bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stress-Fiber Remodeling in 3D: ‘Contact Guidance vs Stretch Avoidance’?
Authors: Foolen Jasper , Baaijens Frank 
Published: July 2012

AbstractWhen engineering heart valves in vitro, matrix anisotropy is considered important for long-term in vivo functionality. However, it is not fully understood how to guide, maintain and control matrix anisotropy. Experiments suggest that collagen anisotropy is affected by actin-mediated cell traction and associated cellular orientation. Although cellular orientation in 2D can be manipulated via imposed uniaxial cyclic stretch, 3D data are lacking. We questioned how cyclic stretch influences actin and collagen orientation in 3D constructs. A novel micro-tissue platform system was designed, able to dynamically and biochemically load small-scale cell-populated fibrous tissues. Flexible membranes of Bioflex culture plates were provided with a rectangular array silicone posts. These silicone posts constrained a contracting gel mixture of human vena saphena cells (HVSC), collagen type I and matrigel. The constrained tissues were subjected to pure uniaxial cyclic stretch (10%, 0.5Hz, in the presence or absence of agents) on the Flexcell system. F-actin was taken as a measure for the cell traction direction, and the F-actin orientation was quantified throughout the complete tissue thickness (~ 300m) using fiber-tracking software, and was fitted using a bi-model distribution function. Uniaxial cyclic stretching for 3 days (preceded by 3 days of static constraint) resulted in stress-fibers that were oriented perpendicular to the stretching direction only at tissue surfaces, as generally observed in 2D. Strikingly, however, in the tissue core F-actin (and cell) and collagen orientation was biaxial. Immediate cyclic stretching, starting before polymerization of the collagen matrix, resulted in a strong stretch avoidance throughout the tissue, of both F-actin and collagen. We systematically investigated the effect of biochemical treatment, including MMP1 to perturb matrix integrity, MMP-1 + ROCK-inhibitor to counteract the possible MMP1-induced response, as well the effect of a lower and a higher initial collagen density. Experimental data suggests that F-actin stress-fibers avoid cyclic stretch in 3D, unless collagen contact guidance dictates otherwise.
Experimental and Computational Studies of the Aortic Bi-leaflet Mechanical Heart Valve (BMHV) Hemodynamics in an Idealized Left Ventricle
Authors: Bao Le Trung , Chaffin Brandon , Mirabella Lucia , Santhanakrishnan Arvind , Yoganathan Ajit , Sotiropoulos Fotis 
Published: July 2012

AbstractWe aim to validate the performance of our fluid structure interaction (FSI) simulations of a bi-leaflet mechanical heart valve in the aortic position., whose motion is driven by the beating left ventricle. We compare in vitro experiments and computations performed on an idealized model of the left ventricle (LV) with a St. Jude Medical Regent heart valve in the aortic position. The idealized LV consists of a truncated tetrahedron representing a simplified LV chamber with a single deformable surface made of silicone. The silicone surface simulates the lateral wall of the LV. The deformation of the LV is controlled by pressurizing the fluid surrounding the LV chamber via a Vivitro Superpump (Vivitro Systems; British Columbia). The experimental model simulates physiological flow rates and pressures that occur in the LV. The three-dimensional motion of the deformable surface is tracked using high speed cameras and reconstructed using a direct linear transformation. The reconstruction of the motion of the deformable surface has been validated against fluid volume flux of the LV measured using two Transonic Systems Inc. flow probes (Model ME-PXN; Ithaca, NY). The leaflet motion of the SJM is tracked using 2D photogrammetry with a single high speed camera. A two-dimensional DPIV system (LaVision GmbH; Goettingen, Germany) is used to acquire fluid velocity measurements within the ventricle and in the aortic position of the flow field through the cardiac cycle. In the computation, the ventricle kinematics, measured from experiment, is treated as an immersed boundary by the Curvilinear Immersed Boundary (CURVIB) method ( Ge et al., J. Comp. Physics, 2007). The leaflet kinematics of the BMHV are computed from the fluid-structure interaction solver FSI-CURVIB (Borazjani et al., J. Comp. Physics, 2008). The computational domain is a structured mesh of 8 million grid points with a physical timestep of 1 ms. We have previously shown the capability of the FSI solver to resolve the BMHV kinematics and the resulting flow patterns in a stand-alone aorta (Borazjani et al., J. Comp. Physics, 2008). The comparison between the experimental and computational results shows good agreement for the ventricular flow pattern. The details of the validation of coupled LV-BMHV simulations will be discussed in the presentation.
Modulating the Inflammatory Response for In Situ Tissue Engineering – The Role of MCP-1
Authors: Smits Anthal I.P.M. , Driessen-Mol Anita , Bouten Carlijin V.C. , Baaijens Frank P.T. 
Published: July 2012

