Time-dependent mechanical behavior of newly developing matrix of bovine primary chondrocytes and bone marrow stromal cells using Atomic Force Microscopy

[摘要] Introduction: Articular cartilage chondrocytes are solely responsible for the synthesis, assembly, and maintenance of the extracellular matrix (ECM) and yet occupy <10% of the cartilage tissue volume. Chondrocytes (equilibrium modulus, E ~ 0.3-4 kPa) develop a micrometer-thick pericellular matrix (PCM) in vivo and in vitro which is softer (equilibrium modulus, E ~40 ~ 70 kPa) than the surrounding mature ECM (E ~ 0.5 MPa). PCM is a jim-thick hydrated, porous macromolecular region surrounding chondrocytes, being rich in fibronectin, proteoglycans (e.g., aggrecan, hyaluronan, and decorin) and collagen (types II, VI, and IX); PCM is primarily defined by the presence of type VI collagen as compared to ECM. Since PCM transfers loads from the ECM to the cell during physiological compression, it is important to cell signaling and mechanotransduction. The structure of chondron, single chondrocyte and surrounding region of PCM, is recently imaged with respect to the temporal evolution. One promising approach to cartilage tissue engineering is embedding chondrocytes in synthetic scaffolds and exposing to various growth factors and mechanical loads to facilitate ECM synthesis and suppress catabolic degradation of ECM macromolecules. Chondrocytes are capable of developing a cell-associated matrix in vitro when seeded in 3-D hydrogel scaffold with similar cell division rate, as compared to isolated chondrons. However, the morphology of pericellular halo from cultured chondrocytes are distinctively different from that of isolated chondrons and mature cartilage, reflecting the disparity in the gene expression of cartilage-related genes between the tissue-engineered constructs and native cartilage (9). Despite of these deficiencies, the use of chondrocytes can be beneficial to accomplish the cell expansion, cell manipulation, a higher cell yield per volume of tissue with ease, as compared to the use of chondron. With this regards, the understanding of mechanics at cellular level in articular cartilage may provide a better picture of the composition-structure-function relations linked to the growth/remodeling activity of articular cartilage in order to achieve the mechanically functional cartilage tissue engineered constructs. While the biomechanical testing of the macroscopic tissue would give an overall outcome of multiple interactions involved, the biomechanical study at cellular level might better examine the consequences of such interactions in a more focused manner.

[发布机构] Massachusetts Institute of Technology