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The key to addressing the challenges facing cardiac tissue engineering is the integration of physical, chemical, and electrical cues into scaffolds. Aligned and conductive scaffolds have been fabricated as synthetic microenvironments to improve the function of cardiomyocytes. However, up to now, the influence of conductive capability and inner structure of fibrous scaffolds have not been determined on the cardiomyocyte morphologies and beating patterns. In the current study, highly aligned fibers were fabricated with loaded up to 6% of carbon nanotubes (CNTs) to modulate the electrical conductivity, while blend and coaxial electrospinning were utilized to create a bulk distribution of CNTs in fiber matrices and a spatial embedment in fiber cores, respectively. Conductive networks were formed in the fibrous scaffolds after the inoculation of over 3% CNTs, and the increase in the conductivity could maintain the cell viabilities, induce the cell elongation, enhance the production of sarcomeric α-actinin and troponin I, and promote the synchronous beating of cardiomyocytes. Although the conductivity of blend fibers is slightly higher than that of coaxial fibers with the same CNT loadings, the lower exposures to CNTs resulted in higher cell viability, elongation, extracellular matrix secretion and beating rates for cardiomyocytes on coaxial fibers. Taken altogether, core-sheath fibers with loaded 5% of CNTs in the fiber cores facilitated the cardiomyocyte growth with a production of organized contractile proteins and a pulsation frequency close to that of the atrium. It is suggested that electrospun scaffolds that couple conductivity and fibrous structure considerations may provide optimal stimuli to foster cell morphology and functions for myocardial regeneration or establishment of in vitro cardiomyocyte culture platform for drug screening., (Copyright © 2016. Published by Elsevier B.V.)

The identification of a biologic substrate for maintaining hepatocyte functions is essential to provide reliable and predictable models for in vitro drug screening. In the current study, a three-dimensional culture of hepatocytes was established on highly porous fibrous scaffolds with grafted galactose and RGD to afford extensive cell-cell and cell-scaffold interactions spatially. The pore size and ligand densities indicated significant effects on the formation of hepatocyte spheroids in balancing the cell retention, adhesion, and migration on fibrous scaffolds. Fibrous scaffolds with an average pore size of 60 μm and surface grafting densities of galactose at 5.9 nmol/cm(2) and RGD at 6.9 pmol/cm(2) provided optimal microenvironments for hepatocyte infiltration and multicellular spheroid formation. Significant promotions were also demonstrated in the syntheses of albumin and urea and the activities of phase I (CYP 3A11 and CYP 2C9) and phase II enzymes. The in vitro metabolism tests on testosterone and acetaminophen by hepatocytes on the optimal scaffolds indicated the predicated clearance rates of 50.7 and 22.6 ml/min/kg, respectively, which were comparable to the in vivo values of rats. The in vitro hepatotoxicity tests on amiodarone hydrochloride and acetaminophen predicted the half maximal effective concentrations (EC50) to reflect the in vivo toxic plasma concentrations in human. In addition, the enzyme activities, predicted clearance rates and hepatotoxicity values of hepatocytes on the optimal scaffolds experienced sensitive responsiveness to specific inducers or inhibitors of CYP 3A11 and phase II enzymes, exhibiting in vivo-in vitro correlations to a certain extent. These results demonstrate the feasibility of hepatocyte spheroid culture on fibrous scaffolds as an potential in vitro testing model to predict the in vivo drug metabolism, hepatotoxicity, and drug-drug interactions., (Copyright © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

Challenges remain in engineering cardiac tissues with functional and morphological properties similar to those of native myocardium. In the current study, micropatterned fibrous mats are obtained by deposition of electrospun fibers on lithographic collectors to reproduce the anisotropic structure of myocardium, and carbon nanotubes are included in fibers to provide conductivities at the same level of cardiac muscles. The patterned mats are assembled layer-by-layer into patterned scaffolds for coculture of primary cardiomyocytes (CMs) with cardiac fibroblasts (CFs) and endothelial cells (ECs). CMs are organized along the fibers with clear cardiac strips of sarcomeric α-actinin and belt-like connexin-43, showing strong cellular extraction forces and intercellular communications. Compared with square and rectangle patterns, honeycomb (Hc)-patterned scaffolds shows higher ultimate tensile strength and strain to failure. The finite element analysis indicates no apparent stress concentration under stress application in the two orthogonal directions. The Hc-patterned coculture demonstrates significantly higher CM viabilities, deeper penetrations of cells into scaffolds, stronger expression of troponin I, connexin-43 and sarcomeric α-actinin by CMs and more abundant formations of capillary-like networks by ECs than other scaffolds. CMs on Hc-patterned scaffolds display spontaneous beating rates at 101 ± 12 times/min after coculture for 5 days and remain synchronously beating at 94 ± 8 times/min after 15 days, which is close to those of adult and neonatal rats. The layered and patterned coculture strategy achieves the spatial arrangement of multiple types of cells and vascularization potential, providing a biomimetic strategy for engineering functional cardiac patches in vitro . [ABSTRACT FROM AUTHOR]