Cells and stimuli in small-caliber blood vessel tissue engineering

Atomic force microscopy in disease-related studies: Exploring tissue and cell mechanics

Despite significant progress in human medicine, certain diseases remain challenging to promptly diagnose and treat. Hence, the imperative lies in the development of more exhaustive criteria and tools. Tissue and cellular mechanics exhibit distinctive traits in both normal and pathological states, suggesting that "force" represents a promising and distinctive target for disease diagnosis and treatment. Atomic force microscopy (AFM) holds great promise as a prospective clinical medical device due to its capability to concurrently assess surface morphology and mechanical characteristics of biological specimens within a physiological setting. This review presents a comprehensive examination of the operational principles of AFM and diverse mechanical models, focusing on its applications in investigating tissue and cellular mechanics associated with prevalent diseases. The findings from these studies lay a solid groundwork for potential clinical implementations of AFM. RESEARCH HIGHLIGHTS: By examining the surface morphology and assessing tissue and cellular mechanics of biological specimens in a physiological setting, AFM shows promise as a clinical device to diagnose and treat challenging diseases.

Role of blood flow in endothelial functionality: a review

Endothelial cells, located on the surface of blood vessel walls, are constantly stimulated by mechanical forces from the blood flow. The mechanical forces, i.e., fluid shear stress, induced by the blood flow play a pivotal role in controlling multiple physiological processes at the endothelium and in regulating various pathways that maintain homeostasis and vascular function. In this review, research looking at different blood fluid patterns and fluid shear stress in the circulation system is summarized, together with the interactions between the blood flow and the endothelial cells. This review also highlights the flow profile as a response to the configurational changes of the endothelial glycocalyx, which is less revisited in previous reviews. The role of endothelial glycocalyx in maintaining endothelium health and the strategies for the restoration of damaged endothelial glycocalyx are discussed from the perspective of the fluid shear stress. This review provides a new perspective regarding our understanding of the role that blood flow plays in regulating endothelial functionality.

Magnetic and Biocompatible Polyurethane Nanofiber Biomaterial for Tissue Engineering

Recruitment of endothelial cells to cardiovascular device surfaces could solve issues of thrombosis, neointimal hyperplasia, and restenosis. Since current targeting strategies are often nonspecific, new technologies to allow for site-specific cell localization and capture in vivo are needed. The development of cytocompatible superparamagnetic iron oxide nanoparticles has allowed for the use of magnetism for cell targeting. In this study, a magnetic polyurethane (PU)-2205 stainless steel (2205-SS) nanofibrous composite biomaterial was developed through analysis of composite sheets and application to stent-grafts. The PU nanofibers provide strength and elasticity while the 2205-SS microparticles provide ferromagnetic properties. Sheets were electrospun at mass ratios of 0-4:1 (2205-SS:PU) and stent-grafts with magnetic or nonmagnetic stents were coated at the optimal ratio of 2:1. These composite materials were characterized by microscopy, mechanical testing, a sessile drop test, magnetic field measurement, magnetic cell capture assays, and cytocompatibility after 14 days of culturing with endothelial cells. Results of this study show that an optimal ratio of 2:1 2205-SS:PU results in a hydrophobic material that balanced mechanical and magnetic properties and was cytocompatible up to 14 days. Significant cell capture required a thicker material of 0.5 mm thickness. Stent-grafts fabricated from a magnetic coating and a magnetic stent demonstrated uniform cell capture throughout the device surface. This novel biomaterial exhibits a combination of mechanical and magnetic properties that enables magnetic capture of cells and other therapeutic agents for vascular and other tissue engineering applications.

