Tissue engineering of blood vessel

Decellularization of human iliac artery: A vascular scaffold for peripheral repairs with human mesenchymal cells

This work presents strong evidence supporting the use of decellularized human iliac arteries combined with adipose tissue-derived stem cells (hASCs) as a promising alternative for vascular tissue engineering, opening the path to future treatments for peripheral artery disease (PAD). PAD is a progressive condition with high rates of amputation and mortality due to ischemic damage and limited graft options. Traditional synthetic grafts often fail due to poor integration, while autologous grafts may be unsuitable for patients with compromised vascular health. This study explores the potential of decellularized human iliac arteries as scaffolds for vascular grafts, focusing on preserving extracellular matrix (ECM) ultrastructure while minimizing immunogenic response. A perfusion-based protocol with enzymatic and detergent agents effectively removed cellular material, resulting in scaffolds with preserved ECM architecture, including organized collagen and elastin fibers. To assess scaffold bioactivity, hASCs were seeded onto the decellularized ECM, demonstrating high viability. Structural assessments, including histological staining and mechanical testing, confirmed that decellularized arteries retained their hierarchical structure and exhibited increased stiffness, suggesting an adaptive realignment of ECM fibers. Thermal and ultrastructural analyses further showed that decellularized scaffolds maintained stability and integrity comparable to native tissue, underscoring their durability for clinical applications. The human iliac artery shows potential as a vascular scaffold due to its accessibility and the ability to support the viability of hASC. Future research will emphasize in vivo validation and strategies for functional recellularization to evaluate the clinical viability of these engineered vascular grafts.

Recent Advances in Polyurethane for Artificial Vascular Application

Artificial blood vessels made from polyurethane (PU) have been researched for many years but are not yet in clinical use. The main reason was that the PU materials are prone to degradation after contact with blood and will also cause inflammation after long-term implantation. At present, PU has made progress in biostability and biocompatibility, respectively. The PU for artificial blood vessels still requires a balance between material stability and biocompatibility to maintain its long-term stability in vivo, which needs to be further optimized. Based on the requirement of PU materials for artificial vascular applications, this paper views the development of biostable PU, bioactive PU, and bioresorbable PU. The improvement of biostable PU from the monomer structure, chemical composition, and additives are discussed to improve the long-term biostability in vivo. The surface grafting and functionalization methods of bioactive PU to reduce thrombosis and promote endothelialization for improving biocompatibility are summarized. In addition, the bioresorbable PU for tissue-engineered artificial blood vessels is discussed to balance between the degradation rate and mechanical properties. The ideal PU materials for artificial blood vessels must have good mechanical properties, stability, and biocompatibility at the same time. Finally, the application potential of PU materials in artificial vascular is prospected.

Harnessing the Regenerative Potential of Fetal Mesenchymal Stem Cells and Endothelial Colony-Forming Cells in the Biofabrication of Tissue-Engineered Vascular Grafts (TEVGs)

Tissue engineering is a promising approach for the production of small-diameter vascular grafts; however, there are limited data directly comparing the suitability of applicable cell types for vessel biofabrication. Here, we investigated the potential of adult smooth muscle cells (SMCs), placental mesenchymal stem cells (MSCs), placental endothelial colony-forming cells (ECFCs), and a combination of MSCs and ECFCs on highly porous biocompatible poly(ɛ-caprolactone) (PCL) scaffolds produced via melt electrowriting (MEW) for the biofabrication of tissue-engineered vascular grafts (TEVGs). Cellular attachment, proliferation, and deposition of essential extracellular matrix (ECM) components were analysed in vitro over four weeks. TEVGs cultured with MSCs accumulated the highest levels of collagenous components within a dense ECM, while SMCs and the coculture were more sparsely populated, ascertained via histological and immunofluorescence imaging, and biochemical assessment. Scanning electron microscopy (SEM) enabled visualisation of morphological differences in cell attachment and growth, with MSCs and SMCs infiltrating and covering scaffolds completely within the 28-day culture period. Coverage and matrix deposition by ECFCs was limited. However, ECFCs lined the ECM formed by MSCs in coculture, visualised via immunostaining. Thus, of cells investigated, placental MSCs were identified as the preferred cell source for the fabrication of tissue-engineered constructs, exhibiting extensive population of porous polymer scaffolds and production of ECM components; with the inclusion of ECFCs for luminal endothelialisation, an encouraging outcome warranting further consideration in future studies. In combination, these findings represent a substantial step toward the development of the next generation of small-diameter vascular grafts in the management of cardiovascular disease.

