Ratner's scaffold is a flexible polymer with interconnected pores all of the same size. This one also includes channels to accommodate cardiac cells' preference for fusing together in long chains. Researchers first verified the design using chicken embryonic heart cells, and confirmed that the scaffold could support heart tissue growth at concentrations similar to those in living heart tissue.
They then seeded the scaffold with cardiac muscle cells derived from human embryonic stem cells. These cells survived and collected in the channels. Over five days, the cardiac muscle cells multiplied faster in the scaffold environment than other cell types, and could survive up to 300 micrometers (about the diameter of four human hairs) from the scaffold edge an important point if the scaffold is to integrate with the body.
The cells expressed two proteins associated with muscle contraction and could contract with sufficient force to deform the scaffold.
Researchers also implanted a bare scaffold into a living rat's heart to verify the scaffold's biocompatibility. Results showed that after four weeks the heart had accepted the foreign body, and new blood vessels had penetrated into the scaffold.
Why blood vessels penetrate so well is unknown. One hypothesis involves the macrophage, a cell in the immune system, and the size of the pores, which seems to be critical. The macrophages first attack the foreign body as an invader and try to digest it. They enter the pores and are themselves entrapped. At this point the macrophage seems to switch from its attack mode to its healing mode. The team is now investigating the blood vessel formation.
Heart tissues need a rich blood supply, and that's been one of the limiting factors to heart repair and vascular tissue engineering, said co-author Chuck Murry, p
|Contact: Hannah Hickey|
University of Washington