Anti-fatigue Properties Research Articles

Shot Peening Numerical Simulation of Aircraft Aluminum Alloy Structure

After shot peening, the 7050 aluminum alloy has good anti-fatigue and anti-stress corrosion properties. In the shot peening process, the pellet collides with target material randomly, and generated residual stress distribution on the target material surface, which has great significance to improve material property. In this paper, a simplified numerical simulation model of shot peening was established. The influence of pellet collision velocity, pellet collision position and pellet collision time interval on the residual stress of shot peening was studied, which is simulated by the ANSYS/LS-DYNA software. The analysis results show that different velocity, different positions and different time intervals have great influence on the residual stress after shot peening. Comparing with the numerical simulation results based on Kriging model, the accuracy of the simulation results in this paper was verified. This study provides a reference for the optimization of the shot peening process, and makes an effective exploration for the precise shot peening numerical simulation.

The anti-fatigue activities of Tuber melanosporum in a mouse model.

Tuber melanosporum (TM) is an edible fungus that exhibits antioxidant and anti-tumor activity via its unique bioactive metabolites. The present study analyzed the anti-fatigue effects of TM using a BALB/c mouse model. The anti-fatigue properties of TM were evaluated by assessing the endurance of mice by performing forced swimming, rotary rod and running tests. Following 2 weeks TM treatment, hepatic and muscular ATP, and glycogen levels were increased in mice subjected to 30 min swimming, compared with controls. Similarly, levels of serum lactic acid and lactic dehydrogenase were decreased in the same group, compared with the control. Additionally, TM treatment reduced reactive oxygen species and malondialdehyde levels, and increased superoxide dismutase and glutathione peroxidase levels in the muscle, liver and/or serum. The effect of TM on hormone levels was also investigated in the present study, as different efficacies of TM were observed in male and female mice. TM treatment increased serum levels of progesterone, estradiol and testosterone in female and male mice, whereas a decrease in serum luteinizing hormone levels was only observed in females. A decrease in serum follicle-stimulating hormone levels was identified in females, whereas an increase was observed in males. The current study demonstrated that the anti-fatigue effects of TM occur via the regulation of oxidative stress, energy metabolism and hormone levels.

Cordyceps sinensis combined with duloxetine improves sleep symptoms in patients with depression: a randomized, double-blind, placebo-controlled study

Background and objectives: Patients with depression can experience sleep disorder. Current treatments for depression, such as duloxetine and selective serotonin reuptake inhibitors, not only have a slow onset of action but also are associated with side effects such as dizziness, blurred vision, and ataxia. The main active ingredient of cordyceps sinensis, cordycepin, may have antidepressant effects, as well as pro-immunity, anti-inflammatory, anti-tumor, anti-fatigue, and anti-viral properties. In this randomized controlled trial, we investigate the safety and effectiveness of cordyceps sinensis (containing approximately 1.0% cordycepin) in combination with duloxetine in treating sleep disorder in patients with depression. Methods: In this randomized, double-blind, placebo-controlled, prospective trial, we plan to include 286 patients with depression receiving treatment at Beijing Anding Hospital of Capital Medical University, China. These patients are randomly assigned to undergo cordyceps sinensis combined with duloxetine or placebo combined with duloxetine. Duloxetine is assigned in an open manner, while cordyceps sinensis and placebo are assigned in a double-blind manner. Participants or their legal guardians are informed of the study protocol and medication and sign informed consent. A total of 246 patients were included in the polit study. Results: The primary outcome measure is the proportion of patients with ≥ 50% difference in 17-item-Hamilton Depression Rating Scale total score after 6 weeks of treatment relative to baseline. The secondary outcome measures are complete remission rate after 6 weeks of treatment; effectiveness rate after 1, 2, and 4 weeks of treatment; changes in Athens Insomnia Scale score, 17-item-Hamilton Depression Rating Scale total score, Arizona Sexual Experience Scale score, Mini-International Neuropsychiatric Interview suicide score, Digit Symbol Substitution Test score, Perceived Deficits Questionnaire-Depression score, 16-item Quick Inventory of Depressive Symptomatology Self-Report Scale score, 7-item Generalized Anxiety Disorder Scale score, and Sheehan Disability Scale score after 1, 2, 4, and 6 weeks of treatment relative to baseline; changes in Insight and Treatment Attitude Questionnaire score, and time and proportion of sleep drug use during the study period after 6 weeks of treatment relative to baseline; electroencephalogram results after 2 and 6 weeks of treatment; and blood biomarkers, safety indicators, and adverse events after 6 weeks of treatment. Results of a pilot study (during 2012–2016) involving 246 patients with depression receiving duloxetine 60 mg/d or fluoxetine 20 mg/d revealed that there was a similar percentage difference in 17-item-Hamilton Depression Rating Scale total score after 6 weeks of treatment relative to baseline and a similar incidence of drug use-related adverse events for both treatments. Discussion: We plan to perform a future study involving 286 patients to validate that cordyceps sinensis combined with duloxetine can effectively improve sleep symptoms of depression. The trial will provide data to support the clinical application of cordyceps sinensis. Ethics and registration: This study was approved by Hospital Ethics Committee, Beijing Anding Hospital of Capital Medical University, China (approval No. 2017-79-2017111-2) on December 20, 2017. This study was registered with the Chinese Clinical Trial Registry (registration number: ChiCTR-INR-17014074). Protocol version: 3.0.

