Nanografted Substrata and Triculture of Human Pericytes, Fibroblasts, and Endothelial Cells for Studying the Effects on Angiogenesis

Human platelet lysate combined with mesenchymal stem cells pretreated with platelet lysate improved cardiac function in rats with myocardial infarction

Myocardial infarction (MI) is a leading cause of heart failure, disability and mortality worldwide. In this study, the effects of intramyocardial injection of human platelet lysate (HPL), bone marrow mesenchymal stem cells pretreated with HPL (PMSCs), and PMSC lysate (lys), alone and in combination were investigated on MI-induced by LAD ligation in male Wistar rats. The experiment was carried out on sham, vehicle (Veh), HPL, PMSCs, PMSC lysate (PMSC lys), HPL + PMSCs, and HPL + PMSC lys groups. SBP, DBP, and ± dp/dt max were monitored by the PowerLab physiograph. The MSC characteristics and CD31, NKX2.5, and cardiac troponin I (cTnI) contents were determined by flow cytometry, immunohistochemistry, and immunofluorescence, respectively. SBP, DBP, and ± dp/dt max that decreased in the MI group were recovered by HPL, PMSC, PMSC lys, HPL + PMSC, and HPL + PMSC lys treatments. CD31 density was higher in all treated groups compared to the Veh group. CD31 density in the HPL + PMSCs and HPL + PMSC lys groups was higher than in the PMSCs group. The number of Dil+/NKX2.5 + and Dil+/cTnI + cells was higher in the HPL + PMSCs group compared to the PMSCs group. The HPL and PMSCs mitigates heart injuries and cardiac dysfunction after MI. HPL provides an appropriate environment for cardiomyocyte differentiation from PMSCs.

The guardian of intracranial vessels: Why the pericyte?

Intracranial atherosclerotic stenosis (ICAS) is a pathological condition characterized by progressive narrowing or complete blockage of intracranial blood vessels caused by plaque formation. This condition leads to reduced blood flow to the brain, resulting in cerebral ischemia and hypoxia. Ischemic stroke (IS) resulting from ICAS poses a significant global public health challenge, especially among East Asian populations. However, the underlying causes of the notable variations in prevalence among diverse populations, as well as the most effective strategies for preventing and treating the rupture and blockage of intracranial plaques, remain incompletely comprehended. Rupture of plaques, bleeding, and thrombosis serve as precipitating factors in the pathogenesis of luminal obstruction in intracranial arteries. Pericytes play a crucial role in the structure and function of blood vessels and face significant challenges in regulating the Vasa Vasorum (VV)and preventing intraplaque hemorrhage (IPH). This review aims to explore innovative therapeutic strategies that target the pathophysiological mechanisms of vulnerable plaques by modulating pericyte biological function. It also discusses the potential applications of pericytes in central nervous system (CNS) diseases and their prospects as a therapeutic intervention in the field of biological tissue engineering regeneration.

Guiding cell migration in 3D with high-resolution photografting

Multi-photon lithography (MPL) has proven to be a suitable tool to precisely control the microenvironment of cells in terms of the biochemical and biophysical properties of the hydrogel matrix. In this work, we present a novel method, based on multi-photon photografting of 4,4′-diazido-2,2′-stilbenedisulfonic acid (DSSA), and its capabilities to induce cell alignment, directional cell migration and endothelial sprouting in a gelatin-based hydrogel matrix. DSSA-photografting allows for the fabrication of complex patterns at a high-resolution and is a biocompatible, universally applicable and straightforward process that is comparably fast. We have demonstrated the preferential orientation of human adipose-derived stem cells (hASCs) in response to a photografted pattern. Co-culture spheroids of hASCs and human umbilical vein endothelial cells (HUVECs) have been utilized to study the directional migration of hASCs into the modified regions. Subsequently, we have highlighted the dependence of endothelial sprouting on the presence of hASCs and demonstrated the potential of photografting to control the direction of the sprouts. MPL-induced DSSA-photografting has been established as a promising method to selectively alter the microenvironment of cells.

