Design Of A Novel On-Chip Recoverable Elastic Barrier Based On Microfluidics And Its Application In Vascularized Organ-on-a-Chip

As an emerging technology,human organ-on-a-chip is expected to replace animal experiments and completely change the process of new drug development in the future,which has attracted more and more pharmaceutical companies and scientists.This technology accurately regulates the microphysiological environment of cells,such as shear stress,interstitial flow,and growth factor gradient on the chip to build a model that simulates the main microphysiological functions and three-dimensional microstructures of human organs or tissues in vitro.In this technology,the key to the organ-on-a-chip design is to achieve the patterning of cells by precisely regulating the distribution of hydrogels in space.At present,the commonly used method is to design physical barriers and microfluidic channels on the two sides of the tissue chamber to achieve the successful loading of hydrogel,nutrient transportation and emissions of metabolites,thereby achieving perfusion culture of tissue.This paper presents a new type of recoverable elastic barrier(REB)design,which uses microfluidic technology to form temporary barriers in the tissue chamber to regulate the spatial distribution of the hydrogel.After the hydrogel is solidified,the temporary barrier disappears to realize the barrier-free perfusion of the medium.Compared with common fixed physical barrier designs(such as micropillars,phaseguide,communication pores),this method enables more uniform stimuli to the cultured cell/tissues in the tissue chamber.Compared with other temporary barrier designs(such as the microfilament method,the chitosan method),this design has the advantages of simple operation and flexible design.First,in order to optimize the design parameters of the chip,COMSOL was used to simulate the REB.The simulation result shows that the membrane thickness is negatively related to the membrane bulging height,and the recover elastic barrier channel width and applied pressure are positively related to the membrane bulging height.When the design parameters of the REB channel are 500 ?m in width and 50 ?m in membrane thickness,it can achieve effective perfusion of hydrogels under 0.2 MPa pressure.At the same time,the fluid distribution of the interstitial flow in the REB,the micropillar and the phaseguide were compared using COMSOL software.The simulation result shows that the fluid distribution in the REB will be more uniform.Furthermore,the theoretical analysis of the meniscus pinning effect between the hydrogel and the REBduring the perfusion process was performed.Second,based on standard photolithography and PDMS demolding technology,organ-on-a-chip with REB is processed.In order to explore the effectiveness of the gel loading of the REB,gel loading tests were performed on rectangular chambers,irregular tissue chambers,multiple tissue chambers and Z-axis tissue chambers using hydrogel containing dyes.Finally,through vasculogenesis and angiogenesis experiments,a 3D vascular model in vitro was successfully cultivated on the organ-on-a-chip integrated with the design,and the feasibility of the design in the organ-on-a-chip was verified.Because the design of the REB can realize the barrier-free distribution of the hydrogel and the uniform stimulation of cells by the medium,it is expected to become a new type of hydrogel spatial distribution regulation method and also compatible with other organ-on-a-chip applications.