Patterned human microvascular grafts enable rapid vascularization and increase perfusion in infarcted rat hearts

Engineering in vitro vascular microsystems

Blood vessels are hierarchical microchannels that transport nutrients and oxygen to different tissues and organs, while also eliminating metabolic waste from the body. Disorders of the vascular system impact both physiological and pathological processes. Conventional animal vascular models are complex, high-cost, time-consuming, and low-validity, which have limited the exploration of effective in vitro vascular microsystems. The morphologies of micro-scaled tubular structures and physiological properties of vascular tissues, including mechanical strength, thrombogenicity, and immunogenicity, can be mimicked in vitro by engineering strategies. This review highlights the state-of-the-art and advanced engineering strategies for in vitro vascular microsystems, covering the domains related to rational designs, manufacturing approaches, supporting materials, and organ-specific cell types. A broad range of biomedical applications of in vitro vascular microsystems are also summarized, including the recent advances in engineered vascularized tissues and organs for physiological and pathological study, drug screening, and personalized medicine. Moreover, the commercialization of in vitro vascular microsystems, the feasibility and limitations of current strategies and commercially available products, as well as perspectives on future directions for exploration, are elaborated. The in vitro modeling of vascular microsystems will facilitate rapid, robust, and efficient analysis in tissue engineering and broader regenerative medicine towards the development of personalized treatment approaches.

Bioprinted platform for parallelized screening of engineered microtissues in vivo

Human engineered tissues hold great promise for therapeutic tissue regeneration and repair. Yet, development of these technologies often stalls at the stage of in vivo studies due to the complexity of engineered tissue formulations, which are often composed of diverse cell populations and material elements, along with the tedious nature of in vivo experiments. We introduce a "plug and play" platform called parallelized host apposition for screening tissues in vivo (PHAST). PHAST enables parallelized in vivo testing of 43 three-dimensional microtissues in a single 3D-printed device. Using PHAST, we screen microtissue formations with varying cellular and material components and identify formulations that support vascular graft-host inosculation and engineered liver tissue function in vivo. Our studies reveal that the cellular population(s) that should be included in engineered tissues for optimal in vivo performance is material dependent. PHAST could thus accelerate development of human tissue therapies for clinical regeneration and repair.

Microvascularization in 3D Human Engineered Tissue and Organoids

The microvasculature, a complex network of small blood vessels, connects systemic circulation with local tissues, facilitating the nutrient and oxygen exchange that is critical for homeostasis and organ function. Engineering these structures is paramount for advancing tissue regeneration, disease modeling, and drug testing. However, replicating the intricate architecture of native vascular systems-characterized by diverse vessel diameters, cellular constituents, and dynamic perfusion capabilities-presents significant challenges. This complexity is compounded by the need to precisely integrate biomechanical, biochemical, and cellular cues. Recent breakthroughs in microfabrication, organoids, bioprinting, organ-on-a-chip platforms, and in vivo vascularization techniques have propelled the field toward faithfully replicating vascular complexity. These innovations not only enhance our understanding of vascular biology but also enable the generation of functional, perfusable tissue constructs. Here, we explore state-of-the-art technologies and strategies in microvascular engineering, emphasizing key advancements and addressing the remaining challenges to developing fully functional vascularized tissues.

Hypoimmunogenic hPSC-derived cardiac organoids for immune evasion and heart repair

Human pluripotent stem cell (hPSC)-derived cardiac therapies hold great promise for heart regeneration but face major translational barriers due to allogeneic immune rejection. Here, we engineered hypoimmunogenic hPSCs using a two-step CRISPR-Cas9 strategy: (1) B2M knockout, eliminating HLA class I surface expression, and (2) knock-in of HLA-E or HLA-G trimer constructs in the AAVS1 safe harbor locus to confer robust immune evasion. Hypoimmunogenic hPSCs maintained pluripotency, efficiently differentiated into cardiac cell types that resisted both T and NK cell-mediated cytotoxicity in vitro , and self-assembled into engineered cardiac organoids. Comprehensive analyses of the hypoimmunogenic cells and organoids revealed preservation of transcriptomic, structural, and functional properties with minimal off-target effects from gene editing. In vivo , hypoimmunogenic cardiac organoids restored contractile function in infarcted rat hearts and demonstrated superior graft retention and immune evasion in humanized mice compared to wild-type counterparts. These findings establish the therapeutic potential of hypoimmunogenic hPSC-CMs in the cardiac organoid platform, laying the foundation for off-the-shelf cardiac cell therapies to treat cardiovascular disease, the leading cause of death worldwide.

3D nanoprinting of PDMS microvessels with tailored tortuosity and microporosity via direct laser writing

Microvessels (e.g., capillaries) are ubiquitous throughout human anatomy, yet recreating their three-dimensional (3D) microfluidic and architectural sophistication at biologically accurate length scales has remained a critical challenge. To overcome this barrier, here we report a hybrid additive manufacturing-or "3D printing"-strategy in which "Two-Photon Direct Laser Writing (DLW)" is used to nanoprint microvessels of arbitrary design directly atop "Liquid-Crystal Display (LCD)" 3D-printed microfluidic chips. Fabrication results indicated effective production of 100 μm-diameter 3D polydimethylsiloxane (PDMS) microfluidic vessels with 5 μm-thick walls-featuring arrays of pre-designed 5 μm-diameter micropores-as well as three discrete spiralled, intertwined microvessels. Experimental results with MDA-MB-231 epithelial breast cancer cells revealed the ability for the 3D PDMS microvessels to support cell culture. In combination, these results suggest that the presented strategy for 3D nanoprinting PDMS microvessels with custom-designed architectures and microporosity offers a promising pathway to enable new classes of "organ-on-a-chip (OOC)" systems for wide-ranging biomedical applications.

Integrating microfluidic and bioprinting technologies: advanced strategies for tissue vascularization

Tissue engineering offers immense potential for addressing the unmet needs in repairing tissue damage and organ failure. Vascularization, the development of intricate blood vessel networks, is crucial for the survival and functions of engineered tissues. Nevertheless, the persistent challenge of ensuring an ample nutrient supply within implanted tissues remains, primarily due to the inadequate formation of blood vessels. This issue underscores the vital role of the human vascular system in sustaining cellular functions, facilitating nutrient exchange, and removing metabolic waste products. In response to this challenge, new approaches have been explored. Microfluidic devices, emulating natural blood vessels, serve as valuable tools for investigating angiogenesis and allowing the formation of microvascular networks. In parallel, bioprinting technologies enable precise placement of cells and biomaterials, culminating in vascular structures that closely resemble the native vessels. To this end, the synergy of microfluidics and bioprinting has further opened up exciting possibilities in vascularization, encompassing innovations such as microfluidic bioprinting. These advancements hold great promise in regenerative medicine, facilitating the creation of functional tissues for applications ranging from transplantation to disease modeling and drug testing. This review explores the potentially transformative impact of microfluidic and bioprinting technologies on vascularization strategies within the scope of tissue engineering.

Stochastic to Deterministic: A Straightforward Approach to Create Serially Perfusable Multiscale Capillary Beds

Generation of in vitro tissue models with serially perfused hierarchical vasculature would allow greater control of fluid perfusion throughout the network and enable direct mechanistic investigation of vasculogenesis, angiogenesis, and vascular remodeling. In this work, we have developed a method to produce a closed, serially perfused, multiscale vessel network fully embedded within an acellular hydrogel, where flow through the capillary bed is required prior to fluid exit. We confirmed that the acellular and cellular gel-gel interface was functionally annealed without preventing or biasing cell migration and endothelial self-assembly. Multiscale connectivity of the vessel network was validated via high-resolution microscopy techniques to confirm anastomosis between self-assembled and patterned vessels. Lastly, using a simple acrylic cassette and fluorescently labeled microspheres, the multiscale network was demonstrated to be perfusable. Directed flow from inlet to outlet mandated flow through the capillary bed. This method for producing closed, multiscale vascular networks was developed with the intention of straightforward fabrication and engineering techniques so as to be a low barrier to entry for researchers who wish to investigate mechanistic questions in vascular biology. This ease of use offers a facile extension of these methods for incorporation into organoid culture, organ-on-a-chip (OOC) models, and bioprinted tissues.

