Abstract: Objective To preliminarily optimize the energy and density of laser radiation for the early treatment of hyperplastic scars in a rabbit ear model, and to explore possible therapeutic mechanisms. Methods Sixty-one hyperplastic scars were successfully established on the ears of 10 healthy New Zealand white rabbits with large ears, and randomly divided into 2 groups: 1-week group （30 scars） and 3-week group （31 scars）. These 2 groups were separately divided into 5 subgroups: group A treated with laser at a density of 100 PPA and an energy of 10 mJ, group B with laser at a density of 100 PPA and an energy of 50 mJ, group C with laser at a density of 169 PPA and an energy of 10 mJ, group D with laser at a density of 169 PPA and an energy of 50 mJ, and group E receiving no treatment. There were 6 scars in each group, except the group E in the 3-week group. Two healthy New Zealand white rabbits with large ears were not subjected to modeling, and served as group F （blank control group）. Immunohistochemical study was performed to determine the of matrix metalloproteinase （MMP）-13 in the skin tissues from the rabbit ears 1 week after the treatment. Three weeks after the treatment, the skin tissues from the rabbit ears were subjected to hematoxylin-eosin （HE） staining and Masson staining. Then, the structure of scars was observed, and scar elevation index was calculated. Statistical analysis was carried out by Kruskal-Wallis H test for the comparison of scar elevation index, and by one-way analysis of variance （ANOVA） for the comparison of the average absorbance value of MMP-13. Results As HE staining revealed, the groups A, B, C and D all showed thicker dermis and increased number of collagen fibers compared with the group F （normal skin tissues）, but showed thinner dermis, decreased number and more ordered arrangement of collagen fibers compared with the group E （untreated scar tissues）. No obvious difference was observed in the thickness of the dermis among the groups A, B, C and D. The scar elevation index significantly differed among the 6 groups （H = 22.757, P < 0.05）. Multiple comparisons showed that the scar elevation index was significantly lower in the groups B, C and D （2.597 ± 0.344, 2.850 ± 0.282, 2.658 ± 0.134, respectively） than in the group E （3.460 ± 0.583, all P < 0.05）. As Masson staining revealed, the groups A, B, C and D all showed thinner dermis and more irregular arrangement of collagen fibers compared with the group E. However, no obvious differences were observed in the dermal thickness or number of collagen fibers among the groups A, B, C and D. Immunohistochemical study showed that the of MMP-13 was significantly higher in the high-energy （50 mJ） laser groups than in the low-energy （10 mJ） laser groups （P < 0.05） at the same laser density. With the same laser energy, the of MMP-13 was significantly higher in the group A than in the group C（P < 0.01）, but there was no significant difference between the group B and D （P > 0.05）. Conclusions Non-ablative fractional laser is effective for the treatment of early-stage hyperplastic scars. At the same laser density, 50-mJ laser was superior to 10-mJ laser for the treatment of hyperplastic scars, likely because high-energy laser can stimulate the recombi-nation of extracellular matrices and up-regulated MMP-13 to a greater extent.

Key words: Cicatrix, hypertrophic, Lasers, Matrix metalloproteinase 13, Fractional laser, Energy