Antifatigue Potential Activity of Sarcodon imbricatus in Acute Excise-Treated and Chronic Fatigue Syndrome in Mice via Regulation of Nrf2-Mediated Oxidative Stress.

Sarcodon imbricatus (SI), a precious edible fungus, contains 35.22% of total sugar, 18.33% of total protein, 24 types of fatty acid, 16 types of amino acid, and 8 types of minerals. Encouragingly, it is rich in potential antioxidants such as total polyphenols (0.41%), total sterols (3.16%), and vitamins (0.44%). In the present study, the antifatigue properties of SI and its potential mechanisms of action were explored by the experiments on acute excise-treated mice and chronic fatigue syndrome (CFS) mice. SI (0.25, 0.5, and 1 g/kg) significantly enhanced exercise tolerance in the weight-loaded forced swimming test (FST) and rota-rod test (RRT) and reduced the immobility in the tail suspension test on CFS mice. SI markedly increased the levels of glycogen in the liver and adenosine triphosphate (ATP) in the liver and muscle and decreased the lactic acid (LD) and blood urea nitrogen (BUN) content in both acute swimming-treated mice and CFS mice. SI improved the endogenous cellular antioxidant enzyme contents in the two mouse models by improving the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) and reducing reactive oxygen species (ROS) and malondialdehyde (MDA) levels in serum, liver, and muscle, respectively. In CFS mice, the enhanced expression levels of nuclear factor erythroid-2-related factor 2 (Nrf2), SOD1, SOD2, heme oxygenase-1 (HO-1), and catalase (CAT) in the liver were observed after a 32-day SI administration. Our data indicated that SI possessed antifatigue activity, which may be related to its ability to normalize energy metabolism and Nrf2-mediated oxidative stress. Consequently, SI can be expected to serve as a novel natural antifatigue supplement in health foods.

