BUILDING STRENGTH IN 3-DIMENSIONS
Tendons, ligaments, and the meniscus of the knee each have an ordered internal structure that provides them their ability to bear mechanical loading. To recreate these structures, researchers have been using nanofiber scaffolds to organize the cells as they colonize the new tissue. But getting the scaffold just right has been tricky, according to Robert L. Mauck, PhD, professor of Orthopaedic Surgery and Bioengineering. If the nanofibers in the scaffold are too densely packed, the cells don't have room to grow. If they are too sparse, the engineered tissue lacks its necessary structure.
Recently, though Mauck and Brendon M. Baker, PhD, previously a graduate student in the Mauck lab at the Perelman School of Medicine, University of Pennsylvania, have found a way around the problem. They mixed some biodegradable nanofibers into their scaffold. As the cells colonize the tissue, the nanofibers dissolve, thereby providing both the space and the structure necessary for tissue growth. The team isn't ready to test the approach in humans just yet, but early tests in a pig model suggest the fibrous engineered tissue can repair the meniscus of the knee.
This isn't the first time Mauck's group has made use of the biodegradable nanofibers either. They reported in 2009 that they could use them to bioengineer tissue that might one day be able to replace damaged discs in the spine.
Cartilage is the cushion that prevents the bones in our joints from banging against one another. But over time it can break down, especially if put under repeated stress through running or other intense activities. Whereas clinicians and researchers have been able to easily characterize the problem, figuring out what to do about it hasn't been straightforward. Cartilage lacks a natural blood supply and therefore has little capacity to regrow and or even bind with cartilage grafts pulled from other parts of the body.
Working with Mauck, Jason Burdick, PhD, professor of Bioengineering, has started to find a way around those issues. He can now coax adult stem cells, harvested from bone marrow, to turn into chondrocytes, the cells that comprise cartilage. If he mixes the chondrocytes in a gel with hyaluronic acid, — a small molecule that stimulates chondrocytes growth — and injects the mixture into a damaged joint, the newly placed cells regenerate the damaged cartilage.
The cartilage repair strategy is still a work in progress, according to Burdick, but one with growing potential.