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Local flow alterations created by a metallic stent in a simulated coronary artery were studied to compare the hemodynamic effects of two different stent geometries. Dye injection flow visualization and computational fluid dynamics were used. Resting and exercise conditions were studied. Flow visualization using the dye injection method provided a qualitative picture of stent hemodynamics while the computational approach provided detailed quantitative information on the flow next to the vessel wall near the intersections of stent wires. Dye injection visualization revealed that more dye became entrapped between the wires where the wire spacing was smallest. The dye washout times were shorter under exercise conditions for both wire spacings tested. The computational results showed that stagnation zones were continuous from one wire to the next when the wire spacing was small. Results from greater wire spacing (more than six wire diameters) showed that the stagnation zones were separate for at least part of the cardiac cycle. The sizes of the stagnation zones were larger under exercise conditions, and the largest stagnation zones were observed distal to the stent. These studies demonstrate that stent geometry has a significant effect on local hemodynamics. The observation that fluid stagnation is continuous in stents with wire spacings of less than six wire diameters may provide a criterion for future stent design.

Current cardiovascular therapies are limited by loss of endothelium, restenosis, and thrombosis. The goal of this study is to develop a biomimetic hybrid nanomatrix that combines unique properties of electrospun polycaprolactone (ePCL) nanofibers with self-assembled peptide amphiphiles (PAs). ePCL nanofibers have interconnected nanoporous structures, but they are hampered by lack of surface bioactivity to control cellular behavior. It is hypothesized that PAs can self-assemble onto the surface of ePCL nanofibers and endow them with characteristic properties of native endothelium. PAs, which comprise hydrophobic alkyl tails attached to functional hydrophilic peptide sequences, contained enzyme-mediated degradable sites coupled to either endothelial cell adhesive ligands (YIGSR) or ploylysine (KKKKK) nitric oxide (NO) donors. Two different PAs (PA-YIGSR and PA-KKKKK) were successfully synthesized and mixed in a 90:10 (YK) ratio to obtain PA-YK. PA-YK was reacted with pure NO to develop PA-YK-NO, which was then self-assembled onto ePCL nanofibers to generate a hybrid nanomatrix, ePCL-PA-YK-NO. Uniform coating of self-assembled PA nanofibers on ePCL was confirmed by TEM. Successful NO release from ePCL-PA-YK-NO was observed. ePCL-YK and ePCL-PA-YK-NO showed significantly increased adhesion of human umbilical vein endothelial cells (HUVECs). Also, ePCL-PA-YK-NO showed significantly increased proliferation of HUVECs and reduced smooth muscle cell proliferation. ePCL-PA-YK-NO also displayed significantly reduced platelet adhesion when compared to ePCL, ePCL-PA-YK, and collagen control. These results indicate that this hybrid nanomatrix has great potential applications in cardiovascular implants.Corresponding author: Dr. Ho-Wook Jun, Assistant Professor, 1825 University Boulevard, Shelby 806, Birmingham, AL, 35211. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Electrospinning has been garnering a lot of attention recently [7][8][9][10][11], due to its ability to fabricate highly interconnected, non-woven fibers with diameters in the nanoscale ranges, which are structurally similar to nanofibrillar extracellular matrix (ECM) proteins [12]. Due to their ability to physically resemble natural ECM protein structure, several studies have been conducted into using electrospun materials as cardiovascular devices such as vascular grafts [13][14][15][16][17]. An important feature of electrospinning is its ability to deposit these nanofibers on a rotating mandrel to form a tubular structure, which is essential for vascular grafts [18,19], and it is also possible to generate scaff...

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Small-caliber synthetic grafts used for coronary bypass artery grafting are compromised by thrombogenicity and accelerated intimal thickening, resulting in early graft occlusion. Herein we describe the fabrication and physical properties of small-caliber blood vessels using decellularized porcine aortic segments. These vessels were further coated with human saphenous vein endothelial cells (HSVECs) for future clinical applications. Chemical staining of decellularized vessels showed that they preserved their native matrix architecture, including several collagen layers in between internal and external elastin layers. The burst pressure for the decellularized vessels was higher than 1,000 mmHg. HSVECs, seeded on the luminal side, adhered to the matrix and formed a uniform monolayer. HSVEC-seeded vessels produced prostaglandin I2 and released vasoactive agents in response to the calcium ionophore A23187. These results show that engineered blood vessels coated with the host endothelial cells possess morphologic and functional characteristics of human small-caliber vessels. Tissue-engineered vessels may potentially be useful clinically as vascular grafts.

To examine the influence of substrate topology on the behavior of fibroblasts, tissue engineering scaffolds were electrospun from polycaprolactone (PCL) and a blend of PCL and gelatin (PCL+Gel) to produce matrices with both random and aligned nanofibrous orientations. The addition of gelatin to the scaffold was shown to increase the hydrophilicity of the PCL matrix and to increase the proliferation of NIH3T3 cells compared to scaffolds of PCL alone. The orientation of nanofibers within the matrix did not have an effect on the proliferation of adherent cells, but cells on aligned substrates were shown to elongate and align parallel to the direction of substrate fiber alignment. A microarray of cyotoskeleton regulators was probed to examine differences in gene expression between cells grown on an aligned and randomly oriented substrates. It was found that transcriptional expression of eight genes was statistically different between the two conditions, with all of them being upregulated in the aligned condition. The proteins encoded by these genes are linked to production and polymerization of actin microfilaments, as well as focal adhesion assembly. Taken together, the data indicates NIH3T3 fibroblasts on aligned substrates align themselves parallel with their substrate and increase production of actin and focal adhesion related genes.

Functional myocardium derived from human induced pluripotent stem cells (hiPSCs) can be impactful for cardiac disease modeling, drug testing, and the repair of injured myocardium. However, when hiPSCs are differentiated into cardiomyocytes, they do not possess characteristics of mature myocytes which limits their application in these endeavors. We hypothesized that mechanical and electrical stimuli would enhance the maturation of hiPSC-derived cardiomyocyte (hiPSC-CM) spheroids on both a structural and functional level, potentially leading to a better model for drug testing as well as cell therapy. Spheroids were generated with hiPSC-CM. For inducing mechanical stimulation, they were placed in a custom-made device with PDMS channels and exposed to cyclic, uniaxial stretch. Spheroids were electrically stimulated in the C-Pace EP from IONOptix for 7 days. Following the stimulations, the spheroids were then analyzed for cardiomyocyte maturation. Both stimulated groups of spheroids possessed enhanced transcript and protein expressions for key maturation markers, such as cTnI, MLC2v, and MLC2a, along with improved ultrastructure of the hiPSC-CMs in both groups with enhanced Z-band/Z-body formation, fibril alignment, and fiber number. Optical mapping showed that spheroids exposed to electrical stimulation were able to capture signals at increasing rates of pacing up to 4 Hz, which failed in unstimulated spheroids. Our results clearly indicate that a significantly improved myocyte maturation can be achieved by culturing iPSC-CMs as spheroids and exposing them to cyclic, uniaxial stretch and electrical stimulation.

Cyclic preconditioning has been shown here to increase the ECs ability to resist blood flow-induced shear stress and the attachment of circulating blood elements, key attributes in minimizing thrombotic events. These studies may ultimately establish protocols for the formation of a more durable endothelial monolayer that may be useful in the context of small vessel arterial reconstruction.