Micropillar array embedded system for single cell encapsulation in hydrogel
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Micropillar array embedded system for single cell encapsulation in hydrogel Kyun Joo Park1, Kyoung G. Lee2, Seunghwan Seok1, Bong Gill Choi3, Seok Jae Lee2, and Do Hyun Kim*1 1 Department of Chemical & Biomolecular Engineering, KAIST, Korea. 2 Center for Nanobio Integration & Convergence Engineering (NICE), National Nanofab Center, Korea. 3 Department of Chemical Engineering, Kangwon National University, Korea. ABSTRACT A cylindrical-shaped micropillar array embedded microfluidic device was proposed to enhance the dispersion of cell clusters and the efficiency of single cell encapsulation in hydrogel. Different sizes of micropillar arrays act as a sieve to break Escherichia coli (E. coli) aggregates into single cells in polyethylene glycol diacrylate (PEGDA) solution. We applied the external force for the continuous breakup of cell clusters, resulting in the production of more than 70% of single cells into individual hydrogel particles. This proposed strategy and device will be a useful platform to utilize genetically modified microorganisms in practical applications. INTRODUCTION Encapsulation of single-microbial cells in hydrogel becomes important for the discovery of valuable biological species in various applications [1]. For practicality, screening the target cells from their heterogeneous cell population is essential. Traditional methods require complicated processes with numerous bench-top instruments including external filters and centrifuges for single-cell analysis and sorting. Recently, the combination of microfluidic systems, hydrogels and fluorescence-activated cell sorting systems (FACSs) has opened a new door to overcome the technical limit in the handling and isolation of cells. Previous single-cell research using a microfluidic system has mainly focused on spherical cells with low cell concentration. However, most of valuable biopharmaceuticals and biomaterials are obtained from non-spherical microbial cells. Therefore, the handling of nonspherical biological entities, such as rod-shaped bacterial cells and concave disc-shaped red blood cells, were desired [2]. As a cell environment mimetic material, polymer-based hydrogels are popular for cell culturing owing to their hydrophilic and non-toxic characteristics [3,4]. They also contain numerous pores that the media easily penetrate for maintaining cell viability and further cultivation [5]. However, polymers can disturb the surface charge of a cell and cause cell clusterization and sedimentation [6,7]. Moreover, this phenomenon decreases the single cell encapsulation efficiency and produces non-uniform sizes of hydrogel particles in microfluidic systems. To solve these problems, a breakthrough technology is necessary to utilize the advantages of both microfluidic systems and hydrogels. In this research, micropillar arrays were employed to disperse the cell aggregations effectively. Installed micropillar arrays acted as a filter to break E. coli clusters into single cell level. The clusters were collided sequentially with three sizes of pillars and sp
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