Applications in engineering science最新文献

LVADs have been in clinical use for a half-century and have advanced through at least 3 generations resulting in compact, durable, and powerful pumps that can deliver blood flow that exceeds the needs of the body at rest. In so doing, these devices have become the best alternative to transplant for patients with end-stage heart failure. That said, the blood contacting interface of these pumps is likely the cause of complications and contraindications that persist with successive generations. Patients with elevated risk for side effects or patients with biventricular failure and other conditions represent the 25% of patients that are not candidates for LVAD therapy. Such patients represent the clinical need for non-blood contacting mechanical circulatory support. The clinical use of direct cardiac compression devices is limited, and there are no devices available for human use. Technological challenges remain, yet these devices continue to be developed and tested in animal models of heart failure.

This paper focuses on applications of recently developed thermoelastic reduced order models (ROMs) for the geometrically nonlinear response and temperature of heated structures. In these ROMs, both displacements and temperature fields with respect to the undeformed, unheated configuration are expressed in a reduced order modeling format, i.e., as modal-type expansions of the spatial and temporal variables with constant basis functions. Accordingly, the time varying generalized coordinates of the response and temperature expansions satisfy a generic set of coupled nonlinear differential equations derived from finite deformations thermoelasticity using a Galerkin approach. Finally, the coefficients of these governing equations, which characterize the structure considered and its loading conditions, are determined from structural and thermal finite element models non intrusively so that commercial finite element software can be used. This approach is considered here for the prediction of the displacements and stress fields in the presence of unsteady temperature distributions to enrich previous investigations limited to steady temperature distributions. Specifically considered here are: (i) a panel undergoing rapid heating and (ii) an oscillating flux on a panel. These problems not only demonstrate the extension of the thermal-structural reduced order framework to unsteady problems but also show the importance of the selection of the basis functions. It is also noted that the temperature dependence of the linear stiffness coefficients on temperature can induce in the unsteady situation the existence of a parametric-type excitation of the structure. This behavior is studied in the oscillating flux example and a strong sub-harmonic resonance is in particular found. The computational benefit of using ROMs is discussed and demonstrated.

Cardiovascular diseases are the leading cause of morbidity and mortality and a huge economic burden on the healthcare system globally. Both pharmacological and device based treatment options have emerged over the years, however, it is still a ‘holy grail’ to effectively treat some cardiovascular conditions, for example, heart failure. Any treatment option whether it is drug therapy or a device therapy, has to go through a rigorous regulatory approval process. This requires robust pre-clinical research and clinical trial results. In order to proceed to the clinical trials, pre-clinical research is very important and may take methodologies which are at the interface of biology and engineering, for example, in-vitro, ex-vivo and in-vivo models. This paper focusses on the 2D and 3D in-vitro models to mimic the pathophysiology of a specific cardiovascular disease and their advantages and limitations.

A non-linear elastic constitutive model for a swelling/shrinking orthotropic wood matrix is proposed. The model is thermodynamically consistent, derived based on the principles of continuum mechanics and the hybrid mixture theory. Moisture induced strains are introduced considering finite deformations by assuming a multiplicative split of the deformation gradient tensor into a swelling and an elastic part. Novel definitions of the Cauchy stress tensor and the moisture-dependent elastic material tangent matrix are obtained. The model is coupled to a multi-phase transient mass and heat transport model developed in Part I of this work. In this part of the work 2-D and 3-D test examples are used to describe the ability of the model to simulate moisture-induced distortions when drying wood within the hygroscopic and also from the over-hygroscopic moisture ranges. Despite deriving the model considering wood, the obtained constitutive relations can be suitably adopted to other orthotropic porous materials displaying properties similar to that of wood.

Over the last 20 years, a diverse number of different approaches have been explored in trying to produce engineered tissue vascular grafts (ETVGs). If successful, this alternative source of living vascular conduits with the ability to grow, remodel, and self-repair could revolutionize vascular surgery by relieving the limiting need for autologous grafts or providing substantial benefit and improved performance over their synthetic counterparts. However, despite tissue engineering being one of the hottest topics in biotechnology in the last three decades, it is generally acknowledged that the field's performance and its potential clinical translation have been somewhat disappointing. Pilot studies with ETVGs in animal models and preclinical human trials have been encouraging, but our understanding of the design requirements for ETVGs, how to effectively create them, and how to direct ETVG integration once implanted must be improved. This article reviews the current state-of-the-art of ETVGs with emphasis on the different manufacturing approaches explored in the past and challenges encountered and tackled, with particular focus on ETVGs that are very close to making a clinical impact and may potentially begin a new era of therapy for vascular disease.

