Tissue engineering in vivo - in vitro
Therapeutic treatments for acquired and inherited skeletal myopathies and loss of functional muscle tissue require the ability to either the implantion of differentiated muscle tissue constructs or the injection of muscle-precursor cells into sites of dysfunction or tissue deficiency for subsequent formation of new muscle tissue  . The implantation of engineered myoblasts has been utilized as a poten
In contrast to these myoblast transfer strategies, other researchers in the field of muscle tissue engineering are more focussing on in vitro differentiation and maturation of satellite cells harvested from adult skeletal muscle. This approach of in vitro development of bioartificial muscle could be an alternative source for treating muscular disorders as described above  . These attempts reflect the two general approaches to engineer skeletal muscle tissue. One approach uses in vitro-designed and pre-fabricated artificial muscle tissue equivalents to reimplant the neo-tissue after differentiation has taken place (in vitro tissue engineering) (Fig. 1A). The second approach uses the application of isolated satellite cells, after expansion of cells in vitro using an appropriate transport matrix, which allows differentiation into myotubes in vivo to occur (in vivo tissue engineering) (Fig.1B). Future developments and the decision regarding which approach is more promising depend on the elucidation of the relationships among cell growth and and differentiation, the cell integration capacity in the host in in vivo experiments and the capability to induce vascularisation of tissue equivalents in vitro.
tial therapy for genetic muscle diseases such as Duchenne´s muscular dystrophy or for the repair of damaged myocardial tissues (Myoblast Transfer Therapy)   . The rationale behind this strategy is that the implantation of large numbers of myoblasts result in the fusion of these cells to the affected tissue, thereby improving the functional status of the muscle . Early results have demonstrated that exogenously introduced myoblasts are incorporated into local target sites and fuse with existing myofibers . However, this techniques, although shown to improve the architecture and function of muscle as the myoblasts incorporate and differentiate, is limited by the large numbers of cells required and sites that must be injected  . Nevertheless implanted and in vitro
transfected myoblasts might serve as vehicles for the delivery of other recombinant proteins such as angiogenic factors and growth factors as insulin like growth factor 1, erythropoeitin and VEGF [21, 63–65]. This myoblast-targeted gene therapy with the potential for local production and release of needed therapeutic proteins holds promise for the treatment of several myopathies as well as other diseases [65–67], lacking important functional proteins [64, 68].