Biomaterials play a critical role in engineering of tissue constructs, working as an artificial extracellular matrix to support regeneration. Because the elastic stretchability is a major mechanical ...property of many tissue types, huge efforts have been invested into the development of elastomeric biomaterials that mimic that of native tissue. Indeed, for the repair of most soft tissue types, one of the major problems encountered by biomaterials scientists has been difficulty in simply replicating this complex elasticity. This article provides a comprehensive review on the elastomeric biomaterials used in tissue engineering. Definitions of biomaterials, biocompatibility and elasticity in the context of tissue engineering are introduced. This is followed by systematic review of thermoplastic rubbers, chemically crosslinked elastomers, elastic proteins and elastomer-based ceramic-filled composites. Each section includes a detailed description of the chemical synthesis of the polymer critical to understanding of its unique properties, followed by discussion of its biocompatibility and biodegradability, two essential features of biomaterials in most tissue engineering applications. The mechanical properties and applications in tissue engineering are then reviewed for each polymer in great detail, with identification of specific challenges for its current and ongoing application in the field. Finally, the major achievements and remaining challenges for elastomeric biomaterials are summarized, with emphasis on the most important candidates to date.
Three-dimensional (3D), highly porous, mechanically competent, bioactive and biodegradable scaffolds have been fabricated for the first time by the replication technique using 45S5 Bioglass
® powder. ...Under an optimum sintering condition (1000
°C/1
h), nearly full densification of the foam struts occurred and fine crystals of Na
2Ca
2Si
3O
9 formed, which conferred the scaffolds the highest possible compressive and flexural strength for this foam structure. Important findings are that the mechanically strong crystalline phase Na
2Ca
2Si
3O
9 can transform into an amorphous calcium phosphate phase after immersion in simulated body fluid for 28 days, and that the transformation kinetics can be tailored through controlling the crystallinity of the sintered 45S5 Bioglass
®. Therefore, the goal of an ideal scaffold that provides good mechanical support temporarily while maintaining bioactivity, and that can biodegrade at later stages at a tailorable rate is achievable with the developed Bioglass
®-based scaffolds.
Myocardial strain is increasingly recognized as an important assessment for myocardial function. In addition, it also improves outcome prediction. However, there is lack of standardization in strain ...evaluation by cardiovascular magnetic resonance (CMR). In this study we compared strain values using multiple techniques and multiple vendor products.
Prospectively recruited patients with cardiomyopathy of diverse etiology (N = 77) and healthy controls (N = 10) underwent CMR on a 1.5 T scanner. Tagging, displacement encoding with stimulated echoes (DENSE) and balanced stead state free precession cine imaging were acquired on all subjects. A single matched mid left ventricular (LV) short axis plane was used for the comparisons of peak circumferential (Ecc) and radial strain (Err) and a 4-chamber view for longitudinal strain (Ell). Tagging images were analyzed using harmonic phase (HARP) and displacement encoding with stimulated echoes (DENSE) images using a proprietary program. Feature tracking (FT) was evaluated using 3 commercially available software from Tomtec Imaging Systems, Cardiac Image Modeller (CIM), and Circle Cardiovascular Imaging. Tagging data were used as reference. Statistic analyses were performed using paired t-test, intraclass correlation coefficient (ICC), Bland Altman limits of agreement and coefficient of variations.
Average LV ejection fraction was 50% (range 32 to 62%). Regional LV wall motion abnormalities were present in 48% of the analyzed planes. The average Ecc was - 13 ± 4%, - 13 ± 4%, - 16 ± 6%, - 10 ± 3% and - 14 ± 4% for tagging, DENSE, Tomtec, CIM and Circle, respectively, with the best agreement seen in DENSE and Circle with tagging. The Err was highly varied with poor agreement across the techniques, 32 ± 24%, 40 ± 28%, 47 ± 26%, 64 ± 33% and 23 ± 9% for tagging, DENSE, Tomtec, CIM and Circle, respectively. The average Ell was - 14 ± 4%, - 8 ± 3%, - 13 ± 5%, - 11 ± 3% and - 12 ± 4% for tagging, DENSE, Tomtec, CIM and Circle, respectively with the best agreement seen in Tomtec and Circle with tagging. In the intra- and inter-observer agreement analysis the reproducibility of each technique was good except for Err by HARP.
Small but important differences are evident in Ecc and Ell comparisons among vendors while large differences are seen in Err assessment. Our findings suggest that CMR strain values are technique and vendor dependent. Hence, it is essential to develop reference standard from each technique and analytical product for clinical use, and to sequentially compare patient data using the same software.
