title: Micromechanical anisotropy and heterogeneity of the meniscus extracellular matrix.
abstract: To understand how the complex biomechanical functions of the meniscus are endowed by the nanostructure of its extracellular matrix (ECM), we studied the anisotropy and heterogeneity in the micromechanical properties of the meniscus ECM. We used atomic force microscopy (AFM) to quantify the time-dependent mechanical properties of juvenile bovine meniscus at deformation length scales corresponding to the diameters of collagen fibrils. At this scale, anisotropy in the elastic modulus of the circumferential fibers, the major ECM structural unit, can be attributed to differences in fibril deformation modes: uncrimping when normal to the fiber axis, and laterally constrained compression when parallel to the fiber axis. Heterogeneity among different structural units is mainly associated with their variations in microscale fiber orientation, while heterogeneity across anatomical zones is due to alterations in collagen fibril diameter and alignment at the nanoscale. Unlike the elastic modulus, the time-dependent properties are more homogeneous and isotropic throughout the ECM. These results enable a detailed understanding of the meniscus structure-mechanics at the nanoscale, and can serve as a benchmark for understanding meniscus biomechanical functions, documenting disease progression and designing tissue repair strategies.
  
  
  
  Meniscal damage is a common cause of joint injury, which can lead to the development of post-traumatic osteoarthritis among young adults. Restoration of meniscus function requires repairing its highly heterogeneous and complex extracellular matrix. Employing AFM, this study quantifies the anisotropic and heterogeneous features of the meniscus ECM structure and mechanics. The micromechanical properties are interpreted within the context of the collagen fibril nanostructure and its variation with tissue anatomical locations. These results provide a fundamental structure-mechanics knowledge benchmark, against which, repair and regeneration strategies can be developed and evaluated with respect to the specialized structural and functional complexity of the native tissue.
authors.affiliation: School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, PA 19104, United States.
authors.forename: Qing
authors.initials: Q
authors.lastname: Li
authors.affiliation: McKay Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, United States; Translational Musculoskeletal Research Center, Philadelphia Veterans Administration Medical Center, Philadelphia, PA 19104, United States.
authors.forename: Feini
authors.initials: F
authors.lastname: Qu
authors.affiliation: School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, PA 19104, United States.
authors.forename: Biao
authors.initials: B
authors.lastname: Han
authors.affiliation: School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, PA 19104, United States.
authors.forename: Chao
authors.initials: C
authors.lastname: Wang
authors.affiliation: College of Architecture and the Built Environment, Philadelphia University, Philadelphia, PA 19144, United States.
authors.forename: Hao
authors.initials: H
authors.lastname: Li
authors.affiliation: McKay Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, United States; Translational Musculoskeletal Research Center, Philadelphia Veterans Administration Medical Center, Philadelphia, PA 19104, United States.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Mauck
authors.affiliation: School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, PA 19104, United States. Electronic address: lh535@drexel.edu.
authors.forename: Lin
authors.initials: L
authors.lastname: Han
mesh_terms: D000818:Animals; D016880:Anisotropy; D002417:Cattle; D005109:Extracellular Matrix / Q000737:chemistry* / Q000648:ultrastructure; D000072600:Meniscus / Q000737:chemistry* / Q000648:ultrastructure; D018625:Microscopy, Atomic Force
keywords: Anisotropy; Extracellular matrix; Heterogeneity; Meniscus; Nanoindentation