FIGURE 1.

Limitations of direct cell transplantation. Cells can be transplanted in vivo by different routes, such as intravenous, intramuscular, intra-cardiac, or intra-vitreous injection. The direct transplantation of stem cells and progenitor cells without using biomaterial platforms may lead to the poor cell-cell and cell-ECM interactions, resulting into the severe loss of the cells through apoptosis in vitro and in vivo. Moreover, the cells can experience rapid loss upon transplantation in vivo due to poor cell survival, retention, and engraftment at the injury site. Poor cell homing and immune rejection may further aggravate this problem. Overall, this can lead to severe cell loss and less functional, more scar-like tissue repair.