Ali Borazjani

Fabrication of cardiac patch with decellularized porcine myocardial scaffold and bone marrow mononuclear cells

Tissue engineered cardiac grafts are a promising therapeutic mode for ventricular wall reconstruction. Recently, it has been found that acellular tissue scaffolds provide natural ultrastructural, mechanical, and compositional cues for recellularization and tissue remodeling. We thus assess the potential of decellularized porcine myocardium as a scaffold for thick cardiac patch tissue engineering. Myocardial sections with 2-mm thickness were decellularized using 0.1% sodium dodecyl sulfate and then reseeded with differentiated bone marrow mononuclear cells. We found that thorough decellularization could be achieved after 2.5 weeks of treatment. Reseeded cells were found to infiltrate and proliferate in the tissue constructs. Immunohistological staining studies showed that the reseeded cells maintained cardiomyocyte-like phenotype and possible endothelialization was found in locations close to vasculature channels, indicating angiogenesis potential. Both biaxial and uniaxial mechanical testing showed a stiffer mechanical response of the acellular myocardial scaffolds; however, tissue extensibility and tensile modulus were found to recover in the constructs along with the culture time, as expected from increased cellular content. The cardiac patch that we envision for clinical application will benefit from the natural architecture of myocardial extracellular matrix, which has the potential to promote stem cell differentiation, cardiac regeneration, and angiogenesis.

The Correlation of 3D DT-MRI Fiber Disruption with Structural and Mechanical Degeneration in Porcine Myocardium

Evaluation of structural parameters following a myocardial infarction (MI) is important to assess left ventricular function and remodeling. In this study, we assessed the capability of 3D diffusion tensor magnetic resonance imaging (DT-MRI) to assess tissue degeneration shortly after an MI using a porcine model of infarction. Two days after an induced infarction, hearts were explanted and immediately scanned by a 3T MRI scanner with a diffusion tensor imaging protocol. 3D fiber tracks and clustering models were generated from the diffusion-weighted imaging data. We found in a normal explanted heart that DT-MRI fibers showed a multilayered helical structure, with fiber architecture and fiber density reflecting the integrity of muscle fibers. For infarcted heart explants, we observed either a lack of fibers or disruption of fibers in the infarcted regions. Contours of the disrupted DT-MRI fibers were found to be consistent with the infarcted regions. Both histological and mechanical analysis of the infarcted hearts suggested DT-MRI fiber disruption correlated with altered microstructure and tissue mechanics. The ability of 3D DT-MRI to accurately distinguish viable myocardium from dead myocardium only 2xa0days post infarct without the use of radioisotopes or ionotropic agents makes it a promising approach to evaluate cardiac damage early post-MI.

Influence of hydrostatic and distortional stress on chondroinduction

Undifferentiated connective tissue that arises during embryonic development and some healing processes contains pluripotent mesenchymal stem cells. It is becoming increasingly evident that the mechanical environment is an important differentiation factor for these cells. In our laboratory, we have focused on the potential for mechanical signals to induce chondrogenic differentiation of mesenchymal stem cells. Using C3H10T1/2 cells as a model, we have investigated the influence of hydrostatic pressure, equibiaxial contraction, and centrifugal pressure on chondroinduction. Cells responded to cyclic hydrostatic compression (5 MPa at 1 Hz) and cyclic contractile strain (15% at 1 Hz) by upregulating aggrecan and collagen type II gene expression. In addition, a preliminary study of the effects of centrifugal pressure (4.1 MPa for 30 min) suggests that it may increase cell proliferation and stimulate proteoglycan and collagen type II production. We speculate that compression, whether it is distortional or hydrostatic in nature, applied to undifferentiated connective tissue triggers differentiation toward a chondrocyte-like phenotype and production of a less permeable extracellular matrix which is capable of sustaining increasingly higher hydrostatic fluid pressure for compressive load support.

A comparative biomechanical analysis of term fetal membranes in human and domestic species.

