Mikko Lammi

Articular cartilage is a tissue which has a limited capacity to heal once injured. The damaged cartilage can be surgically operated with a goal to provide symptomatic relief for the painful patients. However, the cartilage damage tend to be progressive, especially in systematic disease called osteoarthritis.

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A concept of replacing the damaged cartilage by implantation of isolated chondrocytes (1) or laboratory-fabricated tissue-engineered tissue has emerged during the last decades, and numerous efforts using chondrocytes or even differentiated stem cells with or without various types of three-dimensional scaffolds or hydrogels manufactured from natural of synthetic biomaterials (3). Although cartilage-type of tissue may form initially, the long-term stability of the repair-tissue is still a major challenge.

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There are several environmental factors, which can be sensed by the chondrocytes affecting their metabolism and the assembly of the extensive amount of extracellular matrix of normal articular cartilage. First, the cartilage has no blood vessels, therefore, the chondrocytes depend on diffusion of nutrients and waste products, which also leads to decreasing low oxygen tension gradients in articular cartilage from the surface to deeper zones of cartilage. We have investigated whether low oxygen tension would be beneficial for in vitro chondrocyte phenotype and cartilage formation (4,5). Cartilage also has unusually high osmotic pressure, which obviously have impact on the metabolism of chondrocytes. Besides these factors, the chondrocytes face various types of mechanical loading.