Tissue Engineering: An Explanation of How Stem Cells Can be Used to Regrow Cartilage

The perpetual search for the Fountain of Youth has both fascinated as well as eluded human beings for centuries.

What has been particularly interesting has been the observation that other species (eg, earthworms, salamanders, etc.) can regenerate severed body parts... but human beings cannot.

The recent surge in interest in tissue engineering has been prompted by the scientific discoveries that perhaps the use of stem cell technology may allow a certain degree of if tissue healing and regeneration to take place. Certainly, at least some of the impetus arises from the desire of Baby Boomers to remain active and healthy.

In the medical arena, there has been intense interest, particularly in the field of arthritis, regarding the potential use of stem cell technology to regrow cartilage.

It might be useful to quickly review what stem cells are and what types of stem cells might be used.

Stem cells are pluripotential progenitor cells. What this means is that these cells have not yet committed to become a specific type of tissue. Stem cells are the earliest type of cell. They have not yet "committed" to becoming a specific type of organ cell. However, given a specific stimulus, they can differentiate into any type of tissue. A heart cell... a lung cell... a brain cell... and so on.

There are three main types of stem cells that have been used in research to treat medical conditions.

The first are embryonic stem cells. These are obtained from a fetus. Of the three types of stem cells, embryonic stem cells are the cells that probably have the greatest potential to differentiate and multiply. However, there are concerns. Stem cells have been found to lead to cancer in at least one case of a boy who was given stem cells to treat a rare neurologic disorder. According to the Associated Press, "For all the promise, researchers have long warned that they must learn to control newly injected stem cells so they don't grow where they shouldn't, and small studies in people are only just beginning..." In addition, the ethical debate regarding the use of embryonic stem cells is also not over.

The second type of stem cell is called the "mesenchymal donor cell.' These are stem cells that are harvested from the bone marrow of normal volunteers. These have the potential to be quite useful. One advantage is that a large concentration of stem cells can be produced through this process. Questions still remain regarding the possibility of rejection reactions as well as the theoretical danger of transmission of viruses.

The most commonly used stem cells currently are autologous stem cells. These are stem cells that are obtained from the bone marrow of the patient. Stem cells by themselves may not be effective in differentiating into the tissue that is desired.

Stem cells are stimulated to multiply and divide because they have tyrosine kinase receptors on their surface which permit engagement with various growth factors. Growth factors present in blood- and in even higher concentration in platelet rich plasma (PRP) bind to the tyrosine kinase receptors and send a signal to the nucleus of the cell that leads to replication.

In addition to these natural occurring growth factors, scientists are studying the ability of substances such as bone morphogenic protein (BMP) to stimulate bone and cartilage growth.

Also, in order for stem cells to replicate, they require a matrix which is capable of acting as a "home base." Different types of matrices form a framework in which stem cells can multiply and divide. Currently, scientists are studying various types of matrices to see which is the most effective.

From this discussion, it is quite clear that there are many questions that need to be addressed and answered. Regardless of the complexity of stem cell technology, it is clear that this area of regenerative medicine holds a great deal of promise for the future.