Fabrication and Application of Polymer-Based Multi-Shape Micromotors

Author:Liu Li Mei

Supervisor:dong bin


Degree Year:2017





A micromotor is a micrometer size device that can convert chemical energy into the propulsion force.To date,they are still in the experimental stage and far from the practical applications.This may be due to the following reasons:1)The constituent material is based on inorganic materials(metals and/or oxides).As a result,the micromotor can not be easily recycled/removed from the solution,limiting its application in biomedical field or environmental remediation.2)In the absence of remote control,the micromotors have different trajectories.This can be ascribed to the fact that different shaped micromotors have different barycenter,which may deviate from the propulsion force.3)The construction method for a micromotor is rather complex.It is difficult to mass produce them,which hinders its application in the practical field.In this thesis,we first report the utilization of the electrospinning method to fabricate different shaped micromotors(tadpole-like,spindle and spherical).We then systematically study their motion behaviors when placed in the solution.In addition,the all polymer based micromotor is also fabricated by template method and applied in the field of environmental remediation.This thesis includes the following five parts.First,we report for the first time a spindle-like polycaprolactone-based micromotor,which is fabricated by the simple electrospinning method.Different from those reported motion mechanisms(bubble propulsion,light-driven,self-electrophoresis mechanism,etc.),the movements of our micromotors are based on the Marangoni effect.When placed in an aqueous solution,the encapsulated surfactant is slowly released from its body,causing the surface tension gradient,thereby inducing the self-moving behavior of the micromotor.In addition,we also studied its moving behavior over the entire pH range.The results show that the motion behavior of this micromotor is greatly dependent on the pH values from 0 to 14.The higher pH,the faster its velocity.At last,we also compared the movement speed of different-sized micromotors when placed in the same pH solution,and found that smaller sized micromotor has a higher sensitivity to the solution pH.This micromotor represents an important progress toward the development of environmentally friendly micromotors for sensor applications.In addition to the asymmetric spindle-shaped,we have also fabricated a unique tadpole-like structure with a head and a tail through the electrospinning technology.After sputtering platinum nanoparticles on one side of this structure,we obtain the tadpole-like micromotor.When placed in the fuel,this micromotor moved autonomously,similar to a natural tadpole.Also,it can imitate tadpoles’ metamorphosis.The tail of tadpole-like micromotor will fall off upon heating.In addition,by simple polymer encapsulation method,it is easy to incorporate a variety of functional substrances,such as fluorescence and magnetic materials,realizing its functional versatility.This tadpole-like micromotor represents an important step toward the design,construction and application of biomimetic micromotors.Third,We have succeeded in obtaining asymmetric Janus micromotors with ensapsulated platinum nanoparticles or horseradish peroxidase by simple parallel electrospinning method.By changing the voltage,solution concentration,collecting distance and other parameters during the electrospinning process,we have obtained size-controllable micromotors.Meanwhile,we also examine the movement of the micromotors in the hydrogen peroxide solution and study the effects of size and catalyst load on their movement speed.Finally,based on the thermal responsibility of the enzyme-loaded polymer motors,the manipulation of the motor speed is achieved by tuning the temperature of the solution,which paves the way toward its application in biomedical field.Fourth,in the process of studying the above micromotor systems,we find that the molecular weight of the polymer has a great influence on the property of its membrane.The smaller the molecular weight is,the more fragile the film is.In this system,we first obtain the low molecular weight polycaprolactone film by spin coating,and then use the self-assembly and ultrasonic treatment to prepare the sheet-like micromotor.As the fabrication method is very simple and does not require expensive equipment,it can be obtained in a large quantity,which facilitates its potential applications in many fields.In addition,since the micromotor is based on polymers,its shape can be changed from a sheet to a sphere when heated.More importantly,it becomes soft and sticky when heated at a high temperature,this property can be used for the capture,transport and release of a model cargo without the need to introduce specific interactions.We believe that the functionalized polymer-based micromotor reported in this study have a great potential in practical applications such as targeted drug delivery.In the last part of this thesis,we fabricate all-polymer(gelatin and horseradish peroxidase)tubular micromotors by template method.Unlike the conventional micromotors,this micromotor does not require expensive equipment,such as sputtering machine.In addition,we also systematically study the speed changes of the micromotor under different conditions.The results showed that reducing the concentration of hydrogen peroxide or horseradish peroxidase decreases its speed.At last,since the surface of the obtained micromotor is relatively rough,when placed in an oil-containing solution,the oil may adhere to the surface of the motor without the need for a complex surface modification process,thus enhancing its oil seperation capability in the environment.The successful report of the motor provides a fundamental demonstration for its application in the field of environmental remediation.