cdots \cdots )=0$$

**Step 2.**We assume that Equation (6) has the formal solution:

$$u(\xi )={{\displaystyle \sum _{i=0}^{N}{A}_{i}(\mathrm{exp}(-\mathsf{\Phi}(\xi )))}}^{i}$$

$${\mathsf{\Phi}}^{\prime}(\xi )=\mathrm{exp}(-\mathsf{\Phi}(\xi ))+\mu \mathrm{exp}(\mathsf{\Phi}(\xi ))+\lambda $$

Consequently, we get the following possibilities for Equation (8):

**Cluster 1:**When $\mu \ne 0,$ ${\lambda}^{2}-4\mu >0,$ we get,

$$\mathsf{\Phi}(\xi )=\mathrm{ln}(\frac{-\sqrt{({\lambda}^{2}-4\mu )}\mathrm{tanh}(\frac{\sqrt{({\lambda}^{2}-4\mu )}}{2}(\xi +E))-\lambda}{2\mu})$$

**Cluster 2:**When $\mu \ne 0,$ ${\lambda}^{2}-4\mu <0,$ we get,

$$\mathsf{\Phi}(\xi )=\mathrm{ln}(\frac{\sqrt{(4\mu -{\lambda}^{2})}\mathrm{tan}(\frac{\sqrt{(4\mu -{\lambda}^{2})}}{2}(\xi +E))-\lambda}{2\mu})$$

**Cluster 3:**When $\mu =0,$ $\lambda \ne 0,$ and ${\lambda}^{2}-4\mu >0,$ we obtain,

$$\mathsf{\Phi}(\xi )=-\mathrm{ln}(\frac{\lambda}{\mathrm{exp}(\lambda (\xi +E))-1})$$

**Cluster 4:**When $\mu \ne 0,$ $\lambda \ne 0,$ and ${\lambda}^{2}-4\mu =0,$ we obtain

$$\mathsf{\Phi}(\xi )=\mathrm{ln}(-\frac{2(\lambda (\xi +E)+2)}{{\lambda}^{2}(\xi +E)})$$

**Cluster 5:**When $\mu =0,$ $\lambda =0,$ and ${\lambda}^{2}-4\mu =0,$ we then have,

$$\mathsf{\Phi}(\xi )=\mathrm{ln}(\xi +E)$$

**Step 3.**We interchange Equation (7) into Equation (6) and then we expand the function $\mathrm{exp}(-\mathsf{\Phi}(\xi ))$. As a result of this interchange, we get a polynomial of $\mathrm{exp}(-\mathsf{\Phi}(\xi ))$. We equate all the coefficients of same power of $\mathrm{exp}(-\mathsf{\Phi}(\xi ))$ to zero. This procedure yields a system of algebraic equations which could be solved to obtain the values of ${A}_{N},\cdots \cdots ,\hspace{0.17em}V,\hspace{0.17em}\lambda ,\hspace{0.17em}\mu $ which after substitution into Equation (7) along with general solutions of Equation (8) completes the setup for getting the traveling wave solutions of the NPDE in Equation (3).

## 3. Applications

In this section, we will apply the $\mathrm{exp}(-\mathsf{\Phi}(\xi ))$-Expansion Method described in Section 2 to find the exact solutions of the NPDE Equations (1) and (2).

#### 3.1. Exact Solutions of the NPDE Equation(1)

In this subsection, we find the exact wave solutions of Equation (1). To this end, we use the transformation (4) to reduce Equation (1) into the nonlinear ordinary differential equation (NODE),
where,
and,

$$P{\psi}^{\u2033}(\xi )-Q{\psi}^{\prime}(\xi )-\psi (\xi )+{\psi}^{3}(\xi )-R=0$$

$$P=\frac{m{\omega}^{2}-k{l}^{2}{{k}_{1}}^{2}}{A},Q=\frac{\gamma \omega}{A},R=\frac{qE}{A\sqrt{A/B}}$$

$$z(\xi )=\sqrt{\frac{A}{B}}\psi (\xi )$$

Balancing, ${\psi}^{\u2033}(\xi )$, with, ${\psi}^{3}(\xi )$, in Equation (14), we get $N=1$. Consequently, we have,
where ${A}_{0},{A}_{1}$ are constants to be determined such that ${A}_{N}\ne 0,$ while $\lambda ,\hspace{0.17em}\mu $, are arbitrary.

$$\psi (\eta )={A}_{0}+{A}_{1}(\mathrm{exp}(-\mathsf{\Phi}(\xi )))$$

Substituting Equation (17) into Equation (14) and equating the coefficients of $\mathrm{exp}{(-\mathsf{\Phi}(\xi ))}^{3},$ $\mathrm{exp}{(-\mathsf{\Phi}(\xi ))}^{2},$ $\mathrm{exp}{(-\mathsf{\Phi}(\xi ))}^{1},$ $\mathrm{exp}{(-\mathsf{\Phi}(\xi ))}^{0}$, to zero, we respectively obtain,
and,

$$\mathrm{exp}{(-\mathsf{\Phi}(\xi ))}^{3}:2P{A}_{1}+{{A}_{1}}^{3}=0$$

$$\mathrm{exp}{(-\mathsf{\Phi}(\xi ))}^{2}:3{A}_{0}{{A}_{1}}^{2}+Q{A}_{1}+3P{A}_{1}\lambda =0$$

$$\mathrm{exp}{(-\mathsf{\Phi}(\xi ))}^{1}:2P{A}_{1}\mu +P{\lambda}^{2}{A}_{1}-{A}_{1}+Q{A}_{1}\lambda +3{{A}_{0}}^{2}{A}_{1}=0$$

$$\mathrm{exp}{(-\mathsf{\Phi}(\xi ))}^{0}:{A}_{0}-R+P{A}_{1}\mu \lambda +Q{A}_{1}\mu +{{A}_{0}}^{3}=0$$