Bioengineering vascularization

This Review explores the rapidly evolving field of bioengineered vasculature, a key area of focus in tissue engineering and regenerative medicine. The broad relevance of this topic is attributed to its impacts on a wide range of biological processes, enabling studies in tissue development, fundamental biology and drug discovery, and the applications in tissue engineering and regenerative medicine. We outline the design criteria for bioengineered vasculature and the methodologies for constructing these systems by self-assembly and in microfluidics, organs-on-a-chip and macroscale tubular systems that often rely on biofabrication approaches such as 3D printing. We discuss existing challenges in developing functional vasculature that closely mirrors its native equivalent, including achieving hierarchical branching with organ and vessel-specific endothelial and supporting cells, providing perusable vasculature within organoids and scaling the systems for implantation and direct vascular anastomosis.

3D morphometry of endothelial cells angiogenesis in an extracellular matrix composite hydrogel

Human umbilical vein endothelial cells (HUVECs) play a fundamental role in angiogenesis. Herein, we introduce digital holographic microscopy (DHM) for the 3D quantitative morphological analysis of HUVECs in extracellular matrix (ECM)-based biomaterials as an angiogenesis model. The combination of volumetric information from DHM and the physicochemical and cytobiocompatibility data provided by fluorescence microscopy and cytology offers a comprehensive understanding of the angiogenesis-related parameters of HUVECs within the ECM. DHM enables label-free, non-contact, and non-invasive 3D monitoring of living samples in real time, in a quantitative manner. In this study, the human amniotic membrane (HAM) is decellularized, pulverized, and combined with sodium alginate hydrogel to provide an in vitro substrate for modeling HUVEC angiogenesis. Our results demonstrate that modifying alginate hydrogel with HAM enhances its biofunctionality due to the presence of ECM components. Moreover, the DHM results reveal an increase in its porous properties, which, in turn, aids in interpreting the tubulation results.

In vitro vascularization improves in vivo functionality of human engineered cardiac tissues

Engineered human cardiac tissues hold great promise for disease modeling, drug development, and regenerative therapy. For regenerative applications, successful engineered tissue engraftment in vivo requires rapid vascularization and blood perfusion post-implantation. In the present study, we engineered highly functional, vascularized cardiac tissues ("cardiopatches") by co-culturing human induced pluripotent stem cell-derived cardiomyocytes (hiPSCCMs) and endothelial cells (hiPSC-ECs) in optimized serum-free media. The vascularized cardiopatches displayed stable capillary networks over 4 weeks of culture, the longest reported in the field, while maintaining high contractile stress (>15 mN/mm2) and fast conduction velocity (>20 cm/s). Robustness of the method was confirmed using two distinct hiPSC-EC sources. Upon implantation into dorsal-skinfold chambers in immunocompromised mice, in vitro vascularized cardiopatches exhibited improved angiogenesis compared to avascular implants. Significant lumenization of the engineered human vasculature and anastomosis with host mouse vessels yielded the formation of hybrid human-mouse capillaries and robust cardiopatch perfusion by blood. Moreover, compared to avascular tissues, the implanted vascularized cardiopatches exhibited significantly higher conduction velocity and Ca2+ transient amplitude, longitudinally monitored in live mice for the first time. Overall, we demonstrate successful 4-week vascularization of engineered human cardiac tissues without loss of function in vitro, which promotes tissue functionality upon implantation in vivo. STATEMENT OF SIGNIFICANCE: Complex interactions between cardiac muscle fibers and surrounding capillaries are critical for everyday function of the heart. Tissue engineering is a powerful method to recreate functional cardiac muscle and its vascular network, which are both lost during a heart attack. Our study demonstrates in vitro engineering of dense capillary networks within highly functional engineered heart tissues that successfully maintain the structure, electrical, and mechanical function long-term. In mice, human capillaries from these engineered tissues integrate with host mouse capillaries to allow blood perfusion and support improved implant function. In the future, the developed vascularized engineered heart tissues will be used for in vitro studies of cardiac development and disease and as a potential regenerative therapy for heart attack.

FSTL-1 loaded 3D bioprinted vascular patch regenerates the ischemic heart tissue

Cardiac patch strategies are developed as a promising approach to regenerate the injured heart after myocardial infarction (MI). This study integrated 3D bioprinting and cardioprotective paracrine signaling to fabricate vascular patch devices containing endothelial cells (ECs) and the regenerative follistatin-like 1 (FSTL1) peptide. Engineered patch supported the 3D culture of ECs in both static and dynamic culture, forming a uniform endothelium on the printed channels. Implantation of vascular patch onto a rat model of acute MI resulted in significant reduction of scar formation, left ventricle dilation, and wall thinning, as well as enhanced ejection fraction. Furthermore, increased vascularization and proliferation of cardiomyocytes were observed in hearts treated with patches. These findings highlight the remarkable capacity of 3D bioprinted vascular patch to augment the endogenous regenerative capacity of mammalian heart, together with the exogenous cardioprotective function, to serve as a robust therapeutic device to treat acute MI.

3-Dimensional printing in vascular disease: From manufacturer to clinical use

Three-dimensional (3D) printing has been used in medicine with applications in many different fields. 3D printing allows patient education, interventionalists training, preprocedural planning, and assists the interventionalist to improve treatment outcomes. 3D printing represents a potential advancement by allowing the printing of flexible vascular models. In this article, the authors report a clinical case using 3D printing to perform a physician-modified fenestrated endograft. An overview of 3D printing in vascular and endovascular surgery is provided, focusing on its potential applications for training, education, preprocedural planning, and current clinical applications.

Tissue-Engineered Microvessels: A Review of Current Engineering Strategies and Applications

Microvessels, including arterioles, capillaries, and venules, play an important role in regulating blood flow, enabling nutrient and waste exchange, and facilitating immune surveillance. Due to their important roles in maintaining normal function in human tissues, a substantial effort has been devoted to developing tissue-engineered models to study endothelium-related biology and pathology. Various engineering strategies have been developed to recapitulate the structural, cellular, and molecular hallmarks of native human microvessels in vitro. In this review, recent progress in engineering approaches, key components, and culture platforms for tissue-engineered human microvessel models is summarized. Then, tissue-specific models, and the major applications of tissue-engineered microvessels in development, disease modeling, drug screening and delivery, and vascularization in tissue engineering, are reviewed. Finally, future research directions for the field are discussed.

Quantifying Microvascular Structure in Healthy and Infarcted Rat Hearts Using Optical Coherence Tomography Angiography

Myocardial infarction (MI) is a life-threatening medical emergency resulting in coronary microvascular dysregulation and heart muscle damage. One of the primary characteristics of MI is capillary loss, which plays a significant role in the progression of this cardiovascular condition. In this study, we utilized optical coherence tomography angiography (OCTA) to image coronary microcirculation in fixed rat hearts, aiming to analyze coronary microvascular impairment post-infarction. Various angiographic metrics are presented to quantify vascular features, including the vessel area density, vessel complexity index, vessel tortuosity index, and flow impairment. Pathological differences identified from OCTA analysis are corroborated with histological analysis. The quantitative assessments reveal a significant decrease in microvascular density in the capillary-sized vessels and an enlargement for the arteriole/venule-sized vessels. Further, microvascular tortuosity and complexity exhibit an increase after myocardial infarction. The results underscore the feasibility of using OCTA to offer qualitative microvascular details and quantitative metrics, providing insights into coronary vascular network remodeling during disease progression and response to therapy.

