Building patches for damaged hearts is a popular implementation in tissue engineering at the moment: it's an achievable stepping stone on the way to more complex goals, such as the creation of entire organs starting from only a patient's stem cells, something that still lies in the future. Progress towards a long-term goal in any field requires useful intermediary products, as they help pull in the greater support and funding needed for the next phase of research and development.
When heart cells die from lack of blood flow during a heart attack, replacing those dead cells is vital to the heart muscle's recovery. But muscle tissue in the adult human heart has a limited capacity to heal, which has spurred researchers to try to give the healing process a boost. Various methods of transplanting healthy cells into a damaged heart have been tried, but have yet to yield consistent success in promoting healing.
Now, [researchers] have developed a patch composed of structurally modified collagen that can be grafted onto damaged heart tissue. Their studies in mice have demonstrated that the patch not only speeds generation of new cells and blood vessels in the damaged area, it also limits the degree of tissue damage resulting from the original trauma. The key [is] that the patch doesn't seek to replace the dead heart-muscle cells. Instead, it replaces the epicardium, the outer layer of heart tissue, which is not muscle tissue, but which protects and supports the heart muscle, or myocardium.
The epicardium - or its artificial replacement - has to allow the cell migration and proliferation needed to rebuild damaged tissue, as well as be sufficiently permeable to allow nutrients and cellular waste to pass through the network of blood vessels that weaves through it. The mesh-like structure of collagen fibers in the patch has those attributes, serving to support and guide new growth. Because the patch is made of acellular collagen, meaning it contains no cells, recipient animals do not need to be immunosuppressed to avoid rejection. With time, the collagen gets absorbed into the organ.