As the front of the northeastward-growth region of the Qinghai-Tibetan Plateau since the Cenozoic, arcuate fold-and-thrust belts are the main features of local tectonic deformation. However, the ...formation mechanism of these arcuate structures is still an open question. We present 3D finite-element models with elasto-plastic rheology to understand the formation-evolution of arcuate folds here comprising real regional fault-zones including the Haiyuan, Xiang Shan–Tianjing Shan, Yantong Shan, and Niushou Shan faults since ∼10 Ma. The reference-model equivalent-plastic-strain (EPS) concentration zones develop outwardly-NE in spatio-temporal sequence, with development geometry and timing in good agreement with the geologic fault-zone structures. Our reference-model-based sensitivity analysis suggest that the horizontal northeastward compression of the region being bounded by a frictional vicinity (rigid Alxa and Ordos blocks hindering the advancement) have the dominant control on the formation and evolution of these arcuate fold-and-thrust belts perpendicular to the contraction axis. In contrast, the likely-small rotations imprinted by the Ordos and Alxa blocks and the minor shearing of the Qinghai–Tibetan Plateau, have only secondary effects. An additional, generic sensitivity analysis reveals that the folds’ horizontal curvature per unit horizontal shortening-displacement increases with the friction on the bounding vicinity, and this result could be considered for other scenarios of Earth and other planets. Historical regional earthquakes of M > 6 are mostly located in the simulated EPS concentration zones: the 1920 Haiyuan and 1709 Zhongwei earthquakes occurred on the Haiyuan and Xiang Shan–Tianjing Shan faults, respectively, well correlated with our model high-EPS concentration zones.
•3D elastoplastic models simulated the arcuate structural belts formation in the NE margin of the Qinghai-Tibetan Plateau.•Tectonic shortening dominates the development of plasticity bands, while rotations and shearing have secondary effects.•A higher frictional coefficient leads to higher curvature of arcuate deformation bands.•EPS concentration zones in the study area are correlated with historical earthquakes, forming a local seismogenic zone.
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•The fact-condition statements and super relation are introduced for geothemic KG construction.•The rule-based multi-input multi-output model is proposed for information ...extraction.•The geothermic KG is automatically built for the first time with the trained R-MIMO.
Researchers utilize information from the geoscience literature to deduce the regional or global geological evolution. Traditionally this process has relied on the labor of researchers. As the number of papers continues to increase, acquiring domain-specific knowledge becomes a heavy burden. Knowledge Graph (KG) is proposed as a new knowledge representation technology to change this situation. However, the super relation is not considered in the previous KG, which bridges the geological phenomenon (fact) and its precondition (condition). For instance, in the statement (“the late Archean was a crucial transition period in the history of global geodynamics”), the condition statement (“crucial transition for global geodynamics”) works as the complementary fact statement (“the late Archean was a crucial transition period”), which defines the scale of crucial transition accurately in the late Archean. In this study, fact-condition statement extraction is introduced to construct a geological knowledge graph. A rule-based multi-input multi-output model (R-MIMO) is proposed for information extraction. In the R-MIMO, fact-condition statements and their super relation are considered and extracted for the first time. To verify its performances, a GeothCF dataset with 1455 fact tuples and 789 condition tuples is constructed. In experiments, the R-MIMO model achieves the best performance by using BERT as encoder and LSTM-d as decoder, achieving F1 80.24% in tuple extraction and F1 70.03% in tag prediction task. Furthermore, the geothermic KG with super relation is automatically constructed for the first time by trained R-MIMO, which can provide structured data for further geothermic research.
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•An ultrathin Ni-Cu alloy foil was prepared by electrodeposition-vacuum sintering method.•The uniform composition can be achieved through mutual diffusion of atoms.•The Kirkendall ...pores can be avoided by controlling the sintering temperature.•The Ni-Cu alloy foil shows superior corrosion resistance compared with Cu foil.
Cost-effective ultrathin alloy foils (<20 μm) are highly expected with the development of electronic industry and micro-system technology. In this paper, electrodeposition combined with vacuum sintering is used to fabricate a Ni-Cu alloy foil with thickness of 12.0 (±0.2) μm. For the ultrathin Ni-Cu alloy foil, a densified structure without pores can be achieved by prolonging sintering duration at 900 ℃ for 3 h. Under the current density of 10 mA cm−2, 700 s is the optimal electrodeposition time to obtain the highest tensile strength (187 MPa) with the Ni content of 41.5 wt.% in the alloy foil. Compared with Cu foil, Ni-Cu alloy foil shows superior corrosion resistance in 3.5 wt.% NaCl solution and also HCl solutions (0.5 mol/L, 1.0 mol/L, 2.0 mol/L), respectively. The uniform composition and defect-free surface, excellent tensile strength and corrosion resistance together exhibits the great application potential of the obtained Ni-Cu alloy foil, which may provide an inspiration for future development of integrated electronic or medical devices.
