Problem	Possible Cause	Solution
Poor hepatocyte patterning	Issues with the PDMS mask	Ensure that the PDMS buttons are of uniform thickness and that the positive features are properly formed (no air bubbles)
	Issues with clamping the PDMS mask into the plate	Ensure that the clamp is tightened to an appropriate level; under-compression may cause some of the islands to not be properly protected from the oxygen plasma, whereas over-compression may cause the PDMS posts to buckle and form rings around the islands
Lack of proper PHH attachment to collagen domains	Issues with hepatocyte cryopreservation or processing procedures or collagen coating	Try a new collagen patterned plate and/or a different PHH donor lot
Aberrant growth of fibroblasts and/or homogenous morphology	Potential transformation of fibroblasts and/or selection of a specific sub-clone within the population	Discard the transformed fibroblasts and thaw a new cryopreserved vial of fibroblasts for propagation