Fig. 1

Phases of wound healing and differences between human and rodent skin. a An acute wound heals primarily by (i) re-epithelialization in human skin and (ii) contraction in rodent skin. One difference in rodent skin is the presence of the panniculus carnosus, a thin layer of muscle attached to the subcutaneous tissue that serves as the contractile force for wound closure. The overlapping phases of wound healing are similar, with initial inflammation and provisional matrix deposition resulting in the recruitment of neutrophils and macrophages to the wound to assist in clean-up and stimulation of granulation tissue deposition. As the inflammatory phase progresses into the proliferative and remodeling phases, there is a decrease in neutrophils and macrophages. In (i) human skin, a maturation of the granulation tissue extracellular matrix provides a surface for keratinocyte migration and proliferation to occur in a process known as re-epithelialization. In (ii) rodents, the panniculus carnosus and fibroblasts, aid in the contraction of the wound edges and ultimately wound closure by decreasing the overall surface area as the dominant process for wound closure. b Anatomical differences in mouse skin and human skin are illustrated by H&E. Mouse skin contains a higher density of hair follicles (denoted by asterisks) that originate in the subcutaneous tissue, lacks eccrine glands and rete ridges, and has very thin dermis compared to human skin. Human skin hair follicles (denoted by asterisk) originate in the dermis, are less numerous and depend on body location. Additionally, human skin has more structures that contribute to re-epithelialization such as eccrine glands (denoted by hash), and rete ridges that also support the strength of epidermal and dermal adhesion. Scale bar = 500 µm low magnification; 100 µm for high-magnification insets