| Background and Objective: Debridement is the first step in the management of wounds,and the quality of debridement directly affects the outcome of subsequent treatment.The ideal debridement is to remove all necrotic and infected tissue,while to keep the health tissue as much as possible,i.e.precise debridement.Surgical debridement is the most widely used method in hospital.The scope of removal of necrotic tissue is mainly depended on the subjective judgment of physicians.Thus,it is difficult to ensure the accuracy of debridement.In order to control damage,promote the quality of healing,some alternative solutions,such as the autolytic debridement,the enzymatic debridement,the biological debridement,the ultrasonic debridement and the water jet,have been invented and applied clinically.However,the above mentioned methods have their inherent disadvantages and limitations,especially the precision of debridement.Laser is the abbreviation of light amplification by stimulated emission of radiation,with the characteristics of both single direction and high energy density.According to the working state,it can be divided into continuous laser and pulsed laser.The biological effects of laser include thermal effect,pressure effect,biological stimulation and so on.Continuous laser used in gasification of postburn necrotic tissue has been reported both domestic and overseas,but most of these studies reveals the problems include large amount of thermal damage leads to subeschar tissues inviable,and it may require multiple surgeries when the laser surgery was failed.Some studies have indicated that short pulse lasers is a controlled method,when the pulse width of the pulse laser is less than the heat conduction time(thermal relaxation time),the damage to the healthy tissue can be reduced to the minimum.Increase the single pulse energy can significantly improve the vaporization efficiency.The picosecond laser is a short pulse laser with a pulse width of 10-12 s and it's gasification range can be controlled precisely.It is possible to achieve the purpose of precise debridement.Studies about short pulse laser with the single pulse energy up to 100 mJ,pulse width narrow to 30 ps in medical applications are little,so there are many unknown areas in clinical applications of short pulse laser for debridement.Therefore,in this study picosecond pulse laser with high power was used to irradiate porket skin tissue.We explored the dose-effect relationship when the pulse energy and irritation times were changed.In this experiment,the temperature field changes of skin tissue irradiated by high energy femtosecond laser and picosecond laser were also explored.We expect our studies can lay a foundation for the future use of short pulse laser for wound debridement in great precision and efficiency.Methods:1.The thermal response model of laser irradiated skin was established by using Ansys software.The numerical simulation of the high energy density of 1064 nm continuous laser and pulsed laser was carried out,and the advantages and disadvantages of continuous laser and single pulse laser were compared.2.The experiment included normal skin group and full-thickness skin burn group.Made porcine skin in vitro and full-thickness skin burn model.3.The normal porcine skin in vitro were irradiated with different pulse energy at 0(control),20 mJ,40 mJ,60 mJ,80 mJ and 100 mJ(2s,5s,and 10 s endurance/times),which produced 15 different lesioning points and 3 normal control point,every point was repeated 3 times.The experimental conditions of full thickness burn skin group were the same as the normal porcine skin group in vitro.4.The output energy of the laser was measured by a power meter.In order to know the error of laser energy.The laser output energy was set in 0,10,20,...,100 mJ,which generate 11 groups of energy,every group repeated 3 times.Using laser wavelength meter to verify the laser's wavelength,and using ultrashort laser pulse measurement meter to measure the pulse width.5.The K type thermocouples were fixed on the back of the skin specimen,the temperature measuring instrument was used to observe and record the temperature change curve of the spot and the position 2mm away from the spot during the process of irradiation and a period of time after irradiation.6.After irradiation,the width and depth of the evaporated zones of the lesioning points were measured with ultra-depth field microscopy.7.The coronal plane sections of every lesioning point were made into tissue slice,stained by hematoxylin and eosin.The pathological sections were observed by experienced pathologist with a microscope to obtain the datas of coagulation area.8.Use two-way ANOVA to analysis datas that were measured above.If the results of the analysis of variance showed differences between groups,Bonferroni pairwise comparisons were conducted to explore whether the two groups had significant difference.Dose-effect curves were drawn according to the above datas.Then analysis the rules of effect and its clinical significance.Results:1.Numerical simulation results showed that,compared to the pulsed laser,continuous laser needed more energy for skin carbonization but carbonization depth was deeper,the two-dimensional effect(heat along the horizontal direction diffusion)was obvious.When irradiated by pulsed laser,the temperature longitudinal gradient in skin was greater,carbonization depth is shallow,temperature drops faster,two-dimensional effects can be ignored.There was almost no damage to the skin outside of the laser irradiated area.2.The output energy of the laser was measured by a power meter.The outcome showed the error of the picosecond laser was ±0.42 mJ,and the error of the femtosecond laser was ±0.37 mJ.According to the measurement,it was verified that output wavelength of the picosecond laser and femtosecond laser were both 1064nm;the pulse width of the picosecond laser and femtosecond laser were 30 ps and 70 fs respectively.3.Temperature datas showed that the spot temperature was positively correlated to the pulsed energy and irradiation time,2mm away from the spot only made the temperature rise 1-2?.4.Macroscopic observation: When skin tissue was irradiated by laser,the increasing of pulse energy can cause tissue splash effect.With the increase of the dosage of laser,the skin tissue uplifted,then the central area of skin was carbonized and sagged,and circular vaporization zone was appeared,the surrounding area was pale and uplifted5.Observation of ultra-depth field microscopy: The vaporization zone has a small bottom and a large conical shape.In the normal skin experimental group,except the control group and the group of 20 m J,the vaporization zone can be observed by naked eye or microscope in the rest of the groups.The average diameter of vaporization zone was(1168.9 ± 1.89)(range from 740.7 to 1455.3)?m,the average depth was(412.26 ± 289.8)(range from 106.4 to 1314.8)?m.In the burn skin group,the average diameter of vaporization zone was(1180.0±179.3)(range from 810.2 to 1398.5)?m,the average depth was(426.9±223.3)(range from 100.7 to 792.7)?m.6.Pathological observation: In the normal skin experimental group,the average of the width of the coagulation necrosis zones were(141.10 ± 47.68?m)(range from 65.35 to 238.73?m).The maximum width was 217.0±19.9 ?m.7.The experimental results showed that the maximum laser dose which generated coagulation area less than 100?m was 80 mJ×2s.And at this laser dose,the width of vaporization area was(1257.9±22.3?m),the depth of the vaporization was(262.6 ± 15.6?m),the width of coagulation area was(99.5±2.1?m).To control the range of thermal damage was less than 100?m,the laser dosage should be less than 80 mJ×2s.Conclusion: There was a good vaporization effect when 1064 nm wavelength picoseconds pulsed Nd:YAG laser irradiated the porcine skin tissue.The heat along the horizontal direction diffusion was tiny.The thermal damage to the healthy tissues surrounding the lesion point was limited to hundreds microns magnitude.So we speculate that the picosecond laser would be a good choice for accurate debridement in the skin injury in future. |
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