Tissue-Engineering for the Study of Cardiac Biomechanics

Characteristics and toxicity assessment of electrospun gelatin/PCL nanofibrous scaffold loaded with graphene in vitro and in vivo

Background: Electrospun gelatin/polycaprolactone (Gt/PCL) nanofibrous scaffolds loaded with graphene are novel nanomaterials with the uniquely strong property of electrical conductivity, which have been widely investigated for their potential applications in cardiovascular tissue engineering, including in bypass tracts for atrioventricular block.

Purpose: Electrospun Gt/PCL/graphene nanofibrous mats were successfully produced. Scanning electron micrography showed that the fibers with graphene were smooth and homogeneous. In vitro, to determine the biocompatibility of the scaffolds, hybrid scaffolds with different fractions of graphene were seeded with neonatal rat ventricular myocytes. In vivo, Gt/PCL scaffolds with different concentrations of graphene were implanted into rats for 4, 8 and 12 weeks.

Results: CCK-8 assays and histopathological staining (including DAPI, cTNT, and CX43) indicated that cells grew and survived well on the hybrid scaffolds if the mass fraction of graphene was lower than 0.5%. After implanting into rats for 4, 8 or 12 weeks, there was no gathering of inflammatory cells around the nanomaterials according to the HE staining results.

Conclusion: The results indicate that Gt/PCL nanofibrous scaffolds loaded with graphene have favorable electrical conductivity and biological properties and may be suitable scaffolds for use in the treatment of atrioventricular block. These findings alleviate safety concerns and provide novel insights into the potential applications of Gt/PCL loaded with graphene, offering a solid foundation for comprehensive in vivo studies.

Increased Afterload Augments Sunitinib-Induced Cardiotoxicity in an Engineered Cardiac Microtissue Model

Sunitinib, a multitargeted oral tyrosine kinase inhibitor, used widely to treat solid tumors, results in hypertension in up to 47% and left ventricular dysfunction in up to 19% of treated individuals. The relative contribution of afterload toward inducing cardiac dysfunction with sunitinib treatment remains unknown. We created a preclinical model of sunitinib cardiotoxicity using engineered microtissues that exhibited cardiomyocyte death, decreases in force generation, and spontaneous beating at clinically relevant doses. Simulated increases in afterload augmented sunitinib cardiotoxicity in both rat and human microtissues, which suggest that antihypertensive therapy may be a strategy to prevent left ventricular dysfunction in patients treated with sunitinib.

Strategies for directing cells into building functional hearts and parts

This review presents the current state-of-the-art, emerging directions and future trends to direct cells for building functional heart parts.

Fitting tissue chips and microphysiological systems into the grand scheme of medicine, biology, pharmacology, and toxicology

Microphysiological systems (MPS), which include engineered organoids (EOs), single organ/tissue chips (TCs), and multiple organs interconnected to create miniature in vitro models of human physiological systems, are rapidly becoming effective tools for drug development and the mechanistic understanding of tissue physiology and pathophysiology. The second MPS thematic issue of Experimental Biology and Medicine comprises 15 articles by scientists and engineers from the National Institutes of Health, the IQ Consortium, the Food and Drug Administration, and Environmental Protection Agency, an MPS company, and academia. Topics include the progress, challenges, and future of organs-on-chips, dissemination of TCs into Pharma, children's health protection, liver zonation, liver chips and their coupling to interconnected systems, gastrointestinal MPS, maturation of immature cardiomyocytes in a heart-on-a-chip, coculture of multiple cell types in a human skin construct, use of synthetic hydrogels to create EOs that form neural tissue models, the blood-brain barrier-on-a-chip, MPS models of coupled female reproductive organs, coupling MPS devices to create a body-on-a-chip, and the use of a microformulator to recapitulate endocrine circadian rhythms. While MPS hardware has been relatively stable since the last MPS thematic issue, there have been significant advances in cell sourcing, with increased reliance on human-induced pluripotent stem cells, and in characterization of the genetic and functional cell state in MPS bioreactors. There is growing appreciation of the need to minimize perfusate-to-cell-volume ratios and respect physiological scaling of coupled TCs. Questions asked by drug developers are followed by an analysis of the potential value, costs, and needs of Pharma. Of highest value and lowest switching costs may be the development of MPS disease models to aid in the discovery of disease mechanisms; novel compounds including probes, leads, and clinical candidates; and mechanism of action of drug candidates. Impact statement Microphysiological systems (MPS), which include engineered organoids and both individual and coupled organs-on-chips and tissue chips, are a rapidly growing topic of research that addresses the known limitations of conventional cellular monoculture on flat plastic - a well-perfected set of techniques that produces reliable, statistically significant results that may not adequately represent human biology and disease. As reviewed in this article and the others in this thematic issue, MPS research has made notable progress in the past three years in both cell sourcing and characterization. As the field matures, currently identified challenges are being addressed, and new ones are being recognized. Building upon investments by the Defense Advanced Research Projects Agency, National Institutes of Health, Food and Drug Administration, Defense Threat Reduction Agency, and Environmental Protection Agency of more than $200 million since 2012 and sizable corporate spending, academic and commercial players in the MPS community are demonstrating their ability to meet the translational challenges required to apply MPS technologies to accelerate drug development and advance toxicology.

Anisotropic engineered heart tissue made from laser-cut decellularized myocardium

We have developed an engineered heart tissue (EHT) system that uses laser-cut sheets of decellularized myocardium as scaffolds. This material enables formation of thin muscle strips whose biomechanical characteristics are easily measured and manipulated. To create EHTs, sections of porcine myocardium were laser-cut into ribbon-like shapes, decellularized, and mounted in specialized clips for seeding and culture. Scaffolds were first tested by seeding with neonatal rat ventricular myocytes. EHTs beat synchronously by day five and exhibited robust length-dependent activation by day 21. Fiber orientation within the scaffold affected peak twitch stress, demonstrating its ability to guide cells toward physiologic contractile anisotropy. Scaffold anisotropy also made it possible to probe cellular responses to stretch as a function of fiber angle. Stretch that was aligned with the fiber direction increased expression of brain natriuretic peptide, but off-axis stretches (causing fiber shear) did not. The method also produced robust EHTs from cardiomyocytes derived from human embryonic stem cells and induced pluripotent stem cells (hiPSC). hiPSC-EHTs achieved maximum peak stress of 6.5 mN/mm² and twitch kinetics approaching reported values from adult human trabeculae. We conclude that laser-cut EHTs are a viable platform for novel mechanotransduction experiments and characterizing the biomechanical function of patient-derived cardiomyoctyes.