The Remodeling Effect Of The Fractional Er:UAG Laser (2940nm) On Collagen Of Hypertrophic Scar In Rabbit Ears In Different Periods

Objective: Fractional laser has been successfully applied to the treatmentof superficial scars, but on the treatment of hypertrophic scars has barelyreported. This experiment used the fractional Er:YAG laser (2940nm)irradiation on Hypertrophic Scar in rabbit ears. Through observing the changeof the distribution of collagen fibers and the ratio of collagen Ⅰ/Ⅲ of thescar tissue at various experimental groups, investigated the treatment effect onHypertrophic Scar and distinction of the treatment effect at different stages,then providing the theory basis for clinical working of the fractional laser intreatment of Hypertrophic Scar.Methods:4circular-shaped skin defects of the diameter being6mm weremade on each ear in the middle part of each abdominal side rabbit ears of6adult New Zealand rabbits, male, weighing2.5±0.18kg, using circular ringdrilled along the long axis to avoid blood vessel. The wound were intervaled1.0cm as deep as the cartilage surface, and the perichondrium was scraped,forming a total of48round wound. The Hypertrophic Scar in rabbit ears wererandomly divided into6groups:①The treatment group of hyperplasia phase (n=8): were treated byEr:YAG laser on postoperative day30. The parameters of laser treatment:energy density162J/cm2, repeat scan5times. Harvesting of specimens afterLaser therapy for22days.②The control groups of hyperplasia phase (n=8): could not do anytreatment as the space control of①group, Harvesting of specimens at thesame time with①group.③The treatment group of paracmasis (n=8): were treated by Er:YAGlaser on postoperative day60with the same treatment parameters andharvesting time. ④The control group of paracmasis (n=8): could not do any treatment asthe space control of③group, Harvesting of specimens at the same time with③group.⑤The treatment group of Maturity period (n=8): were treated by Er:YAGlaser on postoperative day90with the same treatment parameters andharvesting time.⑥The control group of maturity period (n=8): could not do any treatmentas the space control of⑤group, harvesting of specimens at the same timewith⑤group.The specimens were paraffin-embedded after dehydrated and dipped inparaffin, then were incided to slice, thickness of5μm. The distribution featureof collagen fiber was observed by HE, Masson and Sirius Scarlet staining ofhypertrophic scar in rabbit ears of the experimental group; the ratio ofcollagen Ⅰ/Ⅲ was determinated by sirius red stain and polarizationmicroscopy method and image analysis technique in hypertrophic scar inrabbit ears of the experimental group. That reflected the effect of laser intreatment of hypertrophic scars.The proportion of type Ⅲ collagen fibers was statisticed on experimentagroups of hypertrophic scar in rabbit ears, and the data were represented bythe mean±standard deviation. Factorial experimental design was estimatedwith SAS8.0system, p<0.05as the standard of judgment of significantdifference.Result:1Histomorphological changes:The control groups of hyperplasia phase: Prominent scar tissues in theskin surface was redand hard within the range in the wild. The lightmicroscope revealed microvascular proliferated and large collagen fibersproliferated too, arranged disorderly with a spiral-shaped structure.The treatment group of hyperplasia phase: Compared with the controlgroup, the color of scar tissue was light, and texture was soft and elasticincreased. The light microscope revealed the collagen was lighter and thinner than control groups, arranged orderly.The control group of paracmasis: Scar has shrunk, but remained abovethe skin surface. The color was light, and the quality was hard. The lightmicroscope revealed microvascular reduced, bulky,dense collagen fiberarranged further disorder, and collagen tuberous were rarely.The treatment group of paracmasis: Compared with the control group, thecolor of scar tissue was light, texture was soft and elastic increased. The lightmicroscope revealed the collagen was lighter and thinner than control groups,arranged scatter and ordinationly.The control group of maturity period: Scar has shrunk dramatically,relatively flat, harder than the surrounding normal skin, and the color becamewhite at central part of scar. The light microscope revealed micro-vascular wasless and collagen fibers became thinner than paracmasis, arranged moredisordered, intensive, non-collagen nodules.The treatment group of maturity period: The color and texture of scartissue was more improved and closed to the surrounding normal skin than thecontrol group. The light microscope revealed collagen fibers arranged scatterand uniformly.2polarization microscopy and image analysis:The polarization microscopy revealed distribution bundle,arrangementdisorder and uneven density of type I collagen fibers that showed yellow,largely, and contained roughly56%of the entire field of vision, whereas typeⅢ collagen fibers consisted of green thin fibril with reticulation around type Icollagen, contained roughly44%in scar tissue of proliferation control groups.Compared with the control group, collagen fibers arranged in order, and wasincreased in the proportion of type Ⅲ collagen, about47%in the treatmentgroup. Large amounts of thick type Ⅰ collagen fibers gathered into massive,arranged further disturbances, and accounted for the entire field of vision of82%; the proportion of type Ⅲ collagen in less than18%. Compared with thecontrol group, collagen fibers arranged scatteredly and regularly, theproportion of type Ⅲ collagen fibers was significantly increased in the treatment group. In the control group of maturity period, type Ⅰ collagenfiber arranged more disorderly that showed bamboo-shaped, above93%, andthe proportion of type Ⅲ collagen was less than7%. Compared with thecontrol group, collagen fibers arranged scatteredly and consistently in thetreatment group, and the proportion of type Ⅲ collagen are increasedsignificantly, about24%.3statistical analysis:The proportion of type Ⅲ collagen was different in different periods ofhypertrophic scar. The fractional Er:YAG laser treatment could increase theproportion of type Ⅲ collagen in scar tissue. Increased levels was related totreatment-period: Increased proliferation (3%)<paracmasis (12%)<maturity.According to statistics we concluded: The clear degree was proliferation <paracmasis <maturity that the effect of fractional Er:YAG laser (2940nm) onHypertrophic Scar in rabbit ears.Conclusion:1The morphology of collagen fibers in scar tissue changed to normalskin after fractional Er:YAG laser (2940nm) treating. The ratio of type Ⅰand Ⅲ Collagen fibers reclosed to normal skin. Scar tissue became soft andelastic, and texture was noticeably improved.2The Fractional Er:YAG laser (2940nm) have a therapeutic effect onproliferation of scar, but not at all obvious. The treatment effects onparacmasis of scars have more improved than the proliferation. Maturity is thebest period among the three treatment period.