Fabrication of monodisperse alginate microgel beads by microfluidic picoinjection: a chelate free approach

• Published in: Lab on a chip Vol. 21; no. 11; pp. 2232 - 2243
• Main Authors: Ahmed, Husnain, Stokke, Bjørn Torger
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 01.06.2021
• Subjects: Beads; Biomedical materials; Calcium alginate; Calcium chloride; Chelating agents; Droplets; Encapsulation; Hydrogels; Microfluidics; Microgels; Nanoparticles; Sodium; Sodium alginate
• ISSN: 1473-0197; 1473-0189
• DOI: 10.1039/d1lc00111f

Micron-sized alginate hydrogel beads are extensively employed as an encapsulation medium for biochemical and biomedical applications. Here we report on the microfluidic assisted fabrication of calcium alginate (Ca-alginate) beads by on-chip picoinjection of aqueous calcium chloride (CaCl 2 ) in emulsified aqueous sodium alginate (Na-alginate) droplets or by picoinjection of Na-alginate solution in emulsified aqueous CaCl 2 droplets. There is no added chelator to reduce the Ca activity in either of the two strategies. The two fabrication strategies are implemented using a flow-focusing and picoinjection modules in a single PDMS chip. Aqueous alginate solution was emulsified and infused with CaCl 2 solution as the squeezed droplet pass the picoinjection channel; consequently, monodisperse, spherical, and structurally homogeneous Ca-alginate beads were obtained. Monodisperse alginate microgel populations with a mean diameter in the range of 8 to 28 μm and standard deviation less than 1 μm were successfully generated using microfluidic channels with various dimensions and controlling the flow parameters. Monodisperse but also non-spherical particles with diameters 6 to 15 μm were also fabricated when picoinjecting Na-alginate solution in emulsified aqueous CaCl 2 droplets. The Ca-alginate microbeads fabricated with tailormade size in the range from sub-cellular and upwards were in both strategies realized without any use of chelators or change in pH conditions, which is considered a significant advantage for further exploitation as encapsulation process for improved enzymatic activity and cell viability. Monodisperse microgel beads are fabricated by injecting chelate free aqueous Ca 2+ in aqueous Na-alginate emulsion and vice versa . This method of producing alginate microbeads without reducing activity of Ca 2+ is significant for biological assays.