Influence of porcine urinary bladder matrix and porcine acellular dermal matrix on wound healing of full-thickness skin defect in diabetic mice

Objective To compare the difference of pro-healing effect of porcine urinary bladder matrix (UBM) and porcine acellular dermal matrix (ADM) on full-thickness skin defect wounds in diabetic mice. Methods Thirty-six type 2 diabetic BKS db/db mice aged 10 weeks were divided into UBM group and ADM group according to the random number table, with 18 mice in each group and preoperative molarity of non-fasting blood glucose higher than 16.6 mmol/L. A circular full-thickness skin defect wound with 6 mm in diameter was made on the back of each mouse, and porcine UBM and porcine ADM scaffolds were implanted into the wounds of both groups correspondingly. Immediately after operation and on post operation day (POD) 7, 14, and 28, wounds were observed generally. On POD 7, 14, and 28, 6 mice of each group were collected respectively to calculate the rate of wound epithelialization, and then the corresponding mice were sacrificed after calculation, and the wound tissue was harvested to make slices. Six slices of the mice in the 2 groups on POD 7 and 14 were respectively collected to stain with haematoxylin-eosin (HE), and 6 slices on POD 7 and 28 had Masson′s staining, which were used to observe histopathological changes and scaffold degradation. On POD 7 and 14, 24 slices of each mouse in the 2 groups were collected respectively to detect alpha smooth muscle actin (α-SMA) and CD31 positive expression denoting the growth of myofibroblasts and neovessels respectively and observe the distribution and activation of macrophages with immunohistochemical staining. The wound tissue of mice in the 2 groups on POD 7 and 14 was harvested to detect mRNA expressions of fibroblast growth factor 2 (FGF-2), vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF), and transforming growth factor β₁ (TGF-β₁) by real-time fluorescence quantitative reverse transcription polymerase chain reaction. The sample number of above-mentioned indexes in each group at each time point was 6. Data were statistically analyzed with analysis of variance for factorial design,

test, and Bonferroni correction. Results (1) General observation showed that integration of UBM scaffold into the wounds of mice in UBM group on most time points was superior, and integration of ADM scaffold into the wounds of mice in ADM group on most time points was inferior. On POD 28, epidermis still did not form in some region of scaffold surface of wounds of mice in ADM group, while wounds of mice in UBM group were completely epithelialized. On POD 7, 14, and 28, wound epithelialization rates of mice in UBM group were respectively (22.4±6.4)%, (68.6±12.4)%, and 100.0%, all significantly higher than (4.5±2.2)%, (23.6±4.6)%, and (64.2±13.2)% in ADM group (

=7.427, 9.665, 7.655,

<0.01). (2) HE staining and Masson′s staining showed that a large number of cells appeared in wound scaffold of mice in UBM group on POD 7; cells distributed in the whole region of UBM scaffold on POD 14; dermal tissue with structure similar to normal skin formed in the wounds and the fibrous morph of UBM scaffolds disappeared on POD 28. Only a small number of cells appeared in inside of wound scaffolds of mice in ADM group on POD 7; on POD 14, cells were sparsely distributed in ADM scaffolds; on POD 28, the morph of originally robust collagen fiber of ADM scaffolds was still clear and visible. (3) On POD 7, a large number of accumulated myofibroblasts and neovessels appeared in the lower layers of scaffolds of wounds of mice in UBM group; on POD 14, evenly distributed myofibroblasts and neovessels appeared in the upper layers of UBM scaffolds, and most vessels were perfused. On POD 7 and 14, myofibroblasts were sparsely distributed in scaffolds of wounds of mice in ADM group with no or a few neovascular structures perfused unobviously. On POD 7 and 14, α-SMA positive expressions in scaffolds of wounds of mice in UBM group were significantly higher than those in ADM group (

=25.340, 6.651,

<0.01); CD31 positive expressions were also significantly higher than those in ADM group (

=34.225, 10.581,

<0.01). (4) On POD 7, a large number of macrophages appeared in the lower layers of scaffolds of wounds of mice in UBM group; on POD 14, macrophages infiltrated into the internal region of UBM scaffolds, and M2 polarization occured without M1 polarization. On POD 7, a small number of macrophages appeared in the bottom of scaffolds of wounds of mice in ADM group; on POD 14, macrophages were few in internal region of ADM scaffold, and neither M2 polarization nor M1 polarization occurred. (5) On POD 7 and 14, mRNA expressions of FGF-2, VEGF, PDGF, and TGF-β₁ in the wound tissue of mice in UBM group were all significantly higher than those in ADM group (

=7.007, 14.770, 10.670, 8.939; 7.174, 7.770, 4.374, 4.501,

<0.01). Conclusions Porcine UBM scaffold is better than porcine ADM in facilitating wound repair and dermis reconstruction of full-thickness skin defects in diabetic mice through the induction of myofibroblasts and macrophages immigration, the promotion of neovascularization and expression of pro-healing growth factors.