Differentiation and Engineering of Human Stem Cells for Smooth Muscle Generation

Cardiovascular diseases are responsible for 31% of global deaths and are considered the main cause of death and disability worldwide. Stem cells from various sources have become attractive options for a range of cell-based therapies for smooth muscle tissue regeneration. However, for efficient myogenic differentiation, the stem cell characteristics, cell culture conditions, and their respective microenvironments need to be carefully assessed. This review covers the various approaches involved in the regeneration of vascular smooth muscles by conditioning human stem cells. This article delves into the different sources of stem cells used in the generation of myogenic tissues, the role of soluble growth factors, use of scaffolding techniques, biomolecular cues, relevance of mechanical stimulation, and key transcription factors involved, aimed at inducing myogenic differentiation. Impact statement The review article's main goal is to discuss the recent advances in the field of smooth muscle tissue regeneration. We look at various cell sources, growth factors, scaffolds, mechanical stimuli, and factors involved in smooth muscle formation. These stem cell-based approaches for vascular muscle formation will provide various options for cell-based therapies with long-term beneficial effects on patients.

pH regulates the lumen diameter of tissue-engineered capillaries

Angiogenesis is vital in tissue engineering and the size of the capillary lumen diameter directly affects vascular function. Therefore, the involvement of the pH in the regulation of the capillary lumen diameter was investigated in the present study. The cytosolic pH of different pH medium groups was measured using flow cytometry. Bromodeoxyuridine staining and wound-healing assays were performed to detect cell proliferation and migration, respectively. The expression of angiogenesis-related genes was detected using reverse transcription-quantitative PCR. In addition, cell tube formation under different pH conditions was assessed using a tube formation assay and a 3D Matrigel® model. The results indicated that a change in the pH value of the culture medium affected the cytosolic pH of the endothelial cells, which then led to a change in vascular diameter. When the medium's pH ranged from 7.4 to 7.6, the diameter of the lumen formed in the Matrigel was suitable for capillary formation in tissue engineering. The present results revealed an important role for the pH in the process of capillary formation and provided insight for pH regulation during endothelial cell tube formation and angiogenesis in tissue engineering.

An In Vitro Whole-Organ Liver Engineering for Testing of Genetic Therapies

Explosion of gene therapy approaches for treating rare monogenic and common liver disorders created an urgent need for disease models able to replicate human liver cellular environment. Available models lack 3D liver structure or are unable to survive in long-term culture. We aimed to generate and test a 3D culture system that allows long-term maintenance of human liver cell characteristics. The in vitro whole-organ "Bioreactor grown Artificial Liver Model" (BALM) employs a custom-designed bioreactor for long-term 3D culture of human induced pluripotent stem cells-derived hepatocyte-like cells (hiHEPs) in a mouse decellularized liver scaffold. Adeno-associated viral (AAV) and lentiviral (LV) vectors were introduced by intravascular injection. Substantial AAV and LV transgene expression in the BALM-grown hiHEPs was detected. Measurement of secreted proteins in the media allowed non-invasive monitoring of the system. We demonstrated that humanized whole-organ BALM is a valuable tool to generate pre-clinical data for investigational medicinal products.

Insight on the endothelialization of small silk-based tissue-engineered vascular grafts

Along with an increased incidence of cardiovascular diseases, there is a strong need for small-diameter vascular grafts. Silk has been investigated as a biomaterial to develop such grafts thanks to different processing options. Endothelialization was shown to be extremely important to ensure graft patency and there is ongoing research on the development and behavior of endothelial cells on vascular tissue-engineered scaffolds. This article reviews the endothelialization of silk-based scaffolds processed throughout the years as silk non-woven nets, films, gel spun, electrospun, or woven scaffolds. Encouraging results were reported with these scaffolds both in vitro and in vivo when implanted in small- to middle-sized animals. The use of coatings and heparin or sulfur to enhance, respectively, cell adhesion and scaffold hemocompatibility is further presented. Bioreactors also showed their interest to improve cell adhesion and thus promoting in vitro pre-endothelialization of grafts even though they are still not systematically used. Finally, the importance of the animal models used to study the right mechanism of endothelialization is discussed.

Emulsified Fat Grafting Accelerates Tissue Expansion: An Experimental Study in a Rat Model

INTRODUCTION

Tissue expansion has been applied in tissue repair and reconstruction of large soft tissue defects. Stromal vascular fraction (SVF) transplantation is a promising treatment in raising expansion efficiency. However, the clinical utilization of SVF is limited because of its conventional collagenase-based production. The aim of this study was to evaluate the effect of emulsified fat (EF), SVF obtained by using mechanical method, on accelerating tissue expansion.

