Direct hydrogel encapsulation of pluripotent stem cells enables ontomimetic differentiation and growth of engineered human heart tissues

Cell encapsulation utilizing PEG-fibrinogen hydrogel supports viability and enhances productivity under stress conditions

Recent advances in the bioengineering field have introduced new opportunities enabling cell encapsulation in three-dimensional (3D) structures using either various natural or synthetic materials. However, such hydrogel scaffolds have not been fully biocompatible for cell cultivation due to the lack of physical stability or bioactivity. Here, we utilized a uniquely fabricated semi-synthetic 3D polyethylene glycol-fibrinogen (PEG-Fb) hydrogel scaffold, which exhibits both high stability and high bioactivity, to encapsulate HEK293 cells for the production of human recombinant acetylcholine esterase (AChE). To examine the beneficial bioactive effect of the PEG-Fb scaffold over 2D surfaces, an experimental system was established to compare the viability, proliferation and AChE secretion of encapsulated cells versus non-encapsulated surface-adherent cells in serum starvation. Our results show that the transfer of surface-adherent HEK293 cells from fully enriched medium with 10% FCS to 0.2% FCS resulted in an eightfold reduction in cell number and a fourfold reduction in AChE production. In contrast, the encapsulated cells were highly viable and about twofold more efficient in AChE production. In addition, they had round morphology with a twofold larger cell diameter, supporting the observation of increased AChE production. These results suggest a role of the PEG-Fb scaffold in providing a supportive microenvironment in reduced serum conditions that enhances encapsulated cell functions, opening new directions to study the implementation of this platform in large-scale pharmaceutical protein production.

A Microvascularized Tumor-mimetic Platform for Assessing Anti-cancer Drug Efficacy

Assessment of anti-cancer drug efficacy in in vitro three-dimensional (3D) bioengineered cancer models provides important contextual and relevant information towards pre-clinical translation of potential drug candidates. However, currently established models fail to sufficiently recapitulate complex tumor heterogeneity. Here we present a chip-based tumor-mimetic platform incorporating a 3D in vitro breast cancer model with a tumor-mimetic microvascular network, replicating the pathophysiological architecture of native vascularized breast tumors. The microfluidic platform facilitated formation of mature, lumenized and flow-aligned endothelium under physiological flow recapitulating both high and low perfused tumor regions. Metastatic and non-metastatic breast cancer cells were maintained in long-term 3D co-culture with stromal fibroblasts in a poly(ethylene glycol)-fibrinogen hydrogel matrix within adjoining tissue chambers. The interstitial space between the chambers and endothelium contained pores to mimic the “leaky” vasculature found in vivo and facilitate cancer cell-endothelial cell communication. Microvascular pattern-dependent flow variations induced concentration gradients within the 3D tumor mass, leading to morphological tumor heterogeneity. Anti-cancer drugs displayed cell type- and flow pattern-dependent effects on cancer cell viability, viable tumor area and associated endothelial cytotoxicity. Overall, the developed microfluidic tumor-mimetic platform facilitates investigation of cancer-stromal-endothelial interactions and highlights the role of a fluidic, tumor-mimetic vascular network on anti-cancer drug delivery and efficacy for improved translation towards pre-clinical studies.

Bioengineering an electro-mechanically functional miniature ventricular heart chamber from human pluripotent stem cells

Tissue engineers and stem cell biologists have made exciting progress toward creating simplified models of human heart muscles or aligned monolayers to help bridge a longstanding gap between experimental animals and clinical trials. However, no existing human in vitro systems provide the direct measures of cardiac performance as a pump. Here, we developed a next-generation in vitro biomimetic model of pumping human heart chamber, and demonstrated its capability for pharmaceutical testing. From human pluripotent stem cell (hPSC)-derived ventricular cardiomyocytes (hvCM) embedded in collagen-based extracellular matrix hydrogel, we engineered a three-dimensional (3D) electro-mechanically coupled, fluid-ejecting miniature human ventricle-like cardiac organoid chamber (hvCOC). Structural characterization showed organized sarcomeres with myofibrillar microstructures. Transcript and RNA-seq analyses revealed upregulation of key Ca²⁺-handling, ion channel, and cardiac-specific proteins in hvCOC compared to lower-order 2D and 3D cultures of the same constituent cells. Clinically-important, physiologically complex contractile parameters such as ejection fraction, developed pressure, and stroke work, as well as electrophysiological properties including action potential and conduction velocity were measured: hvCOC displayed key molecular and physiological characteristics of the native ventricle, and showed expected mechanical and electrophysiological responses to a range of pharmacological interventions (including positive and negative inotropes). We conclude that such "human-heart-in-a-jar" technology could facilitate the drug discovery process by providing human-specific preclinical data during early stage drug development.

