Reviewer's commentary: tissue engineering of biological cardiovascular system surrogates

Abstract not available

Numerical investigation of natural convection inside complex enclosures

In this article, the analyses of heat transfer and free convective motion have been carried out numerically for various structures. The solution is based on a finite element method with the frontal solver to examine the flow parameters and heat transfer characteristics. Several dome configurations--such as flat, inclined, and dome shapes--are considered for the top of the enclosure. A general conic equation is considered to represent the dome as circular, elliptical, parabolic, or hyperbolic shape. The findings from this study indicate that the convective phenomenon is greatly influenced by the shape of the top cover dome and tends to form a secondary core even at a moderate Rayleigh number when compared with an equivalent rectangular enclosure. In addition, the circular and elliptical shapes of the dome give higher heat transfer rate. The effect of various &quot;offset&quot; of the dome and inclined roof on convective heat transfer is also found to be quite significant. However, beyond 0.3 of offset of the top cover for the dome and inclined roof, the change in overall heat transfer rate is minimal. The heat transfer coefficients of dome shaped and inclined roof enclosures are given and discussed.<br /

A non-darcian numerical modeling in domed enclosures filled with heat-generating porous media

Numerical study of the natural-convection flow and heat transfer in a dome-shaped, heat-generating, porous enclosure is considered. The general conic equation for the top dome is used to consider various conical top sections such as circular, elliptical, parabolic, and hyperbolic. The individual effect of fluid Rayleigh, Darcy, and heat-generating parameters on flow patterns and heat transfer rates are analyzed and presented. The predicted results show that the heat-generating parameter has the most significant contribution toward the growth of bicellular core flow. Moreover, there is significant change in temperature distribution in comparison to rectangular enclosures, due to the existence of the domed-shape top adiabatic cover. The results also show that, regardless of Darcy and Rayleigh values, a flat adiabatic top cover tends to yield the highest value of Nusselt number, followed by circular, elliptical, parabolic, and hyperbolic top covers, respectively.<br /

Current developments and future challenges for the creation of aortic heart valve

The concept of tissue-engineered heart valves offers an alternative to current heart valve replacements that is capable of addressing shortcomings such as life-long administration of anticoagulants, inadequate durability, and inability to grow. Since tissue engineering is a multifaceted area, studies conducted have focused on different aspects such as hemodynamics, cellular interactions and mechanisms, scaffold designs, and mechanical characteristics in the form of both in vitro and in vivo investigations. This review concentrates on the advancements of scaffold materials and manufacturing processes, and on cell&ndash;scaffold interactions. Aside from the commonly used materials, polyglycolic acid and polylactic acid, novel polymers such as hydrogels and trimethylene carbonate-based polymers are being developed to simulate the natural mechanical characteristics of heart valves. Electrospinning has been examined as a new manufacturing technique that has the potential to facilitate tissue formation via increased surface area. The type of cells utilized for seeding onto the scaffolds is another factor to take into consideration; currently, stem cells are of great interest because of their potential to differentiate into various types of cells. Although extensive studies have been conducted, the creation of a fully functional heart valve that is clinically applicable still requires further investigation due to the complexity and intricacies of the heart valve.<br /

Flow characteristics past jellyfish and St. Vincent valves in the aortic position under physiological pulsatile flow conditions

Thrombus formation and hemolysis have been linked to the dynamic flow characteristics of heart valve prostheses. To enhance our understanding of the flow characteristics past the aortic position of a Jellyfish (JF) valve in the left ventricle, in vitro laser Doppler anemometry (LDA) measurements were carried out under physiological pulsatile flow conditions. The hemodynamic performance of the JF valve was then compared with that of the St. Vincent (SV) valve. The comparison was given in terms of mean systolic pressure drop, back flow energy losses, flow velocity, and shear stresses at various locations downstream of both valves and at cardiac outputs of 3.5 L/min, 4.5 L/min, and 6.5 L/min respectively. The results indicated that both valves created disturbed flow fields with elevated levels of turbulent shear stress as well as higher levels of turbulence in the immediate vicinity of the valve and up to 1 diameter of the pipe (D) downstream of the valve. At a location further downstream, the JF valve showed better flow characteristics than the SV in terms of velocity profiles and turbulent shear stresses. The closure volume of the SV valve was found to be 2.5 times higher than that of the JF valve. Moreover, the total back flow losses and mean systolic pressure drop also were found to be higher in the SV than the JF valve

