Analysis of bending behavior of native and engineered auricular and costal cartilage Rani Roy, 1 Sean S. Kohles, 2, * Victor Zaporojan, 1 Giuseppe M. Peretti, 3 Mark A. Randolph, 3 Jianwei Xu, 3 Lawrence J. Bonassar 1,4 1 Center for Tissue Engineering, One Biotech, Suite 190, University of Massachusetts Medical School, 55 Lake Avenue North, Worcester, Massachusetts 01602 2 Worcester Polytechnic Institute, Worcester, Massachusetts 3 Division of Plastic Surgery, Massachusetts General Hospital, Boston, Massachusetts 4 Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, New York Received 30 September 2002; revised 14 January 2003; accepted 31 January 2003 Abstract: A large-deflection elasticity model was used to describe the mechanical behavior of cartilaginous tissues during three-point bending tests. Force-deflection curves were measured for 20-mm long  4-mm wide 1-mm thick strips of porcine auricular and costal cartilage. Using a least-squares method with elastic modulus in bending as the only adjustable parameter, data were fit to a model based on the von Karman theory for large deflection of plates. This model described the data well, with an average RMS error of 14.8% and an average R 2 value of 0.98. Using this method, the bending modulus of auricular cartilage (4.6 MPa) was found to be statistically lower (p  0.05) than that of costal cartilage (7.1 MPa). Material features of the cartilage samples influenced the mechanical behavior, including the orienta- tion of the perichondrium in auricular cartilage. These meth- ods also were used to determine the elastic moduli of engi- neered cartilage samples produced by seeding chondrocytes into fibrin glue. The modulus of tissue-engineered con- structs increased statistically with time (p  0.05), but still were statistically lower than the moduli of the native tissue samples (p  0.05), reaching only about a third of the values of native samples. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 68A: 597– 602, 2004 Key words: auricular cartilage; tissue engineering; biome- chanics; soft-tissue deformation; large-deflection bending INTRODUCTION The auricle of the ear has a layered structure com- posed of skin, perichondrium, and cartilage. The ex- tracellular matrix (ECM) of auricular cartilage, classi- fied as elastic cartilage, is composed mainly of proteoglycans, type II collagen, and a large network of elastin. 1 These elastic fibers allow the ear to undergo large deformation bending, giving the ear its charac- teristic flexibility. The functional purpose of auricular cartilage is to mechanically support the ear, allowing for large-scale deformation. Auricular cartilage is sur- rounded on both sides by perichondrium, a connec- tive tissue that is the interface between the cartilage and the skin. In native tissue, the perichondrium con- tains the vascular supply, which is important for the growth and maintenance of the avascular auricular cartilage. 2 Ear pathology includes loss of cartilage due to trauma, and congenital defects, such as microtia, a congenital defect characterized by a small, abnormally shaped or absent outer ear that typically requires mul- tiple stages of reconstructive surgery. 3 Traditionally, repair methods have included some sort of biomate- rials for prosthetic implants, such as alloplastic poly- ethylene implants or autogenous costal cartilage grafts. 4 It has been shown that autogenous implants work best with the lowest amount of rejection and compli- cations. However, with autogenous implants there of- ten are problems, such as donor site morbidity or a paucity of available autogenous cartilage. 5 Recently, tissue engineering has shown promise of creating ap- propriately shaped replacement tissue for auricular cartilage. 6 Despite this success, there has been little *Present address: Kohles bioengineering, Portland, Ore- gon Correspondence to: J. Bonassar; e-mail: lb244@cornell.edu Contract grant sponsor: University of Massachusetts Med- ical School Contract grant sponsor: Worcester Polytechnic Institute Contract grant sponsor: AO/ASIF Research Commission; contract grant number: 01-Y51 © 2004 Wiley Periodicals, Inc.