How to fix a broken heart-designing biofunctional cues for effective, environmentally-friendly cardiac tissue engineering

Cardiovascular diseases bear strong socioeconomic and ecological impact on the worldwide healthcare system. A large consumption of goods, use of polymer-based cardiovascular biomaterials, and long hospitalization times add up to an extensive carbon footprint on the environment often turning out to be ineffective at healing such cardiovascular diseases. On the other hand, cardiac cell toxicity is among the most severe but common side effect of drugs used to treat numerous diseases from COVID-19 to diabetes, often resulting in the withdrawal of such pharmaceuticals from the market. Currently, most patients that have suffered from cardiovascular disease will never fully recover. All of these factors further contribute to the extensive negative toll pharmaceutical, biotechnological, and biomedical companies have on the environment. Hence, there is a dire need to develop new environmentally-friendly strategies that on the one hand would promise cardiac tissue regeneration after damage and on the other hand would offer solutions for the fast screening of drugs to ensure that they do not cause cardiovascular toxicity. Importantly, both require one thing-a mature, functioning cardiac tissue that can be fabricated in a fast, reliable, and repeatable manner from environmentally friendly biomaterials in the lab. This is not an easy task to complete as numerous approaches have been undertaken, separately and combined, to achieve it. This review gathers such strategies and provides insights into which succeed or fail and what is needed for the field of environmentally-friendly cardiac tissue engineering to prosper.

Integrating Human-Induced Pluripotent Stem Cell Expansion Capability and Cardiomyocyte Differentiation Potential in a Microcarrier Suspension Culture

Human-induced pluripotent stem cells are known for their high proliferation capacity as well as their ability to differentiate to different lineages (Ban et al., Theranostics 7(7):2067-2077, 2017; Chen et al., Stem Cell Res 15(2):365-375, 2015; Serra et al., Trends Biotechnol 30(6):350-359, 2012). For stem-cell-derived cardiomyocytes to evolve into a scalable therapeutic source, a large quantity of highly pure cardiomyocytes is needed. Thus, lies the challenge of defining an efficient cardiomyocyte differentiation process. This chapter describes a method to evaluate multiple human-induced pluripotent stem cell lines for their cardiac differentiation potentials before evaluating their integrated proliferation and differentiation abilities in microcarrier cultures in a spinner culture format.

Conductive polypyrrole-encapsulated silk fibroin fibers for cardiac tissue engineering

Polypyrrole (PPy) has been utilized in smart scaffolds to improve the functionality of the engineered cardiac tissue. Compared to the commonly used aqueous coating, here, PPy was blended into silk fibroin (SF) solution to electrospin conductive PPy-encapsulated SF nanofibers. Combinations of various SF concentrations (5%, 7%, and 12%) and different PPy-to-SF ratios (15:85, 30:70, and 40:60) were compared. PPy reduced the fiber diameter (0.431 ± 0.060 μm), better-mimicking the myocardium fibrils. Conductive mats with 7% SF showed the closest mechanical properties (1.437 ± 0.044 MPa) to the native myocardium; meanwhile, a PPy-to-SF ratio of 15:85 exhibited sufficient electrical conductivity for cardiomyocytes (CMs). In vitro studies using three different types of CM demonstrated that the hybrid mats support CM contraction. Primary neonatal rat CMs on the mat with a PPy-to-SF ratio of 15:85 were elongated and orientated anisotropically with locally organized sarcomeric striations. By contrast, human-induced pluripotent stem cell derived-CMs on the mat with a PPy-to-SF ratio of 30:70 exhibited the strongest contractions. Contraction synchrony was further improved by external stimulation. Taken together, these findings indicated the great potential of the PPy-encapsulated SF electrospun mat for cardiac tissue engineering.

Conductive Composite Fiber with Optimized Alignment Guides Neural Regeneration under Electrical Stimulation

Conductivity and alignment of scaffolds are two primary factors influencing the efficacy of nerve repair. Herein, conductive composite fibers composed of poly(ɛ-caprolactone) (PCL) and carbon nanotubes (CNTs) with different orientation degrees are prepared by electrospinning at various rotational speeds (0, 500, 1000, and 2000 rpm), and meanwhile the synergistic promotion mechanism of aligned topography and electrical stimulation on neural regeneration is fully demonstrated. Under an optimized rotational speed of 1000 rpm, the electrospun PCL fiber exhibits orientated structure at macroscopic (mean deviation angle = 2.78°) or microscopic crystal scale (orientation degree = 0.73), decreased contact angle of 99.2° ± 4.9°, and sufficient tensile strength in both perpendicular and parallel directions to fiber axis (1.13 ± 0.15 and 5.06 ± 0.98 MPa). CNTs are introduced into the aligned fiber for further improving conductivity (15.69-178.63 S m^-1 ), which is beneficial to the oriented growth of neural cells in vitro as well as the regeneration of injured sciatic nerves in vivo. On the basis of robust cell induction behavior, optimum sciatic nerve function index, and enhanced remyelination/axonal regeneration, such conductive PCL/CNTs composite fiber with optimized fiber alignment may serve as instructive candidates for promoting the scaffold- and cell-based strategies for neural repair.

