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.

tenascin-X (tnX) is a member of the extracellular matrix glycoprotein tenascin family, and tnX deficiency leads to Ehlers-Danlos syndrome, a heritable human disorder characterized mostly by skin hyperextensibility, joint hypermobility, and easy bruising. TNX-deficient patients complain of chronic joint pain, myalgia, paresthesia, and axonal polyneuropathy. However, the molecular mechanisms by which TNX deficiency complicates pain are unknown. Here, we examined the nociceptive behavioral responses of TNX-deficient mice. Compared with wild-type mice, TNX-deficient mice exhibited mechanical allodynia but not thermal hyperalgesia. TNX deficiency also increased pain sensitivity to chemical stimuli and aggravated early inflammatory pain elicited by formalin. TNX-deficient mice were significantly hypersensitive to transcutaneous sine wave stimuli at frequencies of 250 Hz (Aδ fiber responses) and 2000 Hz (Aβ fiber responses), but not to stimuli at frequency of 5 Hz (C fiber responses). in addition, the phosphorylation levels of extracellular signal-related kinase, an active neuronal marker, and the activity of nADpH-diaphorase, a neuronal nitric oxide activation marker, were enhanced in the spinal dorsal horns of TNX-deficient mice. These results suggest that TNX deficiency contributes to the development of mechanical allodynia and hypersensitivity to chemical stimuli, and it induces hypersensitization of myelinated A fibers and activation of the spinal dorsal horn.

A study of the mechanical vibrations of a freely suspended (FS) ferroelectric liquid-crystal film has been carried out. Upon excitations by sound irradiation and also by electric-field application, the mechanical vibration of the FS film of the ferroelectric liquid crystal is effectively excited. In the frequency dependence, resonance vibrations are observed for both excitations and the resonance frequencies, and light reflection patterns are found to be different for both excitations, suggesting the different oscillating modes of the FS film for both excitations. In electric-field excitation, the vibration mode, which is consistent with the molecular model of the origin of the vibration due to the reorientation of Ps by Ps⋅E torque is found. In addition, the application of the FS film of the ferroelectric liquid crystal as sensitive acoustic sensors is proposed.

A study of the deformation of a freely suspended ferroelectric liquid crystal film induced by an alternating electric field has been carried out. A notable peak of the magnitude of the deformation was observed at the damping frequency of the molecular reorientation. A deformation that depends on the polarity of the applied field was observed in the frequency range higher than the damping frequency of the molecular reorientation.

We present a precise electric-field-temperature phase diagram of an antiferroelectric liquid crystal with a short pitch Sm-C ␣ * phase. This was obtained by using a photoelastic modulator. A unique field-induced phase was found inside the Sm-C ␣ * phase, which displayed low birefringence. Two tricritical points related to the phase were also observed. In addition, numerical calculations were made based on the discrete phenomenological model. The numerical results reproduced the experimental ones and it was clarified that the phase has a three-layer structure without spatial modulation. Many phases have been found in antiferroelectric smectic liquid crystals. The variety can be ascribed to the interlayer interactions between the tilts of molecules. The Sm-C ␣ * phase with a short pitch helix arises from competition between nearest-neighbor ͑NN͒ and next-nearest-neighbor ͑NNN͒ interactions ͓1͔, and the distorted four-layer phase ͑Sm-C FI2 * ͒ and the distorted three-layer phase ͑Sm-C FI1 * ͒ from NN nonlinear interaction ͓2͔. A phase diagram in a parameter space of coefficients in the free energy was obtained on the basis of a discrete phenomenological model. As the temperature changes, the interactions change so that sequential transitions take place. Consequently, by changing the temperature one can obtain information on the interactions. In addition, using an electric field can also be a good method for investigating the interactions because in chiral smectic liquid crystals the electric field couples with the order parameter representing the amplitude and phase of the molecular tilt in each layer. The electric-field effect has been extensively studied, mainly by using D-E hysteresis loops, optical transmission measurements under ac electric fields, and conoscopic observations ͓3͔. However, these experiments are not detailed enough to precisely detect small orientational changes in molecules over a wide range of temperatures and electric fields.We adopted an optical system using a photoelastic modulator ͑PEM͒, by means of which we could simplify the si-