A new perfusion culture method with a self-organized capillary network

Direct extrusion of multifascicle prevascularized human skeletal muscle for volumetric muscle loss surgery

Skeletal muscle is composed of multiple fascicles, which are parallel bundles of muscle fibers surrounded by connective tissues that contain blood vessels and nerves. Here, we fabricated multifascicle human skeletal muscle scaffolds that mimic the natural structure of human skeletal muscle bundles using a seven-barrel nozzle. For the core material to form the fascicle structure, human skeletal myoblasts were encapsulated in Matrigel with calcium chloride. Meanwhile, the shell that plays a role as the connective tissue, human fibroblasts and human umbilical vein endothelial cells within a mixture of porcine muscle decellularized extracellular matrix and sodium alginate at a 95:5 ratio was used. We assessed four types of extruded scaffolds monolithic-monoculture (Mo-M), monolithic-coculture (Mo-C), multifascicle-monoculture (Mu-M), and multifascicle-coculture (Mu-C) to determine the structural effect of muscle mimicking scaffold. The Mu-C scaffold outperformed other scaffolds in cell proliferation, differentiation, vascularization, mechanical properties, and functionality. In an in vivo mouse model of volumetric muscle loss, the Mu-C scaffold effectively regenerated the tibialis anterior muscle defect, demonstrating its potential for volumetric muscle transplantation. Our nozzle will be further used to produce other volumetric functional tissues, such as tendons and peripheral nerves.

Engineering aortic valves via transdifferentiating fibroblasts into valvular endothelial cells without using viruses or iPS cells

The technology of induced pluripotent stem cells (iPSCs) has enabled the conversion of somatic cells into primitive undifferentiated cells via reprogramming. This approach provides possibilities for cell replacement therapies and drug screening, but the potential risk of tumorigenesis hampers its further development and in vivo application. How to generate differentiated cells such as valvular endothelial cells (VECs) has remained a major challenge. Utilizing a combinatorial strategy of selective soluble chemicals, cytokines and substrate stiffness modulation, mouse embryonic fibroblasts are directly and efficiently transdifferentiated into induced aortic endothelial cell-like cells (iAECs), or human primary adult fibroblasts are transdifferentiated into induced valvular endothelial cell-like cells (hiVECs), without expressing pluripotency stem cell markers. These iAECs and hiVECs express VEC-associated genes and proteins and VEC-specific marker NFATC1 and are functional in culture and on decellularized porcine aortic valves, like mouse aortic endothelial cells or human primary aortic valvular endothelial cells. The iAECs and hiVECs seeded on decellularized porcine aortic valves stay intact and express VEC-associated proteins for 60 days after grafting into abdominal aorta of immune-compromised rats. In contrast, induced pluripotent stem cells (iPSCs) are less efficient in differentiating into VEC-like cells and pluripotency marker Nanog is expressed in a small subpopulation of iPSC-derived VEC-like cells that generate teratomas in SCID mice whereas hiVECs derived from transdifferentiation do not generate teratomas in vivo. Our findings highlight an approach to efficiently convert fibroblasts into iAECs and hiVECs and seed them onto decellularized aortic valves for safely generating autologous tissue-engineered aortic valves without using viruses or first reprogramming the cells into pluripotent stem cells.

Cholesterol synthesis is essential for the growth of liver metastasis-prone colorectal cancer cells

Metastasis to the liver is a leading cause of death in patients with colorectal cancer. To investigate the characteristics of cancer cells prone to metastasis, we utilized an isogenic model of BALB/c and colon tumor 26 (C26) cells carrying an active KRAS mutation. Liver metastatic (LM) 1 cells were isolated from mice following intrasplenic transplantation of C26 cells. Subsequent injections of LM1 cells generated LM2 cells, and after four cycles, LM4 cells were obtained. In vitro, using a perfusable capillary network system, we found comparable extravasation frequencies between C26 and LM4 cells. Both cell lines showed similar growth rates in vitro. However, C26 cells showed higher glucose consumption, whereas LM4 cells incorporated more fluorescent fatty acids (FAs). Biochemical analysis revealed that LM4 cells had higher cholesterol levels than C26 cells. A correlation was observed between fluorescent FAs and cholesterol levels detected using filipin III. LM4 cells utilized FAs as a source for cholesterol synthesis through acetyl-CoA metabolism. In cellular analysis, cholesterol accumulated in punctate regions, and upregulation of NLRP3 and STING proteins, but not mTOR, was observed in LM4 cells. Treatment with a cholesterol synthesis inhibitor (statin) induced LM4 cell death in vitro and suppressed LM4 cell growth in the livers of nude mice. These findings indicate that colorectal cancer cells prone to liver metastasis show cholesterol-dependent growth and that statin therapy could help treat liver metastasis in immunocompromised patients.

