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The contractility of tissue-engineered muscle on the application of electrical signals is required for the development of bio-actuators and for muscle tissue regeneration. Investigations have already reported on the contraction of myotubes differentiated from myoblasts and the construction of tissue-engineered skeletal muscle using electrical pulses. However, the relationship between myotube contraction and electrical pulses has not been quantitatively evaluated. We quantitatively investigated the effect of electrical pulse frequency on the excitability of myotubes and developed bio-actuators made of tissue-engineered skeletal muscle. C2C12 cells were seeded on a collagen-coated dish and in collagen gel and were cultured in Dulbecco's modified Eagle's medium (DMEM) containing 10% fetal bovine serum and antibiotics. When the cells reached confluence or after 2 days in culture, the medium was shifted to DMEM containing 7% horse serum to allow them to differentiate to C2C12 myotubes. We electrically stimulated the myotubes and tissue-engineered skeletal muscle, and contractions were observed under a microscope. The myotubes contracted synchronously with electrical pulses between 0.5 and 5 Hz and unfused tetanus was generated at 10 Hz. The contractile performance of tissue-engineered skeletal muscle made of collagen gel and C2C12 was similar to that of the myotubes. Both the rheobase and chronaxie of the myotubes were lowest when the electric field was applied parallel to the myotube axis, and the values were 8.33 +/- 2.78 mA and 1.19 +/- 0.38 ms, respectively. The motion of C2C12 myotube contraction depended on the pulse frequency and showed anisotropy in the electric field. These results suggest that a tissue-engineered bio-actuator may be controlled using electrical signals.

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A platinum isocyanide complex bearing a η2-TCNE ligand, (η2-TCNE)Pt(η-CNC6H3-2,6-Me2)2 (1), was synthesized, and its crystallographic study revealed the coordination mode of the η2-TCNE ligand to be a typical metallacyclopropane extreme, in which back-donation from metal to TCNE contributes primarily to the stabilization of 1. Treatment of 1 with 2 equiv of CNC6H3-2,6-Me2 resulted in ring expansion of the platinacyclopropane by insertion of CNC6H3-2,6-Me2 into each Pt−C bond of the metallacycle, leading to formation of a new complex having a platinacyclopentane structure, (TCNE)Pt(η-CNC6H3-2,6-Me2)4 (4). Although the molecular structures of palladium and nickel homologues of 1 were close to the corresponding metallacyclopropane, no metallacyclopentane complex was obtained under similar conditions. Studies on variable-temperature NMR spectroscopy and spin-saturation transfer measurement of 4 showed exchange of the imidoyl CNC6H3-2,6-Me2 group and the coordinated CNC6H3-2,6-Me2 ligand in solution, suggesting the ring expansion to be reversible.