3D-printed hierarchical arrangements of actuators mimicking biological muscular architectures

: Being able to imitate the sophisticated muscular architectures that characterize the animal kingdom in biomimetic machines would allow them to perform articulated movements with the same naturalness. In soft robotics, multiple actuation technologies have been developed to mimic the contraction of a single natural muscle, but a few of them can be implemented in complex architectures capable of diversifying deformations and forces. In this work, we present three different biomimetic muscle architectures, i.e., fusiform, parallel, and bipennate, which are based on hierarchical arrangements of multiple pneumatic actuators. These biomimetic architectures are monolithic structures composed of thirty-six pneumatic actuators each, directly 3D printed through low-cost printers and commercial materials without any assembly phase. The considerable number of actuators involved enabled the adoption and consequent comparison of two regulation strategies: one based on input modulation, commonly adopted in pneumatic systems, and one based on fiber recruitment, mimicking the regulation behavior of natural muscles. The straightforward realization through additive manufacturing processes of muscle architectures regulated by fiber recruitment strategies facilitates the development of articulated muscular systems for biomimetics machines increasingly similar to the natural ones

3D-printed biomimetic artificial muscles using soft actuators that contract and elongate

Biomimetic machines able to integrate with natural and social environments will find ubiquitous applications, from biodiversity conservation to elderly daily care. Although artificial actuators have reached the contraction performances of muscles, the versatility and grace of the movements realized by the complex arrangements of muscles remain largely unmatched. Here, we present a class of pneumatic artificial muscles, named GeometRy-based Actuators that Contract and Elongate (GRACE). The GRACEs consist of a single-material pleated membrane and do not need any strain-limiting elements. They can contract and extend by design, as described by a mathematical model, and can be realized at different dimensional scales and with different materials and mechanical performances, enabling a wide range of lifelike movements. The GRACEs can be fabricated through low-cost additive manufacturing and even built directly within functional devices, such as a pneumatic artificial hand that is fully three-dimensionally printed in one step. This makes the prototyping and fabrication of pneumatic artificial muscle-based devices faster and more straightforward

High Risk of Secondary Infections Following Thrombotic Complications in Patients With COVID-19

Background. This study’s primary aim was to evaluate the impact of thrombotic complications on the development of secondary infections. The secondary aim was to compare the etiology of secondary infections in patients with and without thrombotic complications. Methods. This was a cohort study (NCT04318366) of coronavirus disease 2019 (COVID-19) patients hospitalized at IRCCS San Raffaele Hospital between February 25 and June 30, 2020. Incidence rates (IRs) were calculated by univariable Poisson regression as the number of cases per 1000 person-days of follow-up (PDFU) with 95% confidence intervals. The cumulative incidence functions of secondary infections according to thrombotic complications were compared with Gray’s method accounting for competing risk of death. A multivariable Fine-Gray model was applied to assess factors associated with risk of secondary infections. Results. Overall, 109/904 patients had 176 secondary infections (IR, 10.0; 95% CI, 8.8–11.5; per 1000-PDFU). The IRs of secondary infections among patients with or without thrombotic complications were 15.0 (95% CI, 10.7–21.0) and 9.3 (95% CI, 7.9–11.0) per 1000-PDFU, respectively (P = .017). At multivariable analysis, thrombotic complications were associated with the development of secondary infections (subdistribution hazard ratio, 1.788; 95% CI, 1.018–3.140; P = .043). The etiology of secondary infections was similar in patients with and without thrombotic complications. Conclusions. In patients with COVID-19, thrombotic complications were associated with a high risk of secondary infections

A quasi 2D model for the interpretation of impedance and polarization of a planar solid oxide fuel cell with interconnects

In this work, a one dimensional plus one dimensional (1D+1D) physical model of a high temperature solid oxide fuel cell (HT-SOFC) is presented. The model is distributed-charge and dynamic, and allows to predict polarization curves and impedance spectra of applicative sized planar cells (up to 10 cm x 10 cm) mounted between interconnects with rectangular ducts. The model solves rigorous conservation equations of mass, charge, momentum and energy, along the interconnect channels and within the cell's layers. The kinetic parameters of the hydrogen oxidation reaction and of the oxygen reduction reaction are fitted to a literature dataset measured between 700 °C and 800 °C, with a 20% H2, 5% H2O and 75% N2 mixture, on a standard anode-supported HT-SOFC (Ni-YSZ/YSZ/GDC/LSCF). Once calibrated, the model is used to study the evolution of local impedance spectra along the channel, as well as the occurrence of gradients of temperature, concentration, and current density within and along the cell structure. Remarkable differences emerge between global impedance spectra, based on the average current density extracted from the whole cell's surface, and local impedance spectra, based on the local current density value at each position along the channel. Local spectra reveal very specific features (negative-resistance arcs), which are absent in the average spectra, and which question the opportunity of collecting spatially resolved impedance measurements on a fine scale. The analysis of the steady state behavior highlights the severity of temperature gradients along the channel (150 K at 0.75 V and 50% H2 utilization factor), the onset of current density peaks, and the crucial role of interphase mass transport at the gas/electrode interface. The consequences of external diffusion on the polarization performance are analyzed, and the impact of different channel configurations on the local evolution of the spectra is explored

Embedded sensor/actuator system for aircraft active flow separation control

This work reports on finite element method (FEM) design and fabrication of low cost capacitive pressure sensors for aircraft applications; this work is part of a research activity aimed to develop an embedded sensor - Actuator system composed by multi-measure points pressure sensors for flow turbulence detection and coupled plasma actuators for control of separated flows on aircraft wings structures. The system uses sensors feedback information to provide fast reattachment of boundary layer separation flow on the suction surface of regional aircraft vehicles. Flow separation has great impact on the performance and safety of an aircraft and it can be predicted by quantifying the pressure gradients along the wing wall. Considering the absolute pressure values on a NACA 0012 profile as a function of the angle of attack, high sensitivity measurements of differential pressure can be obtained by positioning the sensor-nodes at points on the airfoil surface where the P/Pstall ratio between the absolute pressure at different angles of attack and the pressure measured in stall condition is maximize

A 18-ms Measurement-Time MLS-Based System for Moisture Assessment in Lubricant Oil

In this article, a system and a measurement approach to reduce the measurement time in the assessment of moisture contamination in lubricant oils is presented. The system's sensing principle leverages the permittivity change of a miniaturized interdigital capacitor (IDC) while immersed in oil. The time-domain impedance concept, that is, the impulse response (IR), is exploited by using maximum length sequences (MLSs) as efficient broadband signals for the sensor's excitation in a wide range of frequencies. Different from conventional impedance spectroscopy (IS), MLS-based measurements are performed with simpler hardware, higher computational efficiency, lower power consumption, and lower measurement time. As a novelty with respect to the state-of-the-art, this article introduces a linear model to relate a single measured quantity from the IR to water concentration in oil. This permits to reduce the digital processing operations, leading to low measurement time and, thus, to low energy-per-measurement parameters with respect to other works which rely on laboratory instrumentation. The validity of the linear model, for the detection of small concentrations of water in lubricant oil, has been verified through experimental measurements. Water-oil samples have been prepared with 0.2 vol%, 0.5 vol%, 1 vol%, 2 vol%, and 3 vol% water concentrations at room temperature, obtaining an estimated limit of detection (LOD) of 6.3 ppm. A low measurement time of 18 ms has been achieved which advances the state-of-the-art