Helical structures are ubiquitous in nature and impart unique mechanical properties and multifunctionality
. So far, synthetic architectures that mimic these natural systems have been fabricated by ...winding, twisting and braiding of individual filaments
, microfluidics
, self-shaping
and printing methods
. However, those fabrication methods are unable to simultaneously create and pattern multimaterial, helically architected filaments with subvoxel control in arbitrary two-dimensional (2D) and three-dimensional (3D) motifs from a broad range of materials. Towards this goal, both multimaterial
and rotational
3D printing of architected filaments have recently been reported; however, the integration of these two capabilities has yet to be realized. Here we report a rotational multimaterial 3D printing (RM-3DP) platform that enables subvoxel control over the local orientation of azimuthally heterogeneous architected filaments. By continuously rotating a multimaterial nozzle with a controlled ratio of angular-to-translational velocity, we have created helical filaments with programmable helix angle, layer thickness and interfacial area between several materials within a given cylindrical voxel. Using this integrated method, we have fabricated functional artificial muscles composed of helical dielectric elastomer actuators with high fidelity and individually addressable conductive helical channels embedded within a dielectric elastomer matrix. We have also fabricated hierarchical lattices comprising architected helical struts containing stiff springs within a compliant matrix. Our additive-manufacturing platform opens new avenues to generating multifunctional architected matter in bioinspired motifs.
Purpose We ascertained the feasibility and safety of image guided targeted photothermal focal therapy for localized prostate cancer. Materials and Methods Twelve patients with biopsy proven low risk ...prostate cancer underwent interstitial photothermal ablation of the cancer. The area of interest was confirmed and targeted using magnetic resonance imaging. Three-dimensional ultrasound was used to guide a laser to the magnetic resonance to ultrasound fused area of interest. Target ablation was monitored using thermal sensors and real-time Definity® contrast enhanced ultrasound. Followup was performed with a combination of magnetic resonance imaging and prostate biopsy. Validated quality of life questionnaires were used to assess the effect on voiding symptoms and erectile function, and adverse events were solicited and recorded. Results Interstitial photothermal focal therapy was technically feasible to perform. Of the patients 75% were discharged home free from catheter the same day with the remainder discharged home the following day. The treatment created an identifiable hypovascular defect which coincided with the targeted prostatic lesion. There were no perioperative complications and minimal morbidity. All patients who were potent before the procedure maintained potency after the procedure. Continence levels were not compromised. Based on multicore total prostate biopsy at 6 months 67% of patients were free of tumor in the targeted area and 50% were free of disease. Conclusions Image guided focal photothermal ablation of low risk and low volume prostate cancer is feasible. Early clinical, histological and magnetic resonance imaging responses suggest that the targeted region can be ablated with minimal adverse effects. It may represent an alternate treatment approach to observation or delayed standard therapy in carefully selected patients. Further trials are required to demonstrate the effectiveness of this treatment concept.
Composite beam theory was previously developed to establish an analytical solution for determining the transfer length of prestressed fiber-reinforced polymers (FRP) tendons in pretensioned concrete ...members. In the present study, a novel finite element (FE) modeling approach is proposed to provide further verification of the developed analytical method. The present FE model takes into account the friction coefficients obtained from pull-out tests on the FRP tendons and prestressed concrete members. Convergence analysis of two numerical simulations with different mesh densities is carried out as well. The results demonstrated that the transfer length predicted by the fine FE model with a friction coefficient of α = 0.3 for high pretension is in good agreement with the measured values and the analytical solutions. The consistency between the analytical solution and FE simulation not only further proves the reliability of composite beam theory but also demonstrates the importance of the bond–slip relationship in predicting the transfer length of pretensioned concrete members prestressed with FRP tendons.
