[Show abstract][Hide abstract] ABSTRACT: Purpose: Since stretching plays a key role in skeletal muscle tissue development in vivo, by making use of an innovative bioreactor and a biodegradable microfibrous scaffold (DegraPol(R)) previously developed by our group, we aimed to investigate the effect of mechanical conditioning on the development of skeletal muscle engineered constructs, obtained by seeding and culturing murine skeletal muscle cells on electrospun membranes. Methods: Following 5 days of static culture, skeletal muscle constructs were transferred into the bioreactor and further cultured for 13 days, while experiencing a stretching pattern adapted from the literature to resemble mouse development and growth. Sample withdrawal occurred at the onset of cyclic stretching and after 7 and 10 days. Myosin heavy chain (MHC) accumulation in stretched constructs (D) was evaluated by Western blot analysis and immunofluorescence staining, using statically cultured samples (S) as controls. Results: Western blot analysis of MHC on dynamically (D) and statically (S) cultured constructs at different time points showed that, at day 10, the applied stretching pattern led to an eight-fold increase in myosin accumulation in cyclically stretched constructs (D) with respect to the corresponding static controls (S). These results were confirmed by immunofluorescence staining of total sarcomeric MHC. Conclusions: Since previous attempts to reproduce skeletal myogenesis in vitro mainly suffered from the difficulty of driving myoblast development into an architecturally organized array of myosin expressing myotubes, the chance of inducing MHC accumulation via mechanical conditioning represents a significant step towards the generation of a functional muscle construct for skeletal muscle tissue engineering applications.
[Show abstract][Hide abstract] ABSTRACT: Gestational diabetes mellitus (GDM) makes women at risk of type 2 diabetes during their life. In order to predict this later abnormal glucose intolerance, several antepartum and postpartum predictors have been identified. In this study we conjecture that future evolution is predictable from morphology of the oral glucose tolerance test (OGTT) curves at baseline. To test our hypothesis, as a first step we evaluated the association between the curve morphologies of normal and diabetic patient condition at baseline. In particular, we analysed glucose and insulin curves of a group of women with a history of GDM. A Self-organizing map (SOM) was proposed to evaluate shape differences among control, normal, impaired glucose tolerance and diabetic curves shape. We compared our results with the currently applied clinical classification. We found that morphology contains information about the current status of the patient, because the SOM analysis clearly allows to discriminate subjects belonging to healthy or diabetic group. Moreover, SOMs highlighted additional information that could be used for prognostic purposes.
Studies in health technology and informatics 01/2010; 160(Pt 2):1145-9.
[Show abstract][Hide abstract] ABSTRACT: Tissue engineering (TE) is the application of principles and methods of engineering and life sciences towards the fundamental
understanding of structure–function relationships in normal and pathological mammalian tissues and the development of biological
substitutes to restore, maintain or improve tissue function.
One key component to TE is using three-dimensional porous scaffolds to guide cells during the regeneration process. These
scaffolds are intended to provide cells with an environment that promotes cell attachment, proliferation, and differentiation.
After sufficient tissue regeneration using in vitro culturing methods, the scaffold/tissue structure is implanted into the
patient, where the scaffold will degrade away, thereby leaving only regenerated tissue; on a different approach, non-cellularised
scaffolds are inserted into the patient to elicit in vivo cell recruitment, growth and tissue regeneration. Tissue-engineered
scaffolds need to meet both the biological goals of tissue formation and the stresses and loading conditions present in the
human body. For this reason, any design approach must ensure that the mechanical properties of the resulting scaffold structure
are compatible and optimally match the requirements from the environment, that, respectively, are the cell adhesion transmembrane
protein, the cytoskeleton structure, the cell population. The need to design scaffold structures, the need for precision control
during their fabrication and for determining the metrological indices and the need to characterise their structural behaviour
at different scales have lead to numerous experimental and computational challenges. In particular, there is a need for modelling
and test tissue at multiple scales to gain insight into issues such as drug delivery, drug interaction, gene expression and
cellular–environment interactions. The analysis of the tissue constructs at different scales includes a macro-scale model
where the macro-scale tissue construct is characterised, a multi-cellular model where a sufficiently large multi-cellular
representative element volume is selected to represent a microstructure of the tissue construct and a single cell model wherein
the microstructures of the cell like the nucleus and the cytoplasm have been incorporated. A multi-scale approach is already
being applied to bridge nano- and micro-scales as well as micro- and macro-scales within various research areas in TE.
In this chapter, a review of the experimental and modelling techniques used for the evaluation, at different scales, of the
mechanical and morphological properties of bioartificial scaffolds and matrices, such as compression testing, nanoindentation,
AFM technique, Dynamical Mechanical Analysis (DMA), micro-CT, microMR, Asymptotic Homogenisation Theory, Finite Element Analysis
(FEA), Rule-of-Mixtures, is proposed.
[Show abstract][Hide abstract] ABSTRACT: Denoising is a fundamental early stage in 2-DE image analysis strongly influencing spot detection or pixel-based methods. A novel nonlinear adaptive spatial filter (median-modified Wiener filter, MMWF), is here compared with five well-established denoising techniques (Median, Wiener, Gaussian, and Polynomial-Savitzky-Golay filters; wavelet denoising) to suggest, by means of fuzzy sets evaluation, the best denoising approach to use in practice. Although median filter and wavelet achieved the best performance in spike and Gaussian denoising respectively, they are unsuitable for contemporary removal of different types of noise, because their best setting is noise-dependent. Vice versa, MMWF that arrived second in each single denoising category, was evaluated as the best filter for global denoising, being its best setting invariant of the type of noise. In addition, median filter eroded the edge of isolated spots and filled the space between close-set spots, whereas MMWF because of a novel filter effect (drop-off-effect) does not suffer from erosion problem, preserves the morphology of close-set spots, and avoids spot and spike fuzzyfication, an aberration encountered for Wiener filter. In our tests, MMWF was assessed as the best choice when the goal is to minimize spot edge aberrations while removing spike and Gaussian noise.
[Show abstract][Hide abstract] ABSTRACT: Thromboembolism and the attendant risk of cardioembolic stroke remains an impediment to the development of prosthetic cardiovascular devices. In particular, altered haemodynamics are implicated in the acute blood cell damage that leads to thromboembolic complications, with platelet activation being the underlying mechanism for cardioemboli formation in blood flow past mechanical heart valves (MHVs) and other blood re-circulating devices. In this work, a new modeling paradigm for evaluating the cardioembolic risk of MHVs is described. In silico fluid-structure interaction (FSI) approach is used for providing a realistic representation of the flow through a bileaflet MHV model, and a Lagrangian analysis is adopted for characterizing the mechanism of mechanically induced activation of platelets by means of a mathematical model for platelet activation state prediction. Additionally, the relationship between the thromboembolic potency of the device and the local flow dynamics is quantified by giving a measure of the role played by the local streamwise and spanwise vorticity components. Our methodology indicates that (i) mechanically induced activation of platelets when passing through the valve is dependent on the phase of the cardiac cycle, where the platelet rate of activation is lower at early systole than late systole; (ii) local spanwise vorticity has greater influence on the activation of platelets (R>or=0.94) than streamwise vorticity (R>or=0.78). In conclusion, an integrated Lagrangian description of key flow characteristics could provide a more complete and quantitative picture of blood flow through MHVs and its potential to activate platelets: the proposed "comprehensive scale" approach could represent an efficient and novel assessment tool for MHV performance and may possibly lead to improved valve designs.
Journal of biomechanics 07/2009; 42(12):1952-60. · 2.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Country-Specific Mortality and Growth Failure in Infancy and Yound Children and
Association With Material Stature
Use interactive graphics and maps to view and sort country-specific infant and early
dhildhood mortality and growth failure data and their association with maternal
[Show abstract][Hide abstract] ABSTRACT: In recent years, interest is growing on compact measures for assessing the role of local hemodynamics in the pathogenesis of atherosclerosis and atherogenesis. CFD and its power in evaluating and predicting the effect of some hemodynamic variables in vascular disease is becoming a key factor in clinical research. Recently, Lee and Steinman  assessed the importance of blood rheology assumptions to ascertain the effect of constitutive relation for blood on local wall shear stress (WSS) and on the correlated vascular pathology. We present a preliminary in silico investigation on the sensitivity of helical flow measure with respect to the blood constitutive adopted model. Our main objective was to verify if, through the carotid bifurcation model, the rheological properties of blood significantly influence the bulk flow topology, whose evolution and stability are strictly linked to helicity. In fact helicity — an invariant in fluid dynamics — has been demonstrated to describe and reveal the global organization in a fluid flow. For this purpose several blood models (Newtonian and non-Newtonian) were implemented. A specific Lagrangian-based “bulk” flow descriptor, the Helical Flow Index (HFI) , was calculated in order to get a “measure” of the helical structure in the blood flow. Therefore, its sensitivity to blood rheology and hematocrit (Ht) was assessed and compared with the sensitivity of WSS based on other fluid dynamics descriptors (Time Averaged WSS, TAWSS, and Oscillating Shear Index, OSI).
[Show abstract][Hide abstract] ABSTRACT: The initiation and progression of vessel wall pathologies have been linked to disturbances of blood flow and altered wall shear stress. The development of computational techniques in fluid dynamics, together with the increasing performances of hardware and software allow to routinely solve problems on a virtual environment, helping to understand the role of biomechanics factors in the healthy and diseased cardiovascular system and to reveal the interplay of biology and local fluid dynamics nearly intractable in the past, opening to detailed investigation of parameters affecting disease progression. One of the major difficulties encountered when wishing to model accurately the cardiovascular system is that the flow dynamics of the blood in a specific vascular district is strictly related to the global systemic dynamics. The multiscale modelling approach for the description of blood flow into vessels consists in coupling a detailed model of the district of interest in the framework of a synthetic description of the surrounding areas of the vascular net . In the present work, we aim at evaluating the effect of boundary conditions on wall shear stress (WSS) related vessel wall indexes and on bulk flow topology inside a carotid bifurcation. To do it, we coupled an image-based 3D model of carotid bifurcation (local computational domain), with a lumped parameters (0D) model (global domain) which allows for physiological mimicking of the haemodynamics at the boundaries of the 3D carotid bifurcation model here investigated. Two WSS based blood-vessel wall interaction descriptors, the Time Averaged WSS (TAWSS), and the Oscillating Shear Index (OSI) were considered. A specific Lagrangian-based “bulk” blood flow descriptor, the Helical Flow Index (HFI) , was calculated in order to get a “measure” of the helical structure in the blood flow. In a first analysis the effects of the coupled 0D models on the 3D model are evaluated. The results obtained from the multiscale simulation are compared with the results of simulations performed using the same 3D model, but imposing a flow rate at internal carotid (ICA) outlet section equal to the maximum (60%) and the minimum (50%) flow division obtained out from ICA in the multiscale model simulation (the presence of the coupled 0D model gives variable internal/external flow division ratio during the cardiac cycle), and a stress free condition on the external carotid (ECA).
[Show abstract][Hide abstract] ABSTRACT: Altered haemodynamics are implicated in the blood cells damage that leads to thromboembolic complications in presence of prosthetic cardiovascular devices, with platelet activation being the underlying mechanism for cardioemboli formation in blood flow past mechanical heart valves (MHVs). Platelet activation can be initiated and maintained by flow patterns arising from blood flowing through the MHV, and can lead to an enhancement in the aggregation of platelets, increasing the risk for thromboemboli formation. Hellums and colleagues compiled numerous experimental results to depict a locus of incipient shear related platelet activation on a shear stress – exposure time plane, commonly used as a standard for platelet activation threshold . However, platelet activation and aggregation is significantly greater under pulsatile or dynamic condition relative to exposure to constant shear stress . Previous studies do not allow to determine the relationship existing between the measured effect — the activation of a platelet, and the cause — the time-varying mechanical loading, and the time of exposure to it as might be expected in vivo when blood flows through the valve. The optimization of the thrombogenic performance of MHVs could be facilitated by formulating a robust numerical methodology with predictive capabilities of flow-induced platelet activation. To achieve this objective, it is essential (i) to quantify the link between realistic valve induced haemodynamics and platelet activation, and (ii) to integrate theoretical, numerical, and experimental approaches that allow for the estimation of the thrombogenic risk associated with a specific geometry and/or working conditions of the implantable device. In this work, a comprehensive analysis of the Lagrangian systolic dynamics of platelet trajectories and their shear histories in the flow through a bileaflet MHV is presented. This study uses information extracted from the numerical simulations performed to resolve the flow field through a realistic model of MHV by means of an experimentally validated fluid-structure interaction approach . The potency of the device to mechanically induce activation/damage of platelets is evaluated using a Lagrangian-based blood damage cumulative model recently identified using in vitro platelet activity measurements [4,5].
[Show abstract][Hide abstract] ABSTRACT: The cellular microtubules MTs are hollow cylinder-shaped biopolymers with inner and outer diameter of about 17 and 25 nm and length ranging from 1 to 10 μm. They are constituted by αβ-tubulins arranged in protofilaments with a head-to-tail motif . The protofilaments bind together laterally along the MT’s long axis with a slight shift generating a spiral with a pitch of 2, 3 or 4 monomers’ length (Fig.1a). The building-block of the MT, the αβ-tubulin, is a hetero-dimer made of two globular monomers, α- and β-tubulin, each of them consisting of about 450 residues with high degree of sequence similarity from the primary to the tertiary structure level .
[Show abstract][Hide abstract] ABSTRACT: A comprehensive computational study modelling the operation of a rotating hollow-fiber bioreactor for artificial liver (BAL) was performed to explore the interactions between the oxygenated culture medium and the cultured hepatocytes. Computational fluid dynamics investigations were carried out using two-dimensional (2D) and 3D time-dependent numerical simulations, integrating calculations of diffusion, convection, and multiphase fluid dynamics. The analysis was aimed at determining the rotational speed value of the chamber to ensure homogenous distribution of the floating microcarrier-attached aggregated cells (microCAACs) and avoid their sedimentation and excessive packing, analyzing oxygen (O(2)) delivery and cellular O(2) consumption as an index of cellular metabolic activity, and analyzing the fluid-induced mechanical stress experienced by cells. According to our results, homogeneous distribution of cells is reached at a rotational speed of 30 rpm; spreading of cellular concentration at around the initial value of 12% was limited (median = 11.97%, 5th percentile = 10.94%, 95th percentile = 13.2%), resulting in uniform suspension of microCAACs, which did not appear to be excessively packed. Mixing within the rotating fluid caused a maximum fluid-induced stress value of 0.05 Pa, which was neither endangering for liver-specific functions of cultured cells, nor causing disruption of the floating aggregates. Moreover, an inlet medium flow rate of 200 mL/m with a partial pressure of oxygen (pO(2)) value of 160 mmHg was found to guarantee an adequate O(2) supply for the hepatocytes (2.7 x 10(8) hepatocytes are simulated); under such conditions, the minimum pO(2) value (23 mmHg) is above the critical threshold value, causing the onset of cellular hypoxia (10 mmHg). We proved that numerical simulation of transport phenomena is a valuable tool for the computer-aided design of BALs, helping overcome the unsolved issues in optimizing the cell-environment conditioning procedure in rotating BALs.