Now, solving Equations (18)–(21) yields,
where, $\alpha =\pm \sqrt{-2P}$, and ${A}_{0},$ $P$, and, $Q$, are arbitrary constants.

$${A}_{0}={A}_{0},{A}_{1}=\alpha ,\lambda =-\frac{1}{3P}(3{A}_{0}\alpha +Q),\text{and},\phantom{\rule{0ex}{0ex}}\mu =\frac{1}{18{P}^{2}}(3{A}_{0}\alpha Q+2{Q}^{2}+9P-9{{A}_{0}}^{2}P),R=\frac{1}{27{P}^{2}}\{Q\alpha (2{Q}^{2}+9P)\}$$

Substituting Equation (22) into Equation (17), we obtain

$$\psi (\xi )={A}_{0}+\alpha (\mathrm{exp}(-\mathsf{\Phi}(\xi )))$$

Now, substituting Equations (9)–(13) into Equation (23) respectively, we get the following five traveling wave solutions of the NPDE Equation (1).

When $\mu \ne 0,$ ${\lambda}^{2}-4\mu >0,$
where $E$ is an arbitrary constant.

$${z}_{1}(\xi )=\sqrt{\frac{A}{B}}\{{A}_{0}-\alpha (\frac{2\mu}{\sqrt{{\lambda}^{2}-4\mu}\mathrm{tanh}(\frac{\sqrt{{\lambda}^{2}-4\mu}}{2}(\xi +E))+\lambda}\}$$

When $\mu \ne 0,$ ${\lambda}^{2}-4\mu <0,$
where, $E$, is an arbitrary constant.

$${z}_{2}(\xi )=\sqrt{\frac{A}{B}}\{{A}_{0}+\alpha (\frac{2\mu}{\sqrt{4\mu -{\lambda}^{2}}\mathrm{tan}(\frac{\sqrt{4\mu -{\lambda}^{2}}}{2}(\xi +E))-\lambda}\}$$

When $\mu =0,$ $\lambda \ne 0,$ and ${\lambda}^{2}-4\mu >0,$
where, $E$, is an arbitrary constant.

$${z}_{3}(\xi )=\sqrt{\frac{A}{B}}\{{A}_{0}+\alpha (\frac{\lambda}{\mathrm{exp}(\lambda (\xi +E))-1})\}$$

When $\mu \ne 0,$ $\lambda \ne 0,$ and ${\lambda}^{2}-4\mu =0,$
where, $E$, is an arbitrary constant.

$${z}_{4}(\xi )=\sqrt{\frac{A}{B}}\{{A}_{0}-\alpha (\frac{{\lambda}^{2}(\xi +E)}{2(\lambda (\xi +E))+2)})\}$$

When $\mu =0,$ $\lambda =0,$ and ${\lambda}^{2}-4\mu =0,$
where, $E$, is an arbitrary constant.

$${z}_{5}(\xi )=\sqrt{\frac{A}{B}}\{{A}_{0}+\alpha (\frac{1}{\xi +E})\}$$

#### 3.2. Exact Solutions of the NPDE Equation (2)

In this subsection, we find the exact solutions of Equation (2). To this end, we use the transformation Equation (4) to reduce Equation (2) into the following NODE,
where,
and,

$$S{\psi}^{\u2033}(\xi )-T{\psi}^{\prime}(\xi )+\psi (\xi )-{\psi}^{3}(\xi )=0$$

$$S=\frac{I{\omega}^{2}-k{l}^{2}{{k}_{1}}^{2}}{pE},T=\frac{\mathrm{\Gamma}\omega}{pE}$$

$$z(\xi )=\sqrt{6}\psi (\xi )$$

Balancing ${\psi}^{\u2033}(\xi )$ with ${\psi}^{3}(\xi )$ in Equation (29), we get $N=1$. Consequently, we have the formal solution of Equation (29), as follows:
where ${A}_{0},{A}_{1}$ are constants to be determined such that ${A}_{N}\ne 0,$ while $\lambda ,\hspace{0.17em}\mu $, are arbitrary. Substituting Equation (32) into Equation (29) and equating the coefficients of $\mathrm{exp}{(-\mathsf{\Phi}(\xi ))}^{3},$ $\mathrm{exp}{(-\mathsf{\Phi}(\xi ))}^{2},$ $\mathrm{exp}{(-\mathsf{\Phi}(\xi ))}^{1},$ $\mathrm{exp}{(-\mathsf{\Phi}(\xi ))}^{0}$ to zero, we respectively obtain
and,

