Effect of elasticity on electrospun styrene-butadiene-styrene fibrous membrane cell culture behaviors.

In this study, elastic styrene-butadiene-styrene (SBS), non-elastic SBS and their blends at different ratios were electrospun into fibrous membranes and their cell biocompatibility was evaluated. The as-spun fibers showed an average fiber diameter of 2 µm, and the fibrous membranes had pore size of 8 ± 0.01 µm. The blending ratios of the elastic with non-elastic SBSs showed little effect on fibrous structure, but affected the mechanical properties. All SBS membrane showed no cytotoxicity on endothelial cells (ECs). ECs attached and proliferated on all the SBS fibrous membrane scaffolds regardless of their elasticity. ECs maintained their polygonal shape on the scaffolds and they tended to orient along the fiber length. The SBS fibrous samples with elastic:non-elastic SBS weight ratios of 1:1 and 2:3 showed better cell viability than that of elastic and non-elastic SBS.

Electrospun Fibrous Scaffolds for Small-Diameter Blood Vessels: A Review.

Small-diameter blood vessels (SDBVs) are still a challenging task to prepare due to the occurrence of thrombosis formation, intimal hyperplasia, and aneurysmal dilation. Electrospinning technique, as a promising tissue engineering approach, can fabricate polymer fibrous scaffolds that satisfy requirements on the construction of extracellular matrix (ECM) of native blood vessel and promote the adhesion, proliferation, and growth of cells. In this review, we summarize the polymers that are deployed for the fabrication of SDBVs and classify them into three categories, synthetic polymers, natural polymers, and hybrid polymers. Furthermore, the biomechanical properties and the biological activities of the electrospun SBVs including anti-thrombogenic ability and cell response are discussed. Polymer blends seem to be a strategic way to fabricate SDBVs because it combines both suitable biomechanical properties coming from synthetic polymers and favorable sites to cell attachment coming from natural polymers.

A review of TiO2 NTs on Ti metal: Electrochemical synthesis, functionalization and potential use as bone implants.

Degenerative diseases of bone such as osteoarthritis and osteoporosis can lead to bone fractures and immobility, compromising quality of life. Titanium (Ti)-based implants have been intensively investigated for bone repair, with these implants, demonstrating improved outcomes compared to stainless steel and cobalt-chrome alloys, owing to superior mechanical properties and biocompatibility. However, osseointegration between the Ti-based implants and the surrounding bone tissue needs to be improved. Surface modification of Ti-based implants provides a solution for addressing this, with electrochemical anodization becoming a realistic approach for the fabrication of hierarchical structured for example nanotubes (NTs), implant surfaces. Using this technique, biocompatibility and osteogenesis of the implant may be improved, by providing an appropriate site for bone cell attachment. In this review, we discuss the anodization of Ti-based implants as an approach for creating titanium dioxide nanotubes (TiO2 NTs) on the implant surface. We further discuss the various ways of functionalizing the NT surface, to reduce post-operative infection and improve implant biocompatibility and osseointegration.

Two-dimensional intraventricular flow pattern visualization using the image-based computational fluid dynamics.

The image-based computational fluid dynamics (IB-CFD) technique, as the combination of medical images and the CFD method, is utilized in this research to analyze the left ventricle (LV) hemodynamics. The research primarily aims to propose a semi-automated technique utilizing some freely available and commercial software packages in order to simulate the LV hemodynamics using the IB-CFD technique. In this research, moreover, two different physiological time-resolved 2D models of a patient-specific LV with two different types of aortic and mitral valves, including the orifice-type valves and integrated with rigid leaflets, are adopted to visualize the process of developing intraventricular vortex formation and propagation. The blood flow pattern over the whole cardiac cycle of two models is also compared to investigate the effect of utilizing different valve types in the process of the intraventricular vortex formation. Numerical findings indicate that the model with integrated valves can predict more complex intraventricular flow that can match better the physiological flow pattern in comparison to the orifice-type model.

Heart blood flow simulation: a perspective review.

Cardiovascular disease (CVD), the leading cause of death today, incorporates a wide range of cardiovascular system malfunctions that affect heart functionality. It is believed that the hemodynamic loads exerted on the cardiovascular system, the left ventricle (LV) in particular, are the leading cause of CVD initiation and propagation. Moreover, it is believed that the diagnosis and prognosis of CVD at an early stage could reduce its high mortality and morbidity rate. Therefore, a set of robust clinical cardiovascular assessment tools has been introduced to compute the cardiovascular hemodynamics in order to provide useful insights to physicians to recognize indicators leading to CVD and also to aid the diagnosis of CVD. Recently, a combination of computational fluid dynamics (CFD) and different medical imaging tools, image-based CFD (IB-CFD), has been widely employed for cardiovascular functional assessment by providing reliable hemodynamic parameters. Even though the capability of CFD to provide reliable flow dynamics in general fluid mechanics problems has been widely demonstrated for many years, up to now, the clinical implications of the IB-CFD patient-specific LVs have not been applicable due to its limitations and complications. In this paper, we review investigations conducted to numerically simulate patient-specific human LV over the past 15 years using IB-CFD methods. Firstly, we divide different studies according to the different LV types (physiological and different pathological conditions) that have been chosen to reconstruct the geometry, and then discuss their contributions, methodologies, limitations, and findings. In this regard, we have studied CFD simulations of intraventricular flows and related cardiology insights, for (i) Physiological patient-specific LV models, (ii) Pathological heart patient-specific models, including myocardial infarction, dilated cardiomyopathy, hypertrophic cardiomyopathy and hypoplastic left heart syndrome. Finally, we discuss the current stage of the IB-CFD LV simulations in order to mimic realistic hemodynamics of patient-specific LVs. We can conclude that heart flow simulation is on the right track for developing into a useful clinical tool for heart function assessment, by (i) incorporating most of heart structures' (such as heart valves) operations, and (ii) providing useful diagnostic indices based hemodynamic parameters, for routine adoption in clinical usage.