Vascularized tumor-on-chip microplatforms for the studies of neovasculature as hope for more effective cancer treatments

Angiogenesis is the development of new blood vessels from pre-existing vasculature. Multiple factors control its course. Disorders of the distribution of angiogenic agents are responsible for development of solid tumors and its metastases. Understanding of the molecular interactions regulating pathological angiogenesis will allow for development of more effective, even personalized treatment. A simulation of angiogenesis under microflow conditions is a promising alternative to previous studies conducted on animals and on 2D cell cultures. In this review, we summarize what has been discovered so far in the field of vascularized tumor-on-a-chip platforms. For this purpose, we describe different vascularization techniques used in microfluidics, present various attempts to induce angiogenesis-on-a-chip and report some approaches to recapitulate vascularized tumor microenvironment under microflow conditions.

New Insights and Advanced Strategies for In Vitro Construction of Vascularized Tissue Engineering

Inadequate vascularization is a significant barrier to clinical application of large-volume tissue engineered grafts. In contrast to in vivo vascularization, in vitro prevascularization shortens the time required for host vessels to grow into the graft core and minimizes necrosis in the core region of the graft. However, the challenge of prevascularization is to construct hierarchical perfusable vascular networks, increase graft volume, and form a vascular tip that can anastomose with host vessels. Understanding advances in in vitro prevascularization techniques and new insights into angiogenesis could overcome these obstacles. In the present review, we discuss new perspectives on angiogenesis, the differences between in vivo and in vitro tissue vascularization, the four elements of prevascularized constructs, recent advances in perfusion-based in vitro prevascularized tissue fabrication, and prospects for large-volume prevascularized tissue engineering.

New Strategy for Promoting Vascularization in Tumor Spheroids in a Microfluidic Assay

Previous studies have developed vascularized tumor spheroid models to demonstrate the impact of intravascular flow on tumor progression and treatment. However, these models have not been widely adopted so the vascularization of tumor spheroids in vitro is generally lower than vascularized tumor tissues in vivo. To improve the tumor vascularization level, a new strategy is introduced to form tumor spheroids by adding fibroblasts (FBs) sequentially to a pre-formed tumor spheroid and demonstrate this method with tumor cell lines from kidney, lung, and ovary cancer. Tumor spheroids made with the new strategy have higher FB densities on the periphery of the tumor spheroid, which tend to enhance vascularization. The vessels close to the tumor spheroid made with this new strategy are more perfusable than the ones made with other methods. Finally, chimeric antigen receptor (CAR) T cells are perfused under continuous flow into vascularized tumor spheroids to demonstrate immunotherapy evaluation using vascularized tumor-on-a-chip model. This new strategy for establishing tumor spheroids leads to increased vascularization in vitro, allowing for the examination of immune, endothelial, stromal, and tumor cell responses under static or flow conditions.

Hierarchical Vessel Network-Supported Tumor Model-on-a-Chip Constructed by Induced Spontaneous Anastomosis

The vascular system in living tissues is a highly organized system that consists of vessels with various diameters for nutrient delivery and waste transport. In recent years, many vessel construction methods have been developed for building vascularized on-chip tissue models. These methods usually focused on constructing vessels at a single scale. In this work, a method that can build a hierarchical and perfusable vessel networks was developed. By providing flow stimuli and proper HUVEC concentration, spontaneous anastomosis between endothelialized lumens and the self-assembled capillary network was induced; thus, a perfusable network containing vessels at different scales was achieved. With this simple method, an in vivo-like hierarchical vessel-supported tumor model was prepared and its application in anticancer drug testing was demonstrated. The tumor growth rate was predicted by combining computational fluid dynamics simulation and a tumor growth mathematical model to understand the vessel perfusability effect on tumor growth rate in the hierarchical vessel network. Compared to the tumor model without capillary vessels, the hierarchical vessel-supported tumor shows a significantly higher growth rate and drug delivery efficiency.