$$\psi (\xi )={A}_{0}+{A}_{1}(\mathrm{exp}(-\mathsf{\Phi}(\xi )))$$

$$\mathrm{exp}{(-\mathsf{\Phi}(\xi ))}^{3}:2S{A}_{1}-{{A}_{1}}^{3}=0$$

$$\mathrm{exp}{(-\mathsf{\Phi}(\xi ))}^{2}:3S{A}_{1}\lambda -3{A}_{0}{{A}_{1}}^{2}+T{A}_{1}=0$$

$$\mathrm{exp}{(-\mathsf{\Phi}(\xi ))}^{1}:{A}_{1}+2S{A}_{1}\mu +S{\lambda}^{2}{A}_{1}+T{A}_{1}\lambda -3{{A}_{0}}^{2}{A}_{1}=0$$

$$\mathrm{exp}{(-\mathsf{\Phi}(\xi ))}^{0}:{A}_{0}+S{A}_{1}\mu \lambda +T{A}_{1}\mu -{{A}_{0}}^{3}=0$$

Solving the Equation (33)–(36) yields:

**Cluster 1**: We have,

$${A}_{0}={A}_{0},{A}_{1}=\frac{2}{3}T,\lambda =\frac{3}{2T}(2{A}_{0}-1),\mu =\frac{9}{4{T}^{2}}({{A}_{0}}^{2}-{A}_{0}),S=\frac{2}{9}{T}^{2}$$

**Cluster 2**: We have,

$${A}_{0}={A}_{0},{A}_{1}=-\frac{2}{3}T,\lambda =-\frac{3}{2T}(2{A}_{0}+1),\mu =\frac{9}{4{T}^{2}}({{A}_{0}}^{2}+{A}_{0}),S=\frac{2}{9}{T}^{2}$$

For cluster 1, substituting Equation (37) into Equation (32), we obtain
while, for cluster 2, substituting Equation (38) into Equation (32), we obtain

$$u(\xi )={A}_{0}+\frac{2T}{3}(\mathrm{exp}(-\mathsf{\Phi}(\xi )))$$

$$u(\xi )={A}_{0}-\frac{2T}{3}(\mathrm{exp}(-\mathsf{\Phi}(\xi )))$$

Now, substituting Equations (9)–(13) into Equation (39), respectively, we get the following five traveling wave solutions of the NPDE Equation (2).

When, $\mu \ne 0,$ ${\lambda}^{2}-4\mu >0,$
where $E$ is an arbitrary constant.

$${z}_{1}(\xi )=\sqrt{6}\{{A}_{0}-\frac{2T}{3}(\frac{2\mu}{\sqrt{{\lambda}^{2}-4\mu}\mathrm{tanh}(\frac{\sqrt{{\lambda}^{2}-4\mu}}{2}(\xi +E))+\lambda}\}$$

When $\mu \ne 0,$ ${\lambda}^{2}-4\mu <0,$
where $E$ is an arbitrary constant.

$${z}_{2}(\xi )=\sqrt{6}\{{A}_{0}+\frac{2T}{3}(\frac{2\mu}{\sqrt{4\mu -{\lambda}^{2}}\mathrm{tan}(\frac{\sqrt{4\mu -{\lambda}^{2}}}{2}(\xi +E))-\lambda})\}$$

When, $\mu =0,$ $\lambda \ne 0,$ and ${\lambda}^{2}-4\mu >0,$
where $E$ is an arbitrary constant.

$${z}_{3}(\xi )=\sqrt{6}\{{A}_{0}+\frac{2T}{3}(\frac{\lambda}{\mathrm{exp}(\lambda (\xi +E))-1})\}$$

When $\mu \ne 0,$ $\lambda \ne 0,$ and ${\lambda}^{2}-4\mu =0,$
where $E$ is an arbitrary constant.

$${z}_{4}(\xi )=\sqrt{6}\{{A}_{0}-\frac{2T}{3}(\frac{{\lambda}^{2}(\xi +E)}{2(\lambda (\xi +E))+2)})\}$$

When $\mu =0,$ $\lambda =0,$ and ${\lambda}^{2}-4\mu =0,$
where $E$ is an arbitrary constant.

$${z}_{5}(\xi )=\sqrt{6}\{{A}_{0}+\frac{2T}{3}(\frac{1}{\xi +E})\}$$

At this point, inserting Equations (9)–(13) into Equation (40), respectively, we get the following other five traveling wave solutions of the NPDE Equation (2).

When, $\mu \ne 0,$ ${\lambda}^{2}-4\mu >0,$
where, $E$, is an arbitrary constant.

$${z}_{6}(\xi )=\sqrt{6}\{{A}_{0}+\frac{2T}{3}(\frac{2\mu}{\sqrt{{\lambda}^{2}-4\mu}\mathrm{tanh}(\frac{\sqrt{{\lambda}^{2}-4\mu}}{2}(\xi +E))+\lambda})\}$$

When $\mu \ne 0,$ ${\lambda}^{2}-4\mu <0,$
where, $E$, is an arbitrary constant.

$${z}_{7}(\xi )=\sqrt{6}\{{A}_{0}-\frac{2T}{3}(\frac{2\mu}{\sqrt{4\mu -{\lambda}^{2}}\mathrm{tan}(\frac{\sqrt{4\mu -{\lambda}^{2}}}{2}(\xi +E))-\lambda})\}$$