Induced cell migration based on a bioactive hydrogel sheet combined with a perfused microfluidic system

Endothelial cell migration is a crucial step in the process of new blood vessel formation-a necessary process to maintain cell viability inside thick tissue constructs. Here, we report a new method for maintaining cell viability and inducing cell migration using a perfused microfluidic platform based on collagen gel and a gradient hydrogel sheet. Due to the helpful role of the extracellular matrix components in cell viability, we developed a hydrogel sheet from decellularized tissue (DT) of the bovine heart and chitosan (CS). The results showed that hydrogel sheets with an optimum weight ratio of CS/DT = 2 possess a porosity of around 75%, a mechanical strength of 23 kPa, and display cell viability up to 78%. Then, we immobilized a radial gradient of vascular endothelial growth factor (VEGF) on the hydrogel sheet to promote human umbilical vein endothelial cell migration. Finally, we incorporated the whole system as an entirety on the top of the microfluidic platform and studied cell migration through the hydrogel sheet in the presence of soluble and immobilized VEGF. The results demonstrated that immobilized VEGF stimulated cell migration in the hydrogel sheet at all depths compared with soluble VEGF. The results also showed that applying a VEGF gradient in both soluble and immobilized states had a significant effect on cell migration at limited depths (<100 μm). The main finding of this study is a significant improvement in cell migration using an in vivo imitating, cost-efficient and highly reproducible platform, which may open up a new perspective for tissue engineering applications.

Controlled Release of Stem Cell Secretome Attenuates Inflammatory Response against Implanted Biomaterials

Inflammatory response against implanted biomaterials impairs their functional integration and induces medical complications in the host's body. To suppress such immune responses, one approach is the administration of multiple drugs to halt inflammatory pathways. This challenges patient's adherence and can cause additional complications such as infection. Alternatively, biologics that regulate multiple inflammatory pathways are attractive agents in addressing the implants immune complications. Secretome of mesenchymal stromal cells (MSCs) is a multipotent biologic, regulating the homeostasis of lymphocytes and leukocytes. Here, it is reported that alginate microcapsules loaded with processed conditioned media (pCM-Alg) reduces the infiltration and/or expression of CD68+ macrophages likely through the controlled release of pCM. In vitro cultures revealed that alginate can dose dependently induce macrophages to secrete TNFα, IL-6, IL-1β, and GM-CSF. Addition of pCM to the cultures attenuates the secretion of TNFα (p = 0.023) and IL-6 (p < 0.0001) by alginate or lipopolysaccharide (LPS) stimulations. Mechanistically, pCM suppressed the NfκB pathway activation of macrophages in response to LPS (p < 0.0001) in vitro and cathepsin activity (p = 0.005) in response to alginate in vivo. These observations suggest the efficacy of using MSC-derived secretome to prevent or delay the host rejection of implants.

Assessment of various crosslinking agents on collagen/chitosan scaffolds for myocardial tissue engineering

Suitable material for scaffolds that support cell attachment, proliferation, vascularization and contraction has always been a challenge in myocardial tissue engineering. Much research effort has been focused on natural polymers including collagen, gelatin, chitosan, fibrin, alginate, etc. Among them, a collagen/chitosan composite scaffold was widely used for myocardial tissue engineering. Due to the non-proliferative and contractile characteristics of cardiomyocytes, the biocompatibility and mechanical properties of the scaffolds are extremely important for supporting intercellular connection and tissue function for myocardial tissue engineering. To the best of our knowledge, the three crosslinking agents (glutaraldehyde (GTA), genipin (GP), tripolyphosphate (TPP)) have not yet been comparatively studied in myocardial tissue engineering. Thus, the aim of this study is to compare and identify the crosslinking effect of GTA, GP and TPP for myocardial tissue engineering. The collagen/chitosan scaffolds prepared with various crosslinking agents were fabricated and evaluated for physical characteristics, biocompatibility and contractile performance. All the groups of scaffolds exhibited high porosity (>65%) and good swelling ratio suitable for myocardial tissue engineering. TPP crosslinked scaffolds showed excellent mechanical properties, with their elastic modulus (81.0 ± 8.1 kPa) in the physiological range of native myocardium (20∼100 kPa). Moreover, GP and TPP crosslinked scaffolds exhibited better biocompatibility than GTA crosslinked scaffolds, as demonstrated by the live/dead staining and proliferation assay. In addition, cardiomyocytes within TPP crosslinked scaffolds showed the highest expression of cardiac-specific marker protein and the best contractile performance. To conclude, of the three crosslinking agents, TPP was recommended as the most suitable crosslinking agent for collagen/chitosan scaffold in myocardial tissue engineering.

