Tissue engineering for myocardial regeneration

Recent progress in stem cell biology has shown the possibility of implantable human myocardial cell sources. It has encouraged myocardial tissue engineering for rescuing damaged hearts. The present strategy is to repair not all of the myocardial tissue, but part of it. There are two approaches. The first is direct injection of dissociated cell suspensions via the pericardium, coronary arteries, or endocardium. Studies using animal models have found improved heart function after transplantation of various types of cells. Myoblasts or bone marrow cells have already been transplanted into patients suffering from severe ischemic heart disease. In direct transplantation of dissociated cells, it is difficult to control the shape, size, and location of the grafts. To solve these problems, further therapies to transplant tissue-engineered three-dimensional (3-D) heart grafts have been investigated. The most popular technique in tissue engineering is to use 3-D biodegradable scaffolds as alternatives to the extracellular matrix. On the basis of this concept, poly(glycolic acid)(PGA), gelatin, alginate, and collagen have been used as scaffolds to fabricate 3-D heart tissues. A new method consisting of layering cell sheets to construct 3-D tissues without any artificial scaffolds has also been applied to myocardial tissue engineering. Electrically communicative pulsatile heart tissues have been achieved both in vitro and in vivo by layering cardiomyocyte sheets. Although myocardial tissue engineering has rapidly progressed, there are several problems to be solved with regard to the source of myocardial cells, tissue reconstruction, neovascularization, and transplantation technology. Further interdisciplinary research will solve these problems, and transplantation of cells or engineered heart tissues will become one of the major treatments for severe heart failure in the near future.