The numerical analysis of non-Newtonian blood flow in human patient-specific left ventricle.

Recently, various non-invasive tools such as the magnetic resonance image (MRI), ultrasound imaging (USI), computed tomography (CT), and the computational fluid dynamics (CFD) have been widely utilized to enhance our current understanding of the physiological parameters that affect the initiation and the progression of the cardiovascular diseases (CVDs) associated with heart failure (HF). In particular, the hemodynamics of left ventricle (LV) has attracted the attention of the researchers due to its significant role in the heart functionality. In this study, CFD owing its capability of predicting detailed flow field was adopted to model the blood flow in images-based patient-specific LV over cardiac cycle. In most published studies, the blood is modeled as Newtonian that is not entirely accurate as the blood viscosity varies with the shear rate in non-linear manner. In this paper, we studied the effect of Newtonian assumption on the degree of accuracy of intraventricular hemodynamics. In doing so, various non-Newtonian models and Newtonian model are used in the analysis of the intraventricular flow and the viscosity of the blood. Initially, we used the cardiac MRI images to reconstruct the time-resolved geometry of the patient-specific LV. After the unstructured mesh generation, the simulations were conducted in the CFD commercial solver FLUENT to analyze the intraventricular hemodynamic parameters. The findings indicate that the Newtonian assumption cannot adequately simulate the flow dynamic within the LV over the cardiac cycle, which can be attributed to the pulsatile and recirculation nature of the flow and the low blood shear rate.

Bioengineering strategies for polymeric scaffold for tissue engineering an aortic heart valve: an update.

The occurrence of dysfunctional aortic valves is increasing every year, and current replacement heart valves, although having been shown to be clinically successful, are only short-term solutions and suffer from many agonizing long-term drawbacks. The tissue engineering of heart valves is recognized as one of the most promising answers for aortic valve disease therapy, but overcoming current shortcomings will require multidisciplinary efforts. The use of a polymeric scaffold to guide the growth of the tissue is the most common approach to generate a new tissue for an aortic heart valve. However, optimizing the design of the scaffold, in terms of biocompatibility, surface morphology for cell attachments and the correct rate of degradation is critical in creating a viable tissue-engineered aortic heart valve. This paper highlights the bioengineering strategies that need to be followed to construct a polymeric scaffold of sufficient mechanical integrity, with superior surface morphologies, that is capable of mimicking the valve dynamics in vivo. The current challenges and future directions of research for creating tissue-engineered aortic heart valves are also discussed.

Fluid structure interaction (FSI) simulation of the left ventricle (LV) during the early filling wave (E-wave), diastasis and atrial contraction wave (A-wave).

In this paper, the hemodynamic characteristics inside a physiologically correct three-dimensional LV model using fluid structure interaction scheme are examined under various heart beat conditions during early filling wave (E-wave), diastasis and atrial contraction wave (A-wave). The time dependent and incompressible viscous fluid, nonlinear viscous fluid and the stress tensor equations are coupled with the full Navier-Stoke's equations together with the Arbitrary Lagrangian-Eulerian and elasticity in the solid domain are used in the analysis. The results are discussed in terms of the variation in the intraventricular pressure, wall shear stress (WSS) and the fluid flow patterns inside the LV model. Moreover, changes in the magnitude of displacements on the LV are also observed during diastole period. The results obtained demonstrate that the magnitude of the intraventricle pressure is found higher in the basal region of the LV during the beginning of the E-wave and A-wave, whereas the Ip is found much higher in the apical region when the flow propagation is in peak E-wave, peak A-wave and diastasis. The magnitude of the pressure is found to be 5.4E2 Pa during the peak E-wave. Additionally, WSS elevates with the rise in the E-wave and A-wave but the magnitude decreases during the diastasis phase. During the peak E-wave, maximum WSS is found to be 5.7 Pa. Subsequent developments, merging and shifting of the vortices are observed throughout the filling wave. Formations of clockwise vortices are evident during the peak E-wave and at the onset of the A-wave, but counter clockwise vortices are found at the end of the diastasis and at the beginning of the A-wave. Moreover, the maximum magnitude of the structural displacement is seen in the ventricle apex with the value of 3.7E-5 m.

A parametric study on mathematical formulation and geometrical construction of a stentless aortic heart valve.

This study presents a novel methodology for constructing an accurate geometrical model of a stentless aortic heart valve replacement (AVR). The main objective is to propose an optimized AVR model that can be used as an ideal scaffold for tissue engineering applications or a biocompatible prosthesis. Current techniques available for creating heart valve geometry, including leaflets, are very complicated and are not precise, due to the extensive use of various complicated parameters. This paper introduces an alternative design procedure that uses limited and effective numbers of controlling parameters to construct the whole valve including the sinus of valsalva. In doing so the hyperbolic curves for multithickness leaflets are used and a 3D elliptical formulation is incorporated for the surface geometry of the sinus of valsalva. Still, the feasibility and the precision of the mathematical method are established by performing standard deviation analysis on the constructed surfaces. The surface fitting residuals are found as low as error 0.2351 mm with standard deviation of 8.83e-5 over the commissural lines. Preliminary validation to the proposed AVR model performance is achieved by testing the generated AVR model under quasi static condition while obtaining the mesh independent setup. The numerical model showed a rapid response of the leaflets to the transvalvular pressure where adequate values of stress are measured over the commissural lines.