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Volume conservation during plastic deformation is the most important feature and should be realized in elastoplastic theories. However, it is found in this paper that an elastoplastic theory is not volume conserved if it improperly sets an arbitrary plastic strain rate tensor to be deviatoric. We discuss how to rigorously realize volume conservation in finite strain regime, especially when the unloading stress free configuration is not adopted in the elastoplastic theories. An accurate condition of volume conservation is first clarified and used in this paper that the density of a volume element after the applied loads are completely removed should be identical to that of the initial stress free states. For the elastoplastic theories that adopt the unloading stress free configuration (i.e., the intermediate configuration), the accurate condition of volume conservation is satisfied only if specific definitions of the plastic strain rate are used among many other different definitions. For the elastoplastic theories that do not adopt the unloading stress free configuration, it is even more difficult to realize volume conservation as the information of the stress free configuration lacks. To find a universal approach of realizing volume conservation for elastoplastic theories whether or not adopt the unloading stress free configuration, we propose a single assumption that the density of material only depends on the trace of the Cauchy stress by using their objectivities. Two strategies are further discussed to satisfy the accurate condition of volume conservation: directly and slightly revising the tangential stiffness tensor or using a properly chosen stress/strain measure and elastic compliance tensor. They are implemented into existing elastoplastic theories, and the volume conservation is demonstrated by both theoretical proof and numerical examples. The potential application of the proposed theories is a better simulation of manufacture process such as metal forming. [ABSTRACT FROM AUTHOR]

Early-stage organ transplant rejection can be difficult to detect. Percutaneous biopsies occur infrequently and are risky, and measuring biomarker levels in blood can lead to false-negative and -positive outcomes. We developed an implantable bioelectronic system capable of continuous, real-time, long-term monitoring of the local temperature and thermal conductivity of a kidney for detecting inflammatory processes associated with graft rejection, as demonstrated in rat models. The system detects ultradian rhythms, disruption of the circadian cycle, and/or a rise in kidney temperature. These provide warning signs of acute kidney transplant rejection that precede changes in blood serum creatinine/urea nitrogen by 2 to 3 weeks and approximately 3 days for cases of discontinued and absent administration of immunosuppressive therapy, respectively. [ABSTRACT FROM AUTHOR]

Tissue-on-chip systems represent promising platforms for monitoring and controlling tissue functions in vitro for various purposes in biomedical research. The two-dimensional (2D) layouts of these constructs constrain the types of interactions that can be studied and limit their relevance to three-dimensional (3D) tissues. The development of 3D electronic scaffolds and microphysiological devices with geometries and functions tailored to realistic 3D tissues has the potential to create important possibilities in advanced sensing and control. This study presents classes of compliant 3D frameworks that incorporate microscale strain sensors for high-sensitivity measurements of contractile forces of engineered optogenetic muscle tissue rings, supported by quantitative simulations. Compared with traditional approaches based on optical microscopy, these 3D mechanical frameworks and sensing systems can measure not only motions but also contractile forces with high accuracy and high temporal resolution. Results of active tension force measurements of engineered muscle rings under different stimulation conditions in long-term monitoring settings for over 5 wk and in response to various chemical and drug doses demonstrate the utility of such platforms in sensing and modulation of muscle and other tissues. Possibilities for applications range from drug screening and disease modeling to biohybrid robotic engineering. [ABSTRACT FROM AUTHOR]

The article focuses on strategies in assembly and heterogeneous materials integration as routes to complex and piezoelectric thin-film actuators for vibratory excitation and precise control. It mentions approach combines transfer printing as a scheme formaterials integration with structural buckling as a means for 2D-to-3D geometric transformation. It also mentions selective excitation of targeted vibrational modes for simultaneous measurements of viscosity and density of surrounding fluids.

The article presents a study, which suggests an automated wrap-like transfer printing prototype to address the challenges associated with three-dimensional (3D) curvy electronics. The prototype uses a petal-like stamp with prefabricated planar circuits that are integrated onto the target surface with full coverage, assisted by a gentle and uniform pressure field.

