| 【Background】Congenital microtia,a common disease in plastic surgery,is of relatively high prevalence in various countries and regions.The main characteristic of congenital microtia is inborn defect of auricula or external auditory canal.And patients are in strong desire to receive surgical treatment.Meanwhile,deformity of external ear provoked by various tramatic events also needs reconstruction of the total auricle.Currently,the classical method for total auricle reconstruction is developed by Tanzer.One shortcoming of Tanzer’s method,however,is the relatively long operation period,which makes patients suffer more.Therefore,Tanzer’s method has been improved by Nagata and Brent,and has been optimized as Nagata’s method and Brent’s method,on the basis of which a modified approach by domestic scholars develops and turns to be well.This modified method makes well combination of expanded flap with sculpture and transplantation of costal cartilage framework.The aforementioned various methods for total auricle reconstruction are all established on simulating cartilage framework of normal auricle.During auricle reconstruction,it is of vital significance for those cartilage frameworks to bear certain stress in maintaining reconstructed auricle shape while presenting aesthetics in all aspects.In consideration of the complicated appearance of auricle,manual framework cannot show all aspects of auricle,which not only influences postoperative outcome but also brings side effect on patients’ satisfaction.Thus,some scholars want to conduct sculpture of framework through computer-aided technologies so as to obtain well-reconstructed auricle,as well as get better understanding of stress distribution of the auricle.Given current disadvantages in total auricle reconstruction,scholars try to build auricular cartilage through tissue engineering,during which essential biomechanics test and basic knowledge of material properties are required due to the lack of directive biomechanical data for building normal cartilage.The process of finite element analysis strongly relies on material properties of biological materials.Thus,during analysis of stress distribution about auricle,it is necessary to get essential biomechanical properties of auricle cartilage.Meanwhile,comprehensive analysis of previous researches also helps clarify essential biomechanical properties.Usually macroscopic biomechanical properties are closely related to microstructure of biological materials.To date,very few data are and its related microstructure available in auricular cartilage.Auricular cartilage mainly consists of chondrocytes and extracellular matrix.In vivo assay,it demonstrats that auricular cartilage matrix is composed of proteoglycans,collagen fibers,and elastic fibers.Auricular cartilage with abnormal development also accompanies with corresponding changes in microconstituents,which in turn affect biomechanical properties of cartilage.With the depletion and disorganization of cartilage fibers,the elasticity and strength decrease.No data are available to fully investigate histology of normal auricle cartilage.Therefore,when we do research concerning macroscopic properties of biomechanics in auricle cartilage,we should get further understanding of its microstructure,as well as its giant microstructure.【Purposes】To conduct tensile test in standard specimen of normal auricle cartilage through instron universal material testing machine so as to get knowledge about its basic biomechanical properties,and get better understanding of its microscopic structure,fibrillar components,and giant microstructure through histological method and electronic microscope.To undergo further analysis of its material properties on the basis of previous researches,conduct three-dimensional reconstruction of normal auricular cartilage and auricular structure via Mimics software,and analyze stress distribution of normal auricle as well as get stress nephogram,following analysis of its significance via Abaqus software.【Materials and methods】Part 1: Conduct tensile test using instron universal material testing machine after obtaining normal auricle cartilage and building standard specimen,and obtain load-displacement curve,as well as basic parameters regarding elastic modulus,stiffness and peak loading.And then perform statistical analysis.Using HE staining,Masson staining,VG staining,EVG staining,and immunohistochemistry technology to analyze pathological and morphological characteristics of normal auricle cartilage,and then subjected to observation under electronic microscope,analyze tissue microstructure closely correlated to biomechanical characteristics.Part 2: We complete three-dimensional reconstruction by MIMICS software after obtaining CT images of normal auricle,and obtain data in the format of STL,following introduction to finite element analysis software of ABAQUS,then undergo assignment on the basis of the results of part 1.After static loading,obtain stress nephogram of finite element analysis,and further analyze stress distribution of normal auricle.【Results】Part 1: We obtain the load-displacement curve of standard specimen of normal auricle cartilage.Steady elevation of the curve was observed during continuous load increased.displacement was positive correlation with loading.After the loading position reached peak,specimen was fractured,and then the curve went down immediately.The elastic modulus,peak loading and stiffness of the standard specimen were(42.59±16.76)MPa,(16.24±6.02)N,(5.78±1.74)N/mm respectively.We found that the microstructure of cartilage consisted of bilateral perichondrium and cartilage matrix.The dorsal perichondrium were made of fibrous layer,proliferative layer,and transitional layer,and were thicker obviously than that of ventral part.Perichondrium were mainly made of typeⅠcollagen fiber,while the matrix of cartilage consisted mainly of typeⅡcollagen fiber and elastic fiber.Besides,we found the formation of anchor structure of perichondrium by insertion into cartilage matrix.Part 2: We completed three-dimensional reconstruction of auricle cartilage and auricle structure after collection of CT images of normal auricle cartilage.The three-dimensional structure was visually the same as real in shape with smooth surface,which could be well used for finite element analysis.The cartilage was in consistence with previously reported in thickness.Through finite element analysis,we found that stress mainly located at the anchor position between auricle cartilage and skull,with focus at the top of auricle.【Conclusions】We obtained essential biomechanical data of auricle cartilage through biomechanical experiments on normal auricle cartilage.This will contribute well to further investigation of biomechanics of auricle cartilage.We also got a comprehensive understanding about characteristics of auricle cartilage and confirmed anisotropic properties of auricle cartilage through histological method and electronic microscopic observation.In addition,we obtained three-dimensional reconstruction model of normal auricle.And this model exhibited good appearance in shape after being polygonized mesh grids.Stress nephogram of normal auricle was obtained by finite elements analysis after doing assignment for material properties.It will help build auricular cartilage in the clinic and tissue engineering field. |
PDF Full Text Request