A thermodynamically consistent model for heat and mass transfer in deformable wood fibers is developed. The hybrid mixture theory is used to model the material as a mixture of three phases, consisting of a solid, a liquid and a gas phase. The solid phase consists of dry fibers and bound water constituents, whereas the gas phase has dry air and water vapor constituents. Emphasis is put on the mass flow and mass exchange of moisture in the material both below and above the saturation point of the solid wood fibers. Generalized forms of Fick’s, Darcy’s and Fourier’s laws are derived, and the chemical potential is used as a driving force for mass flow. Mass exchange due to sorption and evaporation/condensation processes is implemented in the model, where hysteretic properties both within and above the hygroscopic moisture range are described using Frandsen’s hysteresis model. Moisture induced swelling/shrinkage is included where the porosity of the material can vary. A large strain setting formulated for general orthotropy is adopted for the mechanical deformations. To show the performance of the resulting model, it is implemented in a finite element method framework and used to simulate the processes of heat and moisture transport dynamics of a wood sample subjected to drying from an over-hygroscopic moisture state.

Objective: Cell-based therapies utilizing mesenchymal and cardiac progenitor cells have demonstrated promising results in the treatment of congenital heart disease. We hypothesize that autologous human placental-derived progenitor cells share similar characteristics to cardiac progenitor cells (CPC) derived from autologous bone marrow or cardiac sources.

Methods: Fetal portion of the placenta was harvested at the time of delivery from newborns (N = 5), and cells were isolated and expanded from the amnion and chorion layers. Flow cytometry and multi-lineage differentiation potential assays were used to characterize placental-derived progenitor cells. Placenta derived sphere cells were generated and phenotypic and functional characteristics were analyzed.

Results: CD90, CD105, and Vimentin were expressed in <10% placental-derived progenitor cells, and differentiation into mesodermal lineages was not observed. However, placental-derived progenitor cells were able to differentiate into smooth muscle and cardiomyocyte lineages. In placenta derived sphere cells, >65% expressed cardiac lineage marker (SIRPA), but <15% expressed Discoidin domain receptor 2 (DDR2). Compared to placental-derived progenitor cells, placenta derived sphere cells expressed higher levels of cardiac transcription factors, cardiac ion channel genes and cardiac structural genes.

Conclusions: Placental progenitor cells demonstrate similar characteristics to CPC currently utilized in several clinical trials that can serve as a readily available autologous source for cardiac cell therapy.

In drilling and blasting operation, uncoupled charge structure is widely used in pre-split blasting, smooth blasting, pressure relief blasting and other controlled blasting engineering. In order to study the evolution of energy and crack propagation in rock mass during blasting under the uncoupled charge structure, this paper established a three-dimensional numerical test model of single-hole uncoupled charge by numerical simulation method. By changing the uncoupling coefficient, the pressure of hole wall, energy evolution and crack propagation during blasting were compared and analyzed. The results show that under the condition of the same explosive quantity, the strain energy of rock mass, the strain rate and peak pressure of hole wall rock and the area of blasting crack are negatively correlated with the uncoupling coefficient of charge, and the formula of the change with the uncoupling coefficient is obtained. When the uncoupling coefficient is less than 3 and the charge uncoupling coefficient is changed, the peak pressure of hole wall, strain energy of rock mass and blast-induced crack area decrease significantly with the increase of the uncoupling coefficient. When the uncoupling coefficient is greater than 3, the change range of the uncoupling coefficient becomes smaller. The experimental conclusions are analyzed to provide reference for field blasting construction.

A constitutive equation for a class of electro-elastic solid is proposed, neglecting dissipation of energy, and assuming that the gradient of the displacement field is small (the above implies the strains are small). Using the theory of implicit constitutive relations developed by Rajagopal and co-workers, a constitutive equation is proposed where the linearized strain is a function of the Cauchy stress and the electric field. The polarization field is assumed to be a function of the Cauchy stress and the electric field as well. The material parameters are adjusted to model the behaviour of some ceramic-like materials. Several boundary problems are solved to study the predictions of these new constitutive equations.

Ejection Fraction (EF), a measure of the ability of the heart to pump blood, is an important parameter for the diagnosis for heart failure as well as in the monitoring of the therapy provided. The standard method of calculating EF uses the left ventricular volume (LVV) by identifying the end-diastolic and end-systolic volumes. For patients implanted with a continuous flow (CF) left ventricular assist devices (LVADs), there are two pathways for blood ejection, Trans-Aortic Valve Flow (TAVF) which is intermittent and Trans-VAD Flow (TVF) that flows continuously throughout the cardiac cycle. Using the standard method to calculate EF in LVAD patients provides the fraction of the total blood ejected from the ventricle over a cardiac cycle. When monitoring the patient for recovery, it is vital to quantify the precise contribution of the Trans-Aortic Valve path independently from the Trans-VAD contribution. In this paper we demonstrate how this can be accomplished with a mathematical lumped parameter model of the interaction of the cardiovascular system and the LVAD. We introduce the Trans-Aortic Valve Ejection Fraction (TAVEF), which is the measure of the Trans-Aortic Valve contribution to the overall circulation. The dilated failing heart is represented by an unimodal End-Sytolic Pressure Volume Relationship (ESPVR). Our results indicate that TAVEF describes the contribution of the TAVF better as compared to standard EF over the entire range of LVAD speeds, and captures the point of aortic valve closure by becoming 0, whereas the standard EF is non-zero. TAVEF can be a useful, reliable, non-invasive mechanism for monitoring ventricular recovery.