MATERIALS AND METHODS

The microstructure of EF fragments and the proportion of mesenchymal stem cells (MSCs; CD45-/CD34+) in EF were detected. Wistar rats were divided into the following 3 groups randomly: the 1-mL EF group, the 0.5-mL EF group, and the control group. The tissue expansion was carried out twice a week to maintain the capsule pressure at 60 mm Hg. After 4 weeks, inflation volume and histological changes, which includes collagen content, cell proliferation, and capillary density, were observed to evaluate the effect of EF on tissue expansion.

RESULTS

Mechanical emulsification effectively destroyed the mature adipocytes in adipose tissue. The proportion of MSCs population in the EF fragments was 12.40 ± 0.86%. After expansion, the inflation volume and the levels of collagen deposition, cell proliferation, and capillary density of the expanded tissue in the 1-mL EF group were significantly higher than that in the 0.5-mL EF group and the control group (P < 0.05). However, all these regenerative indicators in the 0.5-mL EF group showed no statistical difference from the control group (P > 0.05). The thickness of epidermal and dermal layers showed no significant difference among the 3 groups (P > 0.05).

CONCLUSIONS

Our findings suggested that EF grafting can be used as a new alternative to increase tissue expansion efficiency.

Poly(trimethylene carbonate-co-L-lactide) electrospun scaffolds for use as vascular grafts

Currently, there is great clinical need for suitable synthetic grafts that can be used in vascular diseases. Synthetic grafts have been successfully used in medium and large arteries, however, their use in small diameter vessels is limited and presents a high failure rate. In this context, the aim of this study was to develop tissue engineering scaffolds, using poly(trimethylene carbonate-co-L-lactide) (PTMCLLA), for application as small diameter vascular grafts. For this, copolymers with varying trimethylene carbonate/lactide ratios - 20/80, 30/70, and 40/60 - were submitted to electrospinning and the resulting scaffolds were evaluated in terms of their physicochemical and biological properties. The scaffolds produced with PTMCLLA 20/80, 30/70, and 40/60 showed smooth fibers with an average diameter of 771±273, 606±242, and 697±232 nm, respectively. When the degradation ratio was evaluated, the three scaffold groups had a similar molecular weight (Mw) on the final day of analysis. PTMCLLA 30/70 and 40/60 scaffolds exhibited greater flexibility than the PTMCLLA 20/80. However, the PTMCLLA 40/60 scaffolds showed a large wrinkling and their biological properties were not evaluated. The PTMCLLA 30/70 scaffolds supported the adhesion and growth of mesenchymal stem cells (MSCs), endothelial progenitor cells, and smooth muscle cells (SMCs). In addition, they provided a spreading of MSCs and SMCs. Given the results, the electrospun scaffolds produced with PTMCLLA 30/70 copolymer can be considered promising candidates for future applications in vascular tissue engineering.

Shear-resistant hydrogels to control permeability of porous tubular scaffolds in vascular tissue engineering

Aiming to perfuse porous tubular scaffolds for vascular tissue engineering (VTE) with controlled flow rate, prevention of leakage through the scaffold lumen is required. A gel coating made of 8% w/v alginate and 6% w/v gelatin functionalized with fibronectin was produced using a custom-made bioreactor-based method. Different volumetric proportions of alginate and gelatin were tested (50/50, 70/30, and 90/10). Gel swelling and stability, and rheological, and uniaxial tensile tests reveal superior resistance to the aggressive biochemical microenvironment, and their ability to withstand physiological deformations (~10%) and wall shear stresses (5-20 dyne/cm²). These are prerequisites to maintain the physiologic phenotypes of vascular smooth muscle cells and endothelial cells (ECs), mimicking blood vessels microenvironment. Gels can induce ECs proliferation and colonization, especially in the presence of fibronectin and higher percentages of gelatin. The custom-designed bioreactor enables the development of reproducible and homogeneous tubular gel coating. The permeability tests show the effectiveness of tubular scaffolds coated with 70/30 alginate/gelatin gel to occlude wadding pores, and therefore prevent leakages. The synthesized double-layered tubular scaffolds coated with alginate/gelatin gel and fibronectin represent both promising substrate for ECs and effective leakproof scaffolds, when subjected to pulsatile perfusion, for VTE applications.

