High-throughput culture and embedment of spheroid array using droplet contact-based spheroid transfer

Spheroids are one of the most representative models of 3D cell culture, which can be easily formed using conventional hanging drop method. However, medium change and spheroid transferring process are the bottlenecks that reduce the throughput of the entire process in the hanging drop culture. In addition, the embedment of spheroid into hydrogel still depends on the individual pipetting process. To overcome these issues, we present poly(dimethylsiloxane) (PDMS)-based simple devices which can exploit droplet contact-based spheroid transfer using a drop array chip (DAC) having an array of well structures and peripheral rims. When the upper spheroid-containing drops were in contact with the lower liquid drops, the air-liquid interface disappeared at the merged surface and the spheroids settled down due to gravitational force. This method was applied to repetitive medium change and live/dead staining of spheroids cultured with the hanging drop method. To simultaneously embed the spheroids into the corresponding collagen hydrogel drops, a PDMS-based pillar array chip (PAC) was contacted in advance with the spheroid-containing DAC. The contacted PAC then contained the spheroids trapped in small drops of liquid reduced in volume to around 0.5 μl. Consequently, the spheroids were embedded into the collagen drops at once by contacting the spheroid-containing PAC with the collagen-loaded DAC. The embedded spheroids using the DAC-PAC contacting method showed a reliable invasion behavior compared to the embedded spheroids using conventional manual pipetting.