Previously, I used to seed primary dermal fibroblasts (which initially had slow growth rate) in collagen hydrogel and the cells used to show complete attachment and the normal shape of fibroblasts after culturing the gel in complete media. Now I have new fibroblasts which grow fast in flasks and once seeded in the hydrogel, they show some attachment within few hours but then start to take the circular shape and make colonies which make any further tests difficult.
I have tried different collagen concentrations (1, 1.5 and 2 mg/ml) as well as different cell densities (5000, 10000, 20000, up to 100000 cells per 50 and 100 microlitre hydrogels, but the behaviour of the cells were the same.
Please, could you explain how I can overcome that problem?