When, $\mu =0,$ $\lambda \ne 0,$ and ${\lambda}^{2}-4\mu >0,$
where, $E$, is an arbitrary constant.

$${z}_{8}(\xi )=\sqrt{6}\{{A}_{0}-\frac{2T}{3}(\frac{\lambda}{\mathrm{exp}(\lambda (\xi +E))-1})\}$$

When, $\mu \ne 0,$ $\lambda \ne 0,$ and ${\lambda}^{2}-4\mu =0,$
where, $E$, is an arbitrary constant.

$${z}_{9}(\xi )=\sqrt{6}\{{A}_{0}+\frac{2T}{3}(\frac{{\lambda}^{2}(\xi +E)}{2(\lambda (\xi +E))+2)})\}$$

When, $\mu =0,$ $\lambda =0,$ and ${\lambda}^{2}-4\mu =0,$
where, $E$, is an arbitrary constant.

$${z}_{10}(\xi )=\sqrt{6}\{{A}_{0}-\frac{2T}{3}(\frac{1}{\xi +E})\}$$

## 4. Comparison

The papers [58,59] by Zdravkovic et al. are key to our present work. They collectively considered solutions of the nonlinear PDE describing the nonlinear dynamics of radially dislocated MTs using the simplest equation method. The solutions of the nonlinear PDE describing the nonlinear dynamics of radially dislocated MTs obtained by the $\mathrm{exp}(-\mathsf{\Phi}(\xi ))$-Expansion Method are different from those of the simplest equation method. It is n oteworthy to point out that some of our solutions coincide with already published results, if parameters taken particular values which authenticate our solutions. Moreover, Zdravkovic et al. [58] investigated the nonlinear PDE describing the nonlinear dynamics of radially dislocated MTs using the simplest equation method to obtain exact solutions via the simplest equation method and achieved only two solutions (see Appendix). Furthermore, ten solutions of the nonlinear PDE describing the nonlinear dynamics of radially dislocated MTs are constructed by applying the $\mathrm{exp}(-\mathsf{\Phi}(\xi ))$-Expansion Method. Zdravkovic et al. [58] (see also [59]) apply the simplest equation method to the nonlinear PDE describing the nonlinear dynamics of radially dislocated MTs, and they only solve kink type solutions, but we apply the $\mathrm{exp}(-\mathsf{\Phi}(\xi ))$-Expansion Method to the nonlinear PDE describing the nonlinear dynamics of radially dislocated MTs and solve kink type solutions, singular kink type solutions and plane periodic type solutions. On the other hand, the auxiliary equation used in this paper is different, so obtained solutions are also different. Similarly, for any nonlinear evolution equation, it can be shown that the $\mathrm{exp}(-\mathsf{\Phi}(\xi ))$-Expansion Method is much more direct and user-friendly than other methods.

## 5. Physical Interpretations of Some Obtained Solutions

In this section, attempting to shed lights on the corresponding physical behavior, we to discuss nonlinear dynamics of MTs whether as nano-bioelectronics transmission lines like or radially dislocated MTs, based on the obtained traveling wave solutions, from Equations (24)–(28), and (41)–(50), respectively. We examine the nature of some obtained solutions of Equations (1) and (2) by selecting particular values of the parameters and graphing the resulting exact solutions using mathematical software Maple 13, represented in Figure 1, Figure 2, Figure 3, Figure 4, Figure 5 and Figure 6.

From our obtained solutions, we observe that Equations (24)–(28), and (41)–(50), exude kink type solitons, singular kink shape solitons, and periodic solutions. Equation (24) shows kink shaped soliton profile for, ${A}_{0}=1,$ $m=1,$ $\omega =-1,$ ${k}_{1}=1,$ $k=2,$ $l=2,$ $A=2,$ $B=3,$ $\mu =1,$ $\lambda =3,$ $E=1$, within the interval $-10\le x,\hspace{0.17em}t\le 10$ which is represented in Figure 1 and Figure 2. Equation (25) provides a periodic solution profile for, ${A}_{0}=1,$ $m=1,$ $\omega =-1,$ ${k}_{1}=1,$ $k=2,$ $l=2,$ $A=2,$ $B=3,$ $\mu =3,$ $\lambda =1,$ $E=5$ within the interval $-1\le x,\hspace{0.17em}t\le 1,$ which is represented in Figure 3 and Figure 4. Equation (26) provides a singular kink soliton profile for, ${A}_{0}=1,$ $m=1,$ $\omega =-1,$ ${k}_{1}=1,$ $k=2,$ $l=2,$ $A=2,$ $B=3,$ $\mu =0,$ $\lambda =2,$ $E=1$, within the interval $-10\le x,\hspace{0.17em}t\le 10,$ which is represented in Figure 5 and Figure 6. Equations (27) and (28) also represent singular kink type wave solutions which are similar to Figure 5 and Figure 6. Equations (41) and (46) provide kink soliton profile, for ${A}_{0}=2,$ $T=\frac{3}{2},$ $\omega =-1,$ ${k}_{1}=1,$ $\mu =1,$ $\lambda =3,$ and $E=1$, within the interval, $-10\le x,\hspace{0.17em}t\le 10,$ as in Figure 1 and Figure 2. Equations (42) and (47) provide periodic solutions for, ${A}_{0}=2,$ $T=\frac{3}{2},$ $\omega =-1,$ ${k}_{1}=1,$ $\mu =3,$ $\lambda =1,$ $E=5$, within the interval, $-1\le x,\hspace{0.17em}t\le 1,$ as in Figure 3 and Figure 4. Equations (43) and (48), provide singular kink soliton profiles for, ${A}_{0}=2,$ $T=\frac{3}{2},$ $\omega =-1,$ ${k}_{1}=1,$ $\mu =0,$ $\lambda =2,$ and, $E=1$, within the interval $-10\le x,\hspace{0.17em}t\le 10,$ as in Figure 5 and Figure 6. Equations (44) and (45), as well as Equations (49) and (50), also represent singular Kink type wave solutions which are similar to Figure 5 and Figure 6.

