Table 1. Extracellular matrix concentration determination for spheroid formation with the SUM1315 cell line.

	Condition of Geltrex® adding
Percentage of Geltrex in the culture medium	After cell seeding (Day 0)	24h after cell seeding once aggregateformation (Day 1)
0 (control)	Unique loose aggregate	Unique loose aggregate
0.25 - 0.5	Unique loose aggregate	Unique loose aggregate
1 - 2	Scattered spheroids	Unique compact spheroid
3 - 4 - 5 - 6	Scattered spheroids	Scattered spheroids

Several Geltrex® concentrations from 0.25 to 6% were used. Two conditioning regimens of Geltrex® were tested: addition of Geltrex® (i) in the microplates just after cell seeding (corresponding to Day 0) and (ii) 24h after cell seeding and aggregate formation (corresponding to Day 1).