Reseach On The Preparation And Motion Behavior Of Magnesium Based Janus Micromachine

Micro/nano motors are micro/nano scale devices,which can convert surrounding chemical energy or other forms of energy into kinetic energy supporting their own motion.Biodegradable micro/nano motors have a large potential for applications within the biomedical field,due to their small size and multiple functions.External energy field based driving is requiring permanent energy input,whereby optical stimuli exhibit limited penetration depth,while magnetic fields offer their own limitations especially for low resolutions.In biomedical applications magnetic fields are limited for people with implants.Most motors to this date employ hydrogen peroxide.Due to the strong oxidation potential and the toxicity of hydrogen peroxide,it’s value as fuel for biomedical applications is therefore limited.For this reason,the use of bio-friendly fuel to drive micro-nano motors has received great attention from researchers in recent years.In this thesis,the biodegradable polymer polylactic-co-glycolic acid is asymmetrically laminated onto the surface of magnesium microparticles to prepare a Mgbased Janus micromotor,which generates within acidic media hydrogen bubbles for autonomously propelled motion.The p H value of the utilized acidic environment is close to gastric acid,while the released magnesium ions can provide micronutrients needed by the human body.The motion of Mg-based micromotors depends on the p H and the amount of surfactant added.Janus microparticle fixed onto a solid surface can be utilized as a novel highperformance and fully biodegradable micropump.The opening hole diameter of this Janus micropump depends on the magnesium microparticle diameter that serves as core and fuel.Essentially,the pumping power depends on the surrounding p H environment and can achieve pumping powers accelerating tracer particles to speeds which are comparable to freely dispersed bubble propelled micromotors.Micropump pumping power significantly depends also on surrounding surfactant concentration and thus resulting bubbling frequency and bubble size.For surfactant concentrations below the critical micelle concentration pumping performance can decrease up to factor 5 due to not well stabilized bubbles.The pumping direction of tracer particles depends significantly on the bubble phase it ranges from slow pushing for growing bubble to pulling for released bubbles,whereby latter dominates。In summary,the thesis realizes the construction of Mg-based micromotors and Mgbased micropumps comprising out of exactly the same particles as the micromotors.The work provides new ideas for micro-nanomotors and pumps for biomedical applications,especially in acidic environments like the stomach.