Hi Ester, Thera re several good methods to be found in the literature. (You'll need to go back many years, like back to the 1980's!)

We routinely use the technique from Andrew Shaw [Epithelial Cell Culture: A Practical Approach (Andrew Shaw, Ed). Oxford University Press, 1996.]

Fisher, Lonza, Sigma/Merck, etc., also have good tech documents freely available online. Its worth reading them!

We normally separate the epidermis by using dispase and isolate the keratinocytes by trypsin digestion. Separation of the epidermis might be tricky with small biopsies but it is important to lose the fibroblasts from the dermis as they easily overgrow the keratinocytes. We culture them in collagen IV coated plastic. Skin can be stored at 4C for a few days when wrapped in gauze with saline solution, before doing the isolation.

Article Serial Cultivation of Epidermal Keratinocytes from Psoriatic Plaques

Thank you very much.