Fig. 5.

Microscopic evaluation of wound healing quality. (A–C) Representative histology pictures of the wound area on day 14 post surgery. The whole wound area is shown in (A), while the epidermis and wound bed are shown in (B) and (C), respectively. Different groups are the wounds treated with (i) in vivo printed GelMA containing VEGF (GelMA + VEGF printing), (ii) in vivo printed blank GelMA (GelMA printing), (iii) BPS containing VEGF administrated topically (topical VEGF), and (iv) wounds left untreated (non-treated). A thicker epithelial layer, more rete ridges, and lower amount of infiltrative cells in the wound bed demonstrates a significantly higher quality of healing in the wounds treated GelMA + VEGF printing. (D–I) Quantitate analysis of wound healing quality. (D) Wound re-epithelialization, calculated based on the area of new epithelium over total wound area. Highest amount of re-epithelialization was observed in the wounds treated with GelMA + VEGF. (E) Amount of granulation tissue. The GelMA + VEGF treated wounds had the largest area of granulation tissue. (F) Scar elevation index (SEI), calculated based on the total area of the healed skin over the area of normal skin below the buildup hypertrophic scarring. The wounds treated with GelMA + VEGF demonstrated significantly less scarring compared to the other groups. (G) Epidermal thickness. The thickness of epidermis was increased in the wounds treated with the GelMA + VEGF. (H) Rete ridges. The number of rete ridges in the GelMA + VEGF group was significantly higher compared to the non-treated and VEGF treated wounds. (I) Inflammation. The degree of inflammation was studied by analyzing the H&E stained wound sections for infiltration of inflammatory cells to the wound bed (Representative figures are shown in (C)). The inflammation was present in all wounds while wounds treated with GelMA + VEGF contained the smallest number of inflammatory cells. n = 6 was considered for quantifications.