Developing a Cost-Effective and Scalable Production of Human Hepatic Competent Endoderm from Size-Controlled Pluripotent Stem Cell Aggregates

Dynamic suspension culture of human pluripotent stem cells (hPSCs) in stirred bioreactors provides a valuable scalable culture platform for integrated differentiation toward different lineages for potential research and therapeutic applications. However, current protocols for scalable and integrated differentiation of hPSCs limited due to high cost of growth factors and technical challenges. Here, hPSCs aggregates primed with 6 and 12 μM of CHIR99021 (CHIR), a Wnt agonist, in combination with different concentrations of high cost Activin A (10, 25, 50, 100 ng/mL). We sought to determine the appropriate treatment duration for efficient and cost-effective differentiation protocol for foregut definitive endoderm production in a dynamic suspension culture. Afterward, we evaluated the impact of the initial hPSC aggregate sizes (small: 86 ± 18 μm; medium: 142 ± 32 μm; large: 214 ± 34 μm) as critical bioprocess parameter on differentiation efficacy at the beginning of induction. The results indicated that 1-day priming of hPSCs as 3D aggregates (hPSpheres) with 6 μM CHIR followed by treatment with a low concentration of Activin (10 ng/mL) for 2 days resulted in efficient differentiation to definitive endoderm. This finding confirmed by the presence of ≥70% SOX17/FOXA2-double positive cells that highly expressed the anterior endodermal marker HEX. These endodermal cells differentiated efficiently into mature functional hepatocytes [60% albumin (ALB)-positive cells]. The results showed that the initial size of hPSC aggregates significantly impacted on the efficacy of differentiation. The medium sized-hPSpheres resulted in higher productivity and differentiation efficiency for scalable hepatocytes production, whereas small aggregates resulted in significant cell-loss after CHIR treatment and large aggregates had less efficacious endodermal differentiation. Differentiated cells exhibited multiple characteristics of primary hepatocytes as evidenced by expressions of liver-specific markers, indocyanine green and low-density lipoprotein uptake, and glycogen storage. Thus, this platform could be employed for scalable production of hPSC-derived hepatocytes for clinical and drug discovery applications.

Cardiopatch platform enables maturation and scale-up of human pluripotent stem cell-derived engineered heart tissues

Despite increased use of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) for drug development and disease modeling studies, methods to generate large, functional heart tissues for human therapy are lacking. Here we present a “Cardiopatch” platform for 3D culture and maturation of hiPSC-CMs that after 5 weeks of differentiation show robust electromechanical coupling, consistent H-zones, I-bands, and evidence for T-tubules and M-bands. Cardiopatch maturation markers and functional output increase during culture, approaching values of adult myocardium. Cardiopatches can be scaled up to clinically relevant dimensions, while preserving spatially uniform properties with high conduction velocities and contractile stresses. Within window chambers in nude mice, cardiopatches undergo vascularization by host vessels and continue to fire Ca²⁺ transients. When implanted onto rat hearts, cardiopatches robustly engraft, maintain pre-implantation electrical function, and do not increase the incidence of arrhythmias. These studies provide enabling technology for future use of hiPSC-CM tissues in human heart repair.

Cardiomyocytes derived from human induced pluripotent stem cells could be used to generate cardiac tissues for regenerative purposes. Here the authors describe a method to obtain large bioengineered heart tissues showing advanced maturation, functional features and engraftment capacity.

Engineering Cardiac Muscle Tissue: A Maturating Field of Research

Twenty years after the initial description of a tissue engineered construct, 3-dimensional human cardiac tissues of different kinds are now generated routinely in many laboratories. Advances in stem cell biology and engineering allow for the generation of constructs that come close to recapitulating the complex structure of heart muscle and might, therefore, be amenable to industrial (eg, drug screening) and clinical (eg, cardiac repair) applications. Whether the more physiological structure of 3-dimensional constructs provides a relevant advantage over standard 2-dimensional cell culture has yet to be shown in head-to-head-comparisons. The present article gives an overview on current strategies of cardiac tissue engineering with a focus on different hydrogel methods and discusses perspectives and challenges for necessary steps toward the real-life application of cardiac tissue engineering for disease modeling, drug development, and cardiac repair.

Expansion of 3D human induced pluripotent stem cell aggregates in bioreactors: Bioprocess intensification and scaling-up approaches

Human induced pluripotent stem cells (hiPSC) are attractive tools for drug screening and disease modeling and promising candidates for cell therapy applications. However, to achieve the high numbers of cells required for these purposes, scalable and clinical-grade technologies must be established. In this study, we use environmentally controlled stirred-tank bioreactors operating in perfusion as a powerful tool for bioprocess intensification of hiPSC production. We demonstrate the importance of controlling the dissolved oxygen concentration at low levels (4%) and perfusion at 1.3day^-1 dilution rate to improve hiPSC growth as aggregates in a xeno-free medium. This strategy allowed for increased cell specific growth rate, maximum volumetric concentrations (4.7×10⁶cell/mL) and expansion factors (approximately 19 in total cells), resulting in a 2.6-fold overall improvement in cell yields. Extensive cell characterization, including whole proteomic analysis, was performed to confirm that cells' pluripotent phenotype was maintained during culture. A scalable protocol for continuous expansion of hiPSC aggregates in bioreactors was implemented using mechanical dissociation for aggregate disruption and cell passaging. A total expansion factor of 1100 in viable cells was obtained in 11days of culture, while cells maintained their proliferation capacity, pluripotent phenotype and potential as well as genomic stability after 3 sequential passages in bioreactors.

