Assembly of heterogeneous hydrogel building blocks on a chip

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Hydrogel scaffolds are attractive materials for tissue engineering. A key aspect relies on the hydrogel architecture that must closely mimic complex biological features. Researchers from Taiwan Universities take advantages of both electrowetting and dielectrophoresis to create and assemble heterogeneous hydrogel building blocks.

To do so, 0.1 µL PEGDA or GelMA polymer droplets are dispensed and mixed using electrowetting on an array of 1mm*1mm electrodes. Once positioned, the flat droplets are UV or heat cross-linked, resulting in an assembly of hydrogel building blocks: each block exhibits specific stiffnesses, depending on the initial treatment of each droplet. Otherwise, immediately before crosslinking, refined designs in each electrode allow manipulating particles or cells by dielectrophoresis inside a droplet. Thus, many patterns of cells can be obtained in each hydrogel block before the final assembly: cultures of cardiomyocytes and fibroblasts were successfully performed this way (figure 1).

Figure 1: A-C/ PEGDA droplets manipulated using electrowetting, then cross-linked under UV light. D-F/ PEGDA droplets containing particles manipulated using electrowetting. Particles are positioned using dielectrophoresis before cross-linking. G-H/ Cardiomyocytes seeded on PEGDA/GelMA hybrid hydrogel. Cells adhere and grow mainly on GelMA blocks. I/ Fibrobasts positionned by dielectrophoresis, then encapsulated in GelMA. Scale bars: A-F 1mm, G-I 200µm. Extracted with permission from Sci. Adv. 2, e1600964 (2016). AAAS publishing copyright

While fluid handling by electrowetting-on-dielectric faces strong limitations, the electromicrofluidic platform described here combines electrowetting and dielectrophoresis in an original way, affording complex hydrogel architectures. Such strategy opens interesting perspectives by providing, through the scale-up of the device, centimetric - potentially 3D - hydrogels.