Large-scale perfused tissues via synthetic 3D soft microfluidics

The vascularization of engineered tissues and organoids has remained a major unresolved challenge in regenerative medicine. While multiple approaches have been developed to vascularize in vitro tissues, it has thus far not been possible to generate sufficiently dense networks of small-scale vessels to perfuse large de novo tissues. Here, we achieve the perfusion of multi-mm3 tissue constructs by generating networks of synthetic capillary-scale 3D vessels. Our 3D soft microfluidic strategy is uniquely enabled by a 3D-printable 2-photon-polymerizable hydrogel formulation, which allows for precise microvessel printing at scales below the diffusion limit of living tissues. We demonstrate that these large-scale engineered tissues are viable, proliferative and exhibit complex morphogenesis during long-term in-vitro culture, while avoiding hypoxia and necrosis. We show by scRNAseq and immunohistochemistry that neural differentiation is significantly accelerated in perfused neural constructs. Additionally, we illustrate the versatility of this platform by demonstrating long-term perfusion of developing neural and liver tissue. This fully synthetic vascularization platform opens the door to the generation of human tissue models at unprecedented scale and complexity.

Electrochemical sensing of oxygen metabolism for a three-dimensional cultured model with biomimetic vascular flow

Microphysiological systems (MPSs) with three-dimensional (3D) cultured models have attracted considerable interest because of their potential to mimic human health and disease conditions. Recent MPSs have shown significant advancements in engineering perfusable vascular networks integrated with 3D culture models, realizing a more physiological environment in vitro; however, a sensing system that can monitor their activity under biomimetic vascular flow is lacking. We designed an open-top microfluidic device with sensor capabilities and demonstrated its application in analyzing oxygen metabolism in vascularized 3D tissue models. We first validated the platform by using human lung fibroblast (hLF) spheroids. Then, we applied the platform to a patient-derived cancer organoid and evaluated the changes in oxygen metabolism during drug administration through the vascular network. We found that the platform could integrate a perfusable vascular network with 3D cultured cells, and the electrochemical sensor could detect the change in oxygen metabolism in a quantitative, non-invasive, and real-time manner. This platform would become a monitoring system for 3D cultured cells integrated with a perfusable vascular network.

Improvement of the cell viability of hepatocytes cultured in three-dimensional collagen gels using pump-free perfusion driven by water level difference

Cell-containing collagen gels are one of the materials employed in tissue engineering and drug testing. A collagen gel is a useful three-dimensional (3D) scaffold that improves various cell functions compared to traditional two-dimensional plastic substrates. However, owing to poor nutrient availability, cells are not viable in thick collagen gels. Perfusion is an effective method for supplying nutrients to the gel. In this study, we maintained hepatocytes embedded in a 3D collagen gel using a simple pump-free perfusion cell culture system with ordinary cell culture products. Flow was generated by the difference in water level in the culture medium. Hepatocytes were found to be viable in a collagen gel of thickness 3.26 (± 0.16 S.E.)-mm for 3 days. In addition, hepatocytes had improved proliferation and gene expression related to liver function in a 3D collagen gel compared to a 2D culture dish. These findings indicate that our perfusion method is useful for investigating the cellular functions of 3D hydrogels.

FUCCItrack: An all-in-one software for single cell tracking and cell cycle analysis

Beyond the more conventional single-cell segmentation and tracking, single-cell cycle dynamics is gaining a growing interest in the field of cell biology. Thanks to sophisticated systems, such as the fluorescent ubiquitination-based cell cycle indicator (FUCCI), it is now possible to study cell proliferation, migration, changes in nuclear morphology and single cell cycle dynamics, quantitatively and in real time. In this work, we introduce FUCCItrack, an all-in-one, semi-automated software to segment, track and visualize FUCCI modified cell lines. A user-friendly complete graphical user interface is presented to record and quantitatively analyze both collective cell proliferation as well as single cell information, including migration and changes in nuclear or cell morphology as a function of cell cycle. To enable full control over the analysis, FUCCItrack also contains features for identification of errors and manual corrections.

