Introduction: Fat grafting has antifibrotic effects and it improves scar quality. However, the biological mechanisms of fat grafts on scar healing are poorly understood.

Methods: This was a prospective study to identify differences in the epidermal and dermal structure, macrophage infiltration, or inflammatory and fibrotic markers in hypertrophic scars before and after fat grafting surgery compared to normal skin. Seven patients with hypertrophic scar completed the study. Biopsies from hypertrophic scars and normal skin were taken at the time of fat grafting surgery and follow-up biopsies 6 mo postoperatively. A clinical Patient and Observer Scar Assessment Scale was used to monitor the clinical aspects of the scars. Immunohistochemical stainings were performed to analyze the changes occurring in the hypertrophic scar tissue after fat grafting.

Results: Hypertrophic scars demonstrated decreased presence of rete ridges and increased levels of the profibrotic transforming growth factor beta-1 (TGF-β1) (P < 0.05) compared to normal skin. Fat grafting significantly increased the presence of rete ridges to the level of normal skin and reduced TGF-β1 expression (hypertrophic scars + fat) (P < 0.05). Fat grafting also increased the total macrophage count (CD68 pan-macrophage marker) (P < 0.05) and M1 macrophage count (inducible nitric oxide synthase M1 macrophage marker) (P < 0.05). The clinical evaluation of the scars (Patient and Observer Scar Assessment Scale) by the observer and patients improved after fat grafting (P < 0.05).

Conclusions: Our findings indicate that fat grafting promotes normalization of skin by improving epidermal structure and reducing TGF-β1 levels and favors less fibrotic healing by regulating macrophages levels.