**Figure 1.**The solitary wave 3D graphics of Equation (24) shows a kink shaped soliton profile for, ${A}_{0}=1,$ $m=1,$ $\omega =-1,$ ${k}_{1}=1,$ $k=2,$ $l=2,$ $A=2,$ $B=3,$ $\mu =1,$ $\lambda =3,$ $E=1$ within the interval $-10\le x,\hspace{0.17em}t\le 10$.

**Figure 2.**The solitary wave 2D graphics of Equation (24) shows a kink shaped soliton profile for, ${A}_{0}=1,$ $m=1,$ $\omega =-1,$ ${k}_{1}=1,$ $k=2,$ $l=2,$ $A=2,$ $B=3,$ $\mu =1,$ $\lambda =3,$ $E=1$, $t=2$.

**Figure 3.**The solitary wave 3D graphics of Equiation (25) provides a periodic solution profile for, ${A}_{0}=1,$ $m=1,$ $\omega =-1,$ ${k}_{1}=1,$ $k=2,$ $l=2,$ $A=2,$ $B=3,$ $\mu =3,$ $\lambda =1,$ $E=5$ within the interval $-1\le x,\hspace{0.17em}t\le 1$.

**Figure 4.**The solitary wave 2D graphics of Equation (25) provides a periodic solution profile for, ${A}_{0}=1,$ $m=1,$ $\omega =-1,$ ${k}_{1}=1,$ $k=2,$ $l=2,$ $A=2,$ $B=3,$ $\mu =3,$ $\lambda =1,$ $E=5$, $t=2$.

**Figure 5.**The solitary wave 3D graphics of Equation (26) provides a singular kink soliton profile for, ${A}_{0}=1,$ $m=1,$ $\omega =-1,$ ${k}_{1}=1,$ $k=2,$ $l=2,$ $A=2,$ $B=3,$ $\mu =0,$ $\lambda =2,$ $E=1$ within the interval $-10\le x,\hspace{0.17em}t\le 10$.

**Figure 6.**The solitary wave 2D graphics of Equation (26) provides a singular kink soliton profile for, ${A}_{0}=1,$ $m=1,$ $\omega =-1,$ ${k}_{1}=1,$ $k=2,$ $l=2,$ $A=2,$ $B=3,$ $\mu =0,$ $\lambda =2,$ $E=1$, $t=2$.

## 6. Conclusions

The $\mathrm{exp}(-\mathsf{\Phi}(\xi ))$-Expansion Method has been appliedto Equations (1) and (2), which describe the nonlinear dynamics of microtubules assuming a single longitudinal degree of freedom per tubulin dimer [59] and the dynamics of radial dislocations in MTs, respectively. The said method was instrumental in the provision of new analytical solutions such as kink type solutions, singular kink type solutions and plane periodic type solutions which are shown in Figure 1, Figure 2 and Figure 3. On comparing our results in this paper with the well-known results obtained in [50,58,59], we deduce that our results are new and not published elsewhere. All analytical solutions obtained by The $\mathrm{exp}(-\mathsf{\Phi}(\xi ))$-Expansion Method in the paper have been controlled, whether they are verified to Equation (1) and Equation (2) with the aid of commercial software Maple, and all new solutions have been verified to the original equations Equations (1) and (2). Zayed and Alurrfi [56] recently solved the two equations but used the alternative generalized Ricatti projective method. There, they also obtained trigonometric, hyperbolic and rational solutions but failed to obtain the exponential ones that we got. Our distinction resides mostly in obtaining extra solution types using our method. Of course, the choice of parameters yields different facets of the solutions and their graphic presentation so as to be type representative, without rendering the paper so voluminous, should more realizations be expected.

## Acknowledgments

The authors acknowledge and salute the mathematics editorial board management, and thank the consequent anonymous referees’ diligent efforts and critiques that helped improve the flow, style and scientific veracity of this paper. Furthermore, Fethi Bin Muhammad Belgacem wishes to acknowledge the support of the Public Authority for Applied Education and Training, Kuwait, through the Research Department grant No. PAAET RDBE-13-09.

## Author Contributions

In light of the recent scholarly interest in nano-bioelctronics Microtubules dynamic behavior, both authors agreed to investigate this phenomenon but with the advent of an original method not alreay used in the literature, which gave the authors the opportunity to compare with existing solutions. The contribution is therefore equally and evenly shared between both authors. Due to the subject importance and the desire that common understanding of these physical phenomena be widely spread, the authors invite interested readers to communicate, request, share relevant pieces of information, and collaborate, if so wished!

