Engineered vascular tissue fabricated from aggregated smooth muscle cells.

The goal of this study was to develop a system to rapidly generate engineered tissue constructs from aggregated cells and cell-derived extracellular matrix (ECM) to enable evaluation of cell-derived tissue structure and function. Rat aortic smooth muscle cells seeded into annular agarose wells (2, 4 or 6 mm inside diameter) aggregated and formed thick tissue rings within 2 weeks of static culture (0.76 mm at 8 days; 0.94 mm at 14 days). Overall, cells appeared healthy and surrounded by ECM comprised of glycosoaminoglycans and collagen, although signs of necrosis were observed near the centers of the thickest rings. Tissue ring strength and stiffness values were superior to those reported for engineered tissue constructs cultured for comparable times. The strength (100-500 kPa) and modulus (0.5-2 MPa) of tissue rings increased with ring size and decreased with culture duration. Finally, tissue rings cultured for 7 days on silicone mandrels fused to form tubular constructs. Ring margins were visible after 7 days, but tubes were cohesive and mechanically stable, and histological examination confirmed fusion between ring subunits. This unique system provides a versatile new tool for optimization and functional assessment of cell-derived tissue, and a new approach to creating tissue-engineered vascular grafts.

Planar biaxial characterization of diseased human coronary and carotid arteries for computational modeling.

Computational models have the potential to provide precise estimates of stresses and strains associated with sites of coronary plaque rupture. However, lack of adequate mathematical description of diseased human vessel wall mechanical properties is hindering computational accuracy. The goal of this study is to characterize the behavior of diseased human coronary and carotid arteries using planar biaxial testing. Diseased coronary specimens exhibit relatively high stiffness (50-210 kPa) and low extensibility (1-10%) at maximum equibiaxial stress (250 kPa) compared to human carotid specimens and values commonly reported for porcine coronary arteries. A thick neointimal layer observed histologically appears to be associated with heightened stiffness and the direction of anisotropy of the specimens. Fung, Choi-Vito and modified Mooney-Rivlin constitutive equations fit the multiaxial data from multiple stress protocols well, and parameters from representative coronary specimens were utilized in a finite element model with fluid-solid interactions. Computed locations of maximal stress and strain are substantially altered, and magnitudes of maximum principal stress (48-65 kPa) and strain (6.5-8%) in the vessel wall are lower than previously predicted using parameters from uniaxial tests. Taken together, the results demonstrate the importance of utilizing disease-matched multiaxial constitutive relationships within patient-specific computational models to accurately predict stress and strain within diseased coronary arteries.

Directed cellular self-assembly to fabricate cell-derived tissue rings for biomechanical analysis and tissue engineering.

Each year, hundreds of thousands of patients undergo coronary artery bypass surgery in the United States.(1) Approximately one third of these patients do not have suitable autologous donor vessels due to disease progression or previous harvest. The aim of vascular tissue engineering is to develop a suitable alternative source for these bypass grafts. In addition, engineered vascular tissue may prove valuable as living vascular models to study cardiovascular diseases. Several promising approaches to engineering blood vessels have been explored, with many recent studies focusing on development and analysis of cell-based methods.(2-5) Herein, we present a method to rapidly self-assemble cells into 3D tissue rings that can be used in vitro to model vascular tissues. To do this, suspensions of smooth muscle cells are seeded into round-bottomed annular agarose wells. The non-adhesive properties of the agarose allow the cells to settle, aggregate and contract around a post at the center of the well to form a cohesive tissue ring.(6,7) These rings can be cultured for several days prior to harvesting for mechanical, physiological, biochemical, or histological analysis. We have shown that these cell-derived tissue rings yield at 100-500 kPa ultimate tensile strength(8) which exceeds the value reported for other tissue engineered vascular constructs cultured for similar durations (<30 kPa).(9,10) Our results demonstrate that robust cell-derived vascular tissue ring generation can be achieved within a short time period, and offers the opportunity for direct and quantitative assessment of the contributions of cells and cell-derived matrix (CDM) to vascular tissue structure and function.