Credit: Aaliya Landholt

Arthritis affects millions of people worldwide, causing pain and stiffness in joints. In some cases, arthritis develops after the cartilage in a joint is damaged. Cartilage acts to cushion the joints, allowing for smooth movement. Because cartilage cannot repair itself after injury, tissue engineers have attempted to generate new cartilage that could be transplanted into a damaged joint to repair it before arthritis can set in. However, it has proven difficult to create engineered cartilage with biomechanical properties similar to those of native cartilage. Several factors contribute to this difficulty. First, because cartilage doesn't heal naturally, engineers have no natural process to attempt to copy. Second, many of the biomechanical properties of cartilage (such as its stiffness and strength) are derived not from the cartilage cells themselves, known as chondrocytes, but from a dense mat of collagen and proteoglycans that is woven around them. This extracellular matrix (ECM) is formed during childhood.

But engineered cartilage has now made a leap forward. Tissue engineers at Rice University (Houston, TX) have created engineered cartilage with biomechanical properties that more closely resemble those of native cartilage. Benjamin Elder and Kyriacos Athanasiou isolated chondrocytes from the knees of male calves, engineered them to grow cartilage and then exposed the engineered cartilage to a combination of growth factors and hydrostatic pressure (PLoS ONE 3, e2341; 2008). “The combination of hydrostatic pressure and growth factors used in this process results in an engineered cartilage ECM with properties nearly identical to those of native cartilage,” said Athanasiou.

Most tissue engineering strategies try to simulate the conditions that cells are exposed to in the human body, so Elder and Athanasiou's approach is somewhat unconventional. During daily activities, native chondrocytes may experience pressures approaching the high levels used in Elder and Athanasiou's research, but only for short periods of time.

The techniques have not yet been tested in live animals or humans. But the researchers feel that their work holds promise for treating arthritis in the future. It may also be applicable to engineering other types of tissue to repair bladders, blood vessels, kidneys, heart valves and bones, according to Athanasiou.