Review on WEDM of Shape Memory Alloy

Shape memory alloys (SMAs) have very broad applications in aerospace, medical, automotive, robotics, optometry etc. SMAs are the embryonic advanced materials because of their versatile properties like pseudoelasticity, Shape Memory Effect(SME), superelasticity, high corrosion resistance, biocompatibility, high specific strength, high anti-fatigue property. SMAs are very difficult to machine by conventional processes because of their intricate and complex structures. Non-conventional machining like Water jet machining, laser machining and electrochemical machining (ECM) are used to machine these materials, but due to their mechanical properties and complexity, these processes are limited in use. Electro discharge machining, as well as wire electro discharge machining (WEDM) display high competence to machine SMAs of intricate shapes precisely. In this study, the review of the literature has been carried out to focus the problems associated with the shape memory alloy and to get future scope of the study

Hofmeister Effect‐Assisted One Step Fabrication of Ductile and Strong Gelatin Hydrogels

AbstractHydrogels with high strength and ductility are normally prepared from synthetic polymers, and most protein‐based hydrogels are soft and brittle. Here, a strong, ductile gelatin hydrogel is prepared by simply soaking a virgin gelatin gel in an ammonium sulfate solution. The polymer chains in the covalent, crosslink‐free network can freely move to homogeneously distribute stress, and more importantly, the highly kosmotropic ammonium sulfate ions greatly enhance the hydrophobic interactions and chain bundling within the gelatin gels. As a result, the treated hydrogels have an extraordinary ultimate strength (compressive and tensile strains of over 99% and 500%, respectively, and stresses of 12 and 3 MPa) superior to that of common protein gels. The physical crosslinks introduced by the Hofmeister effect can rapidly absorb energy and sustain large deformations via decrosslinking and dissociation, which result in energy dissipation and antifatigue properties. The effects of the gelatin and (NH4)2SO4 concentrations on the hydrogel mechanics are evaluated, and the possible strengthening mechanism is discussed. The effect of various ions in the Hofmeister series on the gelatin hydrogel is also investigated. Kosmotropic ions enhance the mechanical properties, whereas chaotropic ions soften and dissolve the gel.

Metabonomic analysis of serum reveals antifatigue effects of Yi Guan Jian on fatigue mice using gas chromatography coupled to mass spectrometry.

Yi Guan Jian (YGJ), one of the most commonly used traditional Chinese medicines, has been reported to possess significant antifatigue effects. However, the mechanisms underlying its antifatigue effects remain largely unresolved. In this study, a metabonomics approach, involving gas chromatography coupled to mass spectrometry and a multivariate statistical technique, was developed to estimate the extent to which YGJ alleviated the exhausting swimming-induced fatigue of mice. High-dose treatment with YGJ significantly extended the swimming time of fatigued mice. Significant alterations of metabolites involving amino acids, organic acids and carbohydrates were observed in the serum of fatigued mice, which were reversed by YGJ treatment while biochemical indexes returned to normal. These metabolic changes suggest that the antifatigue effect of YGJ is associated with the impairement of amino acid, organic acids and carbohydrates. It also appears that YGJ can induce significant metabolic alterations independent of the exhausting swimming-induced metabolic changes. The significantly altered metabolites induced by YGJ intervention include l-2-amino-acetoacetate, taurine, fumaric acid, malic acid, oxoadipic acid and l-aspartate, all of which are associated with antifatigue properties. This suggests that YGJ exerts chemopreventive effects via antifatigue mechanisms.

Synergistic production of 20(S)-protopanaxadiol from protopanaxadiol-type ginsenosides by \u03b2-glycosidases from Dictyoglomus turgidum and Caldicellulosiruptor bescii

20(S)-Protopanaxadiol (APPD) has potential uses in the pharmaceutical, cosmetic, and food industries because of its anti-stress, anti-fatigue, anti-cancer, anti-inflammatory, and anti-wrinkle properties. However, APPD production is difficult because β-glycosidases that convert the protopanaxadiol (PPD)-type ginsenoside compound K to APPD are rare. β-Glycosidase from Dictyoglomus turgidum (DT-bgl) has the highest specific activity for converting compound K to APPD, but exhibits no activity towards the α-l-arabinopyranoside moiety in compound Y. Therefore, β-glycosidase from Caldicellulosiruptor bescii (CB-bgl), which has a strong α-l-arabinopyranosidase activity, was used along with DT-bgl. The volumetric and specific productivities of the two-enzyme system for APPD using ginseng root extract were 38.4- and 38.7-fold higher, respectively, than those of β-glycosidase from Pyrococcus furiosus, which had the highest volumetric productivity previously reported, at the same enzyme and substrate concentrations. Thus, DT-bgl combined with CB-bgl completely converted PPD-type ginsenosides to APPD with the highest volumetric and specific productivities reported thus far.