Antimicrobial Properties of Newly Developed Silver-Enriched Red Onion-Polymer Composites

Simple low-cost, nontoxic, environmentally friendly plant-extract-based polymer films play an important role in their application in medicine, the food industry, and agriculture. The addition of silver nanoparticles to the composition of these films enhances their antimicrobial capabilities and makes them suitable for the treatment and prevention of infections. In this study, polymer-based gels and films (AgRonPVA) containing silver nanoparticles (AgNPs) were produced at room temperature from fresh red onion peel extract ("Ron"), silver nitrate, and polyvinyl alcohol (PVA). Silver nanoparticles were synthesized directly in a polymer matrix, which was irradiated by UV light. The presence of nanoparticles was approved by analyzing characteristic local surface plasmon resonance peaks occurring in UV-Vis absorbance spectra of irradiated experimental samples. The proof of evidence was supported by the results of XRD and EDX measurements. The diffusion-based method was applied to investigate the antimicrobial activity of several types of microbes located in the environment of the produced samples. Bacteria Staphylococcus aureus ATCC 29213, Acinetobacter baumannii ATCC BAA 747, and Pseudomonas aeruginosa ATCC 15442; yeasts Candida parapsilosis CBS 8836 and Candida albicans ATCC 90028; and microscopic fungi assays Aspergillus flavus BTL G-33 and Aspergillus fumigatus BTL G-38 were used in this investigation. The greatest effect was observed on Staphylococcus aureus, Acinetobacter baumannii, and Pseudomonas aeruginosa bacteria, defining these films as potential candidates for antimicrobial applications. The antimicrobial features of the films were less effective against fungi and the weakest against yeasts.

Three-dimensional printing and decellularized-extracellular-matrix based methods for advances in artificial blood vessel fabrication: A review

Blood vessels are the tubes through which blood flows and are divided into three types: millimeter-scale arteries, veins, and capillaries as well as micrometer-scale capillaries. Arteries and veins are the conduits that carry blood, while capillaries are where blood exchanges substances with tissues. Blood vessels are mainly composed of collagen fibers, elastic fibers, glycosaminoglycans and other macromolecular substances. There are about 19 feet of blood vessels per square inch of skin in the human body, which shows how important blood vessels are to the human body. Because cardiovascular disease and vascular trauma are common in the population, a great number of researches have been carried out in recent years by simulating the structures and functions of the person's own blood vessels to create different levels of tissue-engineered blood vessels that can replace damaged blood vessels in the human body. However, due to the lack of effective oxygen and nutrient delivery mechanisms, these tissue-engineered vessels have not been used clinically. Therefore, in order to achieve better vascularization of engineered vascular tissue, researchers have widely explored the design methods of vascular systems of various sizes. In the near future, these carefully designed and constructed tissue engineered blood vessels are expected to have practical clinical applications. Exploring how to form multi-scale vascular networks and improve their compatibility with the host vascular system will be very beneficial in achieving this goal. Among them, 3D printing has the advantages of high precision and design flexibility, and the decellularized matrix retains active ingredients such as collagen, elastin, and glycosaminoglycan, while removing the immunogenic substance DNA. In this review, technologies and advances in 3D printing and decellularization-based artificial blood vessel manufacturing methods are systematically discussed. Recent examples of vascular systems designed are introduced in details, the main problems and challenges in the clinical application of vascular tissue restriction are discussed and pointed out, and the future development trends in the field of tissue engineered blood vessels are also prospected.

Acellular carotid scaffold and evaluation the biological and biomechanical properties for tissue engineering

Introduction

The issues associated with the limitation of appropriate autologous vessels for vascular reconstruction via bypass surgery highlight the need for new alternative strategies based on tissue engineering. The present study aimed to prepare decellularized scaffolds from ovine carotid using chemical decellularization method.