Time-Phase Sequential Utilization of Adipose-Derived Mesenchymal Stem Cells on Mesoporous Bioactive Glass for Restoration of Critical Size Bone Defects

The effective transportation of oxygen, nutrients, and metabolic wastes through new blood vessel networks is key to the survival of engineered constructs in large bone defects. Adipose-derived mesenchymal stem cells (ADSCs), which are regarded as excellent candidates for both bone and blood vessel engineering, are the preferred option for the restoration of massive bone defects. Therefore, we propose to induce ADSCs into osteogenic and endothelial cells differently. A modified hierarchical mesoporous bioactive glass (MBG) scaffold with an enhanced compressive strength was constructed and prevascularized by seeding with endothelial-induced ADSCs (EI-ADSCs). The prevascularized scaffolds were combined with osteogenically induced ADSCs (OI-ADSCs) to repair critical-size bone defects. To validate the angiogenesis of the prevascularized MBG scaffolds in vivo, green fluorescent protein (GFP) was used to label EI-ADSCs. The labeled EI-ADSCs were demonstrated to survive and participate in vascularization at day 7 after subcutaneous implantation in nude mice by double immunofluorescence staining of CD31 and GFP. Regarding the restoration of critical size bone defects, early angiogenesis of rat femur plug defects was evaluated by perfusion of Microfil after 3 weeks. Compared to nonvascularized MBG carrying OI-ADSCs (MBG/OI-ADSCs) and non-cell-seeded MBG scaffolds, the prevascularized MBG carrying OI-ADSCs (Pv-MBG/OI-ADSCs) showed enhanced angiogenesis on the surface and interior. Through dynamic bone formation analysis with sequential fluorescent labeling and Van Gieson's picro-fuchsin staining, we found that the Pv-MBG/OI-ADSCs exhibited the highest mineral deposition rate after surgery, which may be contributed by rapid vascular anastomosis facilitating increased survival of the seeded OI-ADSCs and by the recruitment function for bone mesenchymal stem cells. Therefore, the strategy of time-phase sequential utilization of ADSCs on MBG scaffolds is a practical design for the repair of massive bone defects.

Whole Organ Tissue Vascularization: Engineering the Tree to Develop the Fruits

Tissue engineering aims to regenerate and recapitulate a tissue or organ that has lost its function. So far successful clinical translation has been limited to hollow organs in which rudimental vascularization can be achieved by inserting the graft into flaps of the omentum or muscle fascia. This technique used to stimulate vascularization of the graft takes advantage of angiogenesis from existing vascular networks. Vascularization of the engineered graft is a fundamental requirement in the process of engineering more complex organs, as it is crucial for the efficient delivery of nutrients and oxygen following in-vivo implantation. To achieve vascularization of the organ many different techniques have been investigated and exploited. The most promising results have been obtained by seeding endothelial cells directly into decellularized scaffolds, taking advantage of the channels remaining from the pre-existing vascular network. Currently, the main hurdle we need to overcome is achieving a fully functional vascular endothelium, stable over a long time period of time, which is engineered using a cell source that is clinically suitable and can generate, in vitro, a yield of cells suitable for the engineering of human sized organs. This review will give an overview of the approaches that have recently been investigated to address the issue of vascularization in the field of tissue engineering of whole organs, and will highlight the current caveats and hurdles that should be addressed in the future.

iPSCs-based generation of vascular cells: reprogramming approaches and applications

Recent advances in the field of induced pluripotent stem cells (iPSCs) research have opened a new avenue for stem cell-based generation of vascular cells. Based on their growth and differentiation potential, human iPSCs constitute a well-characterized, generally unlimited cell source for the mass generation of lineage- and patient-specific vascular cells without any ethical concerns. Human iPSCs-derived vascular cells are perfectly suited for vascular disease modeling studies because patient-derived iPSCs possess the disease-causing mutation, which might be decisive for full expression of the disease phenotype. The application of vascular cells for autologous cell replacement therapy or vascular engineering derived from immune-compatible iPSCs possesses huge clinical potential, but the large-scale production of vascular-specific lineages for regenerative cell therapies depends on well-defined, highly reproducible culture and differentiation conditions. This review will focus on the different strategies to derive vascular cells from human iPSCs and their applications in regenerative therapy, disease modeling and drug discovery approaches.