Three-Dimensional Vascularized Lung Cancer-on-a-Chip with Lung Extracellular Matrix Hydrogels for In Vitro Screening

Recent advances in immunotherapies and molecularly targeted therapies have led to an increased interest in exploring the field of in vitro tumor mimetic platforms. An increasing need to understand the mechanisms of anti-cancer therapies has led to the development of natural tumor tissue-like in vitro platforms capable of simulating the tumor microenvironment. The incorporation of vascular structures into the in vitro platforms could be a crucial factor for functional investigation of most anti-cancer therapies, including immunotherapies, which are closely related to the circulatory system. Decellularized lung extracellular matrix (ldECM), comprised of ECM components and pro-angiogenic factors, can initiate vascularization and is ideal for mimicking the natural microenvironment. In this study, we used a ldECM-based hydrogel to develop a 3D vascularized lung cancer-on-a-chip (VLCC). We specifically encapsulated tri-cellular spheroids made from A549 cells, HUVECs, and human lung fibroblasts, for simulating solid type lung cancer. Additionally, two channels were incorporated in the hydrogel construct to mimic perfusable vessel structures that resemble arterioles or venules. Our study highlights how a more effective dose-dependent action of the anti-cancer drug Doxorubicin was observed using a VLCC over 2D screening. This observation confirmed the potential of the VLCC as a 3D in vitro drug screening tool.

Stem cell-based small-diameter vascular grafts in dynamic culture

Purpose: Transplantation of autologous and/or allogeneic blood vessels is the most convenient treatment for vascular diseases. With regard to extensive need for blood vessels, developments in vascular tissue engineering are contributing greatly. In this study, our aim is to create intact small-diameter tubular vascular grafts cultivated in pulsatile flow bioreactor. Materials and Methods: CD146+ cell-based small-diameter vascular grafts were fabricated with ECM/glycosaminoglycans and polyurethane nanofibers. Characterization of the vascular graft was performed by SEM and WST-1. To mimic blood circulation in the bioreactor, human CD34+ cells cultured in megakaryocytes/platelets medium; then these cells were transferred inside of the vascular graft to mimic blood circulation. Cell differentiation was evaluated by flow cytometry and colony assay. Wright-Giemsa staining and polyploidy analysis were performed to show the differentiated cell population inside of the vascular graft. Anti-thrombogenic properties of the blood vessel were demonstrated by IF. Results: Polyurethane nanofibers provided a suitable environment for Human umbilical cord vein endothelial cells (HUVECs), and no significant cytotoxic effect was observed. Scanning electron microscopy (SEM) analysis of the tubular graft showed that under perfusion HUVECs, smooth muscle cells (SMCs) and fibroblasts formed layers that aligned on each other, respectively. The vascular graft was strong with a tensile strength of 0.70 MPa and elastic modulus of 0.007 GPa. When cultured in a bioreactor system, platelet adhesion to the vascular graft was remarkably low. Conclusion: In conclusion, this vascular graft may hold the potential to regenerate functional small-diameter vessels for cardiovascular tissue repair.

Implementation of Pericytes in Vascular Regeneration Strategies

For the survival and integration of complex large-sized tissue-engineered (TE) organ constructs that exceed the maximal nutrients and oxygen diffusion distance required for cell survival, graft (pre)vascularization to ensure medium or blood supply is crucial. To achieve this, the morphology and functionality of the microcapillary bed should be mimicked by incorporating vascular cell populations, including endothelium and mural cells. Pericytes play a crucial role in microvascular function, blood vessel stability, angiogenesis, and blood pressure regulation. In addition, tissue-specific pericytes are important in maintaining specific functions in different organs, including vitamin A storage in the liver, renin production in the kidneys and maintenance of the blood-brain-barrier. Together with their multipotential differentiation capacity, this makes pericytes the preferred cell type for application in TE grafts. The use of a tissue-specific pericyte cell population that matches the TE organ may benefit organ function. In this review, we provide an overview of the literature for graft (pre)-vascularization strategies and highlight the possible advantages of using tissue-specific pericytes for specific TE organ grafts. Impact statement The use of a tissue-specific pericyte cell population that matches the tissue-engineered (TE) organ may benefit organ function. In this review, we provide an overview of the literature for graft (pre)vascularization strategies and highlight the possible advantages of using tissue-specific pericytes for specific TE organ grafts.

