Understanding the Stiff-To-Compliant Transition of the Meniscal
Research Article Cite This: ACS Appl. Mater. Interfaces 2019, 11, 26559−26570 www.acsami.org Understanding the Stiff-to-Compliant Transition of the Meniscal Attachments by Spatial Correlation of Composition, Structure, and Mechanics Alexander J. Boys,† Jennie A. M. R. Kunitake,† Corinne R. Henak,‡ Itai Cohen,§ Lara A. Estroff,†,∥ and Lawrence J. Bonassar*,‡,⊥ † ‡ § ∥ Department of Materials Science & Engineering, Meinig School of Biomedical Engineering, Department of Physics, Kavli ⊥ Institute at Cornell for Nanoscale Science, and Sibley School of Mechanical Engineering, Cornell University, Ithaca, New York 14853, United States *S Supporting Information ABSTRACT: Recently, the scientific community has shown considerable interest in engineering tissues with organized compositional and structural gradients to mimic hard-to-soft tissue interfaces. This effort is hindered by an incomplete understanding of the construction of native tissue interfaces. In this work, we combined Raman microscopy and confocal elastography to map compositional, structural, and mechanical features across the stiff-to-compliant interface of the attach- ments of the meniscus in the knee. This study provides new insight into the methods by which biology mediates multiple orders of magnitude changes in stiffness over tens of microns. We identified how the nano- to mesoscale architecture mediates complex microscale transitional regions across the interface: two regions defined by chemical composition, five distinguished by structural features, and three mechanically distinct regions. We identified three major components that lead to a robust interface between a soft tissue and bone: mobile collagen fiber units, a continuous interfacial region, and a local stiffness gradient. This tissue architecture allows for large displacements of collagen fibers in the attachments, enabling meniscal movement without localizing strains to the soft tissue-to-bone interface.
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