Biotribology of regenerated cartilage

What is it about?

This is Chapter 6 of the book “Biotribology of natural and artificial joints” by Teruo Murakami (2023) and composed of 3 sections: 6.1 Medical treatments to repair focal chondral defects, 6.2 The influences of mechanical stimulations on regenerated cartilage tissue, and 6.3 The influences of tribological stimulations on regenerated cartilage tissue. First, main medical treatments to repair focal chondral defects are described under the osteochondral autograft transplant (mosaicplasty), the autologous chondrocyte implantation (ACI) and the implantation of regenerated cartilage tissues derived from native chondrocytes, mesenchymal stem cells, ES cells or iPS cells. Next, the influences of mechanical stimulations on regenerated cartilage tissue are mentioned, like effects of dynamic compression loading and effects of shearing. Dynamic compression stimuli for chondrocyte-agarose construct increased the stiffness and enhanced the extracellular matrix (ECM) network of inner tissue. On intermittent cyclic shearing stimulation, lower amplitudes increased the matrix synthesis. The influences of tribological stimulations on regenerated cartilage tissue during sliding motion and frictional behaviors of regenerated cartilage different in cultivation conditions are discussed. The addition of sliding motion for the chondrocyte-polyurethane construct cultured under dynamic compression loading enhanced stiffness and reduced friction, and exhibited strong immunoreactivity for lubricin at the top surface. Furthermore, the upregulation by multidirectional articular motion was indicated. Finally, the frictional behaviors of the regenerated cartilage as chondrocyte-fibroin sponge construct against a stainless steel plate were examined in physiological saline solution in reciprocating apparatus. It is noticed that at early stage during sliding test, friction coefficient decreased remarkably after 7 days’ cultivation, where surface layer containing proteoglycan had been newly formed. It is indicated that the newly formed regenerated surface layer was partially removed with rubbing and in consequence friction gradually increased.

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Why is it important?

Healthy articular cartilage as compliant and hydrated tissue with high water content as reinforced biphasic material plays very important roles in load-support and smooth movement with very low friction and low wear property as a lubricious rubbing surface in synovial joints under various daily activities. However, cartilage tissue can be deteriorated or damaged due to various diseases with aging, inflammatory activation, and excessive stresses and injuries by high loading. High friction in natural synovial joint with damaged cartilage increases the severity of rubbing to induce further wear and interferes the smooth movement. The articular cartilage has minimal self-healing ability due to the lack of blood supply as avascular nature, lack of nerve supply, and the sparse population of immobile chondrocytes. Therefore, several kinds of medical treatments to repair focal defects of articular cartilage have been applied in clinical field. In particular, to improve the function of regenerated cartilage, three factors of “cell sources”, “scaffolds” and “culture conditions” play important roles. Appropriately regenerated articular cartilage with superior structure and property similar to natural cartilage is expected to be maintained on the rubbing surfaces. To establish proper conditions with long durability, the influences of mechanical and tribological stimulation on the effective function of regenerated cartilage tissue are discussed in related to friction and wear behavior.

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