## Conflicts of Interest

The authors declare no conflict of interest.

## Appendix

Zdravkovic et al. [56] studied solutions of of the nonlinear PDE describing the nonlinear dynamics of radially dislocated MTs using the simplest equation method and achieved the following exact solutions:

$${\psi}_{1}(x,\hspace{0.17em}t)=\pm \frac{1}{2}\left[1+\mathrm{tanh}y+\frac{1}{{\mathrm{cosh}}^{2}y(d+\mathrm{tanh}y)}\right]$$

$${\psi}_{2}(x,\hspace{0.17em}t)=\pm \frac{1}{2}\left[1+\mathrm{tanh}(\frac{y}{2})+\frac{1}{\mathrm{sinh}y)}\right]$$

## References

- Alam, M.A.; Akbar, M.A.; Mohyud-Din, S.T. General traveling wave solutions of the strain wave equation in microstructured solids via the new approach of generalized (G′/G)-Expansion method. Alex. Eng. J.
**2014**, 53, 233–241. [Google Scholar] [CrossRef] - Alam, M.N.; Akbar, M.A.; Hoque, M.F. Exact traveling wave solutions of the (3+1)-dimensional mKdV-ZK equation and the (1+1)-dimensional compound KdVB equation using new approach of the generalized (G′/G)-expansion method. PramanJ. Phys.
**2014**, 83, 317–329. [Google Scholar] [CrossRef] - Alam, M.N.; Akbar, M.A. A new (G′/G)-expansion method and its application to the Burgers equation. Walailak J. Sci. Technol.
**2014**, 11, 643–658. [Google Scholar] - Hafez, M.G.; Alam, M.N.; Akbar, M.A. Exact traveling wave solutions to the Klein-Gordon equation using the novel (G′/G)-expansion method. Results Phys.
**2014**, 4, 177–184. [Google Scholar] [CrossRef] - Alam, M.N.; Akbar, M.A. The new approach of generalized (G′/G)-expansion method for nonlinear evolution equations. Ain Shams Eng.
**2014**, 5, 595–603. [Google Scholar] [CrossRef] - Younis, M.; Rizvi, S.T.R. Dispersive dark optical soliton in (2+1)-dimensions by G′/G-expansion with dual-power law nonlinearity. Opt. Int. J. Light Electron Opt.
**2015**, 126, 5812–5814. [Google Scholar] [CrossRef] - Ma, W.X.; Wu, H.Y.; He, J.S. Partial differential equations possessing Frobeniusintegrable decomposition technique. Phys. Lett. A
**2007**, 364, 29–32. [Google Scholar] [CrossRef] - Yang, Y.J.; Baleanu, D.; Yang, X.J. A Local fractional variational iteration method for Laplace equation within local fractional operators. Abstr. Appl. Anal.
**2013**, 2013, 202650. [Google Scholar] [CrossRef] - Yang, A.M.; Yang, X.J.; Li, Z.B. Local fractional series expansion method for solving wave and diffusion equations on cantor sets. Abstr. Appl. Anal.
**2013**, 2013, 351057. [Google Scholar] [CrossRef] - Ma, W.X.; Zhu, Z. Solving the (3+1)-dimensional generalized KP and BKP equations by the multiple exp-function algorithm. Appl. Math. Comput.
**2012**, 218, 11871–11879. [Google Scholar] [CrossRef] - Ma, W.X.; Huang, T.; Zhang, Y. A multiple exp-function method for nonlinear differential equations and its application. Phys. Scr.
**2010**, 82, 065003. [Google Scholar] [CrossRef] - Ma, W.X.; Lee, J.H. A transformed rational function method and exact solutions to the (3+1) dimensional Jimbo-Miwa equation. Chaos Solitons Fractals
**2009**, 42, 1356–1363. [Google Scholar] [CrossRef] - He, J.H.; Wu, X.H. Exp-function method for nonlinear wave equations. Chaos Solitons Fractals
**2006**, 30, 700–708. [Google Scholar] [CrossRef] - Younis, M.; Rizvi, S.T.R.; Ali, S. Analytical and soliton solutions: Nonlinear model of an obioelectronics transmission lines. Appl. Math. Comput.
**2015**, 265, 994–1002. [Google Scholar] [CrossRef] - Zhang, Z.Y. New exact traveling wave solutions for the nonlinear Klein-Gordonequation. Turk. J. Phys.
**2008**, 32, 235–240. [Google Scholar] - Ablowitz, M.J.; Segur, H. Solitions and Inverse Scattering Transform; SIAM: Philadelphia, PA, USA, 1981. [Google Scholar]
- Fan, E.; Zhang, H. A note on the homogeneous balance method. Phys. Lett. A
