The end goal for tissue engineering is not the generation of organs and tissues outside the body for transplantation, but rather to direct the rebuilding of complex tissue structures in situ inside the body:
What if repairing large segments of damaged muscle tissue was as simple as mobilizing the body's stem cells to the site of the injury? [Researchers have] demonstrated the ability to recruit stem cells that can form muscle tissue to a small piece of biomaterial, or scaffold that had been implanted in the animals' leg muscle. The secret to success was using proteins involved in cell communication and muscle formation to mobilize the cells. "This is a proof-of-concept study that we hope can one day be applied to human patients."
The current treatment for restoring function when large segments of muscle are injured or removed during tumor surgery is to surgically move a segment of muscle from one part of the body to another. Of course, this reduces function at the donor site. Several scientific teams are currently working to engineer replacement muscle in the lab by taking small biopsies of muscle tissue, expanding the cells in the lab, and placing them on scaffolds for later implantation. This approach requires a biopsy and the challenge of standardizing the cells. "Our aim was to bypass the challenges of both of these techniques and to demonstrate the mobilization of muscle cells to a target-specific site for muscle regeneration."
Most tissues in the body contain tissue-specific stem cells that are believed to be the "regenerative machinery" responsible for tissue maintenance. It was these cells, known as satellite or progenitor cells, that the scientists wanted to mobilize. The scientists tested the effects of several proteins known to be involved in muscle formation by designing the scaffolds to release these proteins. The protein with the greatest effect on cell recruitment was insulin-like growth factor 1 (IGF-1). After several weeks of implantation, lab testing showed that the scaffolds with IGF-1 had up to four times the number of cells than the plain scaffolds and also had increased formation of muscle fibers. Next, the scientists will evaluate whether the regenerated muscle is able to restore function and will test clinical feasibility in a large animal model.