Investigation On Generation And Sorting Of Microdroplets By Coaxial Interface Shearing

Microdroplets are widely applied in biomedical,material and other fields.In recent years,microfluidic technologies to generate microdroplets developed rapidly,which can control the size and structure of microdroplets accurately and attracted more and more researchers' attention.As a novel microfluidic technique,interface shearing utilizes a periodically vibrating capillary across the air-liquid interface to generate microdroplets from the disperse phase provided by an injection pump.Owing to its easy operation,reliable process control,high stability,and high reproducibility for producing monodisperse microdroplets with a wide range of materials,the interface shearing technique is expected to gain broad applications in the field of biomedical engineering and chemistry.The objective of this study is to advance theoretical and experimental research in interface shearing by expanding this promising technique to coaxial microencapsulation and on-demand positioning of multifunctional microdroplets.The specific contents are as follows:1.The Coaxial Interface Shearing(CIS)technique was developed to prepare the double emulsions by a coaxial needle with good uniformity,highly controllability,high encapsulation rate and wide applicability of materials.In this study,the influences of vibration frequency,inner and outer flow rates on the process outcome were explored in detail.The CIS process was used to produce an ultrasonically stimulative microcarrier with a chitosan shell and a perfluoropentane core.The ultrasonic excitation characteristics of the microcarrier were studied and its potential application in the field of ultrasound-controlled drug delivery was verified.In addition,the fracture of liquid bridge at the air-liquid interface was extended at the air-solid interface in order to print the double emulsions on the solid surface.Finally,microdroplets with double cores were prepared by the interface shearing process using compound needles.The CIS technique can be potentially used to produce multi-layered drug-laden microdroplets.2.Oblique Interface Shearing(OIS)technique was proposed to realize one-step generation and on-demand positioning of microdroplets through an oblique capillary for interface shearing.The falling microdroplets eventually produced a time-invariant lateral displacement after generation of the microdroplets.In this study,the influences of oblique angle,vibration frequency of capillary,and flow rate of disperse phase on the lateral displacement were investigated experimentally.The dropping trajectory of the prepared microdroplets was observed by a high-speed camera,and the influences of experimental parameters on lateral displacement were explained based on a Stokes drift model.In an OIS process,the lateral displacement of the microdroplets increases with the increased oblique angle,the increased vibration frequency,and the decreased flow rate.By changing the oblique angle,or the ratio of flow rate and vibration frequency,the OIS process is able to realize on-demand positioning of the microdroplets with the same size.Finally,based on the fact that the size and the position of the microdroplets can be predictively controlled by changing the vibration frequency,a receiving pool was used to prepare and collect the microdroplets of different sizes.The OIS technique can be potentially used to produce and sort the monodispersive microdroplets.3.Coaxial Oblique Interface Shearing(COIS)technique was proposed for simultaneous control of the morphology and the lateral displacement of double emulsions by combining the CIS technique and the OIS technique.In this study,the morphologies of double emulsions were controlled by adjusting the inner/outer flow rates and the vibration frequency.Based on the Stokes drift model,the lateral displacement of the double emulsions with different morphologies could be predicted and controlled.With this technique,we demonstrated controlled sorting of double emulsions with different morphologies,such as the same outer diameter and different shell thickness,the same inner diameter and different shell thickness,and the different inner and outer diameters.By controlling the total flow rates and the vibration frequency,we also demonstrated on-demand positioning of double emulsions with the same morphology.Finally,the potential use of the COIS technique in spatially chemical gradient drug release was demonstrated using the microdroplets with a chitosan shell and a perfluoropentane core.The COIS technique can be potentially used for producing spatially gradient materials for controlled drug release and tissue engineering.