Fig. (2) Illustration of wound re-epithelialization models. (A) Leap-frogging model, suprabasal cells migrate by rolling over the leading basal cells and create new leader cells by differentiation at the epidermal tongue. (B) Tractor tread model, the superficial layers passively displace over the basal layers where keratinocytes located at the adjacent healthy skin migrate individually over each other (C) Usui model and Safferling model, basal and suprabasal keratinocytes migrating collectively and continuously in a concentric pattern around the wound.