The effect of protuberance on thermal convection in a square enclosure

This paper documents research that has been undertaken at the Swinburne University of Technology in Melbourne Australia. In this paper, the analyses of heat transfer and free convective motion have been carried out numerically for a semi-cylindrically shaped protuberance in a square enclosure. The solution method is based on the finite element technique with the frontal solver. The numerical results are for a Prandtl Number 0.71 and for a Rayleigh Number up to 105. The change in direction of returning fluid near the cold wall effects the convective heat transfer process significantly. Moreover, increases in the protuberance affect the maximum velocities and their physical location in the domain resulting in dead zones near the bottom corners of the enclosures

1H-Purin-2-amine, 6-[[(2-nitrophenyl)methyl]thio]-

Introduction Tissue engineering (TE) is a multidisciplinary field that combines the principles of engineering and biological sciences to contribute to the development of tissues and organs for the purpose of regeneration, repair or replacement. Although TE was a term that was used and gained popularity in 1987 at the National Science Foun- dation, the concept of TE had been explored as early as the 1930s whereby living cells and tissues were maintained in a bioreactor by Carrel and Lindbergh (Nerem 2006). Langer and Vacanti, eminent research ers of TE, described a technique using bioabsorbable synthetic polymer as matrices for cell transplantation in 1988 and this formed the basis for the concept of T E (Vacanti et al. 1988). S ince isolated cells cannot form new tissue on their own, three-dimensional (3D) scaffolds are required to provide architectural support for the cells and define the anatomical shape of the tissue (Yang et al. 2001)..

Advancement of lung tissue engineering: an overview

Lung diseases can be classified as Chronic Obstructive Pulmonary Disorder (COPD), pulmonary fibrosis and sarcoidosis as well as lung cancer. Current conventional treatment therapies for lung diseases are associated with various drawbacks. The field of Tissue Engineering (TE) is relatively new discipline that offers the potential to create de novo structures and may grant substitutes to replace damaged organs and tissues. This review gives a brief account of lung diseases and debates the research findings as well as the recent developments of TE lung with particular emphasis on the regeneration of alveolar-like structures. Selection of cell sources and the use of biological and synthetic materials as extracellular matrix derivatives and exogenous simulations of tissue growth within specified Three Dimensional (3D) scaffold structures are presented and discussed. Moreover, the critical challenges involved in developing an alternative tissue engineering heart lung and the future directions are also given. Finally, the paper proposes a novel concept of 'the breathing scaffold', which could facilitate the growth of the cells into a 3D alveolar structure while maintaining their gas exchange

Further discussion on in vitro flow analysis of artificial heart valve

Abstract not available

The effect of arterial wall deformability on hemodynamics of CABG

In this study, hemodynamic forces in a threedimensional (3D) computational model of Coronary Artery Bypass Grafting (CABG) with deformable and rigid walls were compared. A physiologic pulsatile non-Newtonian blood flow was considered in the arteries for both models. The artery walls in the distensible model were considered to be hyper-elastic with nonlinear strain dependent Young’s module and axial and radial degrees of freedom, while the deformability in all directions of the rigid model was restricted. The velocity distributions and magnitudes, vortex motions and the occurrence of recirculation zones were selected as the primary hemodynamic parameters in order to show the effect of deformability in the arterial wall and in calculating differences versus the rigid wall model. It was found that during systolic, the velocity magnitude at the host artery bed could vary by up to 80% depending on the longitudinal distance from the center of the anastomosis junction