Macrophages: A missing key in cardiac tissue engineering for sustained vascularization

Macrophages regulate angiogenesis, repair, conduction, and homeostasis in heart tissue. Landau et al.1 demonstrate that incorporating primitive macrophages into engineered heart tissues significantly promotes long-term vascularization and cardiac maturation. This advance demonstrates the importance of resident immune-vascular microenvironments in cardiac tissue engineering, marking an important step forward for heart-on-chip technologies.

A biopsy-sized 3D skin model with a perifollicular vascular plexus enables studying immune cell trafficking in the skin

Human skin vasculature features a unique anatomy in close proximity to the skin appendages and acts as a gatekeeper for constitutive lymphocyte trafficking to the skin. Approximating such structural complexity and functionality in 3D skin models is an outstanding tissue engineering challenge. In this study, we leverage the capabilities of the digital-light-processing bioprinting to generate an anatomically-relevant and miniaturized 3D skin-on-a-chip (3D-SoC) model in the size of a 6 mm punch biopsy. The 3D-SoC contains a perfusable vascular network resembling the superficial vascular plexus of the skin and closely surrounding bioengineered hair follicles. The perfusion capabilities of the 3D-SoC enables the circulation of immune cells, and high-resolution imaging of the immune cell-endothelial cell interactions, namely tethering, rolling, and extravasation in real-time. Moreover, the vascular pattern in 3D-SoC captures the physiological range of shear rates found in cutaneous blood vessels and allows for studying the effect of shear rate on T cell trafficking. In 3D-SoC, as expected,in vitro-polarized T helper 1 (Th1) cells show a stronger attachment on the vasculature compared to naïve T cells. Both naïve and T cells exhibit higher retention in the low-shear zones in the early stages (<5 min) of T cell attachment. Interestingly, at later stages T cell retention rate becomes independent of the shear rate. The attached Th1 cells further transmigrate from the vessel walls to the extracellular space and migrate toward the bioengineered hair follicles and interfollicular epidermis. When the epidermis is not present, Th1 cell migration toward the epidermis is significantly hindered, underscoring the role of epidermal signals on T cell infiltration. Our data validates the capabilities of 3D-SoC model to study the interactions between immune cells and skin vasculature in the context of epidermal signals. The biopsy-sized 3D-SoC model in this study represents a new level of anatomical and cellular complexity, and brings us a step closer to generating a truly functional human skin with its tissue-specific vasculature and appendages in the presence of circulating immune cells.

3D bioprinted mesenchymal stem cell laden scaffold enhances subcutaneous vascularization for delivery of cell therapy

Subcutaneous delivery of cell therapy is an appealing minimally-invasive strategy for the treatment of various diseases. However, the subdermal site is poorly vascularized making it inadequate for supporting engraftment, viability, and function of exogenous cells. In this study, we developed a 3D bioprinted scaffold composed of alginate/gelatin (Alg/Gel) embedded with mesenchymal stem cells (MSCs) to enhance vascularization and tissue ingrowth in a subcutaneous microenvironment. We identified bio-ink crosslinking conditions that optimally recapitulated the mechanical properties of subcutaneous tissue. We achieved controlled degradation of the Alg/Gel scaffold synchronous with host tissue ingrowth and remodeling. Further, in a rat model, the Alg/Gel scaffold was superior to MSC-embedded Pluronic hydrogel in supporting tissue development and vascularization of a subcutaneous site. While the scaffold alone promoted vascular tissue formation, the inclusion of MSCs in the bio-ink further enhanced angiogenesis. Our findings highlight the use of simple cell-laden degradable bioprinted structures to generate a supportive microenvironment for cell delivery.

Stochastic to Deterministic: A straightforward approach to create serially perfusable multiscale capillary beds

Generation of in vitro tissue models with serially perfused hierarchical vasculature would allow greater control of fluid perfusion throughout the network and enable direct mechanistic investigation of vasculogenesis, angiogenesis, and vascular remodeling. In this work, we have developed a method to produce a closed, serially perfused, multiscale vessel network embedded within an acellular hydrogel. We confirmed that the acellular and cellular gel-gel interface was functionally annealed without preventing or biasing cell migration and endothelial self-assembly. Multiscale connectivity of the vessel network was validated via high-resolution microscopy techniques to confirm anastomosis between self-assembled and patterned vessels. Lastly, using fluorescently labeled microspheres, the multiscale network was serially perfused to confirm patency and barrier function. Directional flow from inlet to outlet man-dated flow through the capillary bed. This method for producing closed, multiscale vascular networks was developed with the intention of straightforward fabrication and engineering techniques so as to be a low barrier to entry for researchers who wish to investigate mechanistic questions in vascular biology. This ease of use offers a facile extension of these methods for incorporation into organoid culture, organ-on-a-chip (OOC) models, and bioprinted tissues.

3D Printed Conductive Hydrogel Patch Incorporated with MSC@GO for Efficient Myocardial Infarction Repair

Myocardial infarction (MI) results in an impaired heart function. Conductive hydrogel patch-based therapy has been considered as a promising strategy for cardiac repair after MI. In our study, we fabricated a three-dimensional (3D) printed conductive hydrogel patch made of fibrinogen scaffolds and mesenchymal stem cells (MSCs) combined with graphene oxide (GO) flakes (MSC@GO), capitalizing on GO's excellent mechanical property and electrical conductivity. The MSC@GO hydrogel patch can be attached to the epicardium via adhesion to provide strong electrical integration with infarcted hearts, as well as mechanical and regeneration support for the infarcted area, thereby up-regulating the expression of connexin 43 (Cx43) and resulting in effective MI repair in vivo. In addition, MI also triggers apoptosis and damage of cardiomyocytes (CMs), hindering the normal repair of the infarcted heart. GO flakes exhibit a protective effect against the apoptosis of implanted MSCs. In the mouse model of MI, MSC@GO hydrogel patch implantation supported cardiac repair by reducing cell apoptosis, promoting gap connexin protein Cx43 expression, and then boosting cardiac function. Together, this study demonstrated that the conductive hydrogel patch has versatile conductivity and mechanical support function and could therefore be a promising candidate for heart repair.

Vascularization of PEGylated fibrin hydrogels increases the proliferation of human iPSC-cardiomyocytes

Studies have long sought to develop engineered heart tissue for the surgical correction of structural heart defects, as well as other applications and vascularization of this tissue has presented a challenge. Recent studies suggest that vascular cells and a vascular network may have regenerative effects on implanted cardiomyocytes (CM) and nearby heart tissue separate from perfusion of oxygen and nutrients. The goal of this study was to test whether vascular cells or a formed vascular network in a fibrin-based hydrogel would alter the proliferation of human iPSC-derived CM. First, vascular network formation in a slowly degrading PEGylated fibrin hydrogel was optimized by altering the cell ratio of human umbilical vein endothelial cells to human dermal fibroblasts, the inclusion of growth factors, and the total cell concentration. An endothelial to fibroblast ratio of 5:1 and a total cell concentration of 1.1 × 106 cells/mL without additional growth factors generated robust vascular networks while minimizing the number of cells required. Using this optimized system, human iPSC-derived CM were cultured on hydrogels without vascular cells, hydrogels with unorganized encapsulated vascular cells, or hydrogels with encapsulated vascular cells organized into networks for 7 days. CM proliferation and gene expression were assayed following 7 days of culture on the hydrogels. The presence of vascular cells in the hydrogel, whether unorganized or in vascular networks, significantly increased CM proliferation compared to an acellular hydrogel. Hydrogels with unorganized vascular cells resulted in lower CM maturity evidenced by decreased expression of cardiac troponin t (TNNT2), myosin light chain 7, and phospholamban compared to hydrogels without vascular cells and hydrogels with vascular networks. Altogether, this study details a robust method of forming rudimentary vascular networks in a fibrin-based hydrogel and shows that a hydrogel containing endothelial cells and fibroblasts can induce proliferation in adjacent CM, and these cells do not hinder CM gene expression when organized into a vascular network.