Transforming Capillary Alginate Gel (Capgel) into New 3D-Printing Biomaterial Inks

Three-dimensional (3D) printing has great potential for creating tissues and organs to meet shortfalls in transplant supply, and biomaterial inks are key components of many such approaches. There is a need for biomaterial inks that facilitate integration, infiltration, and vascularization of targeted 3D-printed structures. This study is therefore focused on creating new biomaterial inks from self-assembled capillary alginate gel (Capgel), which possesses a unique microstructure of uniform tubular channels with tunable diameters and densities. First, extrusions of Capgel through needles (0.1–0.8 mm inner diameter) were investigated. It was found that Capgel ink extrudes as slurries of fractured and entangled particles, each retaining capillary microstructures, and that extruded line widths W and particle sizes A were both functions of needle inner diameter D, specifically power-law relationships of W~D^0.42 and A~D^1.52, respectively. Next, various structures were successfully 3D-printed with Capgel ink, thus demonstrating that this biomaterial ink is stackable and self-supporting. To increase ink self-adherence, Capgel was coated with poly-L-lysine (PLL) to create a cationic “skin” prior to extrusion. It was hypothesized that, during extrusion of Capgel-PLL, the sheared particles fracture and thereby expose cryptic sites of negatively-charged biomaterial capable of forming new polyelectrolyte bonds with areas of the positively-charged PLL skin on neighboring entangled particles. This novel approach resulted in continuous, self-adherent extrusions that remained intact in solution. Human lung fibroblasts (HLFs) were then cultured on this ink to investigate biocompatibility. HLFs readily colonized Capgel-PLL ink and were strongly oriented by the capillary microstructures. This is the first description of successful 3D-printing with Capgel biomaterial ink as well as the first demonstration of the concept and formulation of a self-adherent Capgel-PLL biomaterial ink.

The Vascular Microenvironment in Glioblastoma: A Comprehensive Review

Glioblastoma multiforme, the deadliest primary brain tumor, is characterized by an excessive and aberrant neovascularization. The initial expectations raised by anti-angiogenic drugs were soon tempered due to their limited efficacy in improving the overall survival. Intrinsic resistance and escape mechanisms against anti-VEGF therapies evidenced that tumor angiogenesis is an intricate multifaceted phenomenon and that vessels not only support the tumor but exert indispensable interactions for resistance and spreading. This holistic review covers the essentials of the vascular microenvironment of glioblastoma, including the perivascular niche components, the vascular generation patterns and the implicated signaling pathways, the endothelial–tumor interrelation, and the interconnection between vessel aberrancies and immune disarrangement. The revised concepts provide novel insights into the preclinical models and the potential explanations for the failure of conventional anti-angiogenic therapies, leading to an era of new and combined anti-angiogenic-based approaches.

An Agent-Based Interpretation of Leukocyte Chemotaxis in Cancer-on-Chip Experiments

The present paper was inspired by recent developments in laboratory experiments within the framework of cancer-on-chip technology, an immune-oncology microfluidic chip aiming at studying the fundamental mechanisms of immunocompetent behavior. We focus on the laboratory setting where cancer is treated with chemotherapy drugs, and in this case, the effects of the treatment administration hypothesized by biologists are: the absence of migration and proliferation of tumor cells, which are dying; the stimulation of the production of chemical substances (annexin); the migration of leukocytes in the direction of higher concentrations of chemicals. Here, following the physiological hypotheses made by biologists on the phenomena occurring in these experiments, we introduce an agent-based model reproducing the dynamics of two cell populations (agents), i.e., tumor cells and leukocytes living in the microfluidic chip environment. Our model aims at proof of concept, demonstrating that the observations of the biological phenomena can be obtained by the model on the basis of the explicit assumptions made. In this framework, close adherence of the computational model to the biological results, as shown in the section devoted to the first calibration of the model with respect to available observations, is successfully accomplished.

