I will work with bovine keratinocytes and I will supplement the culture medium with Epidermal Growth factor (EGF) and Bovine Pituitary Extract (BPE). I read some papers that this amount can vary from 5 to 20 ng/ml. I have the protocol with concentration to add to the specific keratinocytes medium but I will not use the specific medium for keratinocytes. I will use Williams E media and add EGF and BPE. What is the concentration of EGF that you supplement in the keratinocyte cultivation medium? and do you usually dilute it with distilled water and aliquot before adding it to the medium?