Table 2.

Troubleshooting table.

Step	Problem	Possible reason	Solution
26	Defect in bonding	Mishandling in bonding process	Press the defective region using a pair of tweezers until the unbounded PDMS surface adheres to the glass surface.
	Weak bonding	Weak plasma treatment	Increase plasma treatment time or place the bonded device at 80 °C in an oven for several hours.
41	Collagen solution flows out into the media channel	Hydrophobicity of the device not yet recovered to the required level	Let device dry for a longer time (e.g. 48 hrs after PDL coating) in an 80 °C oven.
54	Non-confluent endothelial monolayer on one day	Low hMVECs seeding density	Wait one more day and increase cell seeding density.
	Unhealthy hMVECs	Poor surface coating	Use fresh surface coating solution.
		Media evaporation in reservoirs	Maintain a stable humidity in the incubator and add more medium into the reservoirs.