Osteoarthritis has been viewed as a condition that is due to imbalance between destructive and reparative processes involving articular cartilage. This is the "gristle" that caps the ends of long bones.
Because articular cartilage is devoid of both nerves and blood vessels, it has very little potential for repairing itself after injury.
This lack of repair ability of weight-bearing articular cartilage and the associated bone changes underlying the cartilage are considered critical to the progression of the disease.
Recent findings by a number of researchers have suggested that what occurs is either a depletion or functional alteration of mesenchymal stem cell (SC) populations in osteoarthritis.
This study of mesenchymal SC function is an ongoing process.
At the same time these investigations into SC alteration has been taking place, other studies looking at possible resolution of cartilage defects with SCs have also taken place.
In one study (Li -J, Tuli R, Okafor C, et al. A three-dimensional nanofibrous scaffold for cartilage tissue engineering using human mesenchymal stem cells. Biomaterials. 2005; 26: 599-609), the authors reiterated the concept that the "utilization of adult SCs in tissue engineering is a promising solution to the problem of tissue or organ shortage."
By way of review, adult bone marrow derived mesenchymal stem cells (MSCs) are undifferentiated, multipotential cells which can become chondrocytes (cartilage cells) when grown in a three-dimensional culture and treated with growth factors.
What the authors did was to make a scaffold of a synthetic biodegradable polymer, and examined its ability to support cartilage growth with MSCs. The experiment lasted 21 days and they determined that MSCs cultured in the presence of growth factors differentiated into an early form of cartilage.
The level of cartilage growth was similar to that seen in other models such as ones using cell aggregates or pellets, a widely used culture protocol for studying MSCs. In fact the mechanical properties of the nanofibers were superior to that seen with the pellet model.
In a related article (Noth U, Tuli R, Osyczka AM. In Vitro engineered cartilage constructs produced by press-coating biodegradable polymer with human mesenchymal stem cells. Tissue Engineering. 2002, 8(1): 131-144), researchers used pellets of MSCs that were pressed into polymer blocks. These press-coated pellets formed cell layers composed of cartilage-like cells. The superficial layer resembled the architecture seen in hyaline cartilage, the ideal type of cartilage.
This model may allow the formation of hyaline cartilage implants without having to resort to harvesting cartilage cells from intact cartilage surfaces. The authors stated these "constructs may be applicable as prototypes for the reconstruction of articular cartilage defects in humans."
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