Recently researchers have made inroads in using the embryonic development process of mesenchymal condensation to generate tissue engineered teeth, or at least to show promising signs of progress along that road. Here this same process is turned to building cartilage, a type of tissue that has proven to be very challenging to engineer. Its mechanical properties are crucial to its role in the body, and these properties depend absolutely on the small-scale arrangement of cells and extracellular matrix. Even slight differences result in artificial tissue that is just an arrangement of cartilage cells, not the real thing, and not up to the task of supporting weight in joints.
Here researchers are claiming to have generated cartilage that is sufficiently similar to natural cartilage to be a candidate for use in the clinic:
[Researchers] have successfully grown fully functional human cartilage in vitro from human stem cells derived from fat tissue. "We've been able - for the first time - to generate fully functional human cartilage from mesenchymal stem cells by mimicking in vitro the developmental process of mesenchymal condensation. This could have clinical impact, as this cartilage can be used to repair a cartilage defect, or in combination with bone in a composite graft grown in the lab for more complex tissue reconstruction."
Many groups studied cartilage as an apparently simple tissue: one single cell type, no blood vessels or nerves, a tissue built for bearing loads while protecting bone ends in the joints. While there has been great success in engineering pieces of cartilage using young animal cells, no one has, until now, been able to reproduce these results using adult human stem cells from bone marrow or fat, the most practical stem cell source. [This] team succeeded in growing cartilage with physiologic architecture and strength by radically changing the tissue-engineering approach.
The general approach to cartilage tissue engineering has been to place cells into a hydrogel and culture them in the presence of nutrients and growth factors and sometimes also mechanical loading. But using this technique with adult human stem cells has invariably produced mechanically weak cartilage. [So the researchers] came up with a new approach: inducing the mesenchymal stem cells to undergo a condensation stage as they do in the body before starting to make cartilage.
The lubricative property and compressive strength - the two important functional properties - of the tissue-engineered cartilage approached those of native cartilage. The researchers then used their method to regenerate large pieces of anatomically shaped and mechanically strong cartilage over the bone, and to repair defects in cartilage. The team plans next to test whether the engineered cartilage tissue maintains its structure and long-term function when implanted into a defect.