Droplet encapsulation

Here at CELLINK, we want to inspire you to print more advanced models using the BIO X. In the following section, we demonstrate how to print two droplets on top of each other to create encapsulated droplets.
Products used:

CELLINK RGD ➝
CELLINK A (discontinued)
BIO X ➝

Drop on drop

In this video, we demonstrate printing of three-layered grids with different infill densities using GelXA SKIN. The GelXA SKIN cartridges were placed in each of the three pneumatic printheads. All filaments were extruded through 22G nozzles at 5-15 kPa with 5 mm/sec on a Petri dish surface. Printhead 1 printed one layer with rectilinear pattern with infill density of 80%, printhead 2 printed two layers with rectilinear pattern with 20% infill density and finally, printhead 3 printed three grid layers with infill density of 10%. Printed layers of different infill density can represent three layers in a skin tissue model: epidermis, papillary dermis and reticular dermis, respectively. GelXA SKIN constructs can be crosslinked by adding our crosslinking agent enhanced with thrombin, which enzymatically converts fibrinogen component into fibrin, thus creating a stable network. After one medium wash, your cell laden droplets are ready to be cultured in standard cultivation environment. In addition, GelXA constructs can be also by photocrosslinked.

The G-code to this three-layered grid structure can be found on Bioverse!

Less viscous than CELLINK A

CELLINK RGD is a viscous bioink and therefore makes a stable inner core. On the other hand, CELLINK A bioink has a lower viscosity, which makes it a good bioink for encapsulating the inner core (Figure 1). CELLINK A will form a shell around the printed CELLINK RGD droplet, creating a protective layer for the cells in CELLINK RGD.

Crosslinked vs non-crosslinked CELLINK RGD

A substantial difference in stiffness between the crosslinked and non-crosslinked CELLINK RGD bioinks has been observed (Figure 2). A softer gel environment can be beneficial for certain cell types, especially for their ability to migrate within the bioink. The construct is crosslinked from the outside and inwards, therefore the outer shell of CELLINK A will be form an encapsulation layer. The degree of crosslinking of the inner core can be controlled by the crosslinking time. A shorter time of immersion in the crosslinking solution will yield a softer core.

Application

To study diffusion of substances through a barrier in 3D and at medium throughput, droplet encapsulation bioprinting can be conducted for a single cell type in two different bioinks. The inner core of the droplet can be CELLINK RGD encapsulating the cells. The RGD peptide, which is incorporated in the bioink, will promote the attachment of cells to the inner bioink. If this bioink is not crosslinked, the softer hydrogel will enable migration of cells through the bioink. The outer shell of the droplet can be created with CELLINK A, which can be crosslinked to protect the inner non-crosslinked CELLINK RGD core from dissolving. That way, CELLINK A can act as a passive shell in which diffusion of substances is facilitated.

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