Strategies for re-vascularization and promotion of angiogenesis in trauma and disease

The maintenance of a healthy vascular system is essential to ensure the proper function of all organs of the human body. While macrovessels have the main role of blood transportation from the heart to all tissues, microvessels, in particular capillaries, are responsible for maintaining tissues' functionality by providing oxygen, nutrients and waste exchanges. Occlusion of blood vessels due to atherosclerotic plaque accumulation remains the leading cause of mortality across the world. Autologous vein and artery grafts bypassing are the current gold standard surgical procedures to substitute primarily obstructed vascular structures. Ischemic scenarios that condition blood supply in downstream tissues may arise from blockage phenomena, as well as from other disease or events leading to trauma. The (i) great demand for new vascular substitutes, arising from both the limited availability of healthy autologous vessels, as well as the shortcomings associated with small-diameter synthetic vascular grafts, and (ii) the challenging induction of the formation of adequate and stable microvasculature are current driving forces for the growing interest in the development of bioinspired strategies to ensure the proper function of vasculature in all its dimensional scales. Here, a critical review of well-established technologies and recent biotechnological advances to substitute or regenerate the vascular system is provided.

Engineering Brain-Specific Pericytes from Human Pluripotent Stem Cells

Pericytes (PCs) are a type of perivascular cells that surround endothelial cells of small blood vessels. In the brain, PCs show heterogeneity depending on their position within the vasculature. As a result, PC interactions with surrounding endothelial cells, astrocytes, and neuron cells play a key role in a wide array of neurovascular functions such as regulating blood-brain barrier (BBB) permeability, cerebral blood flow, and helping to facilitate the clearance of toxic cellular molecules. Therefore, a reliable method of engineering brain-specific PCs from human induced pluripotent stem cells (hiPSCs) is critical in neurodegenerative disease modeling. This review summarizes brain-specific PC differentiation of hiPSCs through mesoderm and neural crest induction. Key signaling pathways (platelet-derived growth factor-B [PDGF-B], transforming growth factor [TGF]-β, and Notch signaling) regulating PC function, PC interactions with adjacent cells, and PC differentiation from hiPSCs are also discussed. Specifically, PDGF-BB-platelet-derived growth factor receptor β signaling promotes PC cell survival, TGF-β signal transduction facilitates PC attachment to endothelial cells, and Notch signaling is critical in vascular development and arterial-venous specification. Furthermore, current challenges facing the use of hiPSC-derived PCs are discussed, and their ongoing uses in neurodegenerative disease modeling are identified. Further investigations into PCs and surrounding cell interactions are needed to characterize the roles of brain PCs in various neurodegenerative disorders. Impact statement This article summarizes the work related to brain-specific pericytes (PCs) derived from human pluripotent stem cells (hPSCs). In particular, key signaling pathways regulating PC function, PC interactions with adjacent cells, and PC differentiation from hPSCs were discussed. Furthermore, current challenges facing the use of hPSC-derived PCs were identified, and their ongoing uses in neurodegenerative disease modeling were discussed. The review highlights the important role of cell-cell interactions in blood-brain barrier (BBB) models and neurodegeneration. The summarized findings are significant for establishing pluripotent stem cell-based BBB models toward the applications in drug screening and disease modeling.

Differential functional roles of fibroblasts and pericytes in the formation of tissue-engineered microvascular networks in vitro

Formation of a perfusable microvascular network (μVN) is critical for tissue engineering of solid organs. Stromal cells can support endothelial cell (EC) self-assembly into a μVN, but distinct stromal cell populations may play different roles in this process. Here we describe the differential effects that two widely used stromal cell populations, fibroblasts (FBs) and pericytes (PCs), have on μVN formation. We examined the effects of adding defined stromal cell populations on the self-assembly of ECs derived from human endothelial colony forming cells (ECFCs) into perfusable μVNs in fibrin gels cast within a microfluidic chamber. ECs alone failed to fully assemble a perfusable μVN. Human lung FBs stimulated the formation of EC-lined μVNs within microfluidic devices. RNA-seq analysis suggested that FBs produce high levels of hepatocyte growth factor (HGF). Addition of recombinant HGF improved while the c-MET inhibitor, Capmatinib (INCB28060), reduced μVN formation within devices. Human placental PCs could not substitute for FBs, but in the presence of FBs, PCs closely associated with ECs, formed a common basement membrane, extended microfilaments intercellularly, and reduced microvessel diameters. Different stromal cell types provide different functions in microvessel assembly by ECs. FBs support μVN formation by providing paracrine growth factors whereas PCs directly interact with ECs to modify microvascular morphology.

