Engineering Vascularized Skeletal Muscle Tissue
Nature Biotechnology 23, 879 - 884 (2005)
Shulamit Levenberg, Jeroen Rouwkema, Mara Macdonald, Evan S Garfein, Daniel S Kohane, Diane C Darland, Robert Marini, Clemens A van Blitterswijk, Richard C Mulligan, Patricia A D'Amore & Robert Langer
Full Text: http://www.nature.com/nbt/journal/v23/n7/full/nbt1109.html

Vascularization is a critical factor in the viability of bioenegineered tissue. In relatively thin tissues with low metabolic activity such as skin, little vascularization is required. Yet in thicker tissues that require a large supply of nutrients and removal of waste, vascularization has been a critical road block in achieving clinical viability.

In most tissue engineering transplantations, vascularization occurs post implant via the host and through the addition of growth factors. Unfortunately this technique has not been successful for large, thick tissues. The other option for tissuevascularization is to begin the process prior to implantation. In the paper, "Engineering vascularized skeletal muscle tissue," Levenberg etal. were able to produce prevascularization prior to implantation and viability post implantation in an in-vivo model.

The first step in the experiment by Leavenberg was creating a co-culture of muscle and endothelial cells. When co-cultured and analyzed over time endothelial tubes formed around the elongated muscle cells showing the beginings of vascularization. This concept was then extended by culturing three different cells together; skeletal muscles, endothelial cells, and fibroblasts. The fibroblasts were added due to their ability to differentiate into smooth muscle cells, which would act to stabilize the endothelial tubes. This tri-culture showed even greater stabilization then the co-culture with the presence of smooth muscle cells and also the increased production of angiogenic growth factors such as VEGF. Having shown proof of concept in-vitro the tri-cultured tissues were then implanted into mice.

In the mice three different sites received tissue, one of which was abdominal muscle. The implant showed evidence of viability, and very interestingly, it appeared that the new muscle appeared toalign with the fibers of the host tissue. This revealed the possibility of both functionality and viability in the implant.

The study by Levenberg etal. was one of the first to show the ability to create prevascularization in thick complex tissues. The results of this research creates great possibilities for advancement of tissue engineering in such complex metabolically active tissues as liver or brain. In addition, the techniques developed could be used for studyingmulticellular processes, such as angiogenesis in-vitro.