In a previous work, we presented an integrated droplet microﬂuidic chip for the high throughput and reliable production of homogeneous spheroids, for their long term culture and multiscale analysis (Sart, Tomasi, Amselem & Baroud, Nat. Commun. 8, 469 (2017)).
In this work, we demonstrate the ability to add some content to the droplets at any given time during the experiment. By adding different cell types on demand, we can produce controlled cell-cell interactions, for instance for immuno-therapy models. This technology also allows to screen hundreds of different conditions in a single chip.
As a proof-of-concept, we exposed an array of liver spheroids (rat hepatomas) to a large range of drug concentrations in a single chip (3 decades of acetaminophen concentration). With these immobilized droplets, we show for the first time a dynamic follow-up of the toxicity results at the spheroid (700 single spheroids analyzed) and cellular level. Dead cells were identified automatically and were found closer and closer to the spheroid center with time, depending on the drug concentration. More interestingly, we identified a previously hidden high heterogeneity of responses close to the IC50 after a 24 h exposure. This dispersion is related to the initial presence and location of dead cells, one spheroid with at least one initial dead cell close to its center at the beginning of the experiment dying significantly faster than a spheroid that was initially completely alive. In addition, this analysis highlights a new dynamic feature of the viability that is characteristic of 3D structures.
This versatile technology could strongly participate in the democratization of high throughput and high content experiments on 3D models and should have a strong impact in phenotypic drug screening, toxicity studies, oncology and personalized medicine.