New design of actuator using shear piezoelectricity of a chiral polymer, and prototype device

Abstract

Chiral polymers have been known to exhibit small shear piezoelectricity for about fifty years. However, recently, we reported that poly(L-lactic acid) treated with supercritical carbon dioxide (sc-PLLA), which is a type of chiral polymer, exhibits much higher shear piezoelectricity than other chiral polymers. On the other hand, we found an important difference between motion due to shear piezoelectricity and that due to tensile piezoelectricity in piezoelectric materials through computer simulations. On the basis of these results, we fabricated a new type of electrically controlled tweezers constructed from a pair of sc-PLLA sheets with shear piezoelectricity. In general, when conventional tweezers open to the left and right, the trajectory of their motion becomes fanlike at the center of the connection (one end of the tweezers). In the new tweezers, the two small sheets making up the tweezers open parallel to each other, without the motion of parts near the connection. Moreover, a prototype 'finger' system using sc-PLLA sheets to realize complex motion in which the finger curled upon stretching of the sc-PLLA sheets was manufactured as a trial device. Using the prototype finger system, we demonstrated the firm grasping of a sample, but the sample could not be removed from a vessel. Thus, sc-PLLA increases the likelihood of realizing a device with highly operational pick-up in a very small region by using the shear piezoelectricity of a chiral polymer.

Biodegradable Piezoelectric Force Sensor

“…Poly-L-lactic acid (PLLA), a biodegradable polymer used extensively in FDA-approved implants, has recently been found to exhibit piezoelectricity when appropriately processed (15)(16)(17). The material exhibits shear piezoelectricity due to electrical polarity present in the carbon-oxygen double-bond branching off from the polymer backbone chain (18,19). Although possessing a modest piezoelectric response (5-15 pC/N), PLLA has a low dielectric constant, which allows the material to perform the same energy-conversion efficacy as the common piezoelectric polymer PVDF (16,20).…”

Piezoelectric materials as stimulatory biomedical materials and scaffolds for bone repair

“…Semi-crystalline PLLA does not require any additional poling treatment to induce piezoelectric effect. This has been attributed to the displacement of the C=O bond in PLLA in response to mechanical stress leading to generation of a net dipole moment and charge [145][146][147]. PLLA has been used to fabricate films, fibres and rods with piezoelectric behaviour [148][149][150][151] and it has been observed that crystallinity and polymer orientation play key role in piezoelectric characteristic [152].…”

Fundamental study on application of piezoelectric chiral polymer to new soft actuator

“…This is a well known buckling phenomenon observed in real fabrics and pipes conveying fluids, diamond-shaped patterns appear under the large axial compression of a cylindrical shell [12]. This phenomenon indicated that a large amount of stress was caused by the resonance phenomenon of the PLLA film roll [1,12,13]. Therefore, we considered that the likelihood of realizing a surface acoustic wave was increased.…”