Application of Organoids in Carcinogenesis Modeling and Tumor Vaccination

Organoids well recapitulate organ-specific functions from their tissue of origin and remain fundamental aspects of organogenesis. Organoids are widely applied in biomedical research, drug discovery, and regenerative medicine. There are various cultivated organoid systems induced by adult stem cells and pluripotent stem cells, or directly derived from primary tissues. Researchers have drawn inspiration by combination of organoid technology and tissue engineering to produce organoids with more physiological relevance and suitable for translational medicine. This review describes the value of applying organoids for tumorigenesis modeling and tumor vaccination. We summarize the application of organoids in tumor precision medicine. Extant challenges that need to be conquered to make this technology be more feasible and precise are discussed.

Dynamic 3D On-Chip BBB Model Design, Development, and Applications in Neurological Diseases

The blood-brain barrier (BBB) is a vital structure for maintaining homeostasis between the blood and the brain in the central nervous system (CNS). Biomolecule exchange, ion balance, nutrition delivery, and toxic molecule prevention rely on the normal function of the BBB. The dysfunction and the dysregulation of the BBB leads to the progression of neurological disorders and neurodegeneration. Therefore, in vitro BBB models can facilitate the investigation for proper therapies. As the demand increases, it is urgent to develop a more efficient and more physiologically relevant BBB model. In this review, the development of the microfluidics platform for the applications in neuroscience is summarized. This article focuses on the characterizations of in vitro BBB models derived from human stem cells and discusses the development of various types of in vitro models. The microfluidics-based system and BBB-on-chip models should provide a better platform for high-throughput drug-screening and targeted delivery.

Engineering life in synthetic systems

The second EMBO-EMBL Symposium 'Synthetic Morphogenesis: From Gene Circuits to Tissue Architecture' was held virtually in March 2021, with participants from all over the world joining from the comfort of their sofas to discuss synthetic morphogenesis at large. Leading scientists from a range of disciplines, including developmental biology, physics, chemistry and computer science, covered a gamut of topics from the principles of cell and tissue organization, patterning and gene regulatory networks, to synthetic approaches for exploring evolutionary and developmental biology principles. Here, we describe some of the high points.

Three-Dimensional in vitro Models of Healthy and Tumor Brain Microvasculature for Drug and Toxicity Screening

Tissue vascularization is essential for its oxygenation and the homogenous diffusion of nutrients. Cutting-edge studies are focusing on the vascularization of three-dimensional (3D) in vitro models of human tissues. The reproduction of the brain vasculature is particularly challenging as numerous cell types are involved. Moreover, the blood-brain barrier, which acts as a selective filter between the vascular system and the brain, is a complex structure to replicate. Nevertheless, tremendous advances have been made in recent years, and several works have proposed promising 3D in vitro models of the brain microvasculature. They incorporate cell co-cultures organized in 3D scaffolds, often consisting of components of the native extracellular matrix (ECM), to obtain a micro-environment similar to the in vivo physiological state. These models are particularly useful for studying adverse effects on the healthy brain vasculature. They provide insights into the molecular and cellular events involved in the pathological evolutions of this vasculature, such as those supporting the appearance of brain cancers. Glioblastoma multiform (GBM) is the most common form of brain cancer and one of the most vascularized solid tumors. It is characterized by a high aggressiveness and therapy resistance. Current conventional therapies are unable to prevent the high risk of recurrence of the disease. Most of the new drug candidates fail to pass clinical trials, despite the promising results shown in vitro. The conventional in vitro models are unable to efficiently reproduce the specific features of GBM tumors. Recent studies have indeed suggested a high heterogeneity of the tumor brain vasculature, with the coexistence of intact and leaky regions resulting from the constant remodeling of the ECM by glioma cells. In this review paper, after summarizing the advances in 3D in vitro brain vasculature models, we focus on the latest achievements in vascularized GBM modeling, and the potential applications for both healthy and pathological models as platforms for drug screening and toxicological assays. Particular attention will be paid to discuss the relevance of these models in terms of cell-cell, cell-ECM interactions, vascularization and permeability properties, which are crucial parameters for improving in vitro testing accuracy.