Functional arteries grown in vitro

Long-Term Functional Efficacy of a Novel Electrospun Poly(Glycerol Sebacate)-Based Arterial Graft in Mice

Many surgical interventions for cardiovascular disease are limited by the availability of autologous vessels or suboptimal performance of prosthetic materials. Tissue engineered vascular grafts show significant promise, but have yet to achieve clinical efficacy in small caliber (<5 mm) arterial applications. We previously designed cell-free elastomeric grafts containing solvent casted, particulate leached poly(glycerol sebacate) (PGS) that degraded rapidly and promoted neoartery development in a rat model over 3 months. Building on this success but motivated by the need to improve fabrication scale-up potential, we developed a novel method for electrospinning smaller grafts composed of a PGS microfibrous core enveloped by a thin poly(ε-caprolactone) (PCL) outer sheath. Electrospun PGS-PCL composites were implanted as infrarenal aortic interposition grafts in mice and remained patent up to the 12 month endpoint without thrombosis or stenosis. Many grafts experienced a progressive luminal enlargement up to 6 months, however, due largely to degradation of PGS without interstitial replacement by neotissue. Lack of rupture over 12 months confirmed sufficient long-term strength, due primarily to the persistent PCL sheath. Immunohistochemistry further revealed organized contractile smooth muscle cells and neotissue in the inner region of the graft, but a macrophage-driven inflammatory response to the residual polymer in the outer region of the graft that persisted up to 12 months. Overall, the improved surgical handling, long-term functional efficacy, and strength of this new graft strategy are promising, and straightforward modifications of the PGS core should hasten cellular infiltration and associated neotissue development and thereby lead to improved small vessel replacements.

Biocompatible 3D Liquid Crystal Elastomer Cell Scaffolds and Foams with Primary and Secondary Porous Architecture

3D biodegradable and highly regular foamlike cell scaffolds based on biocompatible side-chain liquid crystal elastomers have been prepared. Scaffolds with a primary porosity characterized by spatially interlaced, interconnected microchannels or an additional secondary porosity featuring interconnected microchannel networks define the novel elastomeric scaffolds. The macroscale morphology of the dual porosity 3D scaffold resembles vascular networks observed in tissue. 3D elastomer foams show four times higher cell proliferation capability compared to conventional porous templated films and within the channels guide spontaneous cell alignment enabling the possibility of tissue construct fabrication toward more clinically complex environments.

Biomechanical conditioning of tissue engineered heart valves: Too much of a good thing?

Surgical replacement of dysfunctional valves is the primary option for the treatment of valvular disease and congenital defects. Existing mechanical and bioprosthetic replacement valves are far from ideal, requiring concomitant anticoagulation therapy or having limited durability, thus necessitating further surgical intervention. Heart valve tissue engineering (HVTE) is a promising alternative to existing replacement options, with the potential to synthesize mechanically robust tissue capable of growth, repair, and remodeling. The clinical realization of a bioengineered valve relies on the appropriate combination of cells, biomaterials, and/or bioreactor conditioning. Biomechanical conditioning of valves in vitro promotes differentiation of progenitor cells to tissue-synthesizing myofibroblasts and prepares the construct to withstand the complex hemodynamic environment of the native valve. While this is a crucial step in most HVTE strategies, it also may contribute to fibrosis, the primary limitation of engineered valves, through sustained myofibrogenesis. In this review, we examine the progress of HVTE and the role of mechanical conditioning in the synthesis of mechanically robust tissue, and suggest approaches to achieve myofibroblast quiescence and prevent fibrosis.

Advances in tissue engineering

Nearly 30 years ago, we reported on a concept now known as Tissue Engineering. Here, we report on some of the advances in this now thriving area of research. In particular, significant advances in tissue engineering of skin, liver, spinal cord, blood vessels, and other areas are discussed.

Three-dimensional culture of small-diameter vascular grafts

Analysis of efforts to engineer 3D small-diameter (<6 mm) vascular grafts, indicating the importance of stem cells, co-culture, and pulsatile flow.

A multiple covalent crosslinked soft hydrogel for bioseparation

A multiple covalent crosslinked gel of poly(acrylamide–acrylic acid) was synthesized by using acrylic acid and acrylamide both as a monomer and as a covalent crosslinker.

Bioengineered Human Pyloric Sphincters Using Autologous Smooth Muscle and Neural Progenitor Cells

Gastroparesis leads to inadequate emptying of the stomach resulting in severe negative health impacts. Appropriate long-term treatments for these diseases may require pyloric sphincter tissue replacements that possess functional smooth muscle cell (SMC) and neural components. This study aims to bioengineer, for the first time, innervated human pylorus constructs utilizing autologous human pyloric sphincter SMCs and human neural progenitor cells (NPCs). Autologous SMCs and NPCs were cocultured in dual-layered hydrogels and formed concentrically aligned pylorus constructs. Innervated autologous human pylorus constructs were characterized through biochemical and physiologic assays to assess the phenotype and functionality of SMCs and neurons. SMCs within bioengineered human pylorus constructs displayed a tonic contractile phenotype and maintained circumferential alignment. Neural differentiation within bioengineered constructs was verified by positive expression of βIII-tubulin, neuronal nitric oxide synthase (nNOS), and choline acetyltransferase (ChAT). Autologous bioengineered innervated human pylorus constructs generated a robust spontaneous basal tone and contracted in response to potassium chloride (KCl). Contraction in response to exogenous neurotransmitter acetylcholine (ACh), relaxation in response to vasoactive intestinal peptide (VIP), and electrical field stimulation (EFS) were also observed. Neural network integrity was demonstrated by inhibition of EFS-induced relaxation in the presence of a neurotoxin or nNOS inhibitors. Partial inhibition of ACh-induced contraction and VIP-induced relaxation following neurotoxin treatment was observed. These studies provide a proof of concept for bioengineering functional innervated autologous human pyloric sphincter constructs that generate a robust basal tone and contain circumferentially aligned SMCs, which display a tonic contractile phenotype and functional differentiated neurons. These autologous constructs have the potential to be used as (1) functional replacement organs and (2) physiologically relevant models to investigate human pyloric sphincter disorders.