Shear stress: An essential driver of endothelial progenitor cells

The blood flow through vessels produces a tangential, or shear, stress sensed by their innermost layer (i.e., endothelium) and representing a major hemodynamic force. In humans, endothelial repair and blood vessel formation are mainly performed by circulating endothelial progenitor cells (EPCs) characterized by a considerable expression of vascular endothelial growth factor receptor 2 (VEGFR2), CD34, and CD133, pronounced tube formation activity in vitro, and strong reendothelialization or neovascularization capacity in vivo. EPCs have been proposed as a promising agent to induce reendothelialization of injured arteries, neovascularization of ischemic tissues, and endothelialization or vascularization of bioartificial constructs. A number of preconditioning approaches have been suggested to improve the regenerative potential of EPCs, including the use of biophysical stimuli such as shear stress. However, in spite of well-defined influence of shear stress on mature endothelial cells (ECs), articles summarizing how it affects EPCs are lacking. Here we discuss the impact of shear stress on homing, paracrine effects, and differentiation of EPCs. Unidirectional laminar shear stress significantly promotes homing of circulating EPCs to endothelial injury sites, induces anti-thrombotic and anti-atherosclerotic phenotype of EPCs, increases their capability to form capillary-like tubes in vitro, and enhances differentiation of EPCs into mature ECs in a dose-dependent manner. These effects are mediated by VEGFR2, Tie2, Notch, and β1/3 integrin signaling and can be abrogated by means of complementary siRNA/shRNA or selective pharmacological inhibitors of the respective proteins. Although the testing of sheared EPCs for vascular tissue engineering or regenerative medicine applications is still an unaccomplished task, favorable effects of unidirectional laminar shear stress on EPCs suggest its usefulness for their preconditioning.

Bioreactor-induced mesenchymal progenitor cell differentiation and elastic fiber assembly in engineered vascular tissues

In vitro maturation of engineered vascular tissues (EVT) requires the appropriate incorporation of smooth muscle cells (SMC) and extracellular matrix (ECM) components similar to native arteries. To this end, the aim of the current study was to fabricate 4mm inner diameter vascular tissues using mesenchymal progenitor cells seeded into tubular scaffolds. A dual-pump bioreactor operating either in perfusion or pulsatile perfusion mode was used to generate physiological-like stimuli to promote progenitor cell differentiation, extracellular elastin production, and tissue maturation. Our data demonstrated that pulsatile forces and perfusion of 3D tubular constructs from both the lumenal and ablumenal sides with culture media significantly improved tissue assembly, effectively inducing mesenchymal progenitor cell differentiation to SMCs with contemporaneous elastin production. With bioreactor cultivation, progenitor cells differentiated toward smooth muscle lineage characterized by the expression of smooth muscle (SM)-specific markers smooth muscle alpha actin (SM-α-actin) and smooth muscle myosin heavy chain (SM-MHC). More importantly, pulsatile perfusion bioreactor cultivation enhanced the synthesis of tropoelastin and its extracellular cross-linking into elastic fiber compared with static culture controls. Taken together, the current study demonstrated progenitor cell differentiation and vascular tissue assembly, and provides insights into elastin synthesis and assembly to fibers.

