The Research Of Biomechanical Characteristics Of Scar Tissue

Scar tissue is a kind of common skin benign tumor which is caused by excessiveproliferation and hyaline deformation of connective tissue. By now, the pathogenesisof scar tissue is still not expounded clearly. There are various theories andexplanations about it, which haven`t been acknowledged yet. One of these theories iscalled mechanical theory or mechanics theory, which hold that the engendering ofscar tissue is related to the tension in the wound. The study of clinical cases showsthat, the process of wound healing may lead to the formation of scar tissue. There aremany precipitating factors of scar tissue. And one of the most important factors is thetension of the wounds. On clinic, the main positions of scar tissues are mostly relatedto this factor such as chest, shoulders, shoulder area, the lower abdomen, the pubisarea and ear etc. Therefore, the research of the biomechanical characteristics of scartissue is extremely important to the study of biomechanics and clinical medicine.In this study, the keloid samples were all removed from patients in surgeries.After the patients consented, the specimen would be sent to the laboratory. Since theshape of the removed keloids were out-of-shape which did not meet the testrequirements, we did a cut work which made the keloids standard test pieces. Weshould ensure the length-width ratio less than5:1after clamping. Meanwhile, werecorded the basic information of the test pieces including patients`information, thegrowth direction and drawing time. Then placed the test pieces in a freezer. And24hours before the experiment, the test piece was moved out to ensure its recovery toroom temperature before the test.Stress relaxation means loading the test piece to a step load and maintaining therelative displacement unchanged to record the relationship between load and time. Toensure the integrity and stability of the experimental data, this test take three loads,which means that one test piece would separately load to20N,30N and40N to beginthe stress relaxation. The experimental data were recorded by computer during thisprocess. After the experiment, we used the OriginPro software to extract and analysisthe data. And then normalized the three sets of data simultaneously, which meanssetting the maximum displacement to1and the remaining points being divided by this value. After imported the three sets of data into the same coordinate system(horizontal axis is time, vertical axis is displacement), we can get three parallel curves.The average curve of this three could be the relaxation curve of the test piece.Similarly, we could get the relaxation curve of keloid or skin by averaging therelaxation curves of the same kind of test pieces.Creep, that is, loading the test piece to a step load and maintaining this valueunchanged to record the displacement--time. Similar to stress relaxation, theexperiment of creep used three loads20N,30N and40N. The normalization processof the three sets of data was done by OriginPro Software, which set the step load to1and the remaining being divided by this value. Intercept the part of curve after the stepload point as the effective part.Tensile, in this research, was regarded as destructive experiment. After clampingthe test pieces, we loaded on it in a specific rate (5N/s) until breaking up. Dataprocessing was done by the OriginPro which output the stress-strain curve. And thenintercept the elastic phase of the tensile curve which is similar to the linear phase.Linear fit this part to find the slope of the line which is equivalent to the elasticmodulus E. After sample test, we came to the conclusion as follows.1. The elastic modulus of keloid is far less than normal human skin`s (6%).2. The breaking strength of keloid is5%of normal skin`s.3. The mechanical properties of human skin are closely related with the Langer lines.In the meantime, this also found the fitting equation of the tensile curve which furtherimprove the description of tensile properties and biomechanical of keloid and normalhuman skin.In biomechanics theory, we hold that if we get the constitutive equation of amaterial we know the biomechanical properties of it. In order for the integrity of thebiomechanical properties of the specimen, this research carried out the constitutiveequation fitting and parameters solving for each test pieces. In this study, theconstitutive equations we used about stress relaxation and creep were derived byProfessor Feng in “Biomechanics”. The difference from other studies is that weworked out the three parameters by controlling the non-linear fitting rather thansolving equations. If the curve after several iterations completely fit the experimentalcurve, this curve could be the constitutive equation curve of this test piece. At thesame time, we came to the parameters c,τ1and τ2. By the calculation of theconstitutive equation about keloid and normal human skin, we came to the conclusionthat keloid have significant difference from normal human skin in the aspect of biomechanical properties.This study discussed keloids from the perspective of biomechanical properties.The data we got further indicated that the cause of keloids is closely related with thebiomechanics. And in the meanwhile, we obtained the mechanical parameters ofkeloid and normal human skin by the experiment of stress relaxation and creep, whichprovides a kind of standard evolution for scar tissue and a reference of prevention andclinical treatment to keloid. However, from the angle of biomechanics, this study onlydiscussed mechanical properties of keloid macroscopically. We didn`t carry out themicroscopic analysis about the growth condition and characteristic of keloid such ascell mechanics. Thus, just from the angle of biomechanics, there is much unknown forus to explore. In the future research, we will expand our research field and go deeperinto the discussion to provide the best theoretical basis for clinical uses.