Customizable engineered blood vessels using 3D printed inserts

Current techniques for tissue engineering blood vessels are not customizable for vascular size variation and vessel wall thickness. These critical parameters vary widely between the different arteries in the human body, and the ability to engineer vessels of varying sizes could increase capabilities for disease modeling and treatment options. We present an innovative method for producing customizable, tissue engineered, self-organizing vascular constructs by replicating a major structural component of blood vessels - the smooth muscle layer, or tunica media. We utilize a unique system combining 3D printed plate inserts to control construct size and shape, and cell sheets supported by a temporary fibrin hydrogel to encourage cellular self-organization into a tubular form resembling a natural artery. To form the vascular construct, 3D printed inserts are adhered to tissue culture plates, fibrin hydrogel is deposited around the inserts, and human aortic smooth muscle cells are then seeded atop the fibrin hydrogel. The gel, aided by the innate contractile properties of the smooth muscle cells, aggregates towards the center post insert, creating a tissue ring of smooth muscle cells. These rings are then stacked into the final tubular construct. Our methodology is robust, easily repeatable and allows for customization of cellular composition, vessel wall thickness, and length of the vessel construct merely by varying the size of the 3D printed inserts. This platform has potential for facilitating more accurate modeling of vascular pathology, serving as a drug discovery tool, or for vessel repair in disease treatment.

Fabrication of tissue-engineered vascular grafts with stem cells and stem cell-derived vascular cells

INTRODUCTION

Cardiovascular disease is the leading cause of mortality worldwide. Current surgical treatments for cardiovascular disease include vascular bypass grafting and replacement with autologous blood vessels or synthetic vascular grafts. However, there is a call for better alternative biological grafts.

AREAS COVERED

Tissue-engineered vascular grafts (TEVGs) are promising novel alternatives to replace diseased vessels. However, obtaining enough functional and clinically usable vascular cells for fabrication of TEVGs remains a major challenge. New findings in adult stem cells and recent advances in pluripotent stem cells have opened a new avenue for stem cell-based vascular engineering. In this review, recent advances on stem cell sourcing for TEVGs including the use of adult stem cells and pluripotent stem cells and advantages, disadvantages, and possible future implementations of different types of stem cells will be discussed. In addition, current strategies used during the fabrication of TEVGs will be highlighted.

EXPERT OPINION

The application of patient-specific TEVGs constructed with vascular cells derived from immune-compatible stem cells possesses huge clinical potential. Advances in lineage-specific differentiation approaches and innovative vascular engineering strategies will promote the vascular regeneration field from bench to bedside.

Decellularized biological matrices: an interesting approach for cardiovascular tissue repair and regeneration

The repair and replacement of blood vessels is one of the most challenging topics for biomedical research. Autologous vessels are preferred as graft materials, but they still have many issues to overcome: for instance, they need multiple surgical procedures and often patients may not have healthy and surgically valuable arteries useful as an autograft. A tissue-engineering approach is widely desirable to generate biological vascular prostheses. Recently, decellularization of native tissue has gained significant attention in the biomedical research field. This method is used to obtain biological scaffolds that are expected to maintain the complex three-dimensional structure of the extracellular matrix, preserving the biomechanical properties of the native tissues. The decellularizing methods and the biomechanical characteristics of these products are presented in this review. Decellularization of biological matrices induces the loss of major histocompatibility complex (MHC), which is expected to promote an immunological response by the host. All the studies showed that decellularized biomaterials possess adequate properties for xenografting. Concerning their mechanical properties, several studies have demonstrated that, although chemical decellularization methods do not affect the scaffolds' mechanical properties, these materials can be modified through different treatments in order to provide the desired mechanical characteristics, depending on the specific application. A short overview of legislative issues concerning the use of decellularized substitutes and future perspectives in surgical applications is also presented. Copyright © 2015 John Wiley & Sons, Ltd.

Hybrid small-diameter vascular grafts: Anti-expansion effect of electrospun poly ε-caprolactone on heparin-coated decellularized matrices

Small-diameter vascular grafts (SDVGs) (D < 6 mm) are increasingly needed in clinical settings for cardiovascular disease, including coronary artery and peripheral vascular pathologies. Vessels made from synthetic polymers have shortcomings such as thrombosis, intimal hyperplasia, calcification, chronic inflammation and no growth potential. Decellularized xenografts are commonly used as a tissue-engineering substitute for vascular reconstructive procedures. Although acellular allogeneic vascular grafts have good histocompatibility and antithrombotic properties, the decellularization process may damage the biomechanics and accelerate the elastin deformation and degradation, finally resulting in vascular graft expansion and even aneurysm formation. Here, to address these problems, we combine synthetic polymers with natural decellularized small-diameter vessels to fabricate hybrid tissue-engineered vascular grafts (HTEV). The donor aortic vessels were decellularized with a combination of different detergents and dehydrated under a vacuum freeze-drying process. Polycaprolactone (PCL) nanofibers were electrospun (ES) outside the acellular aortic vascular grafts to strengthen the decellularized matrix. The intimal surfaces of the hybrid small-diameter vascular grafts were coated with heparin before the allograft transplantation. Histopathology and scanning electron microscope revealed that the media of the decellularized vessels were severely injured. Mechanical testing of scaffolds showed that ES-PCL significantly enhanced the biomechanics of decellularized vessels. Vascular ultrasound and micro-CT angiography showed that all grafts after implantation in a rat model were satisfactorily patent for up to 6 weeks. ES-PCL successfully prevented the occurrence of vasodilation and aneurysm formation after transplantation and reduced the cell inflammatory infiltration. In conclusion, the HTEV with perfect histocompatibility and biomechanics provide a facile and useful technique for the development of SDVGs.

Successful endothelialization and remodeling of a cell-free small-diameter arterial graft in a large animal model

The large number of coronary artery bypass procedures necessitates development of off-the-shelf vascular grafts that do not require cell or tissue harvest from patients. However, immediate thrombus formation after implantation due to the absence of a healthy endothelium is very likely. Here we present the successful development of an acellular tissue engineered vessel (A-TEV) based on small intestinal submucosa that was functionalized sequentially with heparin and VEGF. A-TEVs were implanted into the carotid artery of an ovine model demonstrating high patency rates and significant host cell infiltration as early as one week post-implantation. At one month, a confluent and functional endothelium was present and the vascular wall showed significant infiltration of host smooth muscle cells exhibiting vascular contractility in response to vaso-agonists. After three months, the endothelium aligned in the direction of flow and the medial layer comprised of circumferentially aligned smooth muscle cells. A-TEVs demonstrated high elastin and collagen content as well as impressive mechanical properties and vascular contractility comparable to native arteries. This is the first demonstration of successful endothelialization, remodeling, and development of vascular function of a cell-free vascular graft that was implanted in the arterial circulation of a pre-clinical animal model.