Upgrading prevascularization in tissue engineering: A review of strategies for promoting highly organized microvascular network formation

Functional and perfusable vascular network formation is critical to ensure the long-term survival and functionality of engineered tissues after their transplantation. Although several vascularization strategies have been reviewed in past, the significance of microvessel organization in three-dimensional (3D) scaffolds has been largely ignored. Advances in high-resolution microscopy and image processing have revealed that the majority of tissues including cardiac, skeletal muscle, bone, and skin contain highly organized microvessels that orient themselves to align with tissue architecture for optimum molecular exchange and functional performance. Here, we review strategies to develop highly organized and mature vascular networks in engineered tissues, with a focus on electromechanical stimulation, surface topography, micro scaffolding, surface-patterning, microfluidics and 3D printing. This review will provide researchers with state of the art approaches to engineer vascularized functional tissues for diverse applications. STATEMENT OF SIGNIFICANCE: Vascularization is one of the critical challenges facing tissue engineering. Recent technological advances have enabled researchers to develop microvascular networks in engineered tissues. Although far from translational applications, current vascularization strategies have shown promising outcomes. This review emphasizes the most recent technological advances and future challenges for developing organized microvascular networks in vitro. The next critical step is to achieve highly perfusable, dense, mature and organized microvascular networks representative of native tissues.

State-of-the-Art Strategies for the Vascularization of Three-Dimensional Engineered Organs

Engineering three-dimensional (3D) implantable tissue constructs is a promising strategy for replacing damaged or diseased tissues and organs with functional replacements. However, the efficient vascularization of new 3D organs is a major scientific and technical challenge since large tissue constructs or organs require a constant blood supply to survive in vivo. Current approaches to solving this problem generally fall into the following three major categories: (a) cell-based, (b) angiogenic factor-based, and (c) scaffold-based. In this review, we summarize state-of-the-art technologies that are used to develop complex, stable, and functional vasculature for engineered 3D tissue constructs and organs; additionally, we have suggested directions for future research.

Reduced fibrous capsule formation at nano-engineered silicone surfaces via tantalum ion implantation

Nano-engineered surface of silicone implant improves the biocompatibility and suppresses the fibrous capsule formation which is the most common side effect of polymeric implants.

Laser-pattern induced contact guidance in biodegradable microfluidic channels for vasculature regeneration

The direct cell control by surface topographic patterns in the micrometer and nanometer range has been proven to be important for the maintenance of tissue structures. This study presents the application of direct laser writing to fabricate micro-gratings on the biodegradable material 1,3-diamino-2-hydroxypropane-co-polyol sebacate (APS). The 193 nm excimer laser is applied to form microgrooves with widths of 2 to 10 μm and depths of 400 to 2884 nm. Two kinds of cells, fibroblasts of the rabbit synoviocyte cell line (HIG-82) and endothelial cells of human umbilical vein endothelial cells (HUVECs), were cultured on the flat and patterned APS to evaluate the biocompatibility of APS as well as the influence of contact guidance for cellular behaviours, respectively. The results show that both HIG-82 and HUVECs grow actively on APS scaffolds with directional growth, which was observed through cell morphology and proliferation rate, indicating their applicability in tissue regeneration. HIG-82 was observed to exhibit directional growth with the highest cell spreading area and density on the scaffolds with 7 μm width and 1350-1500 nm depth of gratings. Meanwhile, high cell spreading area and cell density of HUVECs were observed on laser ablated APS with 5 μm gratings and at depths greater than 1485 nm. The proposed microgrooves on APS could significantly enhance the cell growth, adhesion and even promote selective cell proliferation, which poses potential application for further tissue engineering studies.

Vascularization in Craniofacial Bone Tissue Engineering

Craniofacial bones, separate from the appendicular skeleton, bear a significant amount of strain and stress generated from mastication-related muscles. Current research on the regeneration of craniofacial bone focuses on the reestablishment of an elaborate vascular network. In this review, current challenges and efforts particularly in advances of scaffold properties and techniques for vascularization remodeling in craniofacial bone tissue engineering will be discussed. A microenvironment of ischemia and hypoxia in the biomaterial core drives propagation and reorganization of endothelial progenitor cells (EPCs) to assemble into a primitive microvascular framework. Co-culture strategies and delivery of vasculogenic molecules enhance EPCs' differentiation and stimulate the host regenerative response to promote vessel sprouting and strength. To optimize structural and vascular integration, well-designed microstructures of scaffolds are biologically considered. Proper porous structures, matrix stiffness, and surface morphology of scaffolds have a profound influence on cell behaviors and thus affect revascularization. In addition, advanced techniques facilitating angiogenesis and vaculogenesis have also been discussed. Oxygen delivery biomaterials, scaffold-free cell sheet techniques, and arteriovenous loop-induced axial vascularization strategies bring us new understanding and powerful strategies to manage revascularization of large craniofacial bone defects. Although promising histological results have been achieved, the efficient perfusion and functionalization of newly formed vessels are still challenging.

