Problem	Troubleshooting
Collagen mixture does not solidify	Collagen mixture color should be straw-yellow to pink, otherwise pH is wrong and collagen may not gel. If the color is bright yellow, more sodium bicarbonate should be added drop by drop.
Collagen prematurely precipitates in the mixuture	Keep all components on ice until the collagen mixture is placed onto the insert
Contracted collagen is not even (one side is thicker than the other side)	Calibrate the shelf of incubator
The epidermis is formed with less than three keratinocyte layers.	Use undifferentiated keratinocytes at lower passages