The Tissue-Engineered Vascular Graft-Past, Present, and Future

Cardiovascular disease is the leading cause of death worldwide, with this trend predicted to continue for the foreseeable future. Common disorders are associated with the stenosis or occlusion of blood vessels. The preferred treatment for the long-term revascularization of occluded vessels is surgery utilizing vascular grafts, such as coronary artery bypass grafting and peripheral artery bypass grafting. Currently, autologous vessels such as the saphenous vein and internal thoracic artery represent the gold standard grafts for small-diameter vessels (<6 mm), outperforming synthetic alternatives. However, these vessels are of limited availability, require invasive harvest, and are often unsuitable for use. To address this, the development of a tissue-engineered vascular graft (TEVG) has been rigorously pursued. This article reviews the current state of the art of TEVGs. The various approaches being explored to generate TEVGs are described, including scaffold-based methods (using synthetic and natural polymers), the use of decellularized natural matrices, and tissue self-assembly processes, with the results of various in vivo studies, including clinical trials, highlighted. A discussion of the key areas for further investigation, including graft cell source, mechanical properties, hemodynamics, integration, and assessment in animal models, is then presented.

Potential of Newborn and Adult Stem Cells for the Production of Vascular Constructs Using the Living Tissue Sheet Approach

Bypass surgeries using native vessels rely on the availability of autologous veins and arteries. An alternative to those vessels could be tissue-engineered vascular constructs made by self-organized tissue sheets. This paper intends to evaluate the potential use of mesenchymal stem cells (MSCs) isolated from two different sources: (1) bone marrow-derived MSCs and (2) umbilical cord blood-derived MSCs. When cultured in vitro, a proportion of those cells differentiated into smooth muscle cell- (SMC-) like cells and expressed contraction associated proteins. Moreover, these cells assembled into manipulable tissue sheets when cultured in presence of ascorbic acid. Tubular vessels were then produced by rolling those tissue sheets on a mandrel. The architecture, contractility, and mechanical resistance of reconstructed vessels were compared with tissue-engineered media and adventitia produced from SMCs and dermal fibroblasts, respectively. Histology revealed a collagenous extracellular matrix and the contractile responses measured for these vessels were stronger than dermal fibroblasts derived constructs although weaker than SMCs-derived constructs. The burst pressure of bone marrow-derived vessels was higher than SMCs-derived ones. These results reinforce the versatility of the self-organization approach since they demonstrate that it is possible to recapitulate a contractile media layer from MSCs without the need of exogenous scaffolding material.

Multimaterial and Multiscale Three-Dimensional Bioprinter

We have developed a three-dimensional (3D) bioprinting system capable of multimaterial and multiscale deposition to enable the next generation of “bottom-up” tissue engineering. This area of research resides at the interface of engineering and life sciences. As such, it entails the design and implementation of diverse elements: a novel hydrogel-based bioink, a 3D bioprinter, automation software, and mammalian cell culture. Our bioprinter has three components uniquely combined into a comprehensive tool: syringe pumps connected to a selector valve that allow precise application of up to five different materials with varying viscosities and chemistries, a high velocity/high-precision x–y–z stage to accommodate the most rapid speeds allowable by the printed materials, and temperature control of the bioink reservoirs, lines, and printing environment. Our custom-designed bioprinter is able to print multiple materials (or multiple cell types in the same material) concurrently with various feature sizes (100 μm–1 mm wide; 100 μm–1 cm high). One of these materials is a biocompatible, printable bioink that has been used to test for cell survival within the hydrogel following printing. Hand-printed (HP) controls show that our bioprinter does not adversely affect the viability of the printed cells. Here, we report the design and build of the 3D bioprinter, the optimization of the bioink, and the stability and viability of our printed constructs.

Strategies for skeletal muscle tissue engineering: seed vs. soil

The most commonly used tissue engineering approach includes the ex vivo combination of site-appropriate cell(s) and scaffold material(s) to create three-dimensional constructs for tissue replacement or reconstruction. These three-dimensional combinations are typically subjected to a period of culture and conditioning (i.e., self-assembly and maturation) to promote the development of ex vivo constructs which closely mimic native target tissue. This cell-based approach is challenged by the host response to the engineered tissue construct following surgical implantation. As an alternative to the cell-based approach, acellular biologic scaffolds attract endogenous cells and remodel into partially functional mimics of native tissue upon implantation. The present review examines cell-types (i.e., seed), scaffold materials (i.e., soil), and challenges associated with functional tissue engineering. Skeletal muscle is used as the target tissue prototype but the discussed principles will largely apply to most body systems.

Patient-specific cardiovascular progenitor cells derived from integration-free induced pluripotent stem cells for vascular tissue regeneration

Tissue-engineered blood vessels (TEBVs) are promising in regenerating a live vascular replacement. However, the vascular cell source is limited, and it is crucial to develop a scaffold that accommodates new type of vascular progenitor cells and facilitates in vivo lineage specification of the cells into functional vascular smooth muscle cells (VSMCs) to regenerate vascular tissue. In the present study, integration-free human induced pluripotent stem cells (hiPSCs) were established from patient peripheral blood mononuclear cells through episomal vector nucleofection of reprogramming factors. The established hiPSCs were then induced into mesoderm-originated cardiovascular progenitor cells (CVPCs) with a highly efficient directed lineage specification method. The derived CVPCs were demonstrated to be able to differentiate into functional VSMCs. Subcutaneous implantation of CVPCs seeded on macroporous nanofibrous poly(l-lactide) scaffolds led to in vivo VSMC lineage specification and matrix deposition inside the scaffolds. In summary, we established integration-free patient-specific hiPSCs from peripheral blood mononuclear cells, derived CVPCs through directed lineage specification, and developed an advanced scaffold for these progenitor cells to further differentiate in vivo into VSMCs and regenerate vascular tissue in a subcutaneous implantation model. This study has established an efficient patient-specific approach towards in vivo regeneration of vascular tissue.

