Burrowing soft robots break new ground.

A bioinspired soft robot burrows through shallow dry sand with remarkable speed and maneuverability.

SBOR: a minimalistic soft self-burrowing-out robot inspired by razor clams.

We observe that the Atlantic razor clam (Ensis directus) burrows out of sand rapidly by simply extending and contracting its muscular foot. This is notably different from its well-known downward burrowing strategy or the dual-anchor mechanism, where closing/opening of the shell and dilation of the foot are also involved. Inspired by this burrowing-out strategy, we design a simple self-burrowing-out robot (SBOR) consisting of a single segment of fiber-reinforced silicone tube actuator and an external control board. The reinforcing fibers limit the motion of the actuator to axial extension/contraction under inflation/deflation. For an actuator that is vertically buried in the sand, cyclic inflation and deflation naturally drives it out of the sand, mimicking the motion of a razor clam. We characterize the burrowing-out behavior of the actuator by varying the actuation period and the relative density (packing) of the sand. Each burrowing cycle features an initial upward advancement during inflation, followed by a downward slip during deflation, resulting in a net upward stride. During the burrowing-out process, the stride length first increases due to a drop in the overburden pressure, the end pull-out resistance, and the side frictional resistance; the stride length then decreases after the top of the actuator moves out of the sand layer, due to a reduction in the effective length of the actuator. The results also indicate that the average burrowing-out speed decreases with the relative density of the sand and changes with the actuation pressure. We developed a simplified model based on soil mechanics to predict the burrowing-out processes in relatively loose dry sands, and the modeling results match well with the experiment results. From this model, the burrowing-out behavior is readily explained by the asymmetric nature of the resistant forces on the two ends of the actuator and the flowing nature of sand upon yielding. Our findings imply that razor clams leverage the natural stress gradient of sand deposits to burrow upward. Another insight is that in order to burrow downward into the sand, additional symmetry-breaking features such as asymmetric geometry, friction, stress state or external load are needed to increase the resistant force (anchorage) in the upward direction and to reduce the resistant force (drag) in the downward direction.

A cross-sectional study on health-related knowledge and its predictors among Chinese vocational college students.

OBJECTIVES: This study sought to examine the level of health-related knowledge and its predictors among vocational college students in China. STUDY DESIGN: A cross-sectional study. METHODS: A survey was performed to collect data on heath-related knowledge and potential risk factors among 708 students in four higher vocational colleges at Nanyang, Henan, China. Linear regression models were conducted to identify the predictors of the level of health-related knowledge. RESULTS: The level of health-related knowledge among Chinese vocational college students is extremely low (only 1.4% students have an adequate level of health-related knowledge). According to the multivariate analysis, major, year of class, place of origin and a mother's education level are significantly associated with health-related knowledge in Chinese vocational college students. CONCLUSIONS: Health education and health promotion efforts are encouraged to improve the level of health-related knowledge in this population. Attention and efforts to improve health-related knowledge of Chinese vocational college students who come from rural areas, whose mothers have a lower level of education, who are in non-medicine majors and during the first few years of vocational college is warranted.

Characterization of multiwalled carbon nanotube-polymethyl methacrylate composite resins as denture base materials.

STATEMENT OF PROBLEM: Most fractures of dentures occur during function, primarily because of the flexural fatigue of denture resins. PURPOSE: The purpose of this study was to evaluate a polymethyl methacrylate denture base material modified with multiwalled carbon nanotubes in terms of fatigue resistance, flexural strength, and resilience. MATERIAL AND METHODS: Denture resin specimens were fabricated: control, 0.5 wt%, 1 wt%, and 2 wt% of multiwalled carbon nanotubes. Multiwalled carbon nanotubes were dispersed by sonication. Thermogravimetric analysis was used to determine quantitative dispersions of multiwalled carbon nanotubes in polymethyl methacrylate. Raman spectroscopic analyses were used to evaluate interfacial reactions between the multiwalled carbon nanotubes and the polymethyl methacrylate matrix. Groups with and without multiwalled carbon nanotubes were subjected to a 3-point-bending test for flexural strength. Resilience was derived from a stress and/or strain curve. Fatigue resistance was conducted by a 4-point bending test. Fractured surfaces were analyzed by scanning electron microscopy. One-way ANOVA and the Duncan tests were used to identify any statistical differences (α=.05). RESULTS: Thermogravimetric analysis verified the accurate amounts of multiwalled carbon nanotubes dispersed in the polymethyl methacrylate resin. Raman spectroscopy showed an interfacial reaction between the multiwalled carbon nanotubes and the polymethyl methacrylate matrix. Statistical analyses revealed significant differences in static and dynamic loadings among the groups. The worst mechanical properties were in the 2 wt% multiwalled carbon nanotubes (P<.05), and 0.5 wt% and 1 wt% multiwalled carbon nanotubes significantly improved flexural strength and resilience. All multiwalled carbon nanotubes-polymethyl methacrylate groups showed poor fatigue resistance. The scanning electron microscopy results indicated more agglomerations in the 2% multiwalled carbon nanotubes. CONCLUSIONS: Multiwalled carbon nanotubes-polymethyl methacrylate groups (0.5% and 1%) performed better than the control group during the static flexural test. The results indicated that 2 wt% multiwalled carbon nanotubes were not beneficial because of the inadequate dispersion of multiwalled carbon nanotubes in the polymethyl methacrylate matrix. Scanning electron microscopy analysis showed agglomerations on the fracture surface of 2 wt% multiwalled carbon nanotubes. The interfacial bonding between multiwalled carbon nanotubes and polymethyl methacrylate was weak based on the Raman data and dynamic loading results.

Cloning and molecular characterization of BumaMPs1, a novel metalloproteinases from the venom of scorpion Buthus martensi Karsch.

Scorpion venoms metalloproteinase is involved in a number of important biological, physiological and pathophysiological processes. In this work, a complete sequence of metalloproteinase was first obtained from venom of scorpion Buthus martensi and named as BumaMPs1. BumaMPs1 has 393 amino acid residues containing with a molecular mass of 44.53 kDa, showing an isoelectric point of 5.66. The primary sequence analysis indicated that the BumaMPs1 contains a zinc-binding motif (HELGHNLGISH), methionine-turn motif (YIM), disintegrin-like domain (ETCD) and N-glycosylation site. The multiple alignment of its deduced amino acid sequence and those of other metalloproteinase showed a high structural similarly, mainly among class reprolysin proteases. The phylogenetic analysis showed early divergence and independent evolution of BumaMPs1 from other metalloproteinase.