Regulation of Cell Signaling Factors Using PLGA Nanoparticles Coated/Loaded with Genes and Proteins for Osteogenesis of Human Mesenchymal Stem Cells

Transfection of specific genes and transportation of proteins into cells have been a focus of stem cell differentiation research. However, it is not easy to regulate codelivery of a gene and a protein into cells. For codelivery into undifferentiated cells (human mesenchymal stem cells (hMSCs)), we used biodegradable carriers loaded with Runt-related transcription factor 2 (RUNX2) protein and coated with bone morphogenetic protein 2 (BMP2) plasmid DNA (pDNA) to induce osteogenesis. The released gene and protein were first localized in the cytosol of transfected hMSCs, and the gene then moved into the nucleus. The levels of internalized PLGA nanoparticles were tested using different doses and incubation durations. Then, transfection of BMP2 pDNA was confirmed by determining mRNA and protein levels and acquiring cell images. The same techniques were used to assess osteogenesis of hMSCs both in vitro and in vivo upon internalization of PLGA NPs carrying the BMP2 gene and RUNX2 protein. Detection of specific genes and proteins demonstrated that cells transfected with PLGA NPs carrying both the BMP2 gene and RUNX2 protein were highly differentiated compared with other samples. Histological and immunofluorescence analyses demonstrated that transfection of PLGA nanoparticles carrying both the BMP2 gene and RUNX2 protein dramatically enhanced osteogenesis of hMSCs.

Striated muscle function, regeneration, and repair

As the only striated muscle tissues in the body, skeletal and cardiac muscle share numerous structural and functional characteristics, while exhibiting vastly different size and regenerative potential. Healthy skeletal muscle harbors a robust regenerative response that becomes inadequate after large muscle loss or in degenerative pathologies and aging. In contrast, the mammalian heart loses its regenerative capacity shortly after birth, leaving it susceptible to permanent damage by acute injury or chronic disease. In this review, we compare and contrast the physiology and regenerative potential of native skeletal and cardiac muscles, mechanisms underlying striated muscle dysfunction, and bioengineering strategies to treat muscle disorders. We focus on different sources for cellular therapy, biomaterials to augment the endogenous regenerative response, and progress in engineering and application of mature striated muscle tissues in vitro and in vivo. Finally, we discuss the challenges and perspectives in translating muscle bioengineering strategies to clinical practice.

Direct Production of Human Cardiac Tissues by Pluripotent Stem Cell Encapsulation in Gelatin Methacryloyl

Direct stem cell encapsulation and cardiac differentiation within supporting biomaterial scaffolds are critical for reproducible and scalable production of the functional human tissues needed in regenerative medicine and drug-testing applications. Producing cardiac tissues directly from pluripotent stem cells rather than assembling tissues using pre-differentiated cells can eliminate multiple cell-handling steps that otherwise limit the potential for process automation and production scale-up. Here we asked whether our process for forming 3D developing human engineered cardiac tissues using poly(ethylene glycol)-fibrinogen hydrogels can be extended to widely used and printable gelatin methacryloyl (GelMA) hydrogels. We demonstrate that low-density GelMA hydrogels can be formed rapidly using visible light (<1 min) and successfully employed to encapsulate human induced pluripotent stem cells while maintaining high cell viability. Resulting constructs had an initial stiffness of approximately 220 Pa, supported tissue growth and dynamic remodeling, and facilitated high-efficiency cardiac differentiation (>70%) to produce spontaneously contracting GelMA human engineered cardiac tissues (GEhECTs). GEhECTs initiated spontaneous contractions on day 8 of differentiation, with synchronicity, frequency, and velocity of contraction increasing over time, and displayed developmentally appropriate temporal changes in cardiac gene expression. GEhECT-dissociated cardiomyocytes displayed well-defined and aligned sarcomeres spaced at 1.85 ± 0.1 μm and responded appropriately to drug treatments, including the β-adrenergic agonist isoproterenol and antagonist propranolol, as well as to outside pacing up to 3.0 Hz. Overall results demonstrate that GelMA is a suitable biomaterial for the production of developing cardiac tissues and has the potential to be employed in scale-up production and bioprinting of GEhECTs.