Bioinspired Engineering And Motion Mechanism Of Natural Polysaccharide Micromotors

Artificial micro/nano motors are synthetic devices which could convert chemical energy,magnetic energy,light energy,electric energy or other energy into movement.Synthetic motors are also desired for achieving the tasks such as targeted drug delivery,toxin scavenging,biosensing and other applications in the field of biomedicine.In this doctoral thesis,polysaccharide micromotors were fabricated using biocompatible materials based on the templating method.By use of encapsulated catalyst and magnetic nanoparticles into micromotors,micromotors can move in solutions.The motion behavior and motion mechanism were also investigated and discussed.Biocompatible materials chitosan and sodium alginate was chosen to design and fabricate a polymer multilayer microplate motor modified with platinum nanoparticle and magnetic nanoparticle.Characterisation results showed that the prepared microplate motors were 5 ?m in diameter and 40 nm in thickness.Detailed investigation of the motion of microplate motor showed that the motors were propelled by oxygen bubbles and their movement orientation can be controlled by magnetic field.The relationship between oxygen bubbling and the velocity of microplate motor was further studied.Cell carrying microplates create a Janus-like structure enabling more reliable determination of the cell-microplate agglomerate than isolated plate motors.Polysaccharide multilayer microplates with different shapes were prepared based on the methods of layer-by-layer assembly and micro-contact printing.By using confocal laser scanning microscopy,transmission electron microscopy and scanning electron microscopy,the morphology and structure of the microplates were investigated.The results showed that obtained microplates were 60 nm in thickness,with uniform size and structural stability.Then,polyelectrolyte multilayer microrockets were obtained by using a rolled-up technique and their structure and morphology were studied.The removal of the sacrificial layer on the substrate triggers the release and self-rolling of circular or rectangular microplates,which produces the well-defined microrockets.The self-folding mechanism was investigated.The results showed that the stress release due to the energy stored in the fabrication step should be the main reason for the self-rolling behavior.The motion studies of microrockets showed that the speed of microrocket was 161 ?m/s in a 5% hydrogen peroxide solution.These microrockets show the potential to act as micro-/nanoscale tools for cell manipulation.Due to the biological incompatibility of the hydrogen peroxide,micromotors' applications in the field of biomedicine are limited.To enhance the compatibility of micro/nano motors,a magnetic propelled hydrogel-based star-shape micromotor is demonstrated.This star-shape micromotor can convert magnetic energy into mechanical energy so as to achieve movement.The external magnetic field facilitated two rotation behavior of the star-shaple micromotor,i.e.horizontal and vertical rotation movement.The star micromotor exhibits a speed of 17 ?m/s with magnetic intensity of 7 m T and frequency of 4 Hz.The star micromotor exhibits an markedly reduced speed at frequencies higher than 4Hz(step-out frequency).Once the frequency is beyond the step-out frequency,the fluidic drag exceeds the maximal magnetic torque,resulting in a decrease in velocity.The tangential flow induced in the rotation-plane of the micromotor occurs at tips and is locally minimum at the center.Such asymmetric tangential flow in Y direction during the rotation causes the net force in Y direction,which is attributed to the replacement during the rolling movement of the micromotor.This star micromotor shows good drug loading and controlled release capability.The loaded doxorubicin can be released quickly at the tumor acidic environment.Moreover,the biodegradation experiment results showed that these prepared star micromotors could be degraded by amylase.A series of biocompatible micromotors were fabricated based on controllable assembly and biomimetic design.These micromotors have good movement ability and delivery capacity,and thus hold their promise in the field of biomedical area.