Sadahito Uto

Control of myotube contraction using electrical pulse stimulation for bio-actuator

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.

Electrooptic Measurement of Three-Dimensional Nonuniform Electric Field Mapping in Nitrobenzene

An electrooptic method is useful for measuring electric fields without disturbing them. Our investigations have been concerned with measurements of electric field distribution. Three-dimensional nonuniform electric field distributions were measured in nitrobenzene using the Kerr electrooptic measurement. The field distributions to be measured were produced in a sphere-to-sphere electrode system. The optical system consisted of a He–Ne laser, a polarizer, a quarter-wave plate, an experimental cell, an analyzer, and a photodetector. When a negative high voltage pulse was applied to the electrode system, the light intensity transmitted to the analyzer was measured using the photodetector. Intensity measurements were carried out at many points from θ= 0 to π around the electrode system. From the data obtained, the electric field distribution, i.e., the strength and direction of each electric field vector in the measured plane, was reconstructed using a computed tomography (CT) technique. The measured distributions were compared with the theoretical ones calculated using an analytical method.

Mechanical vibration of freely suspended ferroelectric liquid-crystal film excited by sound and electric field

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.

Molecular reorientation and deformation of a freely suspended ferroelectric liquid crystal film

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.

Kerr Effect for Three-Dimensional Electric Fields

An optical method using the Kerr effect is useful to measure electric fields in dielectric liquids without disturbing the field. A conventional relation of the Kerr effect cannot be applied to the measurement of a three-dimensional field, the direction of which is not always perpendicular to an incident light. We have derived the relation of the Kerr effect which can be applied to three-dimensional measurement and confirmed it experimentally.

A Theory for Three-Dimensional Measurement of Nonuniform Electric Field Using Kerr Effect.

An optical method using the Kerr effect is useful to measure electric fields in dielectric liquids without disturbance. The computed tomography (CT) method has been applied to the measurement of two-dimensional field distributions by us. However, three-dimensional electric field distributions, in which field vectors are not always perpendicular to the transmitted light, have not been measured as yet. A three-dimensional field vector can be reduced to a two-dimensional one. This leads to the application of the CT method to the measurement of a more general distribution. This paper reports on a theory and a simulation of nonuniform three-dimensional electric field measurements.

Characteristics of ultrathin ferroelectric liquid crystal film and optical switching

Electrooptic response in a free-standing (FS) ferroelectric liquid crystal film has been studied. The threshold field of the electrooptic effect in the FS film is negligible compared with that in a sandwich cell. Discontinuous dependence of response speed on the applied field is observed in the FS film. The response of FS film can be classified into three types. In order to clarify the switching mechanism, the texture of FS film has been observed. Looped π-walls appear after low-field inversion, while a disclination line at the film surface disappears in the high-field region in which response speed is proportional to E -1 .

DYNAMIC RESPONSE OF ELECTRO-OPTIC EFFECT IN FREE-STANDING FERROELECTRIC LIQUID CRYSTAL FILM

A study of an electro‐optic response in a free‐standing ferroelectric liquid crystal film has been carried out. The response time becomes shorter with increasing electric field and, especially at a certain threshold of electric field, it changes in stepwise by three orders of magnitude. The response time of the faster kind of response that appears in the higher field region is several hundred milliseconds and is about one thousand times faster than the slower kind of response at lower fields.

Formation of Piled Circular Texture Induced by Alternating Electric Field in Freely Suspended Ferroelectric Liquid Crystal Films.

Unique piled circular textures induced by an alternating electric field have been observed in a freely suspended ferroelectric liquid crystal film using a polarizing microscope. Molecular alignments in the textures are clarified and the formation process of the texture is discussed.

GUEST-HOST ELECTRO-OPTIC SWITCHING IN SPIN-COATED POLYMER FERROELECTRIC LIQUID CRYSTAL FILM

We have proposed an electro-optic effect in dichroic-dye-doped polymer ferroelectric liquid crystal thin films prepared by a spin-coating technique. A high-quality homeotropically aligned film has been realized. Guest-host type electro-optic switching is confirmed in the dye-doped film, and basic properties such as electric field dependence of the response time are studied.