Methods

Ovine carotid were decellularized with Triton X-100 and tri-n-butyl phosphate (TnBP) at 37 °C. Histological analysis, biochemical tests, biomechanical assay and biocompatibility assay were used to investigate the efficacy of decellularization.

Results

Decellularization method could successfully decellularize ovine carotid without leaving any cell remnants. Scaffolds showed minimal destruction of the three-dimensional structure and extracellular matrix, as well as adequate mechanical resistance and biocompatibility for cell growth and proliferation.

Conclusion

Prepared acellular scaffold exhibited the necessary characteristics for clinical applications.

Progress in cardiac tissue engineering and regeneration: Implications of gelatin-based hybrid scaffolds

Cardiovascular diseases, particularly myocardial infarction (MI), remain a leading cause of morbidity and mortality worldwide. Current treatments for MI, more palliative than curative, have limitations in reversing the disease completely. Tissue engineering (TE) has emerged as a promising strategy to address this challenge and may lead to improved therapeutic approaches for MI. Gelatin-based scaffolds, including gelatin and its derivative, gelatin methacrylate (GelMA), have attracted significant attention in cardiac tissue engineering (CTE) due to their optimal physical and biochemical properties and capacity to mimic the native extracellular matrix (ECM). CTE mainly recruits two classes of gelatin/GelMA-based scaffolds: hydrogels and nanofibrous. This article reviews state-of-the-art gelatin/GelMA-based hybrid scaffolds currently applied for CTE and regenerative therapy. Hybrid scaffolds, fabricated by combining gelatin/GelMA hydrogel or nanofibrous scaffolds with other materials such as natural/synthetic polymers, nanoparticles, protein-based biomaterials, etc., are explored for enhanced cardiac tissue regeneration functionality. The engraftment of stem/cardiac cells, bioactive molecules, or drugs into these hybrid systems shows great promise in cardiac tissue repair and regeneration. Finally, the role of gelatin/GelMA scaffolds combined with the 3D bioprinting strategy in CTE will also be briefly highlighted.

Polymeric reinforcements for cellularized collagen-based vascular wall models: influence of the scaffold architecture on the mechanical and biological properties

A previously developed cellularized collagen-based vascular wall model showed promising results in mimicking the biological properties of a native vessel but lacked appropriate mechanical properties. In this work, we aim to improve this collagen-based model by reinforcing it using a tubular polymeric (reinforcement) scaffold. The polymeric reinforcements were fabricated exploiting commercial poly (ε-caprolactone) (PCL), a polymer already used to fabricate other FDA-approved and commercially available devices serving medical applications, through 1) solution electrospinning (SES), 2) 3D printing (3DP) and 3) melt electrowriting (MEW). The non-reinforced cellularized collagen-based model was used as a reference (COL). The effect of the scaffold's architecture on the resulting mechanical and biological properties of the reinforced collagen-based model were evaluated. SEM imaging showed the differences in scaffolds' architecture (fiber alignment, fiber diameter and pore size) at both the micro- and the macrolevel. The polymeric scaffold led to significantly improved mechanical properties for the reinforced collagen-based model (initial elastic moduli of 382.05 ± 132.01 kPa, 100.59 ± 31.15 kPa and 245.78 ± 33.54 kPa, respectively for SES, 3DP and MEW at day 7 of maturation) compared to the non-reinforced collagen-based model (16.63 ± 5.69 kPa). Moreover, on day 7, the developed collagen gels showed stresses (for strains between 20% and 55%) in the range of [5-15] kPa for COL, [80-350] kPa for SES, [20-70] kPa for 3DP and [100-190] kPa for MEW. In addition to the effect on the resulting mechanical properties, the polymeric tubes' architecture influenced cell behavior, in terms of proliferation and attachment, along with collagen gel compaction and extracellular matrix protein expression. The MEW reinforcement resulted in a collagen gel compaction similar to the COL reference, whereas 3DP and SES led to thinner and longer collagen gels. Overall, it can be concluded that 1) the selected processing technique influences the scaffolds' architecture, which in turn influences the resulting mechanical and biological properties, and 2) the incorporation of a polymeric reinforcement leads to mechanical properties closely matching those of native arteries.