OBJECTIVEnThe purpose of this study was to biomechanically characterize and compare human, porcine, equine, and ovine fetal membranes.nnnSTUDY DESIGNnNoncontact metrology was used for topographic analyses. Uniaxial tensile testing was performed to resolve specific biomechanical values. Puncture force and radial stresses were determined with biaxial puncture testing. Microstructure and surface tortuosity were analyzed histologically.nnnRESULTSnEquine and human membranes sustained larger magnitude loading, but ovine and porcine membranes exhibited stronger material properties. Biaxial puncture validated uniaxial results; human and equine groups accommodated the largest loads but lowest stresses. Equine membranes were mostly vascularized; tortuosity was highest in porcine membranes. Species gestation length was correlated positively with membrane thickness.nnnCONCLUSIONnThe anatomy of placentation and length of species gestation show distinct relationships to membrane biomechanics. Unlike other species, human fetal membranes do not compensate for structural weakness with a thicker membrane. This finding may explain the high incidence of preterm premature rupture of membranes in humans.

Effect of collagen hydrolysate on chondrocyte-seeded agarose constructs.

The mechanical properties of engineered cartilage are strongly dependent on collagen content, but the collagen to glycosaminoglycan ratio in engineered cartilage is often much lower than that of the native tissue. Therefore culture medium supplements which increase collagen production by chondrocytes are of interest. It had previously been reported that collagen hydrolysate stimulated type II collagen biosynthesis in short-term, high density monolayer chondrocyte cultures. It was hypothesized that collagen hydrolysate added to the culture medium of three dimensional chondrocyte-agarose constructs would enhance their mechanical properties. Porcine articular chondrocytes were embedded in 2% agarose and cultured for up to 6 weeks with and without 1 mg/ml collagen hydrolysate. The instantaneous compressive modulus and equilibrium compressive modulus were significantly lower in the collagen hydrolysate-treated constructs, consistent with the finding of lower collagen and GAG content. Contrary to our hypothesis, our results indicate that 1 mg/ml collagen hydrolysate may actually inhibit macromolecule biosynthesis and be detrimental to the mechanical properties of long term chondrocyte-agarose constructs.

Stress State Dependence of Human Placenta Mechanical Behavior

Maternal trauma affects 5–8% of all pregnancies and is the leading nonobstetric cause of maternal death in the United States [1]. The most common cause of trauma is motor vehicle accident (MVA) and the most common pathology is abruptio placentae, detachment of the placenta from uterus, which leads to serious maternal and fetal consequences [2].Copyright

Recellularization Potential of Acellular Aortic Valve Scaffolds Treated With Collagenase and Acetic Acid

It is estimated that five million Americans suffer from moderate to severe aortic valve disease, making it the third most common type of cardiovascular disease. Aortic valve replacement, which is second leading reason for undergoing open heart surgery, is the prevailing treatment for patients with extensive aortic valve pathologies. Currently, substitute valves used to replace the disease valves are classified as either mechanical or biological, each of which carry significant disadvantages. Patients with mechanical valves are at a much higher risk for developing blood clots and therefore must remain on anticoagulants for the remainder of their lifetime; and biological valves, which are typically derived from porcine or cadeveric tissues, will deteriorate over time. The ideal replacement valve is one that presents no thrombogenicity or immunogenecity, provides normal hemodynamics, is free of blood damaging elements, offers a practical mode for implantation, is able to grow and remodel, and does not deteriorate over time.© 2009 ASME

The Intrinsic Durability of Aortic Valve ECM in Absence of Cellular Maintenance

In the last two decades, decellularized native aortic valve (AV) has been investigated as tissue engineered heart valve (TEHV) replacements due to their potential to develop into a viable valve.[1] Decellularization removes major immunogenic cellular components. After repopulated with recipient’s cells, TEHV can be readily used because of the necessary functional design.[2] However, several problems with this approach have been identified, such as insufficient cell infiltration, mechanical deterioration, formation of fibrous sheath on implantation, and reduced orifice area after surgery.[3]© 2008 ASME

Detection of myocardial fiber disruption in artificial lesions with 3D DT-MRI tract models

In the United States, it is estimated that in 2008 approximately 1.2 million people will suffer a new or recurrent myocardial infarction. In 2005, the latest full year for which statistics are available, 16 million Americans (7.3% of the population) had some form of coronary heart disease. Loss of myocardium as a result of myocardial infarction increases wall stress locally and globally and triggers adaptive responses at the molecular, cellular, and tissue levels. These adaptive responses can lead to left ventricular dilation and congestive heart failure. Accurate non-invasive evaluation of myocardial structural degeneration (damage) and left ventricular remodeling following an infarct would have both prognostic and therapeutic value clinically.Copyright