AbstractInflammation is not merely a detrimental response to biomaterials. It can be considered as a natural agent of tissue remodeling, which is pivotal for the approach of in situ cardiovascular tissue engineering. Recently, a biodegradable synthetic scaffold was shown to remodel into a fully functional healthy blood vessel via an inflammation-mediated response. In fact, it was shown that initial infiltration of immune cells (i.e. monocytes) is indispensible for long-term remodeling of scaffolds and functionality of neo-tissues. This remodeling process is orchestrated by potent signaling molecules, of which monocyte chemotactic protein-1 (MCP-1) was identified as a key player. However, the exact mechanism remains unclear. We hypothesize that MCP-1 initiates a desired wound healing cascade by recruiting favorable monocyte and macrophage (M2 type) subpopulations in the implanted scaffold. To investigate the interactions between circulating cells and scaffolds, we have developed and validated a meso-fluidics setup that exposes small-scale 3D scaffolds to a circulating cell suspension in pulsatile flow with pressure and shear stress on the scaffold surface in the physiologic range for aortic valve and small diameter arteries. Electrospun polycaprolactone (PCL) scaffolds were loaded with fibrin gel with and without MCP-1 and placed into the fluidics setup. Human peripheral blood mononuclear cells (hPBMC) were isolated from healthy donors by density gradient centrifuging. The cells were resuspended in culture medium and circulated in the fluidics setup for up to 72 hours at a pulsatile flow (1Hz), with a peak pressure of approximately 100 mmHg and peak shear stress of 1.5 Pa on the scaffold surface. The cell suspensions were characterized at various time points by flow cytometry. The hPBMC suspension at the start consisted of CD45+ lymphocytes and monocytes. After 16 hours in the fluidics setup, the distinct monocyte subpopulation (8-20% of hPBMC) was no longer present in the medium, regardless of MCP-1 presence. This suggests monocyte activation by the scaffold, resulting in cell adhesion and monocyte-to-macrophage differentiation. Moreover, whole-mount immunostaining of the scaffolds demonstrated that addition of MCP-1 resulted in a significant increase in CD163 expression, which indicates the presence of a favorable monocyte subpopulation and macrophage polarization towards a wound healing M2 phenotype. Our results show that the PCL/fibrin scaffold evokes a response from circulating monocytes, resulting in rapid cell adhesion and infiltration. Moreover, this initial response can be modulated using MCP-1 to promote favorable M2 macrophage polarization, initiating the wound healing cascade that is necessary for long term remodeling of the synthetic scaffold.
An Analysis of Tissue-Engineered Pulmonary Valves Implanted in the Elderly Ovine Model
Authors: Theodoridis Karolina , Calistru Alexandru , Meyer Tanja , Tudorache Igor , Cebotari Serghei , Sarikouch Samir , Bara Christoph , Brehm Ralph , Hilfiker Andres , Haverich Axel 
Published: July 2012