Sudden myocardial ischaemia causes an acute coronary syndrome. In the case of ST-elevation myocardial infarction (STEMI), this is usually caused by the acute rupture of atherosclerotic plaque and ...obstruction of a coronary artery. Timely restoration of blood flow can reduce infarct size, but ischaemic regions of myocardium remain in up to two-thirds of patients due to microvascular obstruction (MVO). Experimentally, cardioprotective strategies can limit infarct size, but these are primarily intended to target reperfusion injury. Here, we address the question of whether it is possible to specifically prevent ischaemic injury, for example in models of chronic coronary artery occlusion. Two main types of intervention are identified: those that preserve ATP levels by reducing myocardial oxygen consumption, (e.g. hypothermia; cardiac unloading; a reduction in heart rate or contractility; or ischaemic preconditioning), and those that increase myocardial oxygen/blood supply (e.g. collateral vessel dilation). An important consideration in these studies is the method used to assess infarct size, which is not straightforward in the absence of reperfusion. After several hours, most of the ischaemic area is likely to become infarcted, unless it is supplied by pre-formed collateral vessels. Therefore, therapies that stimulate the formation of new collaterals can potentially limit injury during subsequent exposure to ischaemia. After a prolonged period of ischaemia, the heart undergoes a remodelling process. Interventions, such as those targeting inflammation, may prevent adverse remodelling. Finally, harnessing of the endogenous process of myocardial regeneration has the potential to restore cardiomyocytes lost during infarction.
Confined liquid crystals (LC) provide a unique platform for technological applications and for the study of LC properties, such as bulk elasticity, surface anchoring, and topological defects. In this ...work, lyotropic chromonic liquid crystals (LCLCs) are confined in spherical droplets, and their director configurations are investigated as a function of mesogen concentration using bright-field and polarized optical microscopy. Because of the unusually small twist elastic modulus of the nematic phase of LCLCs, droplets of this phase exhibit a twisted bipolar configuration with remarkably large chiral symmetry breaking. Further, the hexagonal ordering of columns and the resultant strong suppression of twist and splay but not bend deformation in the columnar phase, cause droplets of this phase to adopt a concentric director configuration around a central bend disclination line and, at sufficiently high mesogen concentration, to exhibit surface faceting. Observations of director configurations are consistent with Jones matrix calculations and are understood theoretically to be a result of the giant elastic anisotropy of LCLCs.
Soft robotics may enable many new technologies in which humans and robots physically interact, yet the necessary high-performance soft actuators still do not exist. The optimal soft actuators need to ...be fast and forceful and have programmable shape changes. Furthermore, they should be energy efficient for untethered applications and easy to fabricate. Here, we combine desirable characteristics from two distinct active material systems: fast and highly efficient actuation from dielectric elastomers and directed shape programmability from liquid crystal elastomers. Via a top-down photoalignment method, we program molecular alignment and localized giant elastic anisotropy into the liquid crystal elastomers. The linearly actuated liquid crystal elastomer monoliths achieve strain rates over 120% per second with an energy conversion efficiency of 20% while moving loads over 700 times the elastomer weight. The electric actuation mechanism offers unprecedented opportunities toward miniaturization with shape programmability, efficiency, and more degrees of freedom for applications in soft robotics and beyond.
Indonesia is Southeast Asia's largest economy and freest democracy yet vested interests and local politics serve as formidable obstacles to infrastructure reform. In this critical analysis of the ...politics inhibiting infrastructure investment, Jamie S. Davidson utilizes evidence from his research, press reports and rarely used consultancy studies to challenge mainstream explanations for low investment rates and the sluggish adoption of liberalizing reforms. He argues that obstacles have less to do with weak formal institutions and low fiscal capacities of the state than with entrenched, rent-seeking interests, misaligned central-local government relations, and state-society struggles over land. Using a political-sociological approach, Davidson demonstrates that 'getting the politics right' matters as much as getting the prices right or putting the proper institutional safeguards in place for infrastructure development. This innovative account and its conclusions will be of interest to students and scholars of Southeast Asia and policymakers of infrastructure investment and economic growth.