This article considers finite-time trajectory tracking control problem for robotic manipulators with parameter uncertainties and external disturbances. A finite-time controller that achieves high ...precision and strong robustness is proposed without the requirement of the exact dynamic model. First, a novel finite-time model-assisted extended state observer is designed to compensate the system uncertainties with complex and uncertain dynamics. Then, a composite finite-time controller is developed for trajectory tracking control with the help of finite-time model-assisted extended state observer. Compared to the classic extended state observer, it is proved that the estimation error of finite-time model-assisted extended state observer can be stabilized in finite time. Meanwhile, the finite-time convergence of the closed-loop system with the proposed controller can also be proved through Lyapunov’s stability theory. A variable structure term is employed to compensate the estimation errors of finite-time model-assisted extended state observer. The validity of the control scheme is demonstrated by simulations and experiments.
To improve the interpolation accuracy for the non-uniform rational B-spline (NURBS) curves, this paper proposes a novel bidirectional adaptive feedrate scheduling (BAFS) method based on S-shaped ...acceleration/deceleration (ACC/DEC) algorithm. The NURBS interpolator with the proposed BAFS method is also presented. The BAFS method has two meanings. First, to consider the continuous constraints of feedrate especially in the areas near the endpoints of each NURBS curve segment, an adaptive feedrate scheduling method is designed, which can improve the interpolation accuracy compared with the conventional method only considering the constraints of endpoints. Second, a bidirectional adaptive interpolation strategy including an adaptive task scheduling method and a meeting processing method is proposed to conduct the acceleration and deceleration interpolation stages of each NURBS segment separately in two directions. The two directions interpolation can be realized orderly by the adaptive task scheduling and the smoothness of feedrate profile can be guaranteed by the meeting processing method whose solvability is also proved. Therefore, the feedrate constraints at both the start and end points areas can be considered, which can improve the interpolation accuracy. Meanwhile, the round-off errors caused by cycle sampling are also considered and compensated in the bidirectional feedrate scheduling process to maintain the motion smoothness. In addition, an optimized look-ahead strategy is designed to ensure the correctness of the endpoints feedrate. Finally, a series of simulations and experiments are conducted to validate the good performance and applicability of the proposed method.
In regions with sandy soft soil strata, the subway foundation commonly undergoes freeze–thaw cycles during construction. This study focuses on analyzing the microstructural and fractal ...characteristics of frozen–thawed sandy soft soil to improve our understanding of its strength behavior and stability. Pore size distribution curves before and after freeze–thaw cycles were examined using nuclear magnetic resonance technology. Additionally, fractal theory was applied to illustrate the soil’s fractal properties. The strength properties of frozen remolded clay under varying freezing temperatures and sand contents were investigated through uniaxial compression tests, indicating that soil strength is significantly influenced by fractal dimensions. The findings suggest that lower freezing temperatures lead to a more dispersed soil skeleton, resulting in a higher fractal dimension for the frozen–thawed soil. Likewise, an increase in sand content enlarges the soil pores and the fractal dimension of the frozen–thawed soil. Furthermore, an increase in fractal dimension caused by freezing temperatures results in increased soil strength, while an increase in fractal dimension due to changes in sand content leads to a decrease in soil strength.
Terzaghi proposed two-dimensional (2D) arching theory through trapdoor tests based on the assumption of a vertical slip surfaces. However, the original 2D assumption is different from a real ...three-dimensional (3D) excavation condition and actual slip surfaces caused by the downward movement of a trapdoor are inclined surfaces. Therefore, a 3D theoretical model was proposed in this study considering inclined slip surfaces. Horizontal thin-layer differential element method was used to obtain the loosening soil pressure. Using the 3D theoretical model, the effects of the buried depth ratio of loose area, length of loose area, soil parameters, and lateral earth pressure coefficient were investigated. The loosening earth pressure was highly affected by inclination angle of slip surface, buried depth ratio and length of loose area. Neglecting the inclined slip surface will underestimate the value of the loosening earth pressure, which will lead to the insecurity of the design. Loosening earth pressure calculated by this study was also compared with trapdoor tests. Results from this study was in good agreement with the experimental results. Compared with the traditional 2D solution, results from this study can more accurately analyze the soil arching effect in 3D excavation cases.
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