Selection of human induced pluripotent stem cells lines optimization of cardiomyocytes differentiation in an integrated suspension microcarrier bioreactor

Background

The production of large quantities of cardiomyocyte is essential for the needs of cellular therapies. This study describes the selection of a human-induced pluripotent cell (hiPSC) line suitable for production of cardiomyocytes in a fully integrated bioprocess of stem cell expansion and differentiation in microcarrier stirred tank reactor.

Methods

Five hiPSC lines were evaluated first for their cardiac differentiation efficiency in monolayer cultures followed by their expansion and differentiation compatibility in microcarrier (MC) cultures under continuous stirring conditions.

Results

Three cell lines were highly cardiogenic but only one (FR202) of them was successfully expanded on continuous stirring MC cultures. FR202 was thus selected for cardiac differentiation in a 22-day integrated bioprocess under continuous stirring in a stirred tank bioreactor. In summary, we integrated a MC-based hiPSC expansion (phase 1), CHIR99021-induced cardiomyocyte differentiation step (phase 2), purification using the lactate-based treatment (phase 3) and cell recovery step (phase 4) into one process in one bioreactor, under restricted oxygen control (< 30% DO) and continuous stirring with periodic batch-type media exchanges. High density of undifferentiated hiPSC (2 ± 0.4 × 10⁶ cells/mL) was achieved in the expansion phase. By controlling the stirring speed and DO levels in the bioreactor cultures, 7.36 ± 1.2 × 10⁶ cells/mL cardiomyocytes with > 80% Troponin T were generated in the CHIR99021-induced differentiation phase. By adding lactate in glucose-free purification media, the purity of cardiomyocytes was enhanced (> 90% Troponin T), with minor cell loss as indicated by the increase in sub-G1 phase and the decrease of aggregate sizes. Lastly, we found that the recovery period is important for generating purer and functional cardiomyocytes (> 96% Troponin T). Three independent runs in a 300-ml working volume confirmed the robustness of this process.

Conclusion

A streamlined and controllable platform for large quantity manufacturing of pure functional atrial, ventricular and nodal cardiomyocytes on MCs in conventional-type stirred tank bioreactors was established, which can be further scaled up and translated to a good manufacturing practice-compliant production process, to fulfill the quantity requirements of the cellular therapeutic industry.

Supplementary information

The online version of this article (10.1186/s13287-020-01618-6) contains supplementary material, which is available to authorized users.

Unchain My Heart: Integrins at the Basis of iPSC Cardiomyocyte Differentiation

The cellular response to the extracellular matrix (ECM) microenvironment mediated by integrin adhesion is of fundamental importance, in both developmental and pathological processes. In particular, mechanotransduction is of growing importance in groundbreaking cellular models such as induced pluripotent stem cells (iPSC), since this process may strongly influence cell fate and, thus, augment the precision of differentiation into specific cell types, e.g., cardiomyocytes. The decryption of the cellular machinery starting from ECM sensing to iPSC differentiation calls for new in vitro methods. Conveniently, engineered biomaterials activating controlled integrin-mediated responses through chemical, physical, and geometrical designs are key to resolving this issue and could foster clinical translation of optimized iPSC-based technology. This review introduces the main integrin-dependent mechanisms and signalling pathways involved in mechanotransduction. Special consideration is given to the integrin-iPSC linkage signalling chain in the cardiovascular field, focusing on biomaterial-based in vitro models to evaluate the relevance of this process in iPSC differentiation into cardiomyocytes.

Regenerating the Cardiovascular System Through Cell Reprogramming; Current Approaches and a Look Into the Future

Cardiovascular disease (CVD), despite the advances of the medical field, remains one of the leading causes of mortality worldwide. Discovering novel treatments based on cell therapy or drugs is critical, and induced pluripotent stem cells (iPS Cells) technology has made it possible to design extensive disease-specific in vitro models. Elucidating the differentiation process challenged our previous knowledge of cell plasticity and capabilities and allows the concept of cell reprogramming technology to be established, which has inspired the creation of both in vitro and in vivo techniques. Patient-specific cell lines provide the opportunity of studying their pathophysiology in vitro, which can lead to novel drug development. At the same time, in vivo models have been designed where in situ transdifferentiation of cell populations into cardiomyocytes or endothelial cells (ECs) give hope toward effective cell therapies. Unfortunately, the efficiency as well as the concerns about the safety of all these methods make it exceedingly difficult to pass to the clinical trial phase. It is our opinion that creating an ex vivo model out of patient-specific cells will be one of the most important goals in the future to help surpass all these hindrances. Thus, in this review we aim to present the current state of research in reprogramming toward the cardiovascular system's regeneration, and showcase how the development and study of a multicellular 3D ex vivo model will improve our fighting chances.