**1998**, 246, 403–406. [Google Scholar] [CrossRef] - Wang, M.L. Exact solutions for a compound KdV-Burgers equation. Phys. Lett. A
**1996**, 213, 279–287. [Google Scholar] [CrossRef] - Moosaei, H.; Mirzazadeh, M.; Yildirim, A. Exact solutions to the perturbed nonlinear Schrodinger equation with Kerr law nonlinearity by using the first integral method. Nonlinear Anal. Model. Control
**2011**, 16, 332–339. [Google Scholar] - Bekir, A.; Unsal, O. Analytic treatment of nonlinear evolution equations using the first integral method. Pramana J. Phys.
**2012**, 79, 3–17. [Google Scholar] [CrossRef] - Lu, B.H.Q.; Zhang, H.Q.; Xie, F.D. Traveling wave solutions of nonlinear partial differential equations by using the first integral method. Appl. Math. Comput.
**2010**, 216, 1329–1336. [Google Scholar] [CrossRef] - Feng, Z.S. The first integral method to study the Burgers–KdVequation. J. Phys. A Math. Gen.
**2002**, 35, 343–349. [Google Scholar] [CrossRef] - Abdou, M.A. The extended F-expansion method and its application for a class of nonlinear evolution equations. Chaos Solitons Fractals
**2007**, 31, 95–104. [Google Scholar] [CrossRef] - Ren, Y.J.; Zhang, H.Q. A generalized F-expansion method to find abundant families of Jacobi elliptic function solutions of the (2+1)-dimensional Nizhnik-Novikov-Veselovequation. Chaos Solitons Fractals
**2006**, 27, 959–979. [Google Scholar] [CrossRef] - Zhang, J.L.; Wang, M.L.; Wang, Y.M.; Fang, Z.D. The improved F-expansion method and its applications. Phys. Lett. A
**2006**, 350, 103–109. [Google Scholar] [CrossRef] - Dai, C.Q.; Zhang, J.F. Jacobian elliptic function method for nonlinear differential-difference equations. Chaos Solitons Fractals
**2006**, 27, 1042–1049. [Google Scholar] [CrossRef] - Fan, E.; Zhang, J. Applications of the Jacobi elliptic function method to special-type nonlinear equations. Phys. Lett. A
**2002**, 305, 383–392. [Google Scholar] [CrossRef] - Liu, S.; Fu, Z.; Liu, S.; Zhao, Q. Jacobi elliptic function expansion method and periodic wave solutions of nonlinear wave equations. Phys. Lett. A
**2001**, 289, 69–74. [Google Scholar] [CrossRef] - Zhao, X.Q.; Zhi, H.Y.; Zhang, H.Q. Improved Jacobi elliptic function method with symbolic computation to construct new double-periodic solutions for the generalized Ito system. Chaos Solitons Fractals
**2006**, 28, 112–126. [Google Scholar] [CrossRef] - Belgacem, F.B.M. Sumudu Transform Applications to Bessel Functions and Equations. Appl. Math. Sci.
**2010**, 4, 3665–3686. [Google Scholar] - Belgacem, F.B.M.; Karaballi, A.A. Sumudu transform Fundamental Properties investigations and applications. J. Appl. Math. Stoch. Anal.
**2006**, 2006, 1–23. [Google Scholar] [CrossRef] - Belgacem, F.B.M. Sumudu Applications to Maxwell’s Equations. PIERS Online
**2009**, 5, 1–6. [Google Scholar] [CrossRef] - Younis, M.; Ali, S. Bright, dark and singular solitons in magneto-electro-elastic circular rod. Waves Random Complex Media
**2015**, 25, 549–555. [Google Scholar] [CrossRef] - Younis, M.; Ali, S. Solitary wave and shock wave solutions to the transmission line model for nano-ionic currents along microtubules. Appl. Math. Comput.
**2014**, 246, 460–463. [Google Scholar] [CrossRef] - Ali, S.; Rizvi, S.T.R.; Younis, M. Traveling wave solutions for nonlinear dispersive water wave systems with time dependent coefficients. Nonlinear Dyn.
**2015**, 82, 1755–1762. [Google Scholar] [CrossRef] - Younis, M.; Ali, S.; Mahmood, S.A. Solitons for compound KdV-Burgers’ equation with variable coefficients and power law nonlinearity. Nonlinear Dyn.
**2015**, 81, 1191–1196. [Google Scholar] [CrossRef] - Alam, M.N.; Belgacem, F.B.M. Application of the Novel (G′/G)-Expansion Method to the Regularized Long Wave Equation. Waves Wavelets Fractals Adv. Anal.
**2015**, 1, 51–67. [Google Scholar] [CrossRef] - Alam, M.N.; Hafez, M.G.; Belgacem, F.B.M.; Akbar, M.A. Applications of the novel (G′/G)-expansion method to find new exact traveling wave solutions of the nonlinear coupled Higgs field equation. Nonlinear Stud.
**2015**, 22, 613–633. [Google Scholar] - Alam, M.N.; Belgacem, F.B.M.; Akbar, M.A. Analytical treatment of the evolutionary (1+1) dimensional combined KdV-mKdV equation via novel (G′/G)-expansion method. J. Appl. Math. Phys.
**2015**, 3, 61765. [Google Scholar] [CrossRef] - Alam, M.N.; Belgacem, F.B.M. New generalized (G𠄲/G)-expansion method applications to coupled Konno-Oono and right-handed noncommutative Burgers equations. Adv. Pure Math
**2016**, in press. [Google Scholar] - Alam, M.N.; Hafez, M.G.; Akbar, M.A.; Belgacem, F.B.M. Application of new generalized (G′/G)-expansion method to the (3+1)-dimensional Kadomtsev-Petviashvili equation. Ital. J. Pure Appl. Math
**2016**, in press. [Google Scholar] - Alam, M.N.; Belgacem, F.B.M. Traveling Wave Solutions for the (1+1)-Dim Compound KdVB Equation by the Novel (G′/G)-Expansion Method. Int. J. Mod. Nonlinear Theory Appl.