20(S)-protopanaxadiol (PPD) alleviates scopolamine-induced memory impairment via regulation of cholinergic and antioxidant systems, and expression of Egr-1, c-Fos and c-Jun in mice

20(S)-protopanaxadiol (PPD) possesses various biological properties, including anti-inflammatory, antitumor and anti-fatigue properties. Recent studies found that PPD functioned as a neurotrophic agent to ameliorate the sensory deficit caused by glutamate-induced excitotoxicity through its antioxidant effects and exhibited strong antidepressant-like effects in vivo. The objective of the present study was first to investigate the effect of PPD in scopolamine (SCOP)-induced memory deficit in mice and the potential mechanisms involved. In this study, mice were pretreated with PPD (20 and 40 μmol/kg) and donepezil (1.6 mg/kg) intraperitoneally (i.p) for 14 days. Then, open field test was used to assess the effect of PPD on the locomotor activity and mice were daily injected with SCOP (0.75 mg/kg) to induce cognitive deficits and then subjected to behavioral tests by object location recognition (OLR) experiment and Morris water maze (MWM) task. The cholinergic system function, oxidative stress biomarkers and protein expression of Egr-1, c-Fos, and c-Jun in mouse hippocampus were examined. PPD was found to significantly improve the performance of amnesia mice in OLR and MWM tests. PPD regulated cholinergic function by inhibiting SCOP-induced elevation of acetylcholinesterase (AChE) activity, decline of choline acetyltransferase (ChAT) activity and decrease of acetylcholine (Ach) level. PPD suppressed oxidative stress by increasing activities of antioxidant enzymes such as superoxide dismutase (SOD) and lowering maleic diadehyde (MDA) level. Additionally, PPD significantly elevated the expression of Egr-1, c-Fos, and c-Jun in hippocampus at protein level. Taken together, all these results suggested that 20(S)-protopanaxadiol (PPD) may be a candidate compound for the prevention against memory loss in some neurodegenerative diseases such as Alzheimer's disease (AD).

Experimental investigation on low cycle fatigue properties of GH3536 alloy with film cooling holes in different drilling processes

Abstract Low cycle fatigue tests were carried out on thin-walled flat specimens with 14 inclined film cooling holes, using tension cycling under stress control conditions (stress ratio R = 0.1) at 850 °C. The specimen material is GH3536, a kind of Cr and Mo solid solution strengthened with high iron content of nickel-based superalloy, and the film cooling holes were fabricated by forming EDM and high-speed EDM. Comparative analysis of the differences between fatigue life and microscopic fracture morphology were conducted due to the different drilling processes. It is shown that under the same test condition, the average fatigue life of forming EDM specimens and high-speed EDM specimens reach 27 h and 20 h respectively. In other words, the former has better anti-fatigue property. Scanning electron microscope (SEM) analysis of the fracture revealed that the crack initiated from the film cooling holes and all of the fractures were oxidized seriously. However, more crack sources and tiny processing cracks were found in high speed EDM drilling specimens than in the forming EDM ones. Finite element analysis indicates that the existence of film cooling holes causes significant stress concentration.

Optimization of Mixing Ratio to Improve Antioxidant Activity of Aged Garlic with Pine Needle Using Response Surface Methodology.