Nanofibrous Electrospun Heart Decellularized Extracellular Matrix-Based Hybrid Scaffold as Wound Dressing for Reducing Scarring in Wound Healing

Produced through electrospinning, poly(l-lactide-co-caprolactone) (PLCL) membranes, which have a porous structure and are biodegradable, are of interest in various medical fields. The porous-structured electrospun membrane is particularly interesting because of several favorable properties as follows: it exudes fluid from the wound, does not build up under the wound covering, and does not cause wound desiccation. Moreover, extracellular matrix (ECM)-based structures derived by tissue decellularization have application as engineered tissue scaffolds and as supports for cellular regeneration. In particular, heart decellularized ECM (hdECM) has various pro-angiogenic factors that can induce angiogenesis for wound healing. In this regard, a nanofibrous electrospun hdECM-based hybrid scaffold (NEhdHS), which is a PLCL membrane, including hdECM as an active agent, was tested as a wound dressing to assess its fundamental biochemical and physical features in wound healing. Use of NEhdHS with its porous structure and pro-angiogenic factors is expected to provide an effective wound dressing and reduced scarring. We first demonstrate the effectiveness of a proposed decellularization protocol through analysis of dECM components and describe the mechanical properties of the fabricated NEhdHS. Next, we present an in vitro angiogenesis analysis of the NEhdHS, using a coculture system with human dermal fibroblasts and human umbilical vein endothelial cells; the results of which confirm its biocompatibility and show that the NEhdHS can significantly enhance angiogenesis over that obtained from PLCL or gelatin-containing PLCL scaffolds. We also studied the effectiveness of the NEhdHS in vivo. Using a rat excisional wound-splinting model, we show that covering the upper part of the wound with NEhdHS significantly reduces scarring in the wound healing process compared to that with PLCL or gelatin-containing PLCL scaffolds. Based upon its properties, we conclude that the NEhdHS has potential for application in wound dressing.

Simultaneous microfluidic spinning of multiple strands of submicron fiber for the production of free-standing porous membranes for biological application

Microfibers produced using electrospinning and microfluidics-based technologies have been developed as a powerful tool in tissue engineering applications such as drug delivery and scaffolds. The applications of these fibers, however, have been limited because of the hazardous solvents used to make them, difficulties in controlling the pore sizes of their membrane forms, and downscaling the size of the fiber. Nevertheless, extending the use of these fibers, for example in the production of a free-standing porous membrane appropriate for cell-based research, is highly needed for tissue engineering, organ-on-a-chip, and drug delivery research and applications. Here, we fabricated a free-standing porous membrane by using a novel method that involved simultaneously spinning multiple strands of submicron-thick 'noodle-like' fibers. In addition to the novelty of the single noodle fiber in overcoming the size-reducing limitations of conventional microfluidic spinning methods, these fibers can hence form the units of 'noodle membranes' whose pores have sizes that the convention electrospinning method cannot achieve. We confirmed the potential of the noodle membrane to serve as a free-standing porous membrane in two simple experiments. Also, we found that noodle membranes have an advantage in loading different amounts of different materials in itself that it was also shown to be of use as a new type of scaffold for complex tissue regeneration. Therefore, the proposed noodle membrane can be an effective tool in tissue engineering applications and biological studies.

The effects of nanotopography and coculture systems to promote angiogenesis for wound repair

Insufficient angiogenesis in severe wounds delays wound repair because of a lack of blood supply to the wound site. Therefore, pro-angiogenic therapeutics may enhance wound repair. Many studies have investigated various physical and biochemical cues to improve angiogenesis, such as biocompatible materials, surface modifications, angiogenic factors and coculture systems using various cell types. However, the present capability to mimic the micro- and nanostructure of the natural microenvironment, particularly its porous, fibrous features, is limited. Nanotopography may represent a promising tool to overcome these limitations. Here, we discuss various approaches to the use of nanotopography to enhance angiogenesis and consider the combination of coculture systems with nanotopography to mimic the native environment for promotion of angiogenesis in wound healing and repair.