Atomic force microscopy reveals regional variations in the micromechanical properties of the pericellular and extracellular matrices of the meniscus

Regional variations in the composition and architecture of the extracellular matrix (ECM) and pericellular matrix (PCM) of the knee meniscus play important roles in determining the local mechanical environment of meniscus cells. In this study, atomic force microscopy was used to spatially map the mechanical properties of matched ECM and perlecan-labeled PCM sites within the outer, middle, and inner porcine medial meniscus, and to evaluate the properties of the proximal surface of each region. The elastic modulus of the PCM was significantly higher in the outer region (151.4 +/- 38.2kPa) than the inner region (27.5 +/- 8.8kPa), and ECM moduli were consistently higher than region-matched PCM sites in both the outer (320.8 +/- 92.5kPa) and inner (66.1 +/- 31.4kPa) regions. These differences were associated with a higher proportion of aligned collagen fibers and lower glycosaminoglycan content in the outer region. Regional variations in the elastic moduli and some viscoelastic properties were observed on the proximal surface of the meniscus, with the inner region exhibiting the highest moduli overall. These results indicate that matrix architecture and composition play an important role in the regional micromechanical properties of the meniscus, suggesting that the local stress-strain environment of meniscal cells may vary significantly among the different regions. (c) 2013 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 31:1218-1225, 2013