STATEMENT OF SIGNIFICANCE

Incorporation of elastin into engineered vascular tissues represents a critical design goal for both mechanical and biological functions. In the present study, we seeded porous tubular scaffolds with multipotent mesenchymal progenitor cells and cultured in dual-pump pulsatile perfusion bioreactor. Physiological-like stimuli generated by bioreactor not only induced mesenchymal progenitor cell differentiation to vascular smooth muscle lineage but also actively promoted elastin synthesis and fiber assembly. Gene expression and protein synthesis analyses coupled with histological and immunofluorescence staining revealed that elastin-containing vascular tissues were fabricated. More importantly, co-localization and co-immunoprecipitation experiments demonstrated that elastin and fibrillin-1 were abundant throughout the cross-section of the tissue constructs suggesting a process of elastin protein crosslinking. This study paves a way forward to engineer elastin-containing functional vascular substitutes from multipotent progenitor cells in a bioreactor.

Alternating air-medium exposure in rotating bioreactors optimizes cell metabolism in 3D novel tubular scaffold polyurethane foams

Background

In vitro dynamic culture conditions play a pivotal role in developing engineered tissue grafts, where the supply of oxygen and nutrients, and waste removal must be permitted within construct thickness. For tubular scaffolds, mass transfer is enhanced by introducing a convective flow through rotating bioreactors with positive effects on cell proliferation, scaffold colonization and extracellular matrix deposition. We characterized a novel polyurethane-based tubular scaffold and investigated the impact of 3 different culture configurations over cell behavior: dynamic (i) single-phase (medium) rotation and (ii) double-phase exposure (medium-air) rotation; static (iii) single-phase static culture as control.

Methods

A new mixture of polyol was tested to create polyurethane foams (PUFs) as 3D scaffold for tissue engineering. The structure obtained was morphologically and mechanically analyzed tested. Murine fibroblasts were externally seeded on the novel porous PUF scaffold, and cultured under different dynamic conditions. Viability assay, DNA quantification, SEM and histological analyses were performed at different time points.

Results

The PUF scaffold presented interesting mechanical properties and morphology adequate to promote cell adhesion, highlighting its potential for tissue engineering purposes. Results showed that constructs under dynamic conditions contain enhanced viability and cell number, exponentially increased for double-phase rotation; under this last configuration, cells uniformly covered both the external surface and the lumen.

Conclusions

The developed 3D structure combined with the alternated exposure to air and medium provided the optimal in vitro biochemical conditioning with adequate nutrient supply for cells. The results highlight a valuable combination of material and dynamic culture for tissue engineering applications.

Magnetizable stent-grafts enable endothelial cell capture

Emerging nanotechnologies have enabled the use of magnetic forces to guide the movement of magnetically-labeled cells, drugs, and other therapeutic agents. Endothelial cells labeled with superparamagnetic iron oxide nanoparticles (SPION) have previously been captured on the surface of magnetizable 2205 duplex stainless steel stents in a porcine coronary implantation model. Recently, we have coated these stents with electrospun polyurethane nanofibers to fabricate prototype stent-grafts. Facilitated endothelialization may help improve the healing of arteries treated with stent-grafts, reduce the risk of thrombosis and restenosis, and enable small-caliber applications. When placed in a SPION-labeled endothelial cell suspension in the presence of an external magnetic field, magnetized stent-grafts successfully captured cells to the surface regions adjacent to the stent struts. Implantation within the coronary circulation of pigs (n=13) followed immediately by SPION-labeled autologous endothelial cell delivery resulted in widely patent devices with a thin, uniform neointima and no signs of thrombosis or inflammation at 7 days. Furthermore, the magnetized stent-grafts successfully captured and retained SPION-labeled endothelial cells to select regions adjacent to stent struts and between stent struts, whereas the non-magnetized control stent-grafts did not. Early results with these prototype devices are encouraging and further refinements will be necessary in order to achieve more uniform cell capture and complete endothelialization. Once optimized, this approach may lead to more rapid and complete healing of vascular stent-grafts with a concomitant improvement in long-term device performance.