Aged garlic has been reported to possess beneficial pharmacological activities, including anti-stress and anti-fatigue properties, and to exert protective effects on the cardiovascular system and liver. Pine needles are widely used in folk medicine and as food additives owing to their pharmacological properties such as anti-aging and anti-inflammatory effects. It has long been known that combining certain phytochemicals with other phenols or organic acids can produce synergistic effects. Therefore, the purpose of this study was to develop an optimal formula of aged garlic with added pine needle powder for improved antioxidant activity using the statistical technique of response surface methodology. The antioxidant activities of aged garlic mixed with pine needle powder were confirmed by measuring oxygen radical absorbance capacity and total polyphenol content. An optimized antioxidant formula was identified that contained 5.08 g aged garlic and 1.97 g pine needle powder. The antioxidant activities of the mixture prepared using this optimal formula were significantly higher than the predicted values according to an additive model. Hence, this study confirms that the addition of pine needle powder to aged garlic can improve its antioxidant activity. This study demonstrated an optimal mixing ratio to produce an aged garlic product with improved functionality through the addition of pine needle powder that could be successfully employed by the food industry to prepare functional foods.

Geometry distortion and residual stress of alternate double-sided laser peening of thin section component

Laser peening of components with thin section is of great concern in industry to improve anti-fatigue properties. This study proposes alternate double-sided laser peening (ADLP) as an optional way for the surface treatment of thin section component to overcome the risk of internal spallation and facility cost in simultaneous double-sided laser peening (SDLP). Experiments are conducted on the special-designed samples with thin section to investigate the distortion behavior and residual stress under laser peening of both sides sequentially. Numerical model are developed to analyze the generation and recover of geometry distortion for ADLP process. The results shows that the geometry distortion after single-sided laser peening is observed to be sensitive to laser pulse energy to generate different profile directions. The feasibility of ADSP is proved for the treatment of thin section with distortion control because the second laser peening on the other side of thin section can eliminate the distortion. The generation of different distortion behaviors is found to be closely related to the plastic strain field generated by the transmission of shock-induced stress wave across the thickness section. The numerical simulation shows that a symmetric tensile plastic strain field in plane section is generated across the thickness section for each laser pulse energy after completing laser peening on both sides. Furthermore, both experiments and model prediction propose that compressive residual stress is induced on both sides of thin section by ADLP process, which ensures the ADLP process effective for the treatment of thin section.

Study on the effects of brightness contrast on steady-state motion visual evoked potential.

Traditional steady - state visual evoked potential (SSVEP) using light flicker stimulation may easy cause visual fatigue with a consequent reduction of recognition accuracy. In the previous study, we proposed a steady - state motion visual evoked potential (SSMVEP) brain - computer interface (BCI) method. A black - white ring - shaped checkerboard was used as the visual stimulus paradigm in this study. The movement patterns of the checkerboard included contraction and expansion. Based on the signal-to-noise ratio (SNR), recognition accuracy and anti-fatigue properties, the effects of black-white brightness contrast on the brain response were investigated. Experimental results indicated that when the contrast ratio was the highest, it could obtain higher recognition accuracy and SNR, yet it was easy to cause visual fatigue. When the contrast was the lowest, the sensitivity of the eyes against flicker reduced to the lowest, and it could reduce visual fatigue. However the recognition accuracy and SNR were low. In contrast, the appropriate contrast could guarantee high SNR and recognition accuracy, and as much as possible to reduce the visual fatigue.

A Self-Healing Cellulose Nanocrystal-Poly(ethylene glycol) Nanocomposite Hydrogel via Diels–Alder Click Reaction

Self-healing hydrogels are particularly desirable for increased safety and functional lifetimes because of stress-induced deformation and propagation of cracks. In this paper, we report a tough, highly resilient, fast self-recoverable, and self-healing nanocomposite hydrogel, which builds an interpenetrated network encapsulating rod-like cellulose nanocrystals (CNCs) by flexible polymer chains of poly(ethylene glycol) (PEG). A thermally reversible covalent Diels–Alder click reaction between furyl-modified CNCs and maleimide-end-functionalized PEG was confirmed by Fourier transform infrared spectroscopy. Uniaxial tensile tests and unconfined compression tests displayed outstanding mechanical properties of the hydrogels with a high fracture elongation up to 690% and a fracture strength up to 0.3 MPa at a strain of 90%. Cyclic loading–unloading tests showed excellent self-recovery and antifatigue properties of the nanocomposite hydrogels. The self-healing capability of nanocomposite hydrogels assessed by ten...

