Fabrication And Application Of Microcapsule Structure Based On Coaxial Electrohydrodynamics

Encapsulation of biomaterials,such as drugs and biological cells,has been widely used in biomedicine and other fields.The goal is to achieve efficient encapsulation while maintaining its sustained-release characteristics.With the increasing demand for microcapsules with good encapsulation effect,the development of new technology for microcapsule preparation has become an important research goal.Among them,the combination of gelation technology and droplet jet manufacturing technology is a promising research direction to encapsulate biomaterials such as cells and drugs in a miniaturized three-dimensional gel.Micro droplet spray manufacturing technology is a non-contact micro sample application technology.The traditional way of microdroplet injection,which is driven by piezoelectric ceramics,is to squeeze the liquid in the reservoir cavity to obtain microdroplet,and the diameter of the microdroplet is usually larger than the diameter of the nozzle.The most direct way to reduce the droplet size is to reduce the nozzle size.However,with the decrease of nozzle size,the driving force needed to produce micro droplets increases dramatically,and the nozzle is very easy to block when the liquid viscosity is high or contains particles.Electrohydrodynamic(EHD)technology "pulls out" the liquid from the nozzle by electrostatic force to form the Taylor cone which is smaller than the diameter of the nozzle.In recent years,as an extension of EHD technology,a new type of micro droplet injection technology,coaxial electrohydrodynamic micro droplet injection technology,has attracted the attention of researchers.Different from the traditional technology,the coaxial EHD micro droplet injection technology refers to that when two kinds of liquid are extruded from the coaxial pin nozzle at a proper flow rate(usually the outflow velocity is far greater than the internal velocity),the Taylor cone is formed by applying high pressure between the coaxial nozzle and the collecting plate,and the liquid is "stretched" by the electric field force,and the Taylor cone is broken to form a micro droplet with internal and external structure.This technology not only inherits the advantages of traditional single axis EHD method,which can spray out droplets much smaller than the diameter of the nozzle,but also helps to improve the printing resolution and reduce the risk of nozzle blockage.When it is applied in biomedical field,it is easier to wrap effective components such as cells in the center of microcapsules,so as torealize the preparation of monodisperse microcapsules with high success rate of encapsulation Research on this technology.In this paper,we designed and built a set of microcapsule preparation device based on coaxial EHD method.It includes five parts: liquid supply system,coaxial nozzle,collecting electrode,high voltage power supply and shooting system.Alginate solution and RPMI-1640 cell medium were used for shell and core materials respectively.LED lighting and high-speed CMOS camera are used to collect the image of the droplet spraying process,and MATLAB is used to process the image.By analyzing the curve of the axial length of the meniscus with time,the droplet spraying state and its stability are judged.The effects of voltage,velocity and distance between nozzle and collector plate on the frequency and size of droplets were investigated.The prepared droplets react with the calcium chloride solution in the collecting electrode to produce calcium alginate microcapsules with inner and outer structure.The cells are embedded in the inner RPMI-1640 cell culture medium inside the microcapsules,which is more conducive to its activity.In the experiment,lymphocytes stained by fluorescence were mixed into RPMI-1640 cell culture medium.Fluorescence imaging showed that the cells were effectively encapsulated.RPMI-1640 was stained with fluorescein sodium,which showed that the shell of the microcapsule had high water permeability,which initially verified the possibility of the microcapsule for stem cell therapy.In order to further prepare the droplets with smaller size and higher ejection frequency,three possible optimization schemes are proposed in this paper.By reducing the concentration of sodium alginate solution and the outer diameter of the nozzle,the spray frequency was increased.And a design scheme of on-demand coaxial EHD droplet generator based on pulse liquid supply is proposed.