The Hatter Cardiovascular Institute biennial workshop, originally scheduled for April 2020 but postponed for 2 years due to the Covid pandemic, was organised to debate and discuss the future of ...Remote Ischaemic Conditioning (RIC). This evolved from the large multicentre CONDI-2–ERIC–PPCI outcome study which demonstrated no additional benefit when using RIC in the setting of ST-elevation myocardial infarction (STEMI). The workshop discussed how conditioning has led to a significant and fundamental understanding of the mechanisms preventing cell death following ischaemia and reperfusion, and the key target cyto-protective pathways recruited by protective interventions, such as RIC. However, the obvious need to translate this protection to the clinical setting has not materialised largely due to the disconnect between preclinical and clinical studies. Discussion points included how to adapt preclinical animal studies to mirror the patient presenting with an acute myocardial infarction, as well as how to refine patient selection in clinical studies to account for co-morbidities and ongoing therapy. These latter scenarios can modify cytoprotective signalling and need to be taken into account to allow for a more robust outcome when powered appropriately. The workshop also discussed the potential for RIC in other disease settings including ischaemic stroke, cardio-oncology and COVID-19. The workshop, therefore, put forward specific classifications which could help identify so-called responders vs. non-responders in both the preclinical and clinical settings.
Many emerging applications, such as water-based electronic devices and biological sensors, require local control of anisotropic properties. Lyotropic chromonic liquid crystals (LCLCs) are an exciting ...class of materials, which are usually biocompatible and provide uniaxial anisotropy through a director field but, to date, remain difficult to control. In this work, we introduce a simple strategy to realize an arbitrary orientation of LCLCs director field in two dimensions (2D). Our alignment strategy relies on surface topographical micro/nanostructures fabricated by two-photon laser writing. We show that the alignment of LCLCs can be: (a) precisely controlled with a remarkable pixel resolution of 2.5 μm and (b) patterned into an arbitrary 2D alignment (e.g., +2 topological defect) by a pixelated design and arrangement of micro/nanostructures. Using a similar strategy, we achieve a patternable homeotropic alignment of LCLCs with nanopillars. Finally, we demonstrate that a self-assembled three-dimensional alignment of LCLCs can be obtained due to the versatility of our alignment strategy. Our demonstration of LCLC director field control, which is not only straightforward to achieve but also compatible with other conventional micro/nanofabrication techniques, will provide new opportunities for the manufacturing of LC-based electronic and biological devices.
Equilibrium or regime models based on a single formative (channel‐forming) discharge have been instrumental in developing a quantitative understanding of river channel dynamics. However, alternative ...paradigms can be used to ask fundamentally different questions about river channel behavior. In this paper, we present the Stochastic Channel Simulator (STOCHASIM), a simple biogeomorphic model that models the interplay between erosion and vegetation encroachment through changes in channel geometry. Results for a range of flood distributions are compared to predictions from a similar model based upon a traditional regime approach. Flood variability strongly influences the mean channel geometry and channel stability; the regime model and the stochastic model predict the same channel width when flow variability is low but diverge as flow variability increases. The return period of the formative flow required to match the geometry generated by a traditional regime approach increases systematically, from about 2 years for flow regimes in humid regions to nearly 8 years for more variable flow regimes, like those typical of arid regions. While the traditional regime approach provides a reasonable simplification for streams with little variability in the flood distribution, stochastic modeling may provide more realistic estimates of channel size as flood variability increases (e.g., in arid streams or small watersheds). The success of STOCHASIM in replicating realistic patterns of erosion, as well as the historical contingency often observed in natural streams, suggests that adopting a stochastic dynamics paradigm could advance geomorphology, just as it has done in hydrology, ecology, and other natural sciences.
Key Points
Unlike traditional deterministic models, stochastic models can be used to explore the effects of variability in key governing parameters
Streams with higher variability in year‐to‐year flood size have higher rates of bank erosion and a wider average channel geometry
Traditional regime models are likely to underpredict the width of streams with high flow variability and fail to characterize bank erosion
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