Synthesis Of Hydrogels And Dynamics Of Ultrasonically Propelled Microrods In Viscous Environments

Self-propelled micromotors are artificial intelligent biomimetic materials at nanoor microscale,which are able to convert external energy into their own motion.They have attracted much attention among scientists and shown promise in applications such as biomedical microrobots,environmental monitoring,pollution regulation and so on.Since ultrasound at high frequency has been widely used in medical applications,people hope to use ultrasound propelled micromotors to cure tumors.The composition of blood in human body is very complex,composed of plasma and a large number of blood cells.Tumor and its microenvironment are even more complex.The degree of cross-linking and cell density of the extracellular matrix in tumor stromas is particularly high.Above all,it is important to understand how the micromotors can swim in different complex viscous environments in human bodies,such as blood and cell tissues.To solve the above problems and understand the behaviors of ultrasonically driven metal microrods in viscous liquids,this project simulated human blood environment through a mixture of water and glycol/ethylene glycol at various viscosity.The ultrasound resonance frequency is proportional to the sound velocity of the solution at a particular height of the experimental chamber.The velocity of gold microrods was found to follow the Stokes equation.When solution viscosity is high,it was found that gold microrods tend to gather at a particular acoustic resonance point in the experimental cell.Additionally,a new dynamic self-assembly of micro particles was found during this experiment.In this system,gold microrods dynamically formed around the sound wave nodal plane as a ring.In addition,it was also observed that gold microrods orbitted around the nodal point in a similar way to planets orbitting the sun.In this thesis,hydrogels were chosen to simulate the extracellular matrix environment of human tumors.Nonporous PEG-based hydrogels were synthesized by photo-crosslinking aqueous solutions of poly(ethylene glycol)diacrylate(PEGDA).The relationship between velocity of ultrasound propelled micromotors and viscosity of the system was also found to follow the Stokes equation.We thus developed a method for fixing the self-assembly of one dimensional chain pattern composing of ultrasonically driven metal microrods.Porous PEGDA hydrogels were produced by properly matching the photo-crosslinking reaction with a foaming process.To improve the crosslinking and pore uniformity of hydrogels,this thesis used a setup with two lamp tubes.The synthesis was optimized by carefully examining the effect of monomer concentration,initiator dosage,surfactant dosage and foaming agent dosage on gel pore size and the swelling rate.Ultrasonically driven gold microrods demonstrated similar behaviors in the porous hydrogels as in pure water.Our experiments also showed that ultrasonically driven gold microrods do not move in collagen gel in the present condition.