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. 2023 Sep 26;14(10):1828.
doi: 10.3390/mi14101828.

Effect of Flow Rate Modulation on Alginate Emulsification in Multistage Microfluidics

Yudan Whulanza  1   2 , Rithwik Chandur Nathani  1 , Klaugusta Adimillenva  1 , Ridho Irwansyah  1 , Retno Wahyu Nurhayati  2   3   4 , Muhammad Satrio Utomo  5 , Abdul Halim Abdullah  6
Affiliations

Effect of Flow Rate Modulation on Alginate Emulsification in Multistage Microfluidics

Yudan Whulanza et al. Micromachines (Basel). .

Abstract

The encapsulation of stem cells into alginate microspheres is an important aspect of tissue engineering or bioprinting which ensures cell growth and development. We previously demonstrated the encapsulation of stem cells using the hanging drop method. However, this conventional process takes a relatively long time and only produces a small-volume droplet. Here, an experimental approach for alginate emulsification in multistage microfluidics is reported. By using the microfluidic method, the emulsification of alginate in oil can be manipulated by tuning the flow rate for both phases. Two-step droplet emulsification is conducted in a series of polycarbonate and polydimethylsiloxane microfluidic chips. Multistage emulsification of alginate for stem cell encapsulation has been successfully reported in this study under certain flow rates. Fundamental non-dimensional numbers such as Reynolds and capillary are used to evaluate the effect of flow rate on the emulsification process. Reynolds numbers of around 0.5-2.5 for alginate/water and 0.05-0.2 for oil phases were generated in the current study. The capillary number had a maximum value of 0.018 to ensure the formation of plug flow. By using the multistage emulsification system, the flow rates of each process can be tuned independently, offering a wider range of droplet sizes that can be produced. A final droplet size of 500-1000 µm can be produced using flow rates of 0.1-0.5 mL/h and 0.7-2.4 mL/h for the first stage and second stage, respectively.

Keywords: alginate; double emulsification; microfluidics chips; stem cell encapsulation.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Double stage of emulsification of alginate/oil/water (A/O/W).
Figure 2
Figure 2
First stage of alginate-in-oil emulsion; (a) Commercial drop generator chip and interface setup and (b) Microscopic image of alginate-in-oil single emulsion.
Figure 3
Figure 3
Effect of dispersed vs. continuous flow rate for alginate-in-oil emulsion on (a) drop formation frequency, and (b) drop size.
Figure 4
Figure 4
Effect of Re number on plug length for flow rate variation of (a) dispersed phase and (b) continuous phase in alginate-in-oil droplet formation.
Figure 5
Figure 5
Plot of plug length/width ratio vs. flow rate ratio of (a) alginate flow rate variation and (b) oil flow rate variation for alginate-in-oil emulsion.
Figure 6
Figure 6
Second stage oil-in-water emulsion: (a) customized PDMS chip setup and (b) microscopic image of oil-in-water single emulsion.
Figure 7
Figure 7
Effect of dispersed vs. continuous flow rate for oil-in-water emulsion on (a) drop formation frequency and (b) drop size.
Figure 8
Figure 8
Effect of Re number on plug length for flow rate variation of (a) dispersed phase and (b) continuous phase in oil-in-water droplet formation.
Figure 9
Figure 9
Plot of dispersed/continuous flow rate ratio vs. plug length/channel width ratio for (a) oil flow variation and (b) water flow variation.
Figure 10
Figure 10
Double emulsification droplet visualization: (a) under microscope, (b) in the transfer tubing, and (c) in bulk solution.
Figure 11
Figure 11
Forces acting during droplet formation: (a) microscope view of emulsification, (b) schematic view droplet geometry.
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