A 3D printed hydrostatic skeleton for an earthworm-inspired soft burrowing robot.

Moving through soil is challenging for robots, particularly for soft robots. Herein, we propose a support structure, based on the hydrostatic skeleton of earthworms, to overcome this problem. To create extremely flexible, thin-walled, worm-sized deformed segments, a specialized 3D printer for low-hardness rubber was utilized. To obtain large radial deformation, we investigated the properties of the soft materials for 3D printing and the geometry of the segments. Notably, segments are deformed with multiply-wound shape memory alloy wires. We constructed an earthworm robot by connecting shape memory alloy-driven segments in series and experimentally demonstrated that this robot could propel in the soil. The proposed robot is unique in that it has a small diameter of 10 mm and exhibits a peristaltic motion in soil.

Mechanism of eukaryotic serine racemase-catalyzed serine dehydration.

Eukaryotic serine racemase (SR) is a pyridoxal 5'-phosphate enzyme belonging to the Fold-type II group, which catalyzes serine racemization and is responsible for the synthesis of D-Ser, a co-agonist of the N-methyl-d-aspartate receptor. In addition to racemization, SR catalyzes the dehydration of D- and L-Ser to pyruvate and ammonia. The bifuctionality of SR is thought to be important for D-Ser homeostasis. SR catalyzes the racemization of D- and L-Ser with almost the same efficiency. In contrast, the rate of L-Ser dehydration catalyzed by SR is much higher than that of D-Ser dehydration. This has caused the argument that SR does not catalyze the direct D-Ser dehydration and that D-Ser is first converted to L-Ser, then dehydrated. In this study, we investigated the substrate and solvent isotope effect of dehydration of D- and L-Ser catalyzed by SR from Dictyostelium discoideum (DdSR) and demonstrated that the enzyme catalyzes direct D-Ser dehydration. Kinetic studies of dehydration of four Thr isomers catalyzed by D. discoideum and mouse SRs suggest that SR discriminates the substrate configuration at C3 but not at C2. This is probably the reason for the difference in efficiency between L- and D-Ser dehydration catalyzed by SR.

Unwanted sounds generated with test tone presentation can spoil extended high-frequency audiometry.

Unwanted sounds from a commercially available audiometer were evaluated in terms of their effects on extended high-frequency (EHF) audiometry. Although the manufacturer reported that the audiometer conformed to relevant International Electrotechnical Commission (IEC) standards, the audiograms obtained using the audiometer were erroneous because the subjects had responded falsely to noise generated with the test tone presentation before detecting the test tone. Analyses of acoustic and electric output signals revealed that the audiometer generated most of the unwanted sounds, not the earphones that were used. Based on the measurement results, clinical implications of the measurement results are discussed for conducting more reliable EHF audiometry.