The real-time characterization of thin film properties can provide insights into the behavior of film material during process such as phase-transition, hydration, and chemical reaction. The shift of reasonant frequency in structural vibration serves as the basis of an effective approach to determine film properties, but encounters the difficulty that multiple to-be-determined quantites (e.g., film modulus and density) are often related to the resonant frequency simultaneously and therefore cannot be determined by a structure with fixed shape and vibration mode. Determinsitic mechanical buckling provides an effective route for the vibrational structure to rapidly switch between designed shapes and vibration modes. Here, we adopt a ribbon structure in the flat state and buckled state to yield two distinct vibration modes. Theoretical models of the natural frequencies are established for first-order out-of-plane modes of the ribbon with patterned thin films in these two states, respectively. The model suggests that with optimized film pattern the sensitivity of the natural frequencies to the film modulus and density can be partially decoupled. The results lead to a simple and effective method based on tunable vibration to characterize the thin film modulus and density at small scale. [ABSTRACT FROM AUTHOR]

Traditional methods to measure blood pressure are intermittent and may fail to detect the critical blood pressure fluctuations. Continuous blood pressure monitoring offers important clinical value in predicting cardiovascular diseases. Invasive (i.e., artery cannulation) and noninvasive approaches (e.g., volume clamping, pressure sensor, ultrasound, and optical methods) have limitations that prevent their generalized use outside of controlled settings, and few account properly for changes in the properties of the arteries (e.g., after drug administration, aging). This article proposes a method that combines a skin-interfaced pressure sensor with a sensor of pulse wave velocity, to continuously, noninvasively, and accurately measure the blood pressure, in ways that eliminate drifts and other artifacts that can prevent accurate, longitudinal monitoring. A scaling law is established to show that, for a linearly proportional relationship between the blood pressure and sensor pressure, the coefficient of proportionality depends on the elastic moduli Eartery and Etissue of the artery and tissue, respectively, and the artery thickness hartery and radius Rartery via a single, dimensionless combination, Earteryhartery/(EtissueRartery), i.e., the normalized artery stiffness. This scheme determines the blood pressure in a manner that explicitly accounts for changes in the artery elastic modulus and thickness (e.g., due to the administration of drugs, aging). [ABSTRACT FROM AUTHOR]

The article presents a research report on complex three dimensional (3D) microfluidic architectures formed by mechanically guided compressive buckling. Topics include microfluidic technologies have wide-ranging applications in chemical analysis systems, drug delivery platforms, and artificial vascular networks; and transport essential water and biochemical species to and from volumes of living tissue through a combination of pumped fluid flow and diffusive processes.

Traditional methods to measure blood pressure are intermittent and may fail to detect the critical blood pressure fluctuations. Continuous blood pressure monitoring offers important clinical value in predicting cardiovascular diseases. Invasive (i.e., artery cannulation) and noninvasive approaches (e.g., volume clamping, pressure sensor, ultrasound, and optical methods) have limitations that prevent their generalized use outside of controlled settings, and few account properly for changes in the properties of the arteries (e.g., after drug administration, aging). This article proposes a method that combines a skin-interfaced pressure sensor with a sensor of pulse wave velocity, to continuously, noninvasively, and accurately measure the blood pressure, in ways that eliminate drifts and other artifacts that can prevent accurate, longitudinal monitoring. A scaling law is established to show that, for a linearly proportional relationship between the blood pressure and sensor pressure, the coefficient of proportionality depends on the elastic moduli Eartery and Etissue of the artery and tissue, respectively, and the artery thickness hartery and radius Rartery via a single, dimensionless combination, Earteryhartery/(EtissueRartery), i.e., the normalized artery stiffness. This scheme determines the blood pressure in a manner that explicitly accounts for changes in the artery elastic modulus and thickness (e.g., due to the administration of drugs, aging). [ABSTRACT FROM AUTHOR]

Structures that significantly and rapidly change their shapes and sizes upon external stimuli have widespread applications in a diversity of areas. The ability to miniaturize these deployable and morphable structures is essential for applications in fields that require high-spatial resolution or minimal invasiveness, such as biomechanics sensing, surgery, and biopsy. Despite intensive studies on the actuation mechanisms and material/structure strategies, it remains challenging to realize deployable and morphable structures in high-performance inorganic materials at small scales (e.g., several millimeters, comparable to the feature size of many biological tissues). The difficulty in integrating actuation materials increases as the size scales down, and many types of actuation forces become too small compared to the structure rigidity at millimeter scales. Here, we present schemes of electromagnetic actuation and design strategies to overcome this challenge, by exploiting the mechanics-guided three-dimensional (3D) assembly to enable integration of current-carrying metallic or magnetic films into millimeter-scale structures that generate controlled Lorentz forces or magnetic forces under an external magnetic field. Tailored designs guided by quantitative modeling and developed scaling laws allow formation of low-rigidity 3D architectures that deform significantly, reversibly, and rapidly by remotely controlled electromagnetic actuation. Reconfigurable mesostructures with multiple stable states can be also achieved, in which distinct 3D configurations are maintained after removal of the magnetic field. Demonstration of a functional device that combines the deep and shallow sensing for simultaneous measurements of thermal conductivities in bilayer films suggests the promising potential of the proposed strategy toward multimodal sensing of biomedical signals. [ABSTRACT FROM AUTHOR]

The article offers information on Wirelessly controlled, bioresorbable drug delivery device with active valves that exploit electrochemically triggered crevice corrosion. It mentions valves operate through an electrochemical mechanism of geometrically accelerated corrosion induced by passage of electrical current from a wireless, bioresorbable power-harvesting unit.