Elastic large muscular vessel wall engineered with bone marrow‑derived cells under pulsatile stimulation in a bioreactor

Bone marrow‑derived cells (BMCs) have demonstrated their ability to differentiate into multiple cell lineages and may be a promising cell source for vascular tissue engineering. Although much progress has been made in the engineering of small blood vessels (<6 mm in diameter) with biodegradable materials such as polyglycolic acid (PGA), it remains a challenge to engineer large vessels (>6 mm in diameter) due to unsatisfactory biomechanical properties. The present study was to engineered an elastic large vessel wall (6 mm in diameter) using a PGA unwoven fibre scaffold covered with BMCs from canine humeri. The cell‑PGA sheet was then loaded into a bioreactor designed for the present study, with dynamic pulsatile culture conditions to mimic the physiological vessel environment. After four weeks of the pulsatile stimuli culture, an elastic vessel wall was formed. Histological analyses demonstrated that layers of smooth muscle‑like cells and well‑oriented collagenous fibres were evenly oriented in the dynamic group. By contrast, disorganised cells and randomly collagenous fibres were apparent in the static group. Furthermore, the engineered vessel wall in the dynamic group exhibited significantly improved biomechanical properties compared with those in static culture group. The approach developed in the present study was demonstrated to have promising potential to be used for the engineering of large vessel as well as other smooth muscle cell‑containing tissues, including bladder, urethral and intestinal tissues.

The fabrication of double layer tubular vascular tissue engineering scaffold via coaxial electrospinning and its 3D cell coculture

A continuous electrospinning technique was applied to fabricate double layer tubular tissue engineering vascular graft (TEVG) scaffold. The luminal layer was made from poly(ɛ-caprolac-tone)(PCL) ultrafine fibers via common single axial electrospinning followed by the outer layer of core-shell structured nanofibers via coaxial electrospinning. For preparing the outer layernano-fibers, the PCL was electrospun into the shell and both bovine serum albumin (BSA) and tetrapeptide val-gal-pro-gly (VAPG) were encapsulated into the core. The core-shell structure in the outer layer fibers was observed by transmission electron microscope (TEM). The in vitro release tests exhibited the sustainable release behavior of BSA and VAPG so that they provided a better cell growth environment in the interior of tubular scaffold wall. The in vitro culture of smooth muscle cells (SMCs) demonstrated their potential to penetrate into the scaffold wall for the 3D cell culture. Subsequently, 3D cell coculture was conducted. First, SMCs were seeded on the luminal surface of the scaffold and cultured for 5 days, and then endothelial cells (ECs) were also seeded on the luminal surface and cocultured with SMCs for another 2 days. After stained with antibodies, 3D cell distribution on the scaffold was revealed by confocal laser scanning microscopy (CLSM) where ECs were mainly located on the luminal surface whereas SMCs penetrated into the surface and distributed inside the scaffold wall. This double layer tubular scaffold with 3D cell distribution showed the promise to develop it into a novel TEVG for clinical trials in the near future.

MicroRNAs in vascular tissue engineering and post-ischemic neovascularization

Increasing numbers of paediatric patients with congenital heart defects are surviving to adulthood, albeit with continuing clinical needs. Hence, there is still scope for revolutionary new strategies to correct vascular anatomical defects. Adult patients are also surviving longer with the adverse consequences of ischemic vascular disease, especially after acute coronary syndromes brought on by plaque erosion and rupture. Vascular tissue engineering and therapeutic angiogenesis provide new hope for these patients. Both approaches have shown promise in laboratory studies, but have not yet been able to deliver clear evidence of clinical success. More research into biomaterials, molecular medicine and cell and molecular therapies is necessary. This review article focuses on the new opportunities offered by targeting microRNAs for the improved production and greater empowerment of vascular cells for use in vascular tissue engineering or for increasing blood perfusion of ischemic tissues by amplifying the resident microvascular network.

Scaffolds and cells for tissue regeneration: different scaffold pore sizes-different cell effects

During the last decade biomaterial sciences and tissue engineering have become new scientific fields supplying rising demand of regenerative therapy. Tissue engineering requires consolidation of a broad knowledge of cell biology and modern biotechnology investigating biocompatibility of materials and their application for the reconstruction of damaged organs and tissues. Stem cell-based tissue regeneration started from the direct cell transplantation into damaged tissues or blood vessels. However, it is difficult to track transplanted cells and keep them in one particular place of diseased organ. Recently, new technologies such as cultivation of stem cell on the scaffolds and subsequently their implantation into injured tissue have been extensively developed. Successful tissue regeneration requires scaffolds with particular mechanical stability or biodegradability, appropriate size, surface roughness and porosity to provide a suitable microenvironment for the sufficient cell-cell interaction, cell migration, proliferation and differentiation. Further functioning of implanted cells highly depends on the scaffold pore sizes that play an essential role in nutrient and oxygen diffusion and waste removal. In addition, pore sizes strongly influence cell adhesion, cell-cell interaction and cell transmigration across the membrane depending on the various purposes of tissue regeneration. Therefore, this review will highlight contemporary tendencies in application of non-degradable scaffolds and stem cells in regenerative medicine with a particular focus on the pore sizes significantly affecting final recover of diseased organs.

Scaffolds and cells for tissue regeneration: different scaffold pore sizes-different cell effects

During the last decade biomaterial sciences and tissue engineering have become new scientific fields supplying rising demand of regenerative therapy. Tissue engineering requires consolidation of a broad knowledge of cell biology and modern biotechnology investigating biocompatibility of materials and their application for the reconstruction of damaged organs and tissues. Stem cell-based tissue regeneration started from the direct cell transplantation into damaged tissues or blood vessels. However, it is difficult to track transplanted cells and keep them in one particular place of diseased organ. Recently, new technologies such as cultivation of stem cell on the scaffolds and subsequently their implantation into injured tissue have been extensively developed. Successful tissue regeneration requires scaffolds with particular mechanical stability or biodegradability, appropriate size, surface roughness and porosity to provide a suitable microenvironment for the sufficient cell-cell interaction, cell migration, proliferation and differentiation. Further functioning of implanted cells highly depends on the scaffold pore sizes that play an essential role in nutrient and oxygen diffusion and waste removal. In addition, pore sizes strongly influence cell adhesion, cell-cell interaction and cell transmigration across the membrane depending on the various purposes of tissue regeneration. Therefore, this review will highlight contemporary tendencies in application of non-degradable scaffolds and stem cells in regenerative medicine with a particular focus on the pore sizes significantly affecting final recover of diseased organs.