AbstractBioprosthetic heart valve replacement, recommended for patients older than 65 years of age, increases the quality of life, however grafts exhibit limited functionality due to degradation and calcification. Decellularized and tissue-engineered pulmonary valves (PV) get repopulated by autologous interstitial cells when implanted into juvenile sheep. Thus, in vivo matrix guided regeneration results in restored valve function. In this study, we investigated the regeneration capacity in elderly sheep. Sheep (Ø 7 yrs old, Ø weight of 88.5 kg) received pulmonary valve replacement. Decellularized PV (n=6), decellularized PV coated with proangiogenic CCN1 (n=6), and decellularized, CCN1 coated and reendothelized PV (n=6) were implanted in orthotopic position. For endothelialization PV were seeded with autologous endothelial cells (EC) differentiated from EPC from peripheral blood. Cells were flow adapted in a pulsatile bioreactor system prior implantation. PV functional analysis in vivo was realized by echocardiography, directly after implantation and prior explantation. Allografts were explanted after six and twelve months in vivo and investigated in respect to endothelium coverage, to the integrity of the extracellular matrix, and to the degree and cellular identity of invaded cells by histological and immunochemical stains. All allografts showed good to adequate function, no stenosis, low gradients and only occasional insufficiency without clinical symptoms. No signs of degradation of the extracellular matrix and minimal calcification restricted at the anastomosis of the grafts were found. All grafts were repopulated with cells but to various degree. Only one, explanted after one year, showed complete repopulation including the leaflets. In general, cell-density in the pulmonary artery was higher on the adventitial than on the luminal side and leaflets were better repopulated at the ventricular than at the arterial side. The majority of cells expressed sm-alpha-actin. Endothelial cells located on the luminal side appeared in some grafts as intact complete monolayer. Beside a slight tendency of better repopulation observed in the reendothelialized PV group, no significant difference of cell densities was found among the groups.
Autologous repopulation of decellularized heart valve matrices implanted in the orthotopic position in the elderly sheep demonstrates retained regenerative capacity even in the older organism. This observation combined with the fact that no functional loss must have taken into account, implantation of decellularized heart valves matrices in patients over age 65 remains a therapy option to overcome the drawbacks of current used bioprosthesis.
Marrow Stromal Cell based Stem Cell Based Transcatheter Aortic Valve Implantation: First Experiences in a Preclinical Model
Authors: Emmert Maximilian Y. , Weber Benedikt , Petra Petra , Behr Luc , Sammut Sebastien , Frauenfelder Thomas , Frese Laura , Scherman Jacques , Brokopp Chad E. , Templin Christian , Grünenfelder Jürg , Zünd Gregor , Falk Volkmar , Hoerstrup Simon P. 
Published: July 2012

AbstractWe investigate the combination of transcatheter aortic-valve implantation (TAVI) and a novel concept of stem cell-based, tissue-engineered heart-valves (TEHV) comprising minimally-invasive techniques for both, cell-harvest and valve-delivery. TAVI represents an emerging technology for the treatment of aortic-valve disease. The utilized bioprostheses are inherently prone to calcific-degeneration and recent evidence suggests even accelerated degeneration resulting from structural-damage due to the crimping-procedures. Autologous, living heart-valve prosthesis with regeneration and repair capacities would overcome such limitations.
Methods: Within a one-step intervention, tri-leaflet TEHV, generated from biodegradable synthetic-scaffolds, were integrated into self-expanding nitinol-stents, seeded with autologous bone-marrow mononuclear cells, crimped and transapically delivered into adult sheep (n=12). The animals were followed up for up to 2 weeks. TEHV-functionality was assessed by fluoroscopy, echocardiography and computed-tomography. Post-mortem analysis was performed using histology, extracellular-matrix analysis and electron-microscopy. Transapical aortic implantation of TEHV was successful in all animals (n=12) and the entire procedure-time from cell-harvest to TEHV-delivery was 109±14min. Fluoroscopy and echocardiography displayed TEHV-functionality demonstrating an adequate leaflet-mobility and co-aptation. Explanted TEHV showed intact leaflet-structures with well defined cusps without signs of thrombus-formation or structural-damage. Histology and ECM analysis displayed a high cellularity indicative for an early cellular-remodelling and in-growth after 2weeks. For the first time, we demonstrate the principal feasibility of a transcatheter, stem cell-based TEHV implantation into the aortic-valve position within a one-step intervention. Its long term functionality proven, a stem cell-based TEHV approach may represent a next generation heart-valve concept extending the clinical indication of transcatheter valves beyond elderly high-risk patients.
Mechanism of Cardiovascular Tissue Immunogenicity Reduction by Ice-free Cryopreservation
Authors: Brockbank Kelvin G.M. , Bayrak Alexandra , Seifert Martina , Stock Ulrich A. 
Published: July 2012

