Tendons are fibrous tissues that connect bone to muscle. The tendons and muscles that stabilize the shoulder joint are known as the rotator cuff. Rotator cuff tendons tend to tear as people age.
Although many tears don’t cause symptoms, surgery may be needed to repair severe tears that cause significant shoulder pain. Unfortunately, because rotator cuff tendons are so vulnerable to tearing, people who have had surgery may experience another tear later on.
Researchers have been working to develop materials to help surgeons make repairs that are stronger and last longer. They are testing a variety of polymer materials in braided, mesh, and other shapes to find what might work best. One recent advance in the field is to introduce cells and growth factors that coax the body into helping with the repair. The body’s own machinery can knit together the tissues as the polymer material dissolves.
A team led by Dr. Cato Laurencin at the University of Connecticut Health Center set out to improve tissue repair methods by combining stem cells with a scaffold they had previously designed. The research was supported in part by NIH’s National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) and an NIH Director’s Pioneer Award. Results were published on April 3, 2017, in PLoS One.
The team used mesenchymal stem cells derived from rat bone marrow. These cells can mature into many different types of cells in the body. The scientists seeded the cells onto one side of a polymer fiber scaffold. The thin 5 mm by 7 mm scaffold consisted of polymer fibers that mimic the structural organization of natural tendon fibers.
The researchers implanted the seeded scaffolds on top of the torn rat tendons by wrapping them with a suture and trimming them to 3 mm by 3 mm. The sides containing the stem cells were placed against the tendons. To compare the seeded scaffold with other methods, the team repaired torn tendons in other rats with a plain fiber scaffold and suture or with a suture only.
After the surgical sites healed, the team compared the effects of the three test methods on torn tendons. For several measures of tissue composition and healing, tendons repaired with a seeded scaffold more closely resembled normal tendon than tendons repaired with the other methods. For measures of mechanical properties, the seeded scaffold method again was superior to the other two methods of tendon repair.
Only when they used the seeded scaffold did the researchers observe tissue that resembled tendon-like tissue. They hypothesized that the stem cells helped the body to repair the torn tendon.
“We hope to use this technology to create new methodologies in rotator cuff repair,” Laurencin says. Because this proof of concept study was successful, the next step will be to repair torn tendons with seeded matrices in larger animals, such as rabbits. A larger animal will enable the use of surgical approaches and materials that more closely approximate methods used by surgeons with people.