Engineering vascularised organoid-on-a-chip: strategies, advances and future perspectives

In recent years, advances in microfabrication technology and tissue engineering have propelled the development of a novel drug screening and disease modelling platform known as organoid-on-a-chip. This platform integrates organoids and organ-on-a-chip technologies, emerging as a promising approach for in vitro modelling of human organ physiology. Organoid-on-a-chip devices leverage microfluidic systems to simulate the physiological microenvironment of specific organs, offering a more dynamic and flexible setting that can mimic a more comprehensive human biological context. However, the lack of functional vasculature has remained a significant challenge in this technology. Vascularisation is crucial for the long-term culture and in vitro modelling of organoids, holding important implications for drug development and personalised medical approaches. This review provides an overview of research progress in developing vascularised organoid-on-a-chip models, addressing methods for in vitro vascularisation and advancements in vascularised organoids. The aim is to serve as a reference for future endeavors in constructing fully functional vascularised organoid-on-a-chip platforms.

Directly coaxial bioprinting of 3D vascularized tissue using novel bioink based on decellularized human amniotic membrane

Despite several progressions in the biofabrication of large-scale engineered tissues, direct biopri nting of perfusable three-dimensional (3D) vasculature remained unaddressed. Developing a feasible method to generate cell-laden thick tissue with an effective vasculature network to deliver oxygen and nutrient is crucial for preventing the formation of necrotic spots and tissue death. In this study, we developed a novel technique to directly bioprint 3D cell-laden prevascularized construct. We developed a novel bioink by mixing decellularized human amniotic membrane (dHAM) and alginate (Alg) in various ratios. The bioink with encapsulated human vein endothelial cells (HUVECs) and a crosslinker, CaCl2, were extruded via sheath and core nozzle respectively to directly bioprint a perfusable 3D vasculature construct. The various concentration of bioink was assessed from several aspects like biocompatibility, porosity, swelling, degradation, and mechanical characteristics, and accordingly, optimized concentration was selected (Alg 4 %w/v - dHAM 0.6 %w/v). Then, the crosslinked bioink without microchannel and the 3D bioprinted construct with various microchannel distances (0, 1.5 mm, 3 mm) were compared. The 3D bioprinted construct with a 1.5 mm microchannels distance demonstrated superiority owing to its 492 ± 18.8 % cell viability within 14 days, excellent tubulogenesis, remarkable expression of VEGFR-2 which play a crucial role in endothelial cell proliferation, migration, and more importantly angiogenesis, and neovascularization. This perfusable bioprinted construct also possess appropriate mechanical stability (32.35 ± 5 kPa Young's modulus) for soft tissue. Taking these advantages into the account, our new bioprinting method possesses a prominent potential for the fabrication of large-scale prevascularized tissue to serve for regenerative medicine applications like implantation, drug-screening platform, and the study of mutation disease.

Construction of millimeter-scale vascularized engineered myocardial tissue using a mixed gel

Engineering myocardium has shown great clinal potential for repairing permanent myocardial injury. However, the lack of perfusing blood vessels and difficulties in preparing a thick-engineered myocardium result in its limited clinical use. We prepared a mixed gel containing fibrin (5 mg/ml) and collagen I (0.2 mg/ml) and verified that human umbilical vein endothelial cells (HUVECs) and human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) could form microvascular lumens and myocardial cell clusters by harnessing the low-hardness and hyperelastic characteristics of fibrin. hiPSC-CMs and HUVECs in the mixed gel formed self-organized cell clusters, which were then cultured in different media using a three-phase approach. The successfully constructed vascularized engineered myocardial tissue had a spherical structure and final diameter of 1-2 mm. The tissue exhibited autonomous beats that occurred at a frequency similar to a normal human heart rate. The internal microvascular lumen could be maintained for 6 weeks and showed good results during preliminary surface re-vascularization in vitro and vascular remodeling in vivo. In summary, we propose a simple method for constructing vascularized engineered myocardial tissue, through phased cultivation that does not rely on high-end manufacturing equipment and cutting-edge preparation techniques. The constructed tissue has potential value for clinical use after preliminary evaluation.

Perfusability and immunogenicity of implantable pre-vascularized tissues recapitulating features of native capillary network

Vascularization is a key pre-requisite to engineered anatomical scale three dimensional (3-D) constructs to ensure their nutrient and oxygen supply upon implantation. Presently, engineered pre-vascularized 3-D tissues are limited to only micro-scale hydrogels, which meet neither the anatomical scale needs nor the complexity of natural extracellular matrix (ECM) environments. Anatomical scale perfusable constructs are critically needed for translational applications. To overcome this challenge, we previously developed pre-vascularized ECM sheets with long and oriented dense microvascular networks. The present study further evaluated the patency, perfusability and innate immune response toward these pre-vascularized constructs. Macrophage-co-cultured pre-vascularized constructs were evaluated in vitro to confirm micro-vessel patency and perturbations in macrophage metabolism. Subcutaneously implanted pre-vascularized constructs remained viable and formed a functional anastomosis with host vasculature within 3 days of implantation. This completely biological pre-vascularized construct holds great potential as a building block to engineer perfusable anatomical scale tissues.

Manufacturing the multiscale vascular hierarchy: progress toward solving the grand challenge of tissue engineering

In human vascular anatomy, blood flows from the heart to organs and tissues through a hierarchical vascular tree, comprising large arteries that branch into arterioles and further into capillaries, where gas and nutrient exchange occur. Engineering a complete, integrated vascular hierarchy with vessels large enough to suture, strong enough to withstand hemodynamic forces, and a branching structure to permit immediate perfusion of a fluidic circuit across scales would be transformative for regenerative medicine (RM), enabling the translation of engineered tissues of clinically relevant size, and perhaps whole organs. How close are we to solving this biological plumbing problem? In this review, we highlight advances in engineered vasculature at individual scales and focus on recent strategies to integrate across scales.

In vitro microvascular engineering approaches and strategies for interstitial tissue integration

The increasing gap between clinical demand for tissue or organ transplants and the availability of donated tissue highlights the emerging opportunities for lab-grown or synthetically engineered tissue. While the field of tissue engineering has existed for nearly half a century, its clinical translation remains unrealised, in part, due to a limited ability to engineer sufficient vascular supply into fabricated tissue, which is necessary to enable nutrient and waste exchange, prevent cellular necrosis, and support tissue proliferation. Techniques to develop anatomically relevant, functional vascular networks in vitro have made significant progress in the last decade, however, the challenge now remains as to how best incorporate these throughout dense parenchymal tissue-like structures to address diffusion-limited development and allow for the fabrication of large-scale vascularised tissue. This review explores advances made in the laboratory engineering of vasculature structures and summarises recent attempts to integrate vascular networks together with sophisticated in vitro avascular tissue and organ-like structures. STATEMENT OF SIGNIFICANCE: The ability to grow full scale, functional tissue and organs in vitro is primarily limited by an inability to adequately diffuse oxygen and nutrients throughout developing cellularised structures, which generally results from the absence of perfusable vessel networks. Techniques to engineering both perfusable vascular networks and avascular miniaturised organ-like structures have recently increased in complexity, sophistication, and physiological relevance. However, integrating these two essential elements into a single functioning vascularised tissue structure represents a significant spatial and temporal engineering challenge which is yet to be surmounted. Here, we explore a range of vessel morphogenic phenomena essential for tissue-vascular co-development, as well as evaluate a range of recent noteworthy approaches for generating vascularised tissue products in vitro.