Strategies for Anisotropic Fibrillar Hydrogels: Design, Cell Alignment, and Applications in Tissue Engineering

Efficient cellular alignment in biomaterials presents a considerable challenge, demanding the refinement of appropriate material morphologies, while ensuring effective cell-surface interactions. To address this, biomaterials are continuously researched with diverse coatings, hydrogels, and polymeric surfaces. In this context, we investigate the influence of physicochemical parameters on the architecture of fibrillar hydrogels that significantly orient the topography of flexible hydrogel substrates, thereby fostering cellular adhesion and spatial organization. Our Review comprehensively assesses various techniques for aligning polymer fibrils within hydrogels, specifically interventions applied during and after the cross-linking process. These methodologies include mechanical strains, precise temperature modulation, controlled fluidic dynamics, and chemical modulators, as well as the use of magnetic and electric fields. We highlight the intrinsic appeal of these methodologies in fabricating cell-aligning interfaces and discuss their potential implications within the fields of biomaterials and tissue engineering, particularly concerning the pursuit of optimal cellular alignment.

Effect of adipose-derived stem cells seeding and surgical prefabrication on composite scaffold vascularization

The study aimed to evaluate an angiogenic effect of adipose-derived stem cells (ASCs) seeding and surgical prefabrication (placing a vascular pedicle inside the scaffold) on developed composite scaffolds made of poly-ε-caprolactone (PCL), β-tricalcium phosphate (β-TCP), and poly (lactic-co-glycolic acid) (PLGA) (PCL+β-TCP+PLGA). Moreover, we aimed to compare our data with previously tested PCL scaffolds to assess whether the new material has better angiogenic properties. The study included 18 inbred male WAG rats. There were three scaffold groups (six animals each): with non-seeded PCL+β-TCP+PLGA scaffolds, with PCL+β-TCP+PLGA scaffolds seeded with ASCs and with PCL+β-TCP+PLGA scaffolds seeded with ASCs and osteogenic-induced. Each rat was implanted with two scaffolds in the inguinal region (one prefabricated and one non-prefabricated). After 2 months from implantation, the scaffolds were explanted, and vessel density was determined by histopathological examination. Prefabricated ASC-seeded PCL+β-TCP+PLGA scaffolds promoted greater vessel formation than non-seeded scaffolds (19.73 ± 5.46 vs 12.54 ± 0.81; p = .006) and those seeded with osteogenic-induced ASCs (19.73 ± 5.46 vs 11.87±2.21; p = .004). The developed composite scaffold promotes vessel formation more effectively than the previously described PCL scaffold.

Bacterial Nanocellulose Hydrogel: A Promising Alternative Material for the Fabrication of Engineered Vascular Grafts

Blood vessels are crucial in the human body, providing essential nutrients to all tissues while facilitating waste removal. As the incidence of cardiovascular disease rises, the demand for efficient treatments increases concurrently. Currently, the predominant interventions for cardiovascular disease are autografts and allografts. Although effective, they present limitations including high costs and inconsistent success rates. Recently, synthetic vascular grafts, made from artificial materials, have emerged as promising alternatives to traditional methods. Among these materials, bacterial cellulose hydrogel exhibits significant potential for tissue engineering applications, particularly in developing nanoscale platforms that regulate cell behavior and promote tissue regeneration, attributed to its notable physicochemical and biocompatible properties. This study reviews recent progress in fabricating engineered vascular grafts using bacterial nanocellulose, demonstrating the efficacy of bacterial cellulose hydrogel as a biomaterial for synthetic vascular grafts, specifically for stimulating angiogenesis and neovascularization.

Recent advances in modified poly (lactic acid) as tissue engineering materials

As an emerging science, tissue engineering and regenerative medicine focus on developing materials to replace, restore or improve organs or tissues and enhancing the cellular capacity to proliferate, migrate and differentiate into different cell types and specific tissues. Renewable resources have been used to develop new materials, resulting in attempts to produce various environmentally friendly biomaterials. Poly (lactic acid) (PLA) is a biopolymer known to be biodegradable and it is produced from the fermentation of carbohydrates. PLA can be combined with other polymers to produce new biomaterials with suitable physicochemical properties for tissue engineering applications. Here, the advances in modified PLA as tissue engineering materials are discussed in light of its drawbