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Michael S Sacks - One of the best experts on this subject based on the ideXlab platform.

  • a novel bioreactor for mechanobiological studies of Engineered Heart Valve tissue formation under pulmonary arterial physiological flow conditions
    Journal of Biomechanical Engineering-transactions of The Asme, 2014
    Co-Authors: Sharan Ramaswamy, Steven M Boronyak, Andrew Holmes, Fotis Sotiropoulos, Michael S Sacks
    Abstract:

    Engineered tissue approaches for the development of tissue Engineered Heart Valves (TEHVs) offer the possibility of accommodating somatic growth, which in principle present a significant advance over current prosthetic Valve replacements for the treatment of congenital Heart Valve disease [1]. The need for bioreactors designed for improving the physical integrity of Engineered Heart Valve tissues prior to implantation has been well established [2–5]. Several studies have shown enhanced cell activity and tissue formation that can occur when simulated physiological culture environments are created in vitro [6–8]. At the organ level, several bioreactors that can provide TEHV leaflets with a dynamic conditioning environment that replicates hemodynamic parameters such as arterial pressure and flow conditions have been developed [9–11]. Early results using these pulsatile flow loop-based devices showed increased cell viability [4] and graded cell/tissue layering with cells orientated with the flow direction in comparison to unconditioned controls [9]. Previously, we subjected TEHV trileaflet constructs seeded with BMSCs, to simulated pulmonary artery pressure hemodynamic conditions for three weeks [12]. Under these conditions, we found quadrupled collagen mass and enhanced presence of deoxyribonucleic acid (DNA). Moreover, evidence from trileaflet Valve flow patterns, along with similar patterns evident in our earlier bioreactor studies [13,14], led us to speculate that fluid-induced oscillatory shear stresses are a potential mechanism responsible for substantial enhancement in BMSC-derived de novo collagen formation. More recently, additional investigations have demonstrated the utility of other progenitor cell sources such as adipose derived stem cells [15] and periodontal ligament cells [16] for Heart Valve tissue engineering. Therefore, Heart Valve tissue engineering requires an as yet to be determined combination of Heart Valve-relevant mechanical conditions, cell stimulation, and scaffold for the systematic optimization of Engineered Heart Valve tissues. However, use of intact trileaflet Heart Valve constructs in mechanical conditioning studies remain confounded by the complex, simultaneous flow and leaflet deformations that occur during normal function. Moreover, for optimization purposes, the cell type(s), scaffold materials, biochemical constituents of the culturing media, and the specific stress modalities (Valves are subject to coupled fluid, tensile, and flexural stresses [1,12,13,17]) are of primary importance. To this end, the effects of individual and combined stress states together with different scaffold materials and cell sources can be systematically evaluated in terms of outcomes such as bulk protein content, cell differentiation capacity, Engineered tissue mechanical properties and cellular signaling events, all of which may serve to elucidate how external mechanical factors modulate cell to extracellular matrix interactions. These studies can then subsequently lead to the development of optimal in vitro conditioning protocols with the specific intent of mechanically stimulating Engineered tissue formation [1]. We previously developed a bioreactor that permitted coupled or decoupled FSF as applied to rectangular scaffold specimens [13,14,18,19]. The rationale for this bioreactor was to investigate the effects of internal and external stress states found in native Heart Valves to Engineered tissue development. Using this system with BMSCs seeded onto scaffolds, we determined that combined cyclic flexure and fluid-induced shear stresses during conditioning were found to synergistically accelerate tissue production [13]. This study also underscored the need for rational, mechanistic approaches in understanding the role of mechanical conditioning on growing tissues under well-controlled conditions. However, a limitation of these studies was the inability to produce physiological to supraphysiological hemodynamic flow conditions. Previous investigations have experimentally determined the dynamic range of fluid-induced shear stresses on trileaflet Valve geometries, with an upper limit leaflet shear stress of ∼79 dynes/cm2, when a flow rate of 22.5 l/min was prescribed [20–22]. Subsequent studies have used this limit in computational models of Heart Valve dynamics [23] and in the design of shear stress bioreactors [24]. In an in vivo environment, however, native aortic Valve leaflet surfaces on the ventricular side are typically exposed to shear stresses in the order of ∼6 dynes/cm2 during end systole [25]; the stresses are an order of magnitude lower on the arterial side. In addition, dynamic flexure and stretch states need to be coupled to shear stresses in a bioreactor to make it physiologically relevant for Heart Valves. In the present study, we developed a new bioreactor system capable of developing physiologically relevant fluid-induced shear stresses and regionally specific flow patterns to scaffold specimens, and couple these stresses to cyclic flexure and/or stretch states if desired. We utilized a cylindrical conduit configuration for the conditioning chamber to allow for higher fluid velocities, translating to higher shear stresses on the in situ tissue specimens while retaining laminar flow conditions. Moving boundary CFD simulations were performed to predict the flow field under combined cyclic flexure and steady flow (cyclic-flex-flow) states using various combinations of flow rate, and media viscosity. The device was successfully constructed and tested for incubator housing, gas exchange, and sterility. In addition, we performed a pilot experiment using biodegradable polymer scaffolds seeded with BMSCs to demonstrate initial efficacy.

  • computational structural biomechanical models to guide tissue Engineered Heart Valve leaflet fabrication
    5th Biennial Conference on Heart Valve Biology and Tissue Engineering, 2012
    Co-Authors: Antonio Damore, John E. Mayer, William R. Wagner, Ahmed Bayoumi, Nicholas J Amoroso, Michael S Sacks
    Abstract:

    Abstract A computational structural deterministic modeling strategy has been developed and experimentally validated to (1) assist tissue engineering scaffold fabrication, and as a consequence to improve in vivo scaffolds performances, and (2) provide a better understanding of cellular mechanical and metabolic response to local micro-structural deformations of the extracellular matrix (ECM). Image analysis software was developed and tested on electrospun poly (ester urethane) urea (PEUU) scaffolds, collagen gels, decellularized tissues. The algorithm analyzed SEM and multi-photon images (maximum imaging penetration depth: 160 µm) providing a full 3D characterization of Engineered constructs morphology (n ≥ 6). The detected material topologies were adopted to generate statistically equivalent scaffold biomechanical models minimizing the difference between the real material and network model architectural features. The mechanical response at the macro scale was fully characterized by stress control biaxial tests (n ≥ 6). The experimental biaxial response was used to calibrate a Finite Element Model able to predict, for a given material topology, the mechanical response at both organ (cm), cells (100 µm) and fiber (1 µm) levels. Scaffold networks models were imported in Abaqus, Yeoh strain energy with incompressibility hypothesis and t2d2h elements were adopted. Stress vs. strain prediction was produced for four different scaffold groups: isotropic ES-PEUU, anisotropic ES-PEUU, Vascular Smooth Muscle Cells integrated PEUU, Polystyrene micro-spheres integrated (10 µm diameter) proving the flexibility of the modeling approach. At mesoscopic level nuclear aspect ratio vs. strain curve for the rat VSMCs embedded into the scaffold was produced and compared with previous experimental findings. At the microscopic level the single fiber initial shear modulus was quantified from the strain energy function material parameters, and compared with Atomic Force Microscopy measurements on single PEUU fibers. The developed generalist modeling approach bridges scaffold fabrication parameters, micro architecture, and organ level - cell level mechanical response.

  • three dimensional quantitative micromorphology of pre and post implanted Engineered Heart Valve tissues
    Annals of Biomedical Engineering, 2011
    Co-Authors: Chad E. Eckert, John E. Mayer, Brandon Mikulis, Dane Gerneke, Danielle Gottlieb, Ian J Legrice, Robert F Padera, Frederick J Schoen, Michael S Sacks
    Abstract:

    There is a significant gap in our knowledge of Engineered Heart Valve tissue (EHVT) development regarding detailed three-dimensional (3D) tissue formation and remodeling from the point of in vitro culturing to full in vivo function. As a step toward understanding the complexities of EHVT formation and remodeling, a novel serial confocal microscopy technique was employed to obtain 3D microstructural information of pre-implant (PRI) and post-implant for 12 weeks (POI) EHVT fabricated from PGA:PLLA scaffolds and seeded with ovine bone-marrow-derived mesenchymal stem cells. Custom scaffold fiber tracking software was developed to quantify scaffold fiber architectural features such as length, tortuosity, and minimum scaffold fiber–fiber separation distance and scaffold fiber orientation was quantified utilizing a 3D fabric tensor. In addition, collagen and cellular density of ovine pulmonary Valve leaflet tissue were also analyzed for baseline comparisons. Results indicated that in the unseeded state, scaffold fibers formed a continuous, oriented network. In the PRI state, the scaffold showed some fragmentation with a scaffold volume fraction of 7.79%. In the POI specimen, the scaffold became highly fragmented, forming a randomly distributed short fibrous network (volume fraction of 2.03%) within a contiguous, dense collagenous matrix. Both PGA and PLLA scaffold fibers were observed in the PRI and POI specimens. Collagen density remained similar in both PRI and POI specimens (74.2 and 71.5%, respectively), though the distributions in the transmural direction appeared slightly more homogenous in the POI specimen. Finally, to guide future 2D histological studies for large-scale studies (since acquisition of high-resolution volumetric data is not practical for all specimens), we investigated changes in relevant collagen and scaffold metrics (collagen density and scaffold fiber orientation) with varying section spacing. It was found that a sectioning spacing up to 25 μm (for scaffold morphology) and 50 μm (for collagen density) in both PRI and POI tissues did not result in loss of information fidelity, and that sectioning in the circumferential or radial direction provides the greatest preservation of information. This is the first known work to investigate EHVT microstructure over a large volume with high resolution and to investigate time evolving in vivo EHVT morphology. The important scaffold fiber structural changes observed provide morphological information crucial for guiding future structurally based constitutive modeling efforts focused on better understanding EHVT tissue formation and remodeling.

  • Three-Dimensional High Resolution Scaffold Fiber Architecture and Morphology in Tissue Engineered Heart Valve Tissue
    ASME 2010 Summer Bioengineering Conference Parts A and B, 2010
    Co-Authors: Chad E. Eckert, John E. Mayer, Brandon Mikulis, Dane Gerneke, Danielle Gottlieb, Bruce H. Smaill, Michael S Sacks
    Abstract:

    Engineered Heart Valve tissue (EHVT) has received much attention as a potential pediatric Valve replacement therapy, offering prospective long-term functional improvements over current options. A significant gap in the literature exists, however, regarding estimating tissue mechanical properties from tissue-scaffold composites. Detailed three-dimensional structural information prior to implantation (in vitro) and after implantation in (in vivo) is needed for improved modeling of tissue properties. As such, a novel high-resolution imaging technique will be employed to obtain three-dimensional microstructural information. Analysis techniques will be used to fully quantify constituents of interest including scaffold, collagen, and cellular information and to develop appropriate two-dimensional sectioning sampling protocols. It is the intent of this work to guide modeling efforts to better elucidate EHVT tissue-specific mechanical properties.

  • three dimensional high resolution scaffold fiber architecture and morphology in tissue Engineered Heart Valve tissue
    ASME 2010 Summer Bioengineering Conference Parts A and B, 2010
    Co-Authors: Chad E. Eckert, John E. Mayer, Brandon Mikulis, Dane Gerneke, Danielle Gottlieb, Bruce H. Smaill, Michael S Sacks
    Abstract:

    Engineered Heart Valve tissue (EHVT) has received much attention as a potential pediatric Valve replacement therapy, offering prospective long-term functional improvements over current options. A significant gap in the literature exists, however, regarding estimating tissue mechanical properties from tissue-scaffold composites. Detailed three-dimensional structural information prior to implantation (in vitro) and after implantation in (in vivo) is needed for improved modeling of tissue properties. As such, a novel high-resolution imaging technique will be employed to obtain three-dimensional microstructural information. Analysis techniques will be used to fully quantify constituents of interest including scaffold, collagen, and cellular information and to develop appropriate two-dimensional sectioning sampling protocols. It is the intent of this work to guide modeling efforts to better elucidate EHVT tissue-specific mechanical properties.Copyright © 2010 by ASME

John E. Mayer - One of the best experts on this subject based on the ideXlab platform.

  • computational structural biomechanical models to guide tissue Engineered Heart Valve leaflet fabrication
    5th Biennial Conference on Heart Valve Biology and Tissue Engineering, 2012
    Co-Authors: Antonio Damore, John E. Mayer, William R. Wagner, Ahmed Bayoumi, Nicholas J Amoroso, Michael S Sacks
    Abstract:

    Abstract A computational structural deterministic modeling strategy has been developed and experimentally validated to (1) assist tissue engineering scaffold fabrication, and as a consequence to improve in vivo scaffolds performances, and (2) provide a better understanding of cellular mechanical and metabolic response to local micro-structural deformations of the extracellular matrix (ECM). Image analysis software was developed and tested on electrospun poly (ester urethane) urea (PEUU) scaffolds, collagen gels, decellularized tissues. The algorithm analyzed SEM and multi-photon images (maximum imaging penetration depth: 160 µm) providing a full 3D characterization of Engineered constructs morphology (n ≥ 6). The detected material topologies were adopted to generate statistically equivalent scaffold biomechanical models minimizing the difference between the real material and network model architectural features. The mechanical response at the macro scale was fully characterized by stress control biaxial tests (n ≥ 6). The experimental biaxial response was used to calibrate a Finite Element Model able to predict, for a given material topology, the mechanical response at both organ (cm), cells (100 µm) and fiber (1 µm) levels. Scaffold networks models were imported in Abaqus, Yeoh strain energy with incompressibility hypothesis and t2d2h elements were adopted. Stress vs. strain prediction was produced for four different scaffold groups: isotropic ES-PEUU, anisotropic ES-PEUU, Vascular Smooth Muscle Cells integrated PEUU, Polystyrene micro-spheres integrated (10 µm diameter) proving the flexibility of the modeling approach. At mesoscopic level nuclear aspect ratio vs. strain curve for the rat VSMCs embedded into the scaffold was produced and compared with previous experimental findings. At the microscopic level the single fiber initial shear modulus was quantified from the strain energy function material parameters, and compared with Atomic Force Microscopy measurements on single PEUU fibers. The developed generalist modeling approach bridges scaffold fabrication parameters, micro architecture, and organ level - cell level mechanical response.

  • three dimensional quantitative micromorphology of pre and post implanted Engineered Heart Valve tissues
    Annals of Biomedical Engineering, 2011
    Co-Authors: Chad E. Eckert, John E. Mayer, Brandon Mikulis, Dane Gerneke, Danielle Gottlieb, Ian J Legrice, Robert F Padera, Frederick J Schoen, Michael S Sacks
    Abstract:

    There is a significant gap in our knowledge of Engineered Heart Valve tissue (EHVT) development regarding detailed three-dimensional (3D) tissue formation and remodeling from the point of in vitro culturing to full in vivo function. As a step toward understanding the complexities of EHVT formation and remodeling, a novel serial confocal microscopy technique was employed to obtain 3D microstructural information of pre-implant (PRI) and post-implant for 12 weeks (POI) EHVT fabricated from PGA:PLLA scaffolds and seeded with ovine bone-marrow-derived mesenchymal stem cells. Custom scaffold fiber tracking software was developed to quantify scaffold fiber architectural features such as length, tortuosity, and minimum scaffold fiber–fiber separation distance and scaffold fiber orientation was quantified utilizing a 3D fabric tensor. In addition, collagen and cellular density of ovine pulmonary Valve leaflet tissue were also analyzed for baseline comparisons. Results indicated that in the unseeded state, scaffold fibers formed a continuous, oriented network. In the PRI state, the scaffold showed some fragmentation with a scaffold volume fraction of 7.79%. In the POI specimen, the scaffold became highly fragmented, forming a randomly distributed short fibrous network (volume fraction of 2.03%) within a contiguous, dense collagenous matrix. Both PGA and PLLA scaffold fibers were observed in the PRI and POI specimens. Collagen density remained similar in both PRI and POI specimens (74.2 and 71.5%, respectively), though the distributions in the transmural direction appeared slightly more homogenous in the POI specimen. Finally, to guide future 2D histological studies for large-scale studies (since acquisition of high-resolution volumetric data is not practical for all specimens), we investigated changes in relevant collagen and scaffold metrics (collagen density and scaffold fiber orientation) with varying section spacing. It was found that a sectioning spacing up to 25 μm (for scaffold morphology) and 50 μm (for collagen density) in both PRI and POI tissues did not result in loss of information fidelity, and that sectioning in the circumferential or radial direction provides the greatest preservation of information. This is the first known work to investigate EHVT microstructure over a large volume with high resolution and to investigate time evolving in vivo EHVT morphology. The important scaffold fiber structural changes observed provide morphological information crucial for guiding future structurally based constitutive modeling efforts focused on better understanding EHVT tissue formation and remodeling.

  • Three-Dimensional High Resolution Scaffold Fiber Architecture and Morphology in Tissue Engineered Heart Valve Tissue
    ASME 2010 Summer Bioengineering Conference Parts A and B, 2010
    Co-Authors: Chad E. Eckert, John E. Mayer, Brandon Mikulis, Dane Gerneke, Danielle Gottlieb, Bruce H. Smaill, Michael S Sacks
    Abstract:

    Engineered Heart Valve tissue (EHVT) has received much attention as a potential pediatric Valve replacement therapy, offering prospective long-term functional improvements over current options. A significant gap in the literature exists, however, regarding estimating tissue mechanical properties from tissue-scaffold composites. Detailed three-dimensional structural information prior to implantation (in vitro) and after implantation in (in vivo) is needed for improved modeling of tissue properties. As such, a novel high-resolution imaging technique will be employed to obtain three-dimensional microstructural information. Analysis techniques will be used to fully quantify constituents of interest including scaffold, collagen, and cellular information and to develop appropriate two-dimensional sectioning sampling protocols. It is the intent of this work to guide modeling efforts to better elucidate EHVT tissue-specific mechanical properties.

  • three dimensional high resolution scaffold fiber architecture and morphology in tissue Engineered Heart Valve tissue
    ASME 2010 Summer Bioengineering Conference Parts A and B, 2010
    Co-Authors: Chad E. Eckert, John E. Mayer, Brandon Mikulis, Dane Gerneke, Danielle Gottlieb, Bruce H. Smaill, Michael S Sacks
    Abstract:

    Engineered Heart Valve tissue (EHVT) has received much attention as a potential pediatric Valve replacement therapy, offering prospective long-term functional improvements over current options. A significant gap in the literature exists, however, regarding estimating tissue mechanical properties from tissue-scaffold composites. Detailed three-dimensional structural information prior to implantation (in vitro) and after implantation in (in vivo) is needed for improved modeling of tissue properties. As such, a novel high-resolution imaging technique will be employed to obtain three-dimensional microstructural information. Analysis techniques will be used to fully quantify constituents of interest including scaffold, collagen, and cellular information and to develop appropriate two-dimensional sectioning sampling protocols. It is the intent of this work to guide modeling efforts to better elucidate EHVT tissue-specific mechanical properties.Copyright © 2010 by ASME

  • the role of organ level conditioning on the promotion of Engineered Heart Valve tissue development in vitro using mesenchymal stem cells
    Biomaterials, 2010
    Co-Authors: Sharan Ramaswamy, John E. Mayer, George C Engelmayr, Danielle Gottlieb, David E. Schmidt, Elena Aikawa, Virna L. Sales, Diana M Gaitanleon, Michael S Sacks
    Abstract:

    Abstract We have previously shown that combined flexure and flow (CFF) augment Engineered Heart Valve tissue formation using bone marrow-derived mesenchymal stem cells (MSC) seeded on polyglycolic acid (PGA)/poly-L-lactic acid (PLLA) blend nonwoven fibrous scaffolds (Engelmayr, et al., Biomaterials 2006; vol. 27 pp. 6083–95). In the present study, we sought to determine if these phenomena were reproducible at the organ level in a functional tri-leaflet Valve. Tissue Engineered Valve constructs (TEVC) were fabricated using PGA/PLLA nonwoven fibrous scaffolds then seeded with MSCs. Tissue formation rates using both standard and augmented (using basic fibroblast growth factor [bFGF] and ascorbic acid-2-phosphate [AA2P]) media to enhance the overall production of collagen were evaluated, along with their relation to the local fluid flow fields. The resulting TEVCs were statically cultured for 3 weeks, followed by a 3 week dynamic culture period using our organ level bioreactor (Hildebrand et al., ABME, Vol. 32, pp. 1039–49, 2004) under approximated pulmonary artery conditions. Results indicated that supplemented media accelerated collagen formation (∼185% increase in collagen mass/MSC compared to standard media), as well as increasing collagen mass production from 3.90 to 4.43 pg/cell/week from 3 to 6 weeks. Using augmented media, dynamic conditioning increased collagen mass production rate from 7.23 to 13.65 pg/cell/week (88.8%) during the dynamic culture period, along with greater preservation of net DNA. Moreover, when compared to our previous CFF study, organ level conditioning increased the collagen production rate from 4.76 to 6.42 pg/cell/week (35%). Newly conducted CFD studies of the CFF specimen flow patterns suggested that oscillatory surface shear stresses were surprisingly similar to a tri-leaflet Valve. Overall, we found that the use of simulated pulmonary artery conditions resulted in substantially larger collagen mass production levels and rates found in our earlier CFF study. Moreover, given the fact that the scaffolds underwent modest strains (∼7% max) during either CFF or physiological conditioning, the oscillatory surface shear stresses estimated in both studies may play a substantial role in eliciting MSC collagen production in the highly dynamic Engineered Heart Valve fluid mechanical environment.

Carlijn V. C. Bouten - One of the best experts on this subject based on the ideXlab platform.

  • Variation in tissue outcome of ovine and human Engineered Heart Valve constructs: relevance for tissue engineering.
    Regenerative medicine, 2012
    Co-Authors: Daphne Van Geemen, Fpt Frank Baaijens, Anita Anita Driessen-mol, Leonie G M Grootzwagers, R. Sarita Soekhradj-soechit, Paul W. Riem Vis, Carlijn V. C. Bouten
    Abstract:

    Clinical application of tissue Engineered Heart Valves requires precise control of the tissue culture process to predict tissue composition and mechanical properties prior to implantation, and to understand the variation in tissue outcome. To this end we investigated cellular phenotype and tissue properties of ovine (n = 8) and human (n = 7) tissue Engineered Heart Valve constructs to quantify variations in tissue outcome within species, study the differences between species and determine possible indicators of tissue outcome. Tissue constructs consisted of polyglycolic acid/poly-4-hydroxybutyrate scaffolds, seeded with myofibroblasts obtained from the jugular vein (sheep) or the saphenous vein (from humans undergoing cardiac surgery) and cultured under static conditions. Prior to seeding, protein expression of α-smooth muscle actin, vimentin, nonmuscle myosin heavy chain and heat shock protein 47 were determined to identify differences at an early stage of the tissue engineering process. After 4 weeks of culture, tissue composition and mechanical properties were quantified as indicators of tissue outcome. After 4 weeks of tissue culture, tissue properties of all ovine constructs were comparable, while there was a larger variation in the properties of the human constructs, especially the elastic modulus and collagen content. In addition, ovine constructs differed in composition from the human constructs. An increased number of α-smooth muscle actin-positive cells before seeding was correlated with the collagen content in the Engineered Heart Valve constructs. Moreover, tissue stiffness increased with increasing collagen content. The results suggest that the culture process of ovine tissues can be controlled, whereas the mechanical properties, and hence functionality, of tissues originating from human material are more difficult to control. On-line evaluation of tissue properties during culture or more early cellular markers to predict the properties of autologous tissues cultured for individual patients are, therefore, of utmost importance for future clinical application of autologous Heart Valve tissue engineering. As an example, this study shows that α-smooth muscle actin might be an indicator of tissue mechanical properties.

  • variation in tissue outcome of ovine and human Engineered Heart Valve constructs relevance for tissue engineering
    Regenerative Medicine, 2012
    Co-Authors: Daphne Van Geemen, Anita Anita Driessenmol, Fpt Frank Baaijens, Leonie G M Grootzwagers, Paul W. Riem Vis, Sarita R Soekhradjsoechit, Carlijn V. C. Bouten
    Abstract:

    Aim: Clinical application of tissue Engineered Heart Valves requires precise control of the tissue culture process to predict tissue composition and mechanical properties prior to implantation, and to understand the variation in tissue outcome. To this end we investigated cellular phenotype and tissue properties of ovine (n = 8) and human (n = 7) tissue Engineered Heart Valve constructs to quantify variations in tissue outcome within species, study the differences between species and determine possible indicators of tissue outcome. Materials & methods: Tissue constructs consisted of polyglycolic acid/poly-4-hydroxybutyrate scaffolds, seeded with myofibroblasts obtained from the jugular vein (sheep) or the saphenous vein (from humans undergoing cardiac surgery) and cultured under static conditions. Prior to seeding, protein expression of α-smooth muscle actin, vimentin, nonmuscle myosin heavy chain and heat shock protein 47 were determined to identify differences at an early stage of the tissue engineering...

  • Tissue Engineered Heart Valves Develop Native-Like Collagen Architecture
    ASME 2009 Summer Bioengineering Conference Parts A and B, 2009
    Co-Authors: Martijn A. J. Cox, Carlijn V. C. Bouten, Jeroen Kortsmit, Frank P. T. Baaijens
    Abstract:

    Over the last few years, research interest in tissue engineering as an alternative for current treatment and replacement strategies for cardiovascular and Heart Valve diseases has significantly increased. For a tissue Engineered Heart Valve to be functional, it should be able to withstand the high pressures and flows that occur in vivo. Nature’s solution for this challenge can be found in the complex collagen fiber architecture of the native aortic Valve (Fig. 1).

  • hypoxia induces near native mechanical properties in Engineered Heart Valve tissue
    Circulation, 2009
    Co-Authors: Angelique Balguid, Frank P. T. Baaijens, Anita Mol, Marijke A. A. Van Vlimmeren, Carlijn V. C. Bouten
    Abstract:

    Background— Previous attempts in Heart Valve tissue engineering (TE) failed to produce autologous Valve replacements with native-like mechanical behavior to allow for systemic pressure applications. Because hypoxia and insulin are known to promote protein synthesis by adaptive cellular responses, a physiologically relevant oxygen tension and insulin supplements were applied to the growing Heart Valve tissues to enhance their mechanical properties. Methods and Results— Scaffolds of rapid-degrading polyglycolic acid meshes coated with poly-4-hydroxybutyrate were seeded with human saphenous vein myofibroblasts. The tissue-Engineered constructs were cultured under normal oxygen tension (normoxia) or hypoxia (7% O2) and incubated with or without insulin. Glycosaminoglycan production in the constructs approached that of native values under the influence of hypoxia and under the influence of insulin. Both insulin and hypoxia were associated with enhanced matrix production and improved mechanical properties; howe...

  • Intermittent straining accelerates the development of tissue properties in Engineered Heart Valve tissue
    Tissue engineering. Part A, 2009
    Co-Authors: Mp Mirjam Rubbens, Fpt Frank Baaijens, Anita Mol, Ra Ralf Boerboom, Ruud A. Bank, Carlijn V. C. Bouten
    Abstract:

    Tissue-Engineered Heart Valves lack sufficient amounts of functionally organized structures and consequently do not meet in vivo mechanical demands. To optimize tissue architecture and hence improve mechanical properties, various in vitro mechanical conditioning protocols have been proposed, of which intermittent straining is most promising in terms of tissue properties. We hypothesize that this is due to an improved collagen matrix synthesis, maturation, and organization, triggered by periodic straining of cells. To test this hypothesis, we studied the effect of intermittent versus constrained conditioning with time (2-4 weeks), using a novel model system of human Heart Valve tissue. Temporal variations in collagen production, cross-link density, and mechanical properties were quantified in Engineered Heart Valve tissue, cyclically strained for 3-h periods, alternated with 3-h periods rest. In addition, an innovative method for vital collagen imaging was used to monitor collagen organization. Intermittent straining resulted in increased collagen production, cross-link densities, collagen organization, and mechanical properties at faster rates, as compared to constrained controls, leading to stronger tissues in shorter culture periods. This is of utmost importance for Heart Valve tissue engineering, where insufficient mechanical properties are currently the main limiting factor.

Petra Mela - One of the best experts on this subject based on the ideXlab platform.

  • Tissue-Engineered Heart Valve with a Tubular Leaflet Design for Minimally Invasive Transcatheter Implantation
    Tissue engineering. Part C Methods, 2014
    Co-Authors: Ricardo Moreira, Thaddaeus Velz, Nuno Alves, Valentine Gesché, Axel Malischewski, Thomas Schmitz-rode, J. Frese, Stefan Jockenhoevel, Petra Mela
    Abstract:

    Transcatheter aortic Valve implantation of (nonviable) bioprosthetic Valves has been proven a valid alternative to conventional surgical implantation in patients at high or prohibitive mortality risk. In this study we present the in vitro proof-of-principle of a newly developed tissue-Engineered Heart Valve for minimally invasive implantation, with the ultimate aim of adding the unique advantages of a living tissue with regeneration capabilities to the continuously developing transcatheter technologies. The tube-in-stent is a fibrin-based tissue-Engineered Valve with a tubular leaflet design. It consists of a tubular construct sewn into a self-expandable nitinol stent at three commissural attachment points and along a circumferential line so that it forms three coaptating leaflets by collapsing under diastolic back pressure. The tubular constructs were molded with fibrin and human umbilical vein cells. After 3 weeks of conditioning in a bioreactor, the Valves were fully functional with unobstructed openin...

  • tissue Engineered fibrin based Heart Valve with a tubular leaflet design
    Tissue Engineering Part C-methods, 2014
    Co-Authors: Miriam Weber, Ricardo Moreira, Valentine Gesché, J. Frese, Stefan Jockenhoevel, Eriona Heta, Thomas Schermer, Petra Mela
    Abstract:

    The general approach in Heart Valve tissue engineering is to mimic the shape of the native Valve in the attempt to recreate the natural haemodynamics. In this article, we report the fabrication of the first tissue-Engineered Heart Valve (TEHV) based on a tubular leaflet design, where the function of the leaflets of semilunar Heart Valves is performed by a simple tubular construct sutured along a circumferential line at the root and at three single points at the sinotubular junction. The tubular design is a recent development in pericardial (nonviable) bioprostheses, which has attracted interest because of the simplicity of the construction and the reliability of the implantation technique. Here we push the potential of the concept further from the fabrication and material point of view to realize the tube-in-tube Valve: an autologous, living HV with remodelling and growing capability, physiological haemocompatibility, simple to construct and fast to implant. We developed two different fabrication/conditio...

Sharan Ramaswamy - One of the best experts on this subject based on the ideXlab platform.

  • a sweet spot for fluid induced oscillations in the conditioning of stem cell based Engineered Heart Valve tissues
    Journal of Biomechanics, 2017
    Co-Authors: Alexander Williams, Manuel Salinas, Sana Nasim, Arash Moshkforoush, Nikolaos M Tsoukias, Sharan Ramaswamy
    Abstract:

    Abstract Fluid-induced shear stresses are involved in the development of cardiovascular tissues. In a tissue engineering framework, this stimulus has also been considered as a mechanical regulator of stem cell differentiation. We recently demonstrated that the fluid-oscillating effect in combination with a physiologically-relevant shear stress magnitude contributes to the formation of stem cell-derived de novo Heart Valve tissues. However, the range of oscillations necessary to induce favorable gene expression and Engineered tissue formation is unknown. In this study, we took a computational approach to establish a range of oscillatory shear stresses that may optimize in vitro valvular tissue growth. Taking a biomimetic approach, three physiologically-relevant flow waveforms from the human: (i) aorta, (ii) pulmonary artery and (iii) superior vena cava were utilized to simulate pulsatile flow conditions within a bioreactor that housed 3 tissue specimens. Results were compared to non-physiological pulsatile flow (NPPF) and cyclic flexure-steady flow (Flex-Flow) conditions. The oscillatory shear index (OSI) was used to quantify the fluid-induced oscillations occurring on the specimen surfaces. The range of mean OSI under the physiological conditions investigated was found to be 0.18 ≤ OSI ≤ 0.23. On the other hand, NPPF and Flex-Flow environments yielded a mean OSI of 0.37 and 0.11 respectively, which were 46% higher and 45% lower than physiological conditions. Moreover, we subsequently conducted OSI-based human bone marrow stem cell (HBMSC) culture experiments which resulted in preferential valvular gene expression and phenotype (significant upregulation of BMP, KLF2A, CD31 and α-SMA using an OSI of 0.23 in comparison to a lower OSI of 0.10 or a higher OSI of 0.38; p  both fluid-induced oscillations and shear stresses.

  • a novel bioreactor for mechanobiological studies of Engineered Heart Valve tissue formation under pulmonary arterial physiological flow conditions
    Journal of Biomechanical Engineering-transactions of The Asme, 2014
    Co-Authors: Sharan Ramaswamy, Steven M Boronyak, Andrew Holmes, Fotis Sotiropoulos, Michael S Sacks
    Abstract:

    Engineered tissue approaches for the development of tissue Engineered Heart Valves (TEHVs) offer the possibility of accommodating somatic growth, which in principle present a significant advance over current prosthetic Valve replacements for the treatment of congenital Heart Valve disease [1]. The need for bioreactors designed for improving the physical integrity of Engineered Heart Valve tissues prior to implantation has been well established [2–5]. Several studies have shown enhanced cell activity and tissue formation that can occur when simulated physiological culture environments are created in vitro [6–8]. At the organ level, several bioreactors that can provide TEHV leaflets with a dynamic conditioning environment that replicates hemodynamic parameters such as arterial pressure and flow conditions have been developed [9–11]. Early results using these pulsatile flow loop-based devices showed increased cell viability [4] and graded cell/tissue layering with cells orientated with the flow direction in comparison to unconditioned controls [9]. Previously, we subjected TEHV trileaflet constructs seeded with BMSCs, to simulated pulmonary artery pressure hemodynamic conditions for three weeks [12]. Under these conditions, we found quadrupled collagen mass and enhanced presence of deoxyribonucleic acid (DNA). Moreover, evidence from trileaflet Valve flow patterns, along with similar patterns evident in our earlier bioreactor studies [13,14], led us to speculate that fluid-induced oscillatory shear stresses are a potential mechanism responsible for substantial enhancement in BMSC-derived de novo collagen formation. More recently, additional investigations have demonstrated the utility of other progenitor cell sources such as adipose derived stem cells [15] and periodontal ligament cells [16] for Heart Valve tissue engineering. Therefore, Heart Valve tissue engineering requires an as yet to be determined combination of Heart Valve-relevant mechanical conditions, cell stimulation, and scaffold for the systematic optimization of Engineered Heart Valve tissues. However, use of intact trileaflet Heart Valve constructs in mechanical conditioning studies remain confounded by the complex, simultaneous flow and leaflet deformations that occur during normal function. Moreover, for optimization purposes, the cell type(s), scaffold materials, biochemical constituents of the culturing media, and the specific stress modalities (Valves are subject to coupled fluid, tensile, and flexural stresses [1,12,13,17]) are of primary importance. To this end, the effects of individual and combined stress states together with different scaffold materials and cell sources can be systematically evaluated in terms of outcomes such as bulk protein content, cell differentiation capacity, Engineered tissue mechanical properties and cellular signaling events, all of which may serve to elucidate how external mechanical factors modulate cell to extracellular matrix interactions. These studies can then subsequently lead to the development of optimal in vitro conditioning protocols with the specific intent of mechanically stimulating Engineered tissue formation [1]. We previously developed a bioreactor that permitted coupled or decoupled FSF as applied to rectangular scaffold specimens [13,14,18,19]. The rationale for this bioreactor was to investigate the effects of internal and external stress states found in native Heart Valves to Engineered tissue development. Using this system with BMSCs seeded onto scaffolds, we determined that combined cyclic flexure and fluid-induced shear stresses during conditioning were found to synergistically accelerate tissue production [13]. This study also underscored the need for rational, mechanistic approaches in understanding the role of mechanical conditioning on growing tissues under well-controlled conditions. However, a limitation of these studies was the inability to produce physiological to supraphysiological hemodynamic flow conditions. Previous investigations have experimentally determined the dynamic range of fluid-induced shear stresses on trileaflet Valve geometries, with an upper limit leaflet shear stress of ∼79 dynes/cm2, when a flow rate of 22.5 l/min was prescribed [20–22]. Subsequent studies have used this limit in computational models of Heart Valve dynamics [23] and in the design of shear stress bioreactors [24]. In an in vivo environment, however, native aortic Valve leaflet surfaces on the ventricular side are typically exposed to shear stresses in the order of ∼6 dynes/cm2 during end systole [25]; the stresses are an order of magnitude lower on the arterial side. In addition, dynamic flexure and stretch states need to be coupled to shear stresses in a bioreactor to make it physiologically relevant for Heart Valves. In the present study, we developed a new bioreactor system capable of developing physiologically relevant fluid-induced shear stresses and regionally specific flow patterns to scaffold specimens, and couple these stresses to cyclic flexure and/or stretch states if desired. We utilized a cylindrical conduit configuration for the conditioning chamber to allow for higher fluid velocities, translating to higher shear stresses on the in situ tissue specimens while retaining laminar flow conditions. Moving boundary CFD simulations were performed to predict the flow field under combined cyclic flexure and steady flow (cyclic-flex-flow) states using various combinations of flow rate, and media viscosity. The device was successfully constructed and tested for incubator housing, gas exchange, and sterility. In addition, we performed a pilot experiment using biodegradable polymer scaffolds seeded with BMSCs to demonstrate initial efficacy.

  • glycosaminoglycan entrapment by fibrin in Engineered Heart Valve tissues
    Acta Biomaterialia, 2013
    Co-Authors: Abraham Alfonso, Sasmita Rath, Parvin Rafiee, Mario Hernandezespino, Mahreen Din, Florence George, Sharan Ramaswamy
    Abstract:

    Tissue Engineered Heart Valves (TEHVs) may provide a permanent solution to congenital Heart Valve disease by permitting somatic Valve growth in the pediatric patient. However, to date, TEHV studies have focused primarily on collagen, the dominant component of Valve extracellular matrix (ECM). Temporal decreases in other ECM components, such as the glycosaminoglycans (GAGs), generally decrease as cells produce more collagen under mechanically loaded states; nevertheless, GAGs represent a key component of the Valve ECM, providing structural stability and hydration to the leaflets. In an effort to retain GAGs within the Engineered constructs, here we investigated the utility of the protein fibrin in combination with a Valve-like, cyclic flexure and steady flow (flex-flow) mechanical conditioning culture process using adult human periodontal ligament cells (PLCs). We found both fibrin and flex-flow mechanical components to be independently significant (p<0.05), and hence important in influencing the DNA, GAG and collagen contents of the Engineered tissues. In addition, the interaction of fibrin with flex-flow was found to be significant in the case of collagen; specifically, the combination of these environments promoted PLC collagen production resulting in a significant difference compared to dynamic and statically cultured specimens without fibrin. Histological examination revealed that the GAGs were retained by fibrin entrapment and adhesion, which were subsequently confirmed by additional experiments on native Valve tissues. We conclude that fibrin in the flex-flow culture of Engineered Heart Valve tissues: (i) augments PLC-derived collagen production; and (ii) enhances retention of GAGs within the developing ECM.

  • Glycosaminoglycan entrapment by fibrin in Engineered Heart Valve tissues.
    Acta biomaterialia, 2013
    Co-Authors: Abraham Alfonso, Sasmita Rath, Parvin Rafiee, Mahreen Din, Florence George, Mario Hernandez-espino, Sharan Ramaswamy
    Abstract:

    Tissue Engineered Heart Valves (TEHVs) may provide a permanent solution to congenital Heart Valve disease by permitting somatic Valve growth in the pediatric patient. However, to date, TEHV studies have focused primarily on collagen, the dominant component of Valve extracellular matrix (ECM). Temporal decreases in other ECM components, such as the glycosaminoglycans (GAGs), generally decrease as cells produce more collagen under mechanically loaded states; nevertheless, GAGs represent a key component of the Valve ECM, providing structural stability and hydration to the leaflets. In an effort to retain GAGs within the Engineered constructs, here we investigated the utility of the protein fibrin in combination with a Valve-like, cyclic flexure and steady flow (flex-flow) mechanical conditioning culture process using adult human periodontal ligament cells (PLCs). We found both fibrin and flex-flow mechanical components to be independently significant (p

  • Computational Prediction of Fluid Induced Stress States in Dynamically Conditioned Engineered Heart Valve Tissues
    ASME 2012 Summer Bioengineering Conference Parts A and B, 2012
    Co-Authors: Manuel Salinas, David E. Schmidt, Richard R. Lange, Miguel Libera, Sharan Ramaswamy
    Abstract:

    There is extensive documented evidence that mechanical conditioning plays a significant role in the development of tissue grown in-vitro for Heart Valve scaffolds [1–3]. Modern custom made bioreactors have been used to study the mechanobiology of Engineered Heart Valve tissues [1]. Specifically fluid-induced shears stress patterns may play a critical role in up-regulating extracellular matrix secretion by progenitor cell sources such as bone marrow derived stem cells (BMSCs) [2] and increasing the possibility of cell differentiation towards a Heart Valve phenotype. We hypothesize that specific biomimetic fluid induced shear stress environments, particularly oscillatory shear stress (OSS), have significant effects on BMSCs phenotype and formation rates. As a first step here, we attempt to quantify and delineate the entire 3-D flow field by developing a CFD model to predict the fluid induced shear stress environments on Engineered Heart Valves tissue under quasi-static steady flow and dynamic steady flow conditions.