Three-dimensional (3D) serpentine mesostructures assembled by mechanics-guided, deterministic 3D assembly have potential applications in energy harvesting, mechanical sensing, and soft robotics. One limitation is that the serpentine structures are required to have sufficient bending stiffness such that they can overcome the adhesion with the underlying substrate to fully buckle into the 3D shape (global buckling). This note introduces the use of cellular substrate in place of conventional homogeneous substrate to reduce the adhesion energy and therefore ease the above limitation. A theoretical model based on energetic analysis suggests that cellular substrates significantly enlarge the design space of global buckling. Numerical examples show that the enlarged design space enables 3D serpentine structures with reduced maximum strains and resonant frequencies, which offers more possibilities for their potential applications. [ABSTRACT FROM AUTHOR]

Recently developed methods in mechanically guided assembly provide deterministic access to wide-ranging classes of complex, 3D structures in high-performance functional materials, with characteristic length scales that can range from nanometers to centimeters. These processes exploit stress relaxation in prestretched elastomeric platforms to affect transformation of 2D precursors into 3D shapes by in- and out-of-plane translational displacements. This paper introduces a scheme for introducing local twisting deformations into this process, thereby providing access to 3D mesostructures that have strong, local levels of chirality and other previously inaccessible geometrical features. Here, elastomeric assembly platforms segmented into interconnected, rotatable units generate in-plane torques imposed through bonding sites at engineered locations across the 2D precursors during the process of stress relaxation. Nearly 2 dozen examples illustrate the ideas through a diverse variety of 3D structures, including those with designs inspired by the ancient arts of origami/kirigami and with layouts that can morph into different shapes. A mechanically tunable, multilayered chiral 3D metamaterial configured for operation in the terahertz regime serves as an application example guided by finite-element analysis and electromagnetic modeling. [ABSTRACT FROM AUTHOR]

Vibrational microplatforms that exploit complex three-dimensional (3D) architectures assembled via the controlled compressive buckling technique represent promising candidates in 3D micro-electromechanical systems (MEMS), with a wide range of applications such as oscillators, actuators, energy harvesters, etc. However, the accuracy and efficiency of such 3D MEMS might be significantly reduced by the viscoelastic damping effect that arises from material viscosity. Therefore, a clear understanding and characterization of such effects are essential to progress in this area. Here, we present a study on the viscoelastic damping effect in complex 3D structures via an analytical model and finite element analysis (FEA). By adopting the Kelvin-Voigt model to characterize the material viscoelasticity, an analytical solution is derived for the vibration of a buckled ribbon. This solution then yields a scaling law for the half-band width or the quality factor of vibration that can be extended to other classes of complex 3D structures, as validated by FEA. The scaling law reveals the dependence of the half-band width on the geometries of 3D structures and the compressive strain. The results could serve as guidelines to design novel 3D vibrational microplatforms for applications in MEMS and other areas of technology. [ABSTRACT FROM AUTHOR]

The article presents a study on the use of thermoelectric coils for energy harvesting in the miniaturization of semiconductor devices.

Continuous monitoring of blood pressure, an essential measure of health status, typically requires complex, costly, and invasive techniques that can expose patients to risks of complications. Continuous, cuffless, and noninvasive blood pressure monitoring methods that correlate measured pulse wave velocity (PWV) to the blood pressure via the Moens-Korteweg (MK) and Hughes Equations, offer promising alternatives. The MK Equation, however, involves two assumptions that do not hold for human arteries, and the Hughes Equation is empirical, without any theoretical basis. The results presented here establish a relation between the blood pressure P and PWV that does not rely on the Hughes Equation nor on the assumptions used in the MK Equation. This relation degenerates to the MK Equation under extremely low blood pressures, and it accurately captures the results of in vitro experiments using artificial blood vessels at comparatively high pressures. For human arteries, which are well characterized by the Fung hyperelastic model, a simple formula between P and PWV is established within the range of human blood pressures. This formula is validated by literature data as well as by experiments on human subjects, with applicability in the determination of blood pressure from PWV in continuous, cuffless, and noninvasive blood pressure monitoring systems. [ABSTRACT FROM AUTHOR]