Rapid magnetically directed assembly of pre-patterned capillary-scale microvessels

Capillary scale vascularization is critical to the survival of engineered 3D tissues and remains an outstanding challenge for the field of tissue engineering. Current methods to generate micro-scale vasculature such as 3D printing, two photon hydrogel ablation, angiogenesis, and vasculogenic assembly face challenges in rapidly creating organized, highly vascularized tissues at capillary length-scales. Within metabolically demanding tissues, native capillary beds are highly organized and densely packed to achieve adequate delivery of nutrients and oxygen and efficient waste removal. Here, we adopt two existing techniques to fabricate lattices composed of sacrificial microfibers that can be efficiently and uniformly seeded with endothelial cells (ECs) by magnetizing both lattices and ECs. Ferromagnetic microparticles (FMPs) were incorporated into microfibers produced by solution electrowriting (SEW) and fiber electropulling (FEP). By loading ECs with superparamagnetic iron oxide nanoparticles (SPIONs), the cells could be seeded onto magnetized microfiber lattices. Following encapsulation in a hydrogel, the capillary templating lattice was selectively degraded by a bacterial lipase that does not impact mammalian cell viability or function. This work introduces a novel approach to rapidly producing organized capillary networks within metabolically demanding engineered tissue constructs which should have broad utility for the fields of tissue engineering and regenerative medicine.

Research and Clinical Approaches to Assess Platelet Function in Flowing Blood

Platelet adhesion and activation is fundamental to the formation of a hemostatic response to limit loss of blood and instigate wound repair to seal a site of vascular injury. The process of platelet aggregate formation is supported by the coagulation system driving injury-proximal formation of thrombin, which converts fibrinogen to insoluble fibrin. This highly coordinated series of molecular and membranous events must be routinely achieved in flowing blood, at vascular fluid shear rates that place significant strain on molecular and cellular interactions. Platelets have long been recognized to be able to slow down and adhere to sites of vascular injury and then activate and recruit more platelets that forge and strengthen adhesive ties with the vascular wall under these conditions. It has been a major challenge for the Platelet Research Community to construct experimental conditions that allow precise definition of the molecular steps occurring under flow. This brief review will discuss work to date from our group, as well as others that has furthered our understanding of platelet function in flowing blood.

Stacking thick perfusable human microvascular grafts enables dense vascularity and rapid integration into infarcted rat hearts

Fabrication of large-scale engineered tissues requires extensive vascularization to support tissue survival and function. Here, we report a modular fabrication approach, by stacking of patterned collagen membranes, to generate thick (2 mm and beyond), large, three-dimensional, perfusable networks of endothelialized vasculature. In vitro, these perfusable vascular networks exhibit remodeling and evenly distributed perfusion among layers, while maintaining their patterned, open-lumen architecture. Compared to non-perfusable, self-assembled vasculature, constructs with perfusable vasculature demonstrated increased gene expression indicative of vascular development and angiogenesis. Upon implantation onto infarcted rat hearts, perfusable vascular networks attain greater host vascular integration than self-assembled controls, indicated by 2.5-fold greater perfused vascular density measured by histological analysis and 5-fold greater perfusion rate measured by optical microangiography. Together, the success of fabricating thick, perfusable tissues with dense vascularity and rapid anastomoses represents an important step forward for vascular bioengineering, and paves the way towards more complex, large scale, highly metabolic engineered tissues.

Extracellular Matrix Stiffness Regulates Microvascular Stability by Controlling Endothelial Paracrine Signaling to Determine Pericyte Fate

BACKGROUND

The differentiation of pericytes into myofibroblasts causes microvascular degeneration, ECM (extracellular matrix) accumulation, and tissue stiffening, characteristics of fibrotic diseases. It is unclear how pericyte-myofibroblast differentiation is regulated in the microvascular environment. Our previous study established a novel 2-dimensional platform for coculturing microvascular endothelial cells (ECs) and pericytes derived from the same tissue. This study investigated how ECM stiffness regulated microvascular ECs, pericytes, and their interactions.

METHODS

Primary microvessels were cultured in the TGM2D medium (tubular microvascular growth medium on 2-dimensional substrates). Stiff ECM was prepared by incubating ECM solution in regular culture dishes for 1 hour followed by PBS wash. Soft ECM with Young modulus of ≈6 kPa was used unless otherwise noted. Bone grafts were prepared from the rat skull. Immunostaining, RNA sequencing, RT-qPCR (real-time quantitative polymerase chain reaction), Western blotting, and knockdown experiments were performed on the cells.

RESULTS

Primary microvascular pericytes differentiated into myofibroblasts (NG2+αSMA+) on stiff ECM, even with the TGFβ (transforming growth factor beta) signaling inhibitor A83-01. Soft ECM and A83-01 cooperatively maintained microvascular stability while inhibiting pericyte-myofibroblast differentiation (NG2+αSMA-/low). We thus defined 2 pericyte subpopulations: primary (NG2+αSMA-/low) and activated (NG2+αSMA+) pericytes. Soft ECM promoted microvascular regeneration and inhibited fibrosis in bone graft transplantation in vivo. As integrins are the major mechanosensor, we performed RT-qPCR screening of integrin family members and found Itgb1 (integrin β1) was the major subunit downregulated by soft ECM and A83-01 treatment. Knocking down Itgb1 suppressed myofibroblast differentiation on stiff ECM. Interestingly, ITGB1 phosphorylation (Y783) was mainly located on microvascular ECs on stiff ECM, which promoted EC secretion of paracrine factors, including CTGF (connective tissue growth factor), to induce pericyte-myofibroblast differentiation. CTGF knockdown or monoclonal antibody treatment partially reduced myofibroblast differentiation, implying the participation of multiple pathways in fibrosis formation.

CONCLUSIONS

ECM stiffness and TGFβ signaling cooperatively regulate microvascular stability and pericyte-myofibroblast differentiation. Stiff ECM promotes EC ITGB1 phosphorylation (Y783) and CTGF secretion, which induces pericyte-myofibroblast differentiation.

Fluid flow to mimic organ function in 3D in vitro models

Many different strategies can be found in the literature to model organ physiology, tissue functionality, and disease in vitro; however, most of these models lack the physiological fluid dynamics present in vivo. Here, we highlight the importance of fluid flow for tissue homeostasis, specifically in vessels, other lumen structures, and interstitium, to point out the need of perfusion in current 3D in vitro models. Importantly, the advantages and limitations of the different current experimental fluid-flow setups are discussed. Finally, we shed light on current challenges and future focus of fluid flow models applied to the newest bioengineering state-of-the-art platforms, such as organoids and organ-on-a-chip, as the most sophisticated and physiological preclinical platforms.

