Characterization of Immature Knee Joint Tissues Figure 4. Tensile properties of joint tissues. (a) Young’s modulus was highest for the menisci and patellar ligament and lowest for the cranial cruciate ligament. (b) Ultimate tensile strength was also higher for the patellar ligament and the menisci. Groups denoted by different letters are significantly different (p,0.05). doi:10.1371/journal.pone.0026178.g004 MPa, respectively (Figure 4B). MM, LM, and PL exhibited significantly higher stiffnesses (Young’s moduli) and strengths (UTS) compared to the other tissues, while CC, PC, CraCL, and CauCL were among the softest and weakest in tensile properties. Also of note, among the cruciate ligaments, CauCL was significantly stiffer and stronger than CraCL; Young’s modulus and UTS for CauCL were both 5.4x the values for CraCL. Discussion This study examined the major connective tissues of the immature bovine knee joint, motivated by a need to understand the interplay of biomechanics and biochemistry in immature connective tissues, as well as to establish design parameters for in vitro tissue engineering efforts. In the present study, differences were found across tissue types with respect to histology, collagen content, pyridinoline crosslink abundance, and tensile properties. In addition to reinforcing orthopaedic structure-function relation- ships, to our knowledge, this study is the first to examine these parameters in a direct head-to-head comparison among all of the major connective tissues of the knee, the first to assess pyridinoline crosslink abundance in all the tissues of a bovine joint, and the first to report results for pyridinoline crosslink abundance that suggest PLoS ONE | www.plosone.org 5 October 2011 | Volume 6 | Issue 10 | e26178