Engineering Segments of a Human Limb
Almost 2 million people in the United States have amputated limbs. Scientists at the Wake Forest Institute for Regenerative Medicine are actively at work to make replacing these limbs a reality. At WFIRM, researchers are working to develop replacement limbs in the laboratory by first engineering the component parts – skin, bone, muscle, tendons and blood vessels.
One of the technical challenges is to engineer tissue that will function like the muscle-tendon junction. WFIRM researchers are trying to utilize regenerated tissue that make pulling movements, such as flexing the arm and bending the leg, possible. James Yoo, MD, PhD, professor of regenerative medicine, is the lead researcher.
In the project, Yoo and colleagues are using two biodegradable polymers to create a scaffold, or three-dimensional shape, to support muscle cells as they develop and form this junction. The challenge of the project is that there is a ‘mismatch’ in the mechanical properties of tendon and muscle. Muscle tissue must be compliant and contractile in order to generate force for movement. The tendon, on the other hand, is designed to transfer the force generated by the muscle to a bone and create movement and therefore must be strong and stiff.
The scaffold used to engineer this tissue must have three distinct regions in order to mimic the native junction – areas destined to become muscle tissue, tendon tissue and the area where they overlap. In a project to engineer the scaffold, Yoo and colleagues begin by spraying liquid biomaterials onto a spinning mandrel – using different materials for the muscle and tendon regions and allowing them to overlap and create the junction. They are using tensile testing, including uniaxial, cyclic and stress-relaxation, to test mechanical properties of each region.
The scaffold is then seeded with muscle cells to promote tissue formation. The work continues, but so far, the results look promising.