Directional Locomotion Of Active Gel Driven By Photo-controlled Chemical Waves

Active matters are ubiquitous in biological system ranging from cell to living organisms,which is composed of large numbers of self-propelled elements that makes the matter intrinsically away from equilibrium state.The theme of this dissertation is to study the locomotion dynamics of self-oscillating active gel and its sub-system by using mechanism simulation.First,computing methods based on GPU(Graphics Processing Unit)technologies are developed for the mechanism simulation of reaction-transport system(RTS),which will highly benefit the dynamics studies of active gel in high-dimension(2D and 3D).GPU-based methods are applied to the fast computing for multiple RSTs,i.e.,phase diagram of oscillator dynamics(lyapunov phase diagram),1D spatio-temporal patterns(STP),2D STP and the stiff-problems.Results manifest that the speed-up ratio promoted to(60 ~ 1×104)according the property of systems respectively,which showed the high-efficient of GPU methods.So,above efforts of GPU-based methods can widens the field of mechanism studies on RTS.Second,the mechanism of a nonmonotonic relationship exists between light intensity and oscillatory frequency(I–F relationship)in phototaixs BelousovZhabotinsky reaction(P-BZR)is studied.During the formatting and competing of spatiotemporal patterns in oscillatory media,oscillation frequency plays a dominated role.In order to build frequency-controlled STP,we ought to understand all mechanism details of the I-F relationship,because it is the dominant role on the formation of directional chemical waves,which driven the active gel movement under differential illumination.In this part,we identify the essential mechanistic step of the I–F relationship: the previously proposed photoreaction: Ru(II)* + Ru(II)+ BrO3-+ 3H+ ? HBrO2 + 2Ru(III)+ H2 O,which has both effects of frequency-shortening and frequency-lengthening.The concentrations of species can shift the light intensity that produces the maximum frequency,which we simulate and explain with a mechanistic model.This result will benefit studies of pattern formation and biomimetic movement of oscillating polymer gels.Thrid,and also the core of this dissertation focus on the locomotion dynamics of the oscillating active gel.Mechanism studies by using a modified Yashin-Balazs model show that the gel through I-F relationship to sense the spatial differential illumination,which is manifest as the directional chemical wave generated from I-F relationship and high-frequency-domination under differential illumination.Under the driven of directional wave,gel movement undergoes retrograde wave showed both negative and positive phototaxis according illumination schemes,respectively,which reproduced experiment founding and validated the internal effect of I-F relationship during phototaxis.We also found the acceleration of the gel locomotion,which is generated from structure changes of waves(?v changes arise from the velocity variation of chemical waves),during the induction process of waves travels,that increase the driven effect of the waves duo to a more steeper changes of the?v along the space.Further studies found that movement of the gel manifests itself as a transition of the locomotion direction between retrograde and direct waves under both nonuniform and uniform spatial illumination.Our analysis shows that this transitions arise from the asymmetric migration of motors that driven by the successive push and pull generated at the wave front and wave back,respectively,as stimulus-responsive gel driven by chemical waves.This asymmetry of the chemical waves arises from the structure difference of the waves because it self-organizated just after the oscillation undergoes bifurcation,and it can also be enhanced at the boundary between illumination regions by differential illumination according to a relationship between the illumination intensity and the extreme values of v during an oscillation(I-vextreme relationship)in the P-BZR.In the end,we study the periodic migration of the gel under gradient illumination.Periodic back and forth migration plays an essential role in the life cycle of many organisms and in maintaining the ecological balance.By analyzing the reciprocating locomotion of a photosensitivegel undergoing an oscillating chemical reaction in a gradient illumination enviroment,we examine through an analogy whether periodic migration can arise as a adaptive response of a system's internal dynamics,that cause biological functions such growth,breeding,physical tendency et al.,to specific spatial variations in resource distribution,such as food,tempeture,light intensity,et al.,due to the geographic structure or seasonal transition.Even in this relatively simple system,kinematic switching in the mode of locomotion under changing illumination levels leads to reciprocating periodic motion,suggesting that such behavior may occur widely in organisms as a response to a variety of spatially distributed environmental stimuli for their survival and reproduction.In conclusion,locomotion of BZ gel: i.e.,positive and negative phototaxis,acceleration,transition from retrograde waves to direct waves and periodic migration are driven and ultimately determined by the asymmetry of wave's structure which are modulated by kinetic of the chemical part of the system(e.g.,bifurcation of oscillators,I-F and I-vmax relationships).