Convergence of melt electrowriting and extrusion-based bioprinting for vascular patterning of a myocardial construct

To progress cardiac tissue engineering strategies closer to the clinic, thicker constructs are required to meet the functional need following a cardiac event. Consequently, pre-vascularization of these constructs needs to be investigated to ensure survival and optimal performance of implantable engineered heart tissue. The aim of this research is to investigate the potential of combining extrusion-based bioprinting (EBB) and melt electrowriting for the fabrication of a myocardial construct with a precisely patterned pre-vascular pathway. Gelatin methacryloyl (GelMA) was investigated as a base hydrogel for the respective myocardial and vascular bioinks with collagen, Matrigel and fibrinogen as interpenetrating polymers to support myocardial functionality. Subsequently, extrusion-based printability and viability were investigated to determine the optimal processing parameters for printing into melt electrowritten meshes. Finally, an anatomically inspired vascular pathway was implemented in a dual EBB set-up into melt electrowritten meshes, creating a patterned pre-vascularized myocardial construct. It was determined that a blend of 5% GelMA and 0.8 mg·ml-1collagen with a low crosslinked density was optimal for myocardial cellular arrangement and alignment within the constructs. For the vascular fraction, the optimized formulation consisted of 5% GelMA, 0.8 mg·ml-1collagen and 1 mg·ml-1fibrinogen with a higher crosslinked density, which led to enhanced vascular cell connectivity. Printability assessment confirmed that the optimized bioinks could effectively fill the microfiber mesh while supporting cell viability (∼70%). Finally, the two bioinks were applied using a dual EBB system for the fabrication of a pre-vascular pathway with the shape of a left anterior descending artery within a myocardial construct, whereby the distinct cell populations could be visualized in their respective patterns up to D14. This research investigated the first step towards developing a thick engineered cardiac tissue construct in which a pre-vascularization pathway is fabricated within a myocardial construct.

Patterned Arteriole-Scale Vessels Enhance Engraftment, Perfusion, and Vessel Branching Hierarchy of Engineered Human Myocardium for Heart Regeneration

Heart regeneration after myocardial infarction (MI) using human stem cell-derived cardiomyocytes (CMs) is rapidly accelerating with large animal and human clinical trials. However, vascularization methods to support the engraftment, survival, and development of implanted CMs in the ischemic environment of the infarcted heart remain a key and timely challenge. To this end, we developed a dual remuscularization-revascularization therapy that is evaluated in a rat model of ischemia-reperfusion MI. This study details the differentiation of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) for engineering cardiac tissue containing patterned engineered vessels 400 μm in diameter. Vascularized engineered human myocardial tissues (vEHMs) are cultured in static conditions or perfused in vitro prior to implantation and evaluated after two weeks. Immunohistochemical staining indicates improved engraftment of hiPSC-CMs in in vitro-perfused vEHMs with greater expression of SMA+ vessels and evidence of inosculation. Three-dimensional vascular reconstructions reveal less tortuous and larger intra-implant vessels, as well as an improved branching hierarchy in in vitro-perfused vEHMs relative to non-perfused controls. Exploratory RNA sequencing of explanted vEHMs supports the hypothesis that co-revascularization impacts hiPSC-CM development in vivo. Our approach provides a strong foundation to enhance vEHM integration, develop hierarchical vascular perfusion, and maximize hiPSC-CM engraftment for future regenerative therapy.

Shexiang Tongxin Dropping Pill alleviates M1 macrophage polarization-induced inflammation and endothelial dysfunction to reduce coronary microvascular dysfunction via the dectin-1/Syk/IRF5 pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Shexiang Tongxin Dropping Pill (STDP), a traditional Chinese medicine compound, is fragrant, invigorates the qi, unblocks pulses, activates the blood circulation, removes blood stasis, and relieves pain. It is used clinically to treat coronary heart disease and angina pectoris. Coronary microvascular dysfunction (CMD) is associated with increased morbidity and mortality from cardiovascular events. Endothelial dysfunction and inflammation have been verified as its underlying causes. STDP can ameliorate CMD, but the mechanism has not been fully elucidated.

AIM OF THE STUDY

To explore the effects of STDP on M1 macrophage polarization-induced inflammation and endothelial dysfunction as an inhibitor of CMD, and to determine its mechanisms of action.

MATERIALS AND METHODS

The CMD rat model was established by left anterior descending artery (LAD) ligation. The efficacy of STDP against CMD was evaluated by echocardiography, optical microangiography, Evans blue staining, and histological examination. The OGD/R-induced endothelial injury model, the endothelial injury-induced sterile inflammation model, the Dectin-1 overexpression model, and the Dectin-1-overexpressing RAW264.7 macrophage supernatant-stimulated HUVEC-induced secondary injury of endothelial function model were established to confirm the efficacy of STDP against M1 macrophage polarization-induced inflammation and endothelial dysfunction.

RESULTS

STDP blunted the deterioration of cardiac function and ameliorated CMD by reducing inflammatory cell infiltration and endothelial dysfunction in CMD rats. Endothelial injury and Dectin-1 overexpression induced M1 macrophage polarization and inflammation. Mechanically, STDP hindered M1 macrophage polarization and inflammation by inhibiting the Dectin-1/Syk/IRF5 pathway both in vivo and in vitro. STDP alleviated endothelial dysfunction induced by Dectin-1 overexpression in macrophages.

CONCLUSION

STDP can alleviate M1 macrophage polarization-induced inflammation and endothelial dysfunction against CMD via the Dectin-1/Syk/IRF5 pathway. Dectin-1-associated M1 macrophage polarization might be developed as a novel target for ameliorating CMD.

Amyloid beta peptides (Aβ) from Alzheimer's disease neuronal secretome induce endothelial activation in a human cerebral microvessel model

In Alzheimer's disease (AD), secretion and deposition of amyloid beta peptides (Aβ) have been associated with blood-brain barrier dysfunction. However, the role of Aβ in endothelial cell (EC) dysfunction remains elusive. Here we investigated AD mediated EC activation by studying the effect of Aβ secreted from human induced pluripotent stem cell-derived cortical neurons (hiPSC-CN) harboring a familial AD mutation (Swe+/+) on human brain microvascular endothelial cells (HBMECs) in 2D and 3D perfusable microvessels. We demonstrated that increased Aβ levels in Swe+/+ conditioned media (CM) led to stress fiber formation and upregulation of genes associated with endothelial inflammation and immune-adhesion. Perfusion of Aβ-rich Swe+/+ CM induced acute formation of von Willebrand factor (VWF) fibers in the vessel lumen, which was attenuated by reducing Aβ levels in CM. Our findings suggest that Aβ peptides can trigger rapid inflammatory and thrombogenic responses within cerebral microvessels, which may exacerbate AD pathology.

Engineered Vasculature for Cancer Research and Regenerative Medicine

Engineered human tissues created by three-dimensional cell culture of human cells in a hydrogel are becoming emerging model systems for cancer drug discovery and regenerative medicine. Complex functional engineered tissues can also assist in the regeneration, repair, or replacement of human tissues. However, one of the main hurdles for tissue engineering, three-dimensional cell culture, and regenerative medicine is the capability of delivering nutrients and oxygen to cells through the vasculatures. Several studies have investigated different strategies to create a functional vascular system in engineered tissues and organ-on-a-chips. Engineered vasculatures have been used for the studies of angiogenesis, vasculogenesis, as well as drug and cell transports across the endothelium. Moreover, vascular engineering allows the creation of large functional vascular conduits for regenerative medicine purposes. However, there are still many challenges in the creation of vascularized tissue constructs and their biological applications. This review will summarize the latest efforts to create vasculatures and vascularized tissues for cancer research and regenerative medicine.