Study on the optimum rice husk ash content added in asphalt binder and its modification with bio-oil

By-products and waste materials have become the main cause of environment contamination. In this study, Rice Husk Ash (RHA) was used as modifier to improve the high temperature property of asphalt binder. Bio-oil (BO) was selected as viscosity reducer to enhance the low-temperature and anti-fatigue properties of RHA Modified Asphalt (RHA-MA). Physical and rheological indexes were measured to determine the optimal RHA and BO content. The Scanning Electron Micrographs (SEM) and Energy Dispersive Spectrometer (EDS) analysis were adopted to reveal the modification mechanism of RHA and BO. Results show that RHA-MA possessed desirable high-temperature but unsatisfactory low-temperature performance compared with base asphalt and Limestone Filler Mixed Asphalt (LA). However, asphalt binder with 1% RHA and 20% BO (RB-MA) obtained ductility (15°C) nearly 50% higher and loss modulus approximately 20% lower than those of RHA-MA. Meanwhile, the softening point is 4.2°C more and G∗/Sinδ at all temperatures is higher than those of BO Modified Asphalt (BA). Furthermore, SEM observation illustrates that BO is able to reduce RHA agglomeration and increase the uniformity of RHA-MA mix system, contributing greatly to the excellent comprehensive performance of RB-MA. Consequently, the joint modification of base asphalt with RHA and BO could obtain desirable high temperature, low temperature and anti-fatigue performance. Therefore, it is likely that the development of RB-MA could be helpful to make conventional asphalt qualified for complex service ambient, as well as improve the recycling rate of agricultural waste to reduce environmental pollution and reduce the life cycle cost of asphalt pavement.

Electrospun gelatin nanofiber based self-powered bio-e-skin for health care monitoring

Progress on smart self-powered electronic skin (e-skin) presents unique opportunities to detect and discriminate static human physiological signals and dynamic tactile stimuli. Nevertheless, development of piezoelectric materials possessing adequate flexibility, light weight, ease of large-area processing, low cost and environmental safety are attractive but remains a challenging choice for next-generation pressure/force sensors and mechanical energy harvesters. Here, we design a wearable bio-inspired piezoelectric pressure sensor (i.e., bio-e-skin) from structurally stable fish gelatin nanofibers (GNFs) using large area compatible electrospining technology. Owing to superior mechanosensitivity (~0.8VkPa−1), the bio-e-skin can mimic spatiotemporal human perception and monitors real-time human physiological signals in non-invasive rational strategy. More importantly, nanoscale ferro– and piezo–electricity (d33~−20pm/V) in GNFs, realized by piezoresponse force microscopy allow the bio-e-skin to be self-powered with excellent operational stability (over 108,000 cycles) and anti-fatigue (over 6 months) properties which solve the complication of external power supply for pressure sensing applications.

Design of a Rubbery Carboxymethyl Cellulose/Polyacrylic Acid Hydrogel via Visible-Light-Triggered Polymerization

Hydrogels, as soft and wet materials, have attracted great attention in the field of functional biomaterials. Most recently, the designed hydrogels, according to the energy dissipation principle, overcome the low mechanical strength, poor toughness, and limited recoverability of common hydrogels and show excellent mechanical properties. However, most of these novel designed hydrogels are lacking of instantaneous recovery and antifatigue properties. In this study, a mesoscopic inhomogeneous hydrogel consisting of carboxymethyl cellulose and poly acrylic acid is synthesized through a facile, one-pot, visible-light-triggered polymerization. The prepared hydrogel can be stretched over 700% with fracture strength as high as 850 kPa, and shows a high elastic modulus (180 kPa). The microgel aggregated structure endows an efficient energy dissipation mechanism to the hydrogel. After the internal network structure stabilizing, the hydrogel exhibits a recovery time within 10 ms and over 92% resilience during impact and cyclic tensile tests, respectively. The hydrogel with such excellent mechanical properties can extend its application in biomaterial fields.