Compared to the amniotic membrane, Wharton's jelly may be a more suitable source of mesenchymal stem cells for cardiovascular tissue engineering and clinical regeneration

BACKGROUND

The success of developing cardiovascular tissue engineering (CTE) grafts greatly needs a readily available cell substitute for endothelial and interstitial cells. Perinatal annexes have been proposed as a valuable source of mesenchymal stem cells (MSCs) for tissue engineering and regenerative medicine. The objective of the present study is to evaluate the potential of human Wharton's jelly MSCs (WJ-MSCs) and amniotic membrane MSCs (AM-MSCs) as a seeding cell in CTE and cardiovascular regenerative medicine.

METHODS

WJ-MSCs/AM-MSCs were isolated and characterized in vitro according to their morphology, proliferation, self-renewal, phenotype, and multipotency. More importantly, the characteristics of hemocompatibility, extracellular matrix deposition, and gene expression and viability of both MSCs were investigated.

RESULTS

Fibroblast-like human WJ-MSCs and AM-MSCs were successfully isolated and positively expressed the characteristic markers CD73, CD90, and CD105 but were negative for CD34, CD45, and HLA-DR. Both MSCs shared trilineage differentiation toward the adipogenic, osteogenic, and chondrogenic lineages. The proliferative and self-renewal capacity of WJ-MSCs was significantly higher than that of AM-MSCs (P < 0.001). WJ-MSCs provided comparable properties of antiplatelet adhesion and did not activate the coagulation cascade to endothelial cells. However, aggregated platelets were visualized on the surface of AM-MSCs-derived cell sheets and the intrinsic pathway was activated. Furthermore, WJ-MSCs have superior properties of collagen deposition and higher viability than AM-MSCs during cell sheet formation.

CONCLUSIONS

This study highlights that WJ-MSCs could act as a functional substitute of endothelial and interstitial cells, which could serve as an appealing and practical single-cell source for CTE and regenerative therapy.

Arterial Decellularized Scaffolds Produced Using an Innovative Automatic System

There is still an unmet clinical need for small-caliber artery substitution. Decellularized scaffolds in tissue engineering represent a promising solution. We have developed an innovative system for the automatic decellularization of blood vessels, used to process pig arteries. The system is able to automatically drive a decellularization process in a safe and reliable environment, with complex time patterns, using up to three different decellularization solutions, and providing at the same time a physical stress to improve the decellularization. The decellularization of pig arteries was evaluated by means of histology, DNA quantification and mechanical testing. Outcomes showed scaffolds with no cellular or nuclear remnants and a well-preserved tissue structure, corroborated by mechanical properties similar to native tissue. Decellularized scaffolds were seeded on the inner layer with human endothelial cells and implanted as iliac artery replacement in 4 pharmacologically immune-compromised pigs. This chimeric model was performed as a very preliminary evaluation to investigate the performances of these scaffolds in vivo, and to investigate the fate of seeded cells. Recipients were sacrificed on day 14 and day 70 after surgery, and vessels were found to be patent and with no evidence of thrombi formation. The inner layer was covered by endothelial cells, and the migration of cells positive for α-smooth-muscle actin was observed from the outer layer towards the tunica media. Intriguingly, the endothelial cells on explanted vessels were entirely derived from the host while the seeded cells were lost. In conclusion, this work presents a novel tool for a safe and controlled production of arterial scaffolds, with good decellularization outcomes and a good performance in a short-term, large-animal implantation.

Stem cell-derived vasculature: A potent and multidimensional technology for basic research, disease modeling, and tissue engineering

Proper blood vessel networks are necessary for constructing and re-constructing tissues, promoting wound healing, and delivering metabolic necessities throughout the body. Conversely, an understanding of vascular dysfunction has provided insight into the pathogenesis and progression of diseases both common and rare. Recent advances in stem cell-based regenerative medicine - including advances in stem cell technologies and related progress in bioscaffold design and complex tissue engineering - have allowed rapid advances in the field of vascular biology, leading in turn to more advanced modeling of vascular pathophysiology and improved engineering of vascularized tissue constructs. In this review we examine recent advances in the field of stem cell-derived vasculature, providing an overview of stem cell technologies as a source for vascular cell types and then focusing on their use in three primary areas: studies of vascular development and angiogenesis, improved disease modeling, and the engineering of vascularized constructs for tissue-level modeling and cell-based therapies.