Promoting Angiogenesis Using Immune Cells for Tissue-Engineered Vascular Grafts

Implantable tissue-engineered vascular grafts (TEVGs) usually trigger the host reaction which is inextricably linked with the immune system, including blood-material interaction, protein absorption, inflammation, foreign body reaction, and so on. With remarkable progress, the immune response is no longer considered to be entirely harmful to TEVGs, but its therapeutic and impaired effects on angiogenesis and tissue regeneration are parallel. Although the implicated immune mechanisms remain elusive, it is certainly worthwhile to gain detailed knowledge about the function of the individual immune components during angiogenesis and vascular remodeling. This review provides a general overview of immune cells with an emphasis on macrophages in light of the current literature. To the extent possible, we summarize state-of-the-art approaches to immune cell regulation of the vasculature and suggest that future studies are needed to better define the timing of the activity of each cell subpopulation and to further reveal key regulatory switches.

Realizations of vascularized tissues: From in vitro platforms to in vivo grafts

Vascularization is essential for realizing thick and functional tissue constructs that can be utilized for in vitro study platforms and in vivo grafts. The vasculature enables the transport of nutrients, oxygen, and wastes and is also indispensable to organ functional units such as the nephron filtration unit, the blood-air barrier, and the blood-brain barrier. This review aims to discuss the latest progress of organ-like vascularized constructs with specific functionalities and realizations even though they are not yet ready to be used as organ substitutes. First, the human vascular system is briefly introduced and related design considerations for engineering vascularized tissues are discussed. Second, up-to-date creation technologies for vascularized tissues are summarized and classified into the engineering and cellular self-assembly approaches. Third, recent applications ranging from in vitro tissue models, including generic vessel models, tumor models, and different human organ models such as heart, kidneys, liver, lungs, and brain, to prevascularized in vivo grafts for implantation and anastomosis are discussed in detail. The specific design considerations for the aforementioned applications are summarized and future perspectives regarding future clinical applications and commercialization are provided.

Perfusable cell-laden matrices to guide patterning of vascularization in vivo

The survival and function of transplanted tissue engineered constructs and organs require a functional vascular network. In the body, blood vessels are organized into distinct patterns that enable optimal nutrient delivery and oxygen exchange. Mimicking these same patterns in engineered tissue matrices is a critical challenge for cell and tissue transplantation. Here, we leverage bioprinting to assemble endothelial cells in to organized networks of large (>100 μm) diameter blood vessel grafts to enable spatial control of vessel formation in vivo. Acellular PEG/GelMA matrices with perfusable channels were bioprinted and laminar flow was confirmed within patterned channels, beneficial for channel endothelialization and consistent wall shear stress for endothelial maturation. Next, human umbilical vein endothelial cells (HUVECs) were seeded within the patterned channel and maintained under perfusion culture for multiple days, leading to cell-cell coordination within the construct in vitro. HUVEC and human mesenchymal stromal cells (hMSCs) were additionally added to bulk matrix to further stimulate anastomosis of our bioprinted vascular grafts in vivo. Among multiple candidate matrix designs, the greatest degree of biomaterial vascularization in vivo was seen within matrices fabricated with HUVECs and hMSCs encapsulated within the bulk matrix and HUVECs lining the walls of the patterned channels, dubbed design M-C_E. For this lead design, vasculature was detected within the endothelialized, perfusable matrix channels as early as two weeks and αSMA+ CD31+ vessels greater than 100 μm in diameter had formed by eight weeks, resulting in durable and mature vasculature. Notably, vascularization occurred within the endothelialized, bioprinted channels of the matrix, demonstrating the ability of bioprinted perfusable structures to guide vascularization patterns in vivo. The ability to influence vascular patterning in vivo can contribute to the future development of vascularized tissues and organs.

Reconstructing vascular networks promotes the repair of skeletal muscle following volumetric muscle loss by pre-vascularized tissue constructs

Current treatment for complex and large-scale volumetric muscle loss (VML) injuries remains a limited success and have substantial disadvantages, due to the irreversible loss of muscle mass, slow muscle regeneration, and rapid formation of non-functional fibrosis scars. These VML injuries are accompanied by denervation and the destruction of native vasculature which increases difficulties in the functional restoration of muscle. Here, reconstruction of the vascular network at the injury site was offered as a possible solution for improving the repair of muscle defects through the timely supply of nutrients and oxygen to surrounding cells. A hydrogel-based tissue construct containing various densities of the vascular network was successfully created in the subcutaneous space of mice by manipulating hydrogel properties, and then implanted into the VML injury site. One month after implantation, the mouse treated with the highly vascularized tissue had extensive muscle repair at the injury site and only spent a shorter time completing the inclined plane tests. These findings suggest that the reconstruction of the functional vascular network at the VML injury site accelerated muscle fiber repair through a timely supply of sufficient blood and avoided invasion by host fibroblasts.

Bioengineering for vascularization: Trends and directions of photocrosslinkable gelatin methacrylate hydrogels

Gelatin methacrylate (GelMA) hydrogels have been widely used in various biomedical applications, especially in tissue engineering and regenerative medicine, for their excellent biocompatibility and biodegradability. GelMA crosslinks to form a hydrogel when exposed to light irradiation in the presence of photoinitiators. The mechanical characteristics of GelMA hydrogels are highly tunable by changing the crosslinking conditions, including the GelMA polymer concentration, degree of methacrylation, light wavelength and intensity, and light exposure time et al. In this regard, GelMA hydrogels can be adjusted to closely resemble the native extracellular matrix (ECM) properties for the specific functions of target tissues. Therefore, this review focuses on the applications of GelMA hydrogels for bioengineering human vascular networks in vitro and in vivo. Since most tissues require vasculature to provide nutrients and oxygen to individual cells, timely vascularization is critical to the success of tissue- and cell-based therapies. Recent research has demonstrated the robust formation of human vascular networks by embedding human vascular endothelial cells and perivascular mesenchymal cells in GelMA hydrogels. Vascular cell-laden GelMA hydrogels can be microfabricated using different methodologies and integrated with microfluidic devices to generate a vasculature-on-a-chip system for disease modeling or drug screening. Bioengineered vascular networks can also serve as build-in vasculature to ensure the adequate oxygenation of thick tissue-engineered constructs. Meanwhile, several reports used GelMA hydrogels as implantable materials to deliver therapeutic cells aiming to rebuild the vasculature in ischemic wounds for repairing tissue injuries. Here, we intend to reveal present work trends and provide new insights into the development of clinically relevant applications based on vascularized GelMA hydrogels.

Engineering Neutrophil Immunomodulatory Hydrogels Promoted Angiogenesis

Timely restoration of blood supply following ischemia is critical to rescue damaged tissue. However, clinical efficacy is hampered by the inflammatory response after ischemia. Whether inflammation fine tunes the angiogenesis and the function of blood vessels via the heterogeneity of neutrophils remain poorly understood. Herein, the objective of this work is to incorporate the growth factors secreted by neutrophils into a porous gelatin methacrylate (GelMA) hydrogel, which subsequently is used as a novel regenerative scaffold with defined architecture for ischemia. We demonstrate that anti-inflammatory neutrophils (N₂-polarized neutrophils) play an important role in promoting the migration of human umbilical vein endothelial cells (HUVECs) and formation of capillary-like networks in vitro. More importantly, vascular anastomosis can be achieved by modulating the neutrophils to N₂ phenotype. In addition, N₂-polarized composite hydrogel scaffolds can regulate inflammation, maintain the survival of exogenous cells, and promote angiogenesis in vivo. Notably, the composite hydrogel scaffolds promote neovascularization during exogenous introduction of endothelial cells by anastomosis. Taken together, this study highlights N₂-polarized neutrophils composite hydrogels can achieve vascularization rapidly by regulating inflammation and promoting vascular anastomosis. This work lays the foundation for research into the treatment of ischemia and may inspire further research into novel treatment options.

Time-regulated transcripts with the potential to modulate human pluripotent stem cell-derived cardiomyocyte differentiation

Background

Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) are a promising disease model, even though hiPSC-CMs cultured for extended periods display an undifferentiated transcriptional landscape. MiRNA–target gene interactions contribute to fine-tuning the genetic program governing cardiac maturation and may uncover critical pathways to be targeted.

