Stem cells do not always stay where they are put. When they are used to regenerate tissue, many wind up migrating away from the repair site, which disrupts the healing process. Researchers at the University of Rochester, under the direction of Assistant Professor of Biomedical Engineering Danielle Benoit, Ph.D., have developed a technique that keeps the stem cells in place. The key, as explained in a paper published in Acta Biomateerialia, is to encase the stem cells in polymers that attract water and then disappear when their task is completed.
Benoit explains that this has been used to repair other types of tissue but never before tried on bone. “Our success opens the door for many types of bone repairs. We should be able to pinpoint repairs within the periosteum, or outer membrane of bone material, ” she said.
The polymers used by Benoit and her team are called hydrogels because they hold water, necessary to keep the stem cells alive. The hydrogels are designed to degrade and disappear before the body interprets them as foreign bodies and begins a defense response.
The research team transplanted cells onto the surface of mouse bone grafts and studied the cell behavior both inside and outside the body. They removed all living cells from the donor bone fragments so that tissue regeneration could be accomplished only by the stem cells. They genetically modified the stem cells to include genes that give off fluorescence signals. The bone material was then coated with the hydrogels, which contained the fluorescently labeled stem cells, and planted them into the defect of the damaged mouse bone.
At that point the researchers began monitoring the repair process with longitudinal fluorescence to determine if there would be an appreciable loss of stem cells in the in vivo samples as compared to those in the in vitro environments. They found that there was no measurable difference between the concentrations of stem cells in the various samples. Virtually all of the stem cells stayed in place to complete their work in generating new bone tissue. Benoit believes that, as a result of this research, degradable hydrogels show promise in many research areas as, for example, in tissue regeneration after heart failure.