Tissue Engineering Part C Methods 04/2009; 15(1):41-55. · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The mechanics of blood flow in arteries plays a key role in the health of individuals. In this framework, the role played by the presence of helical flow in the human aorta is still not clear in its relation to physiology and pathology. We report here a method for quantifying helical flow in vivo employing time-resolved cine phase contrast magnetic resonance imaging to obtain the complete spatio-temporal description of the three-dimensional pulsatile blood flow patterns in aorta. The method is applied to data of one healthy volunteer. Particle traces were calculated from velocity data: to them we applied a Lagrangian-based method for helical flow quantification, the Helical Flow Index, which has been developed and evaluated in silico in order to reveal global organization of blood flow. Our results: (i) put in evidence that the systolic hemodynamics in aorta is characterized by an evolving helical flow (we quantified a 24% difference in terms of the content of helicity in the streaming blood, between mid and early systole); (ii) indicate that in the first part of the systole helicity is ascrivable mainly to the asymmetry of blood flow in the left ventricle, joined with the laterality of the aorta. In conclusion, this study shows that the quantification of helical blood flow in vivo is feasible, and it might allow detection of anomalies in the expected physiological development of helical flow in aorta and accordingly, could be used in a diagnostic/prognostic index for clinical practice.
Annals of Biomedical Engineering 01/2009; 37(3):516-31. · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this work we used molecular simulations to investigate the elastic properties of collagen single chain and triple helix with the aim of understanding its features starting from first principles. We analysed ideal collagen peptides, homotrimeric and heterotrimeric collagen type I and pathological models of collagen. Triple helices were found much more rigid than single chains, thus enlightening the important role of interchain stabilizing forces, like hydrophobic interaction and hydrogen bonds. We obtained Young's moduli close to 4.5GPa for the ideal model of collagen and for the physiological heterotrimer, while the physiological homotrimer presented a Young's modulus of 2.51GPa, that can be related to a mild form of Osteogenesis Imperfecta in which only the homotrimeric form of collagen type I is produced. Otherwise, the pathological model (presenting a glycine to alanine substitution) showed an elastic modulus of 4.32GPa, thus only slightly lower than the ideal model. This suggests that this mutation only slightly affects the mechanical properties of the collagen molecule, but possibly acts on an higher scale, such as the packing of collagen fibrils.
Journal of Biomechanics 10/2008; 41(14):3073-7. · 2.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The assessment of cardiovascular function by means of arterial pulse wave analysis (PWA) is well established in clinical practice. PWA is applied to study risk stratification in hypertension, with emphasis on the measurement of the augmentation index as a measure of aortic pressure wave reflections. Despite the fact that the prognostic power of PWA, in its current form, still remains to be demonstrated in the general population, there is general agreement that analysis and interpretation of the waveform might provide a deeper insight in cardiovascular pathophysiology. We propose here the use of wavelet analysis (WA) as a tool to quantify arterial pressure waveform features, with a twofold aim. First, we discuss a specific use of wavelet transform in the study of pressure waveform morphology, and its potential role in ascertaining the dynamics of temporal properties of arterial pressure waveforms. Second, we apply WA to evaluate a database of carotid artery pressure waveforms of healthy middle-aged women and men. Wavelet analysis has the potential to extract specific features (wavelet details), related to wave reflection and aortic valve closure, from a measured waveform. Analysis showed that the fifth detail, one of the waveform features extracted applying the wavelet decomposition, appeared to be the most appropriate for the analysis of carotid artery pressure waveforms. What remains to be assessed is how the information embedded in this detail can be further processed and transformed into quantitative data, and how it can be rendered useful for automated waveform classification and arterial function parameters with potential clinical applications.
Medical & Biological Engineering 10/2008; 47(2):165-73. · 1.76 Impact Factor