Altered expression of TRAIL on mouse T cells via ERK phosphorylation by Rhodiola rosea L. and its marker compounds

Rhodiola rosea L. extracts have shown neuroprotective, anti-fatigue, anti-inflammatory and anti-tumor properties. However, the studies on their effect on T cell function are rather scarce. We examined the potential of R. rosea extract and its major constituents – salidroside, rosarin, rosavin and rosin to alter cell growth of human Jurkat T cells, apoptosis of splenic mouse CD3 T cells and expression of the surface markers and phosphorylation of extracellular signal-regulated kinase (ERK). The initial screening for cell viability in Jurkat T cells and for apoptosis of mouse T cells showed the strongest activity for rosavin and rosarin. Rosarin and rosavin did not alter significantly the dynamic of CD69 expression upon stimulation, but altered TNF-related apoptosis-inducing ligand (TRAIL) expression. Rosavin inhibited TRAIL up-regulation, while rosarin showed an opposite effect. Indeed, rosarin increased the frequencies of CD3+TRAIL+ T cells and the fold inhibition of ERK phosphorylation. Our data showed that different effects of rosarin and rosavin on TRAIL expression can involve distinct action on ERK signaling and hence highlighted their potential to manipulate TRAIL as a tool to rescue the resistance to apoptosis in autoimmune diseases and cancer.

Structural control and biomechanical tremor suppression: Comparison between different types of passive absorber

Active and semi-active control devices can be used as advanced and accurate controllers to reduce the undesired vibration of a structure. However, some of these controllers may have a complex design, especially for systems excited with multi-degree-of-freedom frequencies, which demand the use of high anti-fatigue material properties, and others that may require a large power source. So, improvements in the design of passive controllers are of high interest for researchers. These controllers have a very simple design and aim to counteract vibration with no power requirements. In this paper, six different passive controllers were designed to analyze and compare their performance. The performance is considered in terms of the percentage of reduction in the primary system’s displacement amplitude and the bandwidth of each designed passive controller. The system of interest is taken as the three-degree-of-freedom dynamic hand system reflecting the behavior of Parkinsonian patients. Four joint muscles operating at two resonance harmonic excitation frequencies are considered to produce movements. Each controller was attached to the forearm of the hand set in the horizontal plane to analyze their capability in reducing the rest tremor (3–7 Hz) at the proximal joint. The dual series elastic–viscous absorber is shown to be a very effective controller. It is formed from a series connection between an elastic absorber (mass–spring) and a viscous absorber (mass–dashpot). It causes about 80% reduction in tremor amplitude with 4 Hz wide frequency band at the shoulder, elbow and wrist joints. This range of operational frequency is close to that of healthy cases, 4.5 Hz.

Hydraulic hydrogel actuators and robots optically and sonically camouflaged in water

Sea animals such as leptocephali develop tissues and organs composed of active transparent hydrogels to achieve agile motions and natural camouflage in water. Hydrogel-based actuators that can imitate the capabilities of leptocephali will enable new applications in diverse fields. However, existing hydrogel actuators, mostly osmotic-driven, are intrinsically low-speed and/or low-force; and their camouflage capabilities have not been explored. Here we show that hydraulic actuations of hydrogels with designed structures and properties can give soft actuators and robots that are high-speed, high-force, and optically and sonically camouflaged in water. The hydrogel actuators and robots can maintain their robustness and functionality over multiple cycles of actuations, owing to the anti-fatigue property of the hydrogel under moderate stresses. We further demonstrate that the agile and transparent hydrogel actuators and robots perform extraordinary functions including swimming, kicking rubber-balls and even catching a live fish in water.