**2016**, in press. [Google Scholar] - Younis, M.; Rehman, H.; Iftikhar, M. Travelling wave solutions to some nonlinear evolution equations. Appl. Math. Comput.
**2014**, 249, 81–88. [Google Scholar] [CrossRef] - Hereman, W.; Banerjee, P.P.; Korpel, A.; Assanto, G.; van Immerzeele, A.; Meerpoel, A. Exact solitary wave solutions of nonlinear evolution and wave equations using a direct algebraic method. J. Phys. A: Math. Gen.
**1986**, 19, 607. [Google Scholar] [CrossRef] - Hafez, M.G.; Alam, M.N.; Akbar, M.A. Traveling wave solutions for some important coupled nonlinear physical models via the coupled Higgs equation and the Maccarisystem. J. King Saud Univ.Sci.
**2015**, 27, 105–112. [Google Scholar] [CrossRef] - Hafez, M.G.; Alam, M.N.; Akbar, M.A. Application of the $\mathrm{exp}(-\mathsf{\Phi}(\xi ))$-expansion method to find exact solutions for the solitary wave equation in an un-magnetized dusty plasma. World Appl. Sci. J.
**2014**, 32, 2150–2155. [Google Scholar] - Alam, M.N.; Hafez, M.G.; Akbar, M.A.; Roshid, H.O. Exact traveling wave solutions to the (3+1)-dimensionalmKdV-ZK and the (2+1)-dimensional Burgers equations via $\mathrm{exp}(-\mathsf{\Phi}(\xi ))$-expansion method. Alex. Eng. J.
**2015**, 54, 635–644. [Google Scholar] - Alam, M.N.; Hafez, M.G.; Akbar, M.A.; Roshid, H.O. Exact Solutions to the (2+1)-Dimensional Boussinesq Equation via $\mathrm{exp}(-\mathsf{\Phi}(\xi ))$-Expansion Method. J. Sci. Res.
**2015**, 7, 1–10. [Google Scholar] [CrossRef] - Zayed, E.M.E.; Amer, Y.A.; Shohid, R.M.A. The (G′/G)-expansion method and the $\mathrm{exp}(-\mathsf{\Phi}(\xi ))$-Expansion Method with applications to a higher order dispersive nonlinear schrodingerequation. Sci. Res. Essays
**2015**, 10, 218–231. [Google Scholar] - Zekovic, S.; Muniyappan, A.; Zdravkovic, S.; Kavitha, L. Employment of Jacobian elliptic functions for solving problems in nonlinear dynamics of microtubules. Chin. Phys. B
**2014**, 23, 020504. [Google Scholar] [CrossRef] - Sataric, M.V.; Sekulic, D.L.; Sataric, B.M.; Zdravkovic, S. Role of nonlinear localized Ca
^{2+}pulses along microtubules in tuning the mechano-Sensitivity of hair cells. Prog. Biophys. Mol. Biol.**2015**, 119, 162–174. [Google Scholar] [CrossRef] [PubMed] - Sekulic, D.; Sataric, M.V. An improved nanoscale transmission line model of microtubules: The effect of nonlinearity on the propagation of electrical signals. Facta Univ. Ser. Electron. Energ.
**2015**, 28, 133–142. [Google Scholar] [CrossRef] - Sekulic, D.L.; Sataric, B.M.; Tuszynski, J.A.; Sataric, M.V. Nonlinear ionic pulses along microtubules. Eur. Phys. J. E Soft Matter
**2011**, 34, 1–11. [Google Scholar] [CrossRef] [PubMed] - Sekulic, D.; Sataric, M.V.; Zivanov, M.B. Symbolic computation of some new nonlinear partial differential equations of nanobiosciences using modified extended tanh-function method. Appl. Math. Comput.
**2011**, 218, 3499–3506. [Google Scholar] [CrossRef] - Sataric, M.V.; Sekulic, D.; Zivanov, M.B. Solitoniclonic currents along microtubules. J. Comput. Theor. Nanosci.
**2010**, 7, 2281–2290. [Google Scholar] [CrossRef] - Zayed, E.M.E.; Alurrfi, K.A.E. The generalized projective riccati equations method and its applications for solving two nonlinear PDEs describing microtubules. Int. J. Phys. Sci.
**2015**, 10, 391–402. [Google Scholar] - Sekulic, D.L.; Sataric, M.V. Microtubule as Nanobioelectronic nonlinear circuit. Serbian J. Electr. Eng.
**2012**, 9, 107–119. [Google Scholar] [CrossRef] - Zdravkovic, S.; Sataric, M.V.; Maluckov, A.; Balaz, A. A nonlinear model of the dynamics of radial dislocations in microtubules. Appl. Math. Comput.
**2014**, 237, 227–237. [Google Scholar] [CrossRef] - Zdravkovic, S.; Sataric, M.V.; Zekovic, S. Nonlinear Dynamics of Microtibules—A longitudinal Model. Europhys. Lett.
**2013**, 102, 38002. [Google Scholar] [CrossRef]

© 2016 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons by Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).