AbstractA variety of reasons for allograft heart valve failure have been discussed in the past and most investigators have emphasized immunological issues. Standard quantitative and qualitative cellular and matrix evaluations have not helped to solve the discussion of whether remaining allogeneic cells or potentially altered extracellular matrix contributed to the observed degeneration. Preliminary data on patients treated with decellularized allografts has recently demonstrated that decellularization did not significantly improve outcome in terms of pressure gradients and structural deterioration compared to non-decellularized allografts. These early clinical results question the validity of theories suggesting that an immune reaction to the remaining donor cells in allogeneic heart valves is the sole cause of structural deterioration.Porcine and ovine pulmonary and aortic heart valves were cryopreserved using traditional cryopreservation by freezing with 10% dimethylsulfoxide or ice-free cryopreservation in an 83% cryoprotectant formulation consisting of 4.65 mol/L dimethylsulfoxide, 4.65 mol/L formamide and 3.31 mol/L 1,2-propanediol. Cell viability was assessed using a water soluble fluorometric viability oxidation-reduction (REDOX) indicator which detects metabolic activity by both fluorescing and changing color in response to chemical reduction of the growth medium. Statistical analyses were performed using a t-test or one-way analysis of variance, p values<0.05 were considered statistically significant. Viability assessment revealed that heart valve tissues were significantly less viable in ice-free cryopreserved valves compared with frozen valves, p<0.05, due to cryoprotectant cytotoxicity. Juvenile sheep studies demonstrated that ice-free cryopreserved heart valves had minimal T-cell mediated inflammation in the valve leaflet stroma compared with frozen controls. Severe valvular stenosis with right heart failure was observed in recipients of frozen valves, the echo data revealed increased velocity and pressure gradients compared to ice-free valve recipients (p=0.0403, p=0.0591). In vitro studies have demonstrated retention of hemocompatibility, biocompatibility and reduction of ice-free cryopreserved heart valve tissue immunogenicity. Based upon these observations, it is hypothesized that preservation of extracellular matrix structure due to the absence of ice and minimal cell viability due to cryoprotectant cytotoxicity combine to decrease tissue repair activity and reduced immunogenicity. Work in progress is extending ice-free cryopreservation to other cardiovascular and orthopedic tissue engineering applications including in vitro and in vivo cell repopulation.
Scaffolds and Stem Cells for Patient-Tailored Aortic Heart Valve Tissue Engineering
Authors: Simionescu Dan , Jaeggli Michael , Liao Jun , Simionescu Agneta 
Published: July 2012

AbstractValve reconstruction or regeneration with living tissue is a daunting project for biomedical engineers and surgeons alike. Our translational approach to development of living valve replacements embraces three main principles: a) the accurate replication of each patient’s 3D aortic valve architecture for optimal functionality, b) layered scaffolds that mimic the aortic valve fibrosa, ventricularis and spongiosa to prevent buckling and enhance mechanical durability and c) the presence of autologous, valvular interstitial cells (VICs) to maintain matrix homeostasis. To create anatomically correct constructs, we used digital image processing of patient chest CT images and generated solid aortic valve root 3D structures using a stereo-lithography printer. Collagenous scaffolds to be used as the fibrosa and ventricularis layers were prepared from acellular porcine pericardium and collagen/GAG hydrogels to be used as the spongiosa layer. Layered scaffolds were attached to the molds, dried, stabilized with a non-toxic polyphenolic agent, rehydrated, the spongiosa seeded with human mesenchymal stem cells and valves subjected to functionality tests in a physiological heart valve bioreactor in sterile culture medium. Engineered valves exhibited excellent functional characteristics; most cells were alive, elongated significantly and stained positive for vimentin and actin, among other markers, suggestive of mechanical stimuli-induced stem cell differentiation into VICs. Ongoing studies are focused on endothelialization of the novel valve surfaces using stem cell-derived endothelial cells and rotational 3D seeding devices. In conclusion, autologous stem cell-seeded tri-layered collagenous scaffolds shaped to recapitulate the aortic heart valve shape and mechanics may provide future foundations for patient-tailored heart valve tissue engineering.
Adipose Fat Derived Tissue-Engineered Heart Valves
Authors: Frese Laura , Sanders Bart , Dijkman Petra E. , Weber Benedikt , Emmert Maximilian Y. , Brokopp Chad , Beer G. , Driessen-Mol Anita , Baaijens Frank P.T. , Hoerstrup Simon P. 
Published: July 2012

