To begin, place the PDMS microwell molds, anti-adherence rinsing solution and necessary lab wear in a tissue culture hood. To wash the PDMS microwell molds, use a 1, 000 microliter pipette to add 300 microliters of anti-adherence rinsing solution to each well. Then centrifuge the plate, 1, 620 G for three minutes.
Use a vacuum pump and a Pasteur pipette to aspirate the solution. Next, place 500 microliters of cell suspension at the desired concentration in the microwells and centrifuge the plate at 1, 620 G for three minutes. Place the plate in a humidified incubator to allow spheroid formation.
To harvest the spheroids, using a 1, 000 microliter pipette, firmly add 500 microliters of complete medium into each well. Pipette the added medium up and down at each quadrant three to four times to dislodge the speroids. Then use the pipette to gently aspirate the medium containing the spheroids into a microcentrifuge tube.
Transfer 50 microliters of the steroid suspension in a microcentrifuge tube. Then sequentially add 4-Arm PEG acrylate and PEG dithiol into it. Mix the resultant solution by pipetting it up and down about 10 times.
To yield 100 microliters of a 10%weight by volume PEG hydrogel precursor solution, pipette 20 microliters of the gel precursor solution in between two parafilm-lined glass slides separated with one millimeter silicon spacers and incubate the slides with gel precursor solution to allow for gelation. Once hydrogel gelation is complete, using a spatula, gently peel the gels off the separated glass slides. Place one gel per well into a 24-well plate, ensuring the surface containing the spheroids faces up.
Add 500 microliters of complete medium to each well to submerge the hydrogel completely. Place the multi-well plate in a humidified incubator to culture the cells. The described technique using microwell molds resulted in the formation of spheroids with spherical shapes and tightly-controlled polydispersity.
For spheroids with 3, 300 cells per microwell, the average spheroid size was about 250 microns and circularity was greater than 0.8, considering a value of 1 as a perfect sphere. Spheroid diameters were dependent on the microwell size and the number of cells per microwell.
