Abstract
Chondrocytes reorganize the extracellular matrix of articular cartilage in response to externally applied loads. Thereby, different loading characteristics lead to different biological responses. Despite of active research in this area, it is still unclear which parts of the extracellular matrix adapt in what ways, and how specific loading characteristics affect matrix changes. This review focuses on the influence of cyclic tensile strain on chondrocyte metabolism in vitro. It also aimed to identify anabolic or catabolic chondrocyte responses to different loading protocols. The key findings show that loading cells up to 3% strain, 0.17 Hz, and 2 h, resulted in weak or no biological responses. Loading between 3–10% strain, 0.17–0.5 Hz, and 2–12 h led to anabolic responses; and above 10% strain, 0.5 Hz, and 12 h catabolic events predominated. However, this review also discusses that various other factors are involved in the remodeling of the extracellular matrix in response to loading, and that parameters like an inflammatory environment might influence the biological response.
Highlights
Articular cartilage has the function to transmit forces across joints, to minimize peak stresses and to provide nearly frictionless gliding of the articular surfaces
We summarized the previous studies on the effect of cyclic tensile strain (CTS) on chondrocytes
Two others were excluded because the chondrocytes were not from healthy joints; and one was excluded because there was a discrepancy between the data described in the text and the same data presented in a figure
Summary
Articular cartilage has the function to transmit forces across joints, to minimize peak stresses and to provide nearly frictionless gliding of the articular surfaces. The chondrocytes are permanently exposed to a combination of different forces, like compression, tension, and shear. These mechanical signals acting on articular cartilage are critical regulators of tissue adaptation, structure, and function [1]. It is well accepted that different kinds of mechanical loading lead to different biological responses [2,3]. Distinct anabolic or catabolic loading protocols, and the subsequent processes of adaptation remain to be elucidated. The effects of compression and shear forces on chondrocytes in three-dimensional in vivo and in vitro experiments have been investigated in details, and have already been summarized in several reviews [4–7]. It is difficult to eliminate the effects of other physical factors with in situ or in vivo investigations.
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