Drought, water loss and soil erosion are the main factors limiting agricultural production in semi-arid regions of China. A field study was conducted to determine (1) the runoff efficiencies of different ridge widths (30, 45 and 60 cm) covered with different materials (common plastic film, biodegradable mulching film and manual compacted soil) and (2) the effects of different ridge–furrow ratios (30:60, 45:60 and 60:60) and ridge-covering materials on soil water storage, topsoil temperature, hay yield, grain yield and water use efficiency (WUE) of oats in ridge–furrow rainwater harvesting (RFRH) system at the Dingxi Agri-meteorological station, during 2 consecutive years of 2012 and 2013. Average runoff efficiency was 18%, 20%, 22%, 71%, 77%, 83%, 76%, 77% and 84% for SR 30 , SR 45 , SR 60 , BMR 30 , BMR 45 , BMR 60 , CMR 30 , CMR 45 and CMR 60 (SR, BMR and CMR were ridges with compacted soil, covered with biodegradable mulch film and common plastic film, respectively, and subscript numbers 30, 45 and 60 stand for ridge widths (cm)) over 2 years, respectively. The field experiment using oats as an indicator crop showed that mulching materials and ridge widths had distinct effects on topsoil temperature on the top of the ridges, but not in the bottom of the furrows. The soil water storage in the 140 cm depth of soil at the bottom of furrows increased with increasing ridge widths and in the order of CMR ≈ BMR > SR > FP (FP was the flat planting). The total precipitation was 414.4 mm in 2012 and 448.8 mm in 2013, which were higher than the average of rainfall (388.1 mm), leading to a significant increase of hay and grain yield in CMR, and an equivalent of hay and grain yield in BMR compared with FP in most cases. In the SR system, the positive effects of rainwater harvesting could not compensate for the negative effects of planting area reduction resulting in decrease in hay and grain yield. Compared with FP, the average grain yield decreased by 19%, 27% and 34% for SR 30 , SR 45 and SR 60 , and increased by 6%, 4%, 1%, 12%, 9% and 6% for BMR 30 , BMR 45 , BMR 60 , CMR 30 , CMR 45 and CMR 60 over 2 years, respectively. The WUE of SR, BMR and CMR was 1.31, 1.41 and 1.47 times greater than that in FP over 2 years, and increased with increasing ridge width. The optimum furrow width was 32–38 cm for CMR and was 30–34 cm for BMR. Future study is needed to investigate the impact of RFRH on crop production, WUE and economic benefit under different precipitations, soil types, slopes and plant species using biodegradable mulching materials. [ABSTRACT FROM AUTHOR]

The dynamic buckling behavior of thin films from substrate is studied in this work. The experimental results show that the buckling morphology of the constantan film lines from the polymer substrate is inconsistent and non-sinusoidal, which is different from the sinusoidal form of the buckling morphology under static loads. The plastic deformation of the film lines results in the non-sinusoidal buckling morphology and residual deformation when unloaded. Finite element modeling results with regard to the plastic dissipation of the constantan film lines reveal that the plastic dissipation suppresses the buckling-driven delaminating under impact loads. This study will give some new perspectives on the buckling behavior of thin film from substrate. [ABSTRACT FROM AUTHOR]

The aim of the present study was to investigate the possible effects of temperature on cadmium (Cd), lead (Pb), copper (Cu) and zinc (Zn) accumulation in five vegetable species collected at different sites (Shuichuan, Beiwan, Dongwan and Wufe) in northwest China. The meteorological data of air and soil temperatures were recorded daily during the period from sowing to harvest for the five vegetables. The air and soil temperatures affected the capacity of pumpkin, cabbage, brassica napus and Chinese cabbage to accumulate Zn, Cd, Cu and Pb. Principal component analysis showed that temperature, photosynthetic and physiological factors all contributed to the soil–plant transfer properties of DTPA-extractable heavy metals. Temperature played a more important role in Cd, Pb, Cu and Zn accumulation in four vegetables in this semiarid area. However, the enormous surface area of spinach was likely to elevate heavy metal loads owing to atmospheric deposits. For most vegetables studied, there was a striking dissimilarity in the uptake and translocation ability of Cd, Zn and Cu in soil, but similar accumulation to translocation for Pb in soil. [ABSTRACT FROM PUBLISHER]