AbstractA major challenge in tissue engineering of heart valves is the in vitro creation of mature tissue structures compliant with the native valve function. Concerning the remodeling capacity of the extracellular matrix (ECM), various cell types have been investigated, including prenatal cells, umbilical cord and vascular derived cells. The pluripotency and availability of human mesenchymal stem cells has made them highly attractive for tissue engineering purposes. However, for clinical use, adult bone marrow derived mesenchymal stem cells (MSC) are suboptimal due to the highly invasive donation procedure, and the decline in MSC number and differentiation potential with increasing age of the patient. Adipose derived stem cells (ADSC) represent an interesting alternative of mesodermal origin. The easy and repeatable access to subcutaneous adipose tissue and the simple isolation procedures provide a clear advantage. Here, we investigate the suitability of ADSC as a novel cell source for tissue engineered heart valves (TEHV). Tissue Engineered (TE) heart valve leaflets (n=6) were produced, based on PGA/P4HB scaffolds seeded with human ADSC isolated from fat tissue excisions from plastic surgery. To stimulate tissue formation and induce matrix alignment, the TE leaflets were cultivated in dynamic strain bioreactors for 4 weeks. We subsequently reseeded the cultivated valves with ADSC derived endothelial cells. Differentiation into endothelial-like cells was induced by cultivation of ADSC in the presence of vascular endothelial growth factor. To determine the ECM composition of the TE leaflets, biochemical analyses for glycosaminoglycans (GAG), hydroxyproline (HYP) and DNA were performed. To further evaluate the microstructural features, tissue samples of TE leaflets were analyzed by stainings as well as by scanning electron microscopy. The mechanical properties of the ADSC derived TE leaflets were analyzed using a biaxial tensile tester. TE leaflets based on ADSC showed a homogenous vital cell distribution throughout the whole leaflet structure and the formation of a confluent endothelial lining. Furthermore, a mechanically stable matrix with GAG and collagen was demonstrated. These results indicate that ADSC represent an interesting alternative autologous mesenchymal human cell source with clinical relevance due to their easy accessibility and excellent proliferation and tissue formation capacities.
Innovative biotechnology industry strategies in the U.S.â€™ rapidly evolving payer environment
Authors: Collins Sarah Stanton , Collins Will 
Published: July 2012

In 2010 healthcare represented 17.9% of GDP; its cost is growing significantly faster (~5%) than economic growth (~ 2%).Â This growth presents a challenge to all payers, whether they are governments, employers, or individuals.Â Within healthcare, one of the most rapidly growing areas is â€œspecialty drugsâ€ which are frequently biotechnology agents, or drugs for cancer or orphan conditions.Â This article starts by discussing the issues of specialty drug cost and the challenges payers face in managing specialty drugs.Â It then presents market structure and firm strategy theories that provide insight into firm behavior in specialty drug categories.Â Lastly, it discusses possible events and actions that could dramatically change the biotechnology industry and lead to increased value within the U.S. health care system.
Innovating in the New Austerity
Authors: Burrill G. Steven 
Published: July 2012

We are in the midst of dramatic changes in the way life sciences companies are funded. The model of funding a company with venture capital leading to an IPO is now the exception rather than the rule for life sciences companies. Venture investors are no longer willing or able to fund companies with an indefinite exit. Instead, they are waiting later to fund companies, building exits into their investments from the start, and looking to innovative technologies other than therapeutics that can address medical and healthcare system needs, but provide a more predictable path to revenue. The financial pressures of today are leading to creative efforts to forge new business and financing models. They are driving capital efficiency and putting a proper emphasis on value creation. The resulting discipline is welcome. The result is that companies that fail to pursue true innovation and products that create value will find funding difficult to obtain and markets unwilling to pay premiums.Â For those of us who invest in the sector, the good news is that valuations are historically attractive and power at the negotiating table lies with those who have capital. The opportunities before us have never been greater.