**2. Principles of tissue regeneration**

Tissue regeneration requires 3 key elements: 1) cells that are harvested and dissociated from the donor tissue, 2) scaffold substrates as biomaterials in which cells are attached and cultured resulting in the implantation at the desired site of the functioning tissue, and 3) cell signals that promote or prevent cell adhesion, proliferation, migration, and differentiation by upre‐ gulating or downregulating the synthesis of proteins, growth factors, and receptors (Figure 1). Combined with these 3 key elements at different rates, timings, and so on, the clinical strategy of tissue regeneration mainly comprises cell transplantation, implantation of bioarti‐ ficial tissue constructs, and chemical induction of regeneration from tissue at the site of injury. According to the nature of the target tissue and the extent of the damage to be repaired, the treatment strategy needs to be modified. For bone tissue regeneration, mesenchymal cell

© 2013 Hibi and Ueda; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Hibi and Ueda; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

transplantation and osteogenic chemical induction are preferred for small tissue deficiencies, while bioartificial mineral construct implantation is considered suitable for large deficiencies.

**Figure 1.** Elements required for tissue regeneration