Methods

We analyzed a hiPSC-CM public dataset to identify time-regulated miRNA–target gene interactions based on three logical steps of filtering. We validated this process in silico using 14 human and mouse public datasets, and further confirmed the findings by sampling seven time points over a 30-day protocol with a hiPSC-CM clone developed in our laboratory. We then added miRNA mimics from the top eight miRNAs candidates in three cell clones in two different moments of cardiac specification and maturation to assess their impact on differentiation characteristics including proliferation, sarcomere structure, contractility, and calcium handling.

Results

We uncovered 324 interactions among 29 differentially expressed genes and 51 miRNAs from 20,543 transcripts through 120 days of hiPSC-CM differentiation and selected 16 genes and 25 miRNAs based on the inverse pattern of expression (Pearson R-values < − 0.5) and consistency in different datasets. We validated 16 inverse interactions among eight genes and 12 miRNAs (Person R-values < − 0.5) during hiPSC-CMs differentiation and used miRNAs mimics to verify proliferation, structural and functional features related to maturation. We also demonstrated that miR-124 affects Ca²⁺ handling altering features associated with hiPSC-CMs maturation.

Conclusion

We uncovered time-regulated transcripts influencing pathways affecting cardiac differentiation/maturation axis and showed that the top-scoring miRNAs indeed affect primarily structural features highlighting their role in the hiPSC-CM maturation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-03138-x.

Challenges and opportunities for the next generation of cardiovascular tissue engineering

Engineered cardiac tissues derived from human induced pluripotent stem cells offer unique opportunities for patient-specific disease modeling, drug discovery and cardiac repair. Since the first engineered hearts were introduced over two decades ago, human induced pluripotent stem cell-based three-dimensional cardiac organoids and heart-on-a-chip systems have now become mainstays in basic cardiovascular research as valuable platforms for investigating fundamental human pathophysiology and development. However, major obstacles remain to be addressed before the field can truly advance toward commercial and clinical translation. Here we provide a snapshot of the state-of-the-art methods in cardiac tissue engineering, with a focus on in vitro models of the human heart. Looking ahead, we discuss major challenges and opportunities in the field and suggest strategies for enabling broad acceptance of engineered cardiac tissues as models of cardiac pathophysiology and testbeds for the development of therapies.

Spatial patterning of PCL µ-scaffolds directs 3D vascularized bio-construct morphogenesis in vitro

Modular tissue engineering (mTE) strategies aim to build three-dimensional tissue analogues in vitro by the sapient combination of cells, micro-scaffolds (μ-scaffs) and bioreactors. The translation of these newly engineered tissues into current clinical approaches is, among other things, dependent on implant-to-host microvasculature integration, a critical issue for cells and tissue survival in vivo. In this work we reported, for the first time, a computer-aided modular approach suitable to build fully vascularized hybrid (biological/synthetic) constructs (bio-constructs) with micro-metric size scale control of blood vessels growth and orientation. The approach consists of four main steps, starting with the fabrication of polycaprolactone μ-scaffs by fluidic emulsion technique, which exhibit biomimetic porosity features. In the second step, layers of μ-scaffs following two different patterns, namely ordered and disordered, were obtained by a soft lithography-based process. Then, the as obtained μ-scaff patterns were used as template for human dermal fibroblasts and human umbilical vein endothelial cells co-culture, aiming to promote and guide the biosynthesis of collagenous extracellular matrix and the growth of new blood vessels within the mono-layered bio-constructs. Finally, bi-layered bio-constructs were built by the alignment, stacking and fusion of two vascularized mono-layered samples featuring ordered patterns. Our results demonstrated that, if compared to the disordered pattern, the ordered one provided better control over bio-constructs shape and vasculature architecture, while minor effect was observed with respect to cell colonization and new tissue growth. Furthermore, by assembling two mono-layered bio-constructs it was possible to build 1-mm thick fully vascularized viable bio-constructs and to study tissue morphogenesis during 1 week of in vitro culture. In conclusion, our results highlighted the synergic role of μ-scaff architectural features and spatial patterning on cells colonization and biosynthesis, and pay the way for the possibility to create in silico designed vasculatures within modularly engineered bio-constructs.

Endothelial-derived von Willebrand factor accelerates fibrin clotting within engineered microvessels

BACKGROUND

Von Willebrand factor (VWF) is classically associated with primary hemostasis and platelet-rich arterial thromboses, but recently has also been implicated in fibrin clotting and venous thrombosis. Direct interaction between fibrin and VWF may mediate these processes, although prior reports are conflicting.

OBJECTIVES

We combined two complementary platforms to characterize VWF-fibrin(ogen) interactions and identify their potential physiologic significance.

METHODS

Engineered microvessels were lined with human endothelial cells, cultured under flow, and activated to release VWF and form transluminal VWF fibers. Fibrinogen, fibrin monomers, or polymerizing fibrin were then perfused, and interactions with VWF evaluated. Thrombin and fibrinogen were perfused into living versus paraformeldahyde-fixed microvessels and the pressure drop across microvessels monitored. Separately, protein binding to tethered VWF was assessed on a single-molecule level using total internal reflection fluorescence (TIRF) microscopy.

RESULTS

Within microvessels, VWF fibers colocalized with polymerizing fibrin, but not fibrinogen. TIRF microscopy showed no colocalization between VWF and fibrinogen or fibrin monomers in a microfluidic flow chamber across a range of shear rates and protein concentrations. Thrombin-mediated fibrin polymerization within living microvessels triggered endothelial VWF release, increasing the rate and amount of microvessel obstruction compared to fixed vessels with an inert endothelium.

CONCLUSIONS

We did not identify specific binding between fibrin(ogen) and VWF at a single-molecule level. Despite this, our results suggest that rapid release of endothelial VWF during clotting may provide a physical support for fibrin polymerization and accelerate thrombosis. This interaction may be of fundamental importance for the understanding and treatment of human thrombotic disease.

100 plus years of stem cell research-20 years of ISSCR

The International Society for Stem Cell Research (ISSCR) celebrates its 20th anniversary in 2022. This review looks back at some of the key developments in stem cell research as well as the evolution of the ISSCR as part of that field. Important discoveries from stem cell research are described, and how the improved understanding of basic stem cell biology translates into new clinical therapies and insights into disease mechanisms is discussed. Finally, the birth and growth of ISSCR into a leading stem cell society and a respected voice for ethics, advocacy, education and policy in stem cell research are described.

Engineering the multiscale complexity of vascular networks

The survival of vertebrate organisms depends on highly regulated delivery of oxygen and nutrients through vascular networks that pervade nearly all tissues in the body. Dysregulation of these vascular networks is implicated in many common human diseases such as hypertension, coronary artery disease, diabetes and cancer. Therefore, engineers have sought to create vascular networks within engineered tissues for applications such as regenerative therapies, human disease modelling and pharmacological testing. Yet engineering vascular networks has historically remained difficult, owing to both incomplete understanding of vascular structure and technical limitations for vascular fabrication. This Review highlights the materials advances that have enabled transformative progress in vascular engineering by ushering in new tools for both visualizing and building vasculature. New methods such as bioprinting, organoids and microfluidic systems are discussed, which have enabled the fabrication of 3D vascular topologies at a cellular scale with lumen perfusion. These approaches to vascular engineering are categorized into technology-driven and nature-driven approaches. Finally, the remaining knowledge gaps, emerging frontiers and opportunities for this field are highlighted, including the steps required to replicate the multiscale complexity of vascular networks found in nature.