Extracellular matrix biomimicry for the creation of investigational and therapeutic devices

The extracellular matrix (ECM) is a web of fibrous proteins that serves as a scaffold for tissues and organs, and is important for maintaining homeostasis and facilitating cellular adhesion. Integrin transmembrane receptors are the primary adhesion molecules that anchor cells to the ECM, thus integrating cells with their microenvironments. Integrins play a critical role in facilitating cell-matrix interactions and promoting signal transduction, both from the cell to the ECM and vice versa, ultimately mediating cell behavior. For this reason, many advanced biomaterials employ biomimicry by replicating the form and function of fibrous ECM proteins. The ECM also acts as a reservoir for small molecules and growth factors, wherein fibrous proteins directly bind and present these bioactive moieties that facilitate cell activity. Therefore biomimicry can be enhanced by incorporating small molecules into ECM-like substrates. Biomimetic ECM materials have served as invaluable research tools for studying interactions between cells and the surrounding ECM, revealing that cell-matrix signaling is driven by mechanical forces, integrin engagement, and small molecules. Mimicking pathological ECMs has also elucidated disease specific cell behaviors. For example, biomimetic tumor microenvironments have been used to induce metastatic cell behaviors, and have thereby shown promise for in vitro cancer drug testing and targeting. Further, ECM-like substrates have been successfully employed for autologous cell recolonization for tissue engineering and wound healing. As we continue to learn more about the mechanical and biochemical characteristics of the ECM, these properties can be harnessed to develop new biomaterials, biomedical devices, and therapeutics.

Mechanical properties of endothelialized fibroblast-derived vascular scaffolds stimulated in a bioreactor

There is an ongoing clinical need for tissue-engineered small-diameter (<6mm) vascular grafts since clinical applications are restricted by the limited availability of autologous living grafts or the lack of suitability of synthetic grafts. The present study uses our self-assembly approach to produce a fibroblast-derived decellularized vascular scaffold that can then be available off-the-shelf. Briefly, scaffolds were produced using human dermal fibroblasts sheets rolled around a mandrel, maintained in culture to allow for the formation of cohesive and three-dimensional tubular constructs, and then decellularized by immersion in deionized water. Constructs were then endothelialized and perfused for 1week in an appropriate bioreactor. Mechanical testing results showed that the decellularization process did not influence the resistance of the tissue and an increase in ultimate tensile strength was observed following the perfusion of the construct in the bioreactor. These fibroblast-derived vascular scaffolds could be stored and later used to deliver readily implantable grafts within 4weeks including an autologous endothelial cell isolation and seeding process. This technology could greatly accelerate the clinical availability of tissue-engineered blood vessels.

The role of mechanotransduction on vascular smooth muscle myocytes' [corrected] cytoskeleton and contractile function

Smooth muscle (SM) exhibits a highly organized structural hierarchy that extends over multiple spatial scales to perform a wide range of functions at the cellular, tissue, and organ levels. Early efforts primarily focused on understanding vascular SM (VSM) function through biochemical signaling. However, accumulating evidence suggests that mechanotransduction, the process through which cells convert mechanical stimuli into biochemical cues, is requisite for regulating contractility. Cytoskeletal proteins that comprise the extracellular, intercellular, and intracellular domains are mechanosensitive and can remodel their structure and function in response to external mechanical cues. Pathological stimuli such as malignant hypertension can act through the same mechanotransductive pathways to induce maladaptive remodeling, leading to changes in cellular shape and loss of contractile function. In both health and disease, the cytoskeletal architecture integrates the mechanical stimuli and mediates structural and functional remodeling in the VSM.

Surgical technique for the implantation of tissue engineered vascular grafts and subsequent in vivo monitoring

The development of Tissue Engineered Vessels (TEVs) is advanced by the ability to routinely and effectively implant TEVs (4-5 mm in diameter) into a large animal model. A step by-step protocol for inter-positional placement of the TEV and real-time digital assessment of the TEV and native carotid arteries is described here. In vivo monitoring is made possible by the implantation of flow probes, catheters and ultrasonic crystals (capable of recording dynamic diameter changes of implanted TEVs and native carotid arteries) at the time of surgery. Once implanted, researchers can calculate arterial blood flow patterns, invasive blood pressure and artery diameter yielding parameters such as pulse wave velocity, augmentation index, pulse pressures and compliance. Data acquisition is accomplished using a single computer program for analysis throughout the duration of the experiment. Such invaluable data provides insight into TEV matrix remodeling, its resemblance to native/sham controls and overall TEV performance in vivo.

Arterial specification of endothelial cells derived from human induced pluripotent stem cells in a biomimetic flow bioreactor

Endothelial cells (ECs) exist in different microenvironments in vivo, including under different levels of shear stress in arteries versus veins. Standard stem cell differentiation protocols to derive ECs and EC-subtypes from human induced pluripotent stem cells (hiPSCs) generally use growth factors or other soluble factors in an effort to specify cell fate. In this study, a biomimetic flow bioreactor was used to subject hiPSC-derived ECs (hiPSC-ECs) to shear stress to determine the impacts on phenotype and upregulation of markers associated with an anti-thrombotic, anti-inflammatory, arterial-like phenotype. The in vitro bioreactor system was able to efficiently mature hiPSC-ECs into arterial-like cells in 24 h, as demonstrated by qRT-PCR for arterial markers EphrinB2, CXCR4, Conexin40 and Notch1, as well protein-level expression of Notch1 intracellular domain (NICD). Furthermore, the exogenous addition of soluble factors was not able to fully recapitulate this phenotype that was imparted by shear stress exposure. The induction of these phenotypic changes was biomechanically mediated in the shear stress bioreactor. This biomimetic flow bioreactor is an effective means for the differentiation of hiPSC-ECs toward an arterial-like phenotype, and is amenable to scale-up for culturing large quantities of cells for tissue engineering applications.

Design and Use of a Novel Bioreactor for Regeneration of Biaxially Stretched Tissue-Engineered Vessels

Conventional bioreactors are used to enhance extracellular matrix (ECM) production and mechanical strength of tissue-engineered vessels (TEVs) by applying circumferential strain, which is uniaxial stretching. However, the resulting TEVs still suffer from inadequate mechanical properties, where rupture strengths and compliance values are still very different from native arteries. The biomechanical milieu of native arteries consists of both circumferential and axial loading. Therefore, to better simulate the physiological stresses acting on native arteries, we built a novel bioreactor system to enable biaxial stretching of engineered arteries during culture. This new bioreactor system allows for independent control of circumferential and axial stretching parameters, such as displacement and beat rate. The assembly and setup processes for this biaxial bioreactor system are reliable with a success rate greater than 75% for completion of long-term sterile culture. This bioreactor also supports side-by-side assessments of TEVs that are cultured under three types of mechanical conditions (static, uniaxial, and biaxial), all within the same biochemical environment. Using this bioreactor, we examined the impact of biaxial stretching on arterial wall remodeling of TEVs. Biaxial TEVs developed the greatest wall thickness compared with static and uniaxial TEVs. Unlike uniaxial loading, biaxial loading led to undulated collagen fibers that are commonly found in native arteries. More importantly, the biaxial TEVs developed the most mature elastin in the ECM, both qualitatively and quantitatively. The presence of mature extracellular elastin along with the undulated collagen fibers may contribute to the observed vascular compliance in the biaxial TEVs. The current work shows that biaxial stretching is a novel and promising means to improve TEV generation. Furthermore, this novel system allows us to optimize biomechanical conditioning by unraveling the interrelationships among the applied mechanical stress, the resulting ECM properties, and the mechanics of TEVs.

Differential effects of culture senescence and mechanical stimulation on the proliferation and leiomyogenic differentiation of MSC from different sources: implications for engineering vascular grafts

We examined the effects of senescence on the proliferation and leiomyogenic differentiation potential of mesenchymal stem cells (MSCs) isolated from bone marrow (BM-MSCs) or hair follicles (HF-MSCs). To this end, we compared ovine HF-MSCs and BM-MSCs in terms of their proliferation and differentiation potential to the smooth muscle cell lineage. We discovered that HF-MSCs are less susceptible to culture senescence compared with BM-MSCs. We hypothesized that application of mechanical forces may enhance the contractility and mechanical properties of vascular constructs prepared from senescent MSCs. Interestingly, HF-MSCs and BM-MSCs responded differently to changes in the mechanical microenvironment, suggesting that despite phenotypic similarities, MSCs from different anatomic locations may activate different pathways in response to the same microenvironmental factors. In turn, this may also suggest that cell-based tissue regeneration approaches may need to be tailored to the stem cell origin, donor age, and culture time for optimal results.

A new tissue-engineered biodegradable surgical patch for high-pressure systems †

OBJECTIVES

Ideal alternatives for replacing native arteries, which have biocompatibility such as growth potential, anti-thrombogenesis and durability, have yet to be discovered. We previously demonstrated the utility of tissue-engineered vascular autografts; however, the use of these autografts is limited to low-pressure conditions. The aim of this study was to create the tissue-engineered arterial patch (TEAP) that could be used in high-pressure systems, and to evaluate the maturation in this regenerative tissue.

METHODS

We developed a new biodegradable polymer scaffold, which is composed of a co-polymer of epsilon-caprolactone and lactide acid [P(CL/LA)] and a poly-L-lactide acid (PLLA). To obtain mechanical strength, we modified PLLA that is degraded by hydrolysis for 1-2 years in contrast to polyglycolic acid in our low-pressure study previously. We implanted an oval-shaped patch (30 × 15 mm) of this polymer without cell seeding into the descending aorta of 12 dogs, and followed the animals for 1, 3 and 6 months (n = 4 in each group). The cell proliferation in the patch was evaluated with histological and immunohistochemical methods. Additionally, the expression of vascular endothelial growth factor (VEGF) and smooth muscle myosin heavy chain (smMHC) mRNA in the patches was determined with reverse transcriptase-polymerase chain reaction.

RESULTS

Macroscopically, there was no incidence of rupture or aneurysmal formation on the patch. The luminal surface of the TEAP was covered with a single layer of endothelial cells stained with vWF immunohistochemically at 1 month after implantation. αSMA-positive cells that indicated smooth muscle cells and collagen fibres were observed in the patch and they increased over time. The VEGF mRNA expression in the patch at 1 month was significantly higher than that of native arterial tissue (1 month; 0.124 ± 0.017 ng/µl, native; 0.009 ± 0.003 ng/µl, P < 0.05). The smMHC mRNA expression gradually increased, and reached ∼ 60% of that of the native artery at 6 months (6 months: 0.351 ± 0.028 ng/µl, native: 0.540 ± 0.027 ng/µl).

CONCLUSIONS

We demonstrated the maturation of endothelial and smooth muscle cells in TEAP, suggesting that this biodegradable polymer scaffold could be used as an alternative vascular material even in high-pressure systems.

Capture of endothelial cells under flow using immobilized vascular endothelial growth factor

We demonstrate the ability of immobilized vascular endothelial growth factor (VEGF) to capture endothelial cells (EC) with high specificity under fluid flow. To this end, we engineered a surface consisting of heparin bound to poly-L-lysine to permit immobilization of VEGF through the C-terminal heparin-binding domain. The immobilized growth factor retained its biological activity as shown by proliferation of EC and prolonged activation of KDR signaling. Using a microfluidic device we assessed the ability to capture EC under a range of shear stresses from low (0.5 dyne/cm²) to physiological (15 dyne/cm²). Capture was significant for all shear stresses tested. Immobilized VEGF was highly selective for EC as evidenced by significant capture of human umbilical vein and ovine pulmonary artery EC but no capture of human dermal fibroblasts, human hair follicle derived mesenchymal stem cells, or mouse fibroblasts. Further, VEGF could capture EC from mixtures with non-EC under low and high shear conditions as well as from complex fluids like whole human blood under high shear. Our findings may have far reaching implications, as they suggest that VEGF could be used to promote endothelialization of vascular grafts or neovascularization of implanted tissues by rare but continuously circulating EC.

Experimental study on the construction of small three-dimensional tissue engineered grafts of electrospun poly-ε-caprolactone

Studies on three-dimensional tissue engineered graft (3DTEG) have attracted great interest among researchers as they present a means to meet the pressing clinical demand for tissue engineering scaffolds. To explore the feasibility of 3DTEG, high porosity poly-ε-caprolactone (PCL) was obtained via the co-electrospinning of polyethylene glycol and PCL, and used to construct small-diameter poly-ε-caprolactone-lysine (PCL-LYS-H) scaffolds, whereby heparin was anchored to the scaffold surface by lysine groups. A variety of small-diameter 3DTEG models were constructed with different PCL layers and the mechanical properties of the resulting constructs were evaluated in order to select the best model for 3DTEGs. Bone marrow mononuclear cells were induced and differentiated to endothelial cells (ECs) and smooth muscle cells (SMCs). A 3DTEG (labeled '10-4%') was successfully produced by the dynamic co-culture of ECs on the PCL-LYS-H scaffolds and SMCs on PCL. The fluorescently labeled cells on the 3DTEG were subsequently observed by laser confocal microscopy, which showed that the ECs and SMCs were embedded in the 3DTEG. Nitric oxide and endothelial nitric oxide synthase assays showed that the ECs behaved normally in the 3DTEG. This study consequently provides a new thread to produce small-diameter tissue engineered grafts, with excellent mechanical properties, that are perfusable to vasculature and functional cells.

Click-coated, heparinized, decellularized vascular grafts

A novel method enabling the engineering of a dense and appropriately oriented heparin-containing layer on decellularized aortas has been developed. Amino groups of decellularized aortas were first modified to azido groups using 3-azidobenzoic acid. Azide-clickable dendrons were attached onto the azido groups through "alkyne-azide" click chemistry, affording a tenfold amplification of adhesions sites. Dendron end groups were finally decorated with end-on modified heparin chains. Heparin chains were oriented like heparan sulfate groups on native endothelial cells surface. X-ray photoelectron spectroscopy, nuclear magnetic resonance imaging, mass spectrometry and Fourier transform infrared FTIR spectroscopy were used to characterize the synthesis steps, building the final heparin layered coatings. The continuity of the heparin coating was verified using fluorescent microscopy and histological analysis. The efficacy of heparin linkage was demonstrated with factor Xa anti-thrombogenic assay and platelet adhesion studies. The results suggest that oriented heparin immobilization to decellularized aortas may improve the in vivo blood compatibility of decellularized aortas and vessels.

Scaffolds in vascular regeneration: current status

An ideal vascular substitute, especially in <6 mm diameter applications, is a major clinical essentiality in blood vessel replacement surgery. Blood vessels are structurally complex and functionally dynamic tissue, with minimal regeneration potential. These have composite extracellular matrix (ECM) and arrangement. The interplay between ECM components and tissue specific cells gives blood vessels their specialized functional attributes. The core of vascular tissue engineering and regeneration relies on the challenges in creating vascular conduits that match native vessels and adequately regenerate in vivo. Out of numerous vascular regeneration concerns, the relevance of ECM emphasizes much attention toward appropriate choice of scaffold material and further scaffold development strategies. The review is intended to be focused on the various approaches of scaffold materials currently in use in vascular regeneration and current state of the art. Scaffold of choice in vascular tissue engineering ranges from natural to synthetic, decellularized, and even scaffold free approach. The applicability of tubular scaffold for in vivo vascular regeneration is under active investigation. A patent conduit with an ample endothelial luminal layer that can regenerate in vivo remains an unanswered query in the field of small diameter vascular tissue engineering. Besides, scaffolds developed for vascular regeneration, should aim at providing functional substitutes for use in a regenerative approach from the laboratory bench to patient bedside.

Concise review: Engineering myocardial tissue: the convergence of stem cells biology and tissue engineering technology

Advanced heart failure represents a leading public health problem in the developed world. The clinical syndrome results from the loss of viable and/or fully functional myocardial tissue. Designing new approaches to augment the number of functioning human cardiac muscle cells in the failing heart serve as the foundation of modern regenerative cardiovascular medicine. A number of clinical trials have been performed in an attempt to increase the number of functional myocardial cells by the transplantation of a diverse group of stem or progenitor cells. Although there are some encouraging suggestions of a small early therapeutic benefit, to date, no evidence for robust cell or tissue engraftment has been shown, emphasizing the need for new approaches. Clinically meaningful cardiac regeneration requires the identification of the optimum cardiogenic cell types and their assembly into mature myocardial tissue that is functionally and electrically coupled to the native myocardium. We here review recent advances in stem cell biology and tissue engineering and describe how the convergence of these two fields may yield novel approaches for cardiac regeneration.

A hypothesis-driven parametric study of effects of polymeric scaffold properties on tissue engineered neovessel formation

Continued advances in the tissue engineering of vascular grafts have enabled a paradigm shift from the desire to design for adequate suture retention, burst pressure and thrombo-resistance to the goal of achieving grafts having near native properties, including growth potential. Achieving this far more ambitious outcome will require the identification of optimal, not just adequate, scaffold structure and material properties. Given the myriad possible combinations of scaffold parameters, there is a need for a new strategy for reducing the experimental search space. Toward this end, we present a new modeling framework for in vivo neovessel development that allows one to begin to assess in silico the potential consequences of different combinations of scaffold structure and material properties. To restrict the number of parameters considered, we also utilize a non-dimensionalization to identify key properties of interest. Using illustrative constitutive relations for both the evolving fibrous scaffold and the neotissue that develops in response to inflammatory and mechanobiological cues, we show that this combined non-dimensionalization computational approach predicts salient aspects of neotissue development that depend directly on two key scaffold parameters, porosity and fiber diameter. We suggest, therefore, that hypothesis-driven computational models should continue to be pursued given their potential to identify preferred combinations of scaffold parameters that have the promise of improving neovessel outcome. In this way, we can begin to move beyond a purely empirical trial-and-error search for optimal combinations of parameters and instead focus our experimental resources on those combinations that are predicted to have the most promise.

Biodegradable, thermoplastic polyurethane grafts for small diameter vascular replacements

Biodegradable vascular grafts with sufficient in vivo performance would be more advantageous than permanent non-degradable prostheses. These constructs would be continuously replaced by host tissue, leading to an endogenous functional implant which would adapt to the need of the patient and exhibit only limited risk of microbiological graft contamination. Adequate biomechanical strength and a wall structure which promotes rapid host remodeling are prerequisites for biodegradable approaches. Current approaches often reveal limited tensile strength and therefore require thicker or reinforced graft walls. In this study we investigated the in vitro and in vivo biocompatibility of thin host-vessel-matched grafts (n=34) formed from hard-block biodegradable thermoplastic polyurethane (TPU). Expanded polytetrafluoroethylene (ePTFE) conduits (n=34) served as control grafts. Grafts were analyzed by various techniques after retrieval at different time points (1 week; 1, 6, 12 months). TPU grafts showed significantly increased endothelial cell proliferation in vitro (P<0.001). Population by host cells increased significantly in the TPU conduits within 1 month of implantation (P=0.01). After long-term implantation, TPU implants showed 100% patency (ePTFE: 93%) with no signs of aneurysmal dilatation. Substantial remodeling of the degradable grafts was observed but varied between subjects. Intimal hyperplasia was limited to ePTFE conduits (29%). Thin-walled TPU grafts offer a new and desirable form of biodegradable vascular implant. Degradable grafts showed equivalent long-term performance characteristics compared to the clinically used, non-degradable material with improvements in intimal hyperplasia and ingrowth of host cells.

Biocompatible and biodegradable elastomer/fibrinogen composite electrospun scaffolds for cardiac tissue regeneration

Schematic for nanofiber with HCMs in cardiac tissue engineering.

Tissue-engineered vascular grafts created from human induced pluripotent stem cells

The utility of human induced pluripotent stem cells (hiPSCs) to create tissue-engineered vascular grafts was evaluated in this study. hiPSC lines were first induced into a mesenchymal lineage via a neural crest intermediate using a serum-free, chemically defined differentiation scheme. Derived cells exhibited commonly known mesenchymal markers (CD90, CD105, and CD73 and negative marker CD45) and were shown to differentiate into several mesenchymal lineages (osteogenic, chondrogenic, and adipogenic). Functional vascular grafts were then engineered by culturing hiPSC-derived mesenchymal progenitor cells in a pulsatile bioreactor system over 8 weeks to induce smooth muscle cell differentiation and collagenous matrix generation. Histological analyses confirmed layers of calponin-positive smooth muscle cells in a collagen-rich matrix. Mechanical tests revealed that grafts had an average burst pressure of 700 mmHg, which is approximately half that of native veins. Additionally, studies revealed that karyotypically normal mesenchymal stem cell clones led to generation of grafts with predicted features of engineered vascular grafts, whereas derived clones having chromosomal abnormalities generated calcified vessel constructs, possibly because of cell apoptosis during culture. Overall, these results provide significant insight into the utility of hiPS cells for vascular graft generation. They pave the way for creating personalized, patient-specific vascular grafts for surgical applications, as well as for creating experimental models of vascular development and disease.

Tissue engineering vascular grafts a fortiori: looking back and going forward

INTRODUCTION

Cardiovascular diseases such as coronary heart disease often necessitate the surgical repair using conduits. Although autografts still remain the gold standard, the inconvenience of harvesting and/or insufficient availability in patients with atherosclerotic disease has given impetus to look into alternative sources for vascular grafts.

AREAS COVERED

There are four main techniques to produce tissue-engineered vascular grafts (TEVGs): i) biodegradable synthetic scaffolds; ii) gel-based scaffolds; iii) decellularised scaffolds and iv) self-assembled cell-sheet-based techniques. The first three techniques can be grouped together as scaffold-guided approach as it involves the use of a construct to function as a supportive framework for the vascular graft. The most significant advantages of TEVGs are that it possesses the ability to grow, remodel and respond to environmental factors. Cell sources for TEVGs include mature somatic cells, stem cells, adult progenitor cells and pluripotent stem cells.

EXPERT OPINION

TEVG holds great promise with advances in nanotechnology, coupled with important refinements in tissue engineering and decellularisation techniques. This will undoubtedly be an important milestone for cardiovascular medicine when it is eventually translated to clinical use.

Variation in Cardiac Pulse Frequencies Modulates vSMC Phenotype Switching During Vascular Remodeling

In vitro perfusion systems have exposed vascular constructs to mechanical conditions that emulate physiological pulse pressure and found significant improvements in graft development. However, current models maintain constant, or set pulse/shear mechanics that do not account for the natural temporal variation in frequency. With an aim to develop clinically relevant small diameter vascular grafts, these investigations detail a perfusion culture model that incorporates temporal pulse pressure variation. Our objective was to test the hypothesis that short-term variation in heart rate, such as changes in respiratory activity, plays a significant role in vascular remodeling and graft development. The pulse rate of a healthy volunteer was logged to model the effect of daily activities on heart rate. Vascular bioreactors were used to deliver perfusion conditions based on modeled frequencies of temporal pulse variability, termed Physiologically Modeled Pulse Dynamics (PMPD). Acellular scaffolds derived from the human umbilical vein were seeded with human vascular smooth muscle cells and perfused under defined pulsatile conditions. vSMC exposed to constant pulse frequencies expressed a contractile phenotype, while exposure to PMPD drove cells to a synthetic state with continued cell proliferation, increased tensile strength and stiffness as well as diminished vasoactivity. Results show the temporal variation associated with normal heart physiology to have a profound effect on vascular remodeling and vasoactive function. While these models are representative of vascular regeneration further investigation is required to understanding these and other key regulators in vSMC phenotype switching in non-pathological or wound healing states. This understanding has important clinical implications that may lead to improved treatments that enhance vessel regeneration.

Manipulating the intersection of angiogenesis and inflammation

There exists a critical need to develop strategies that promote blood vessel formation (neovascularization) in virtually all tissue engineering and regenerative medicine efforts. While research typically focuses on understanding and exploiting the role of angiogenic factors and vascular cells on new blood vessel formation, the activity of the immune system is being increasingly recognized to impact vascular formation and adaptation. This review will provide both an overview of the intersection of angiogenesis and the immune system, and how biomaterials may be designed to promote favorable interactions between these two systems to promote effective vascularization.

Fabrication of polyurethane and polyurethane based composite fibres by the electrospinning technique for soft tissue engineering of cardiovascular system

Electrospinning is a unique technique, which provides forming of polymeric scaffolds for soft tissue engineering, which include tissue scaffolds for soft tissues of the cardiovascular system. Such artificial soft tissues of the cardiovascular system may possess mechanical properties comparable to native vascular tissues. Electrospinning technique gives the opportunity to form fibres with nm- to μm-scale in diameter. The arrangement of obtained fibres and their surface determine the biocompatibility of the scaffolds. Polyurethanes (PUs) are being commonly used as a prosthesis of cardiovascular soft tissues due to their excellent biocompatibility, non-toxicity, elasticity and mechanical properties. PUs also possess fine spinning properties. The combination of a variety of PU properties with an electrospinning technique, conducted at the well tailored conditions, gives unlimited possibilities of forming novel polyurethane materials suitable for soft tissue scaffolds applied in cardiovascular tissue engineering. This paper can help researches to gain more widespread and deeper understanding of designing electrospinable PU materials, which may be used as cardiovascular soft tissue scaffolds. In this paper we focus on reagents used in PU synthesis designed to increase PU biocompatibility (polyols) and biodegradability (isocyanates). We also describe suggested surface modifications of electrospun PUs, and the direct influence of surface wettability on providing enhanced biocompatibility of scaffolds. We indicate a great influence of electrospinning parameters (voltage, flow rate, working distance) and used solvents (mostly DMF, THF and HFIP) on fibre alignment and diameter - what impacts the biocompatibility and hemocompatibility of such electrospun PU scaffolds. Moreover, we present PU modifications with natural polymers with novel approach applied in electrospinning of PU scaffolds. This work may contribute with further developing of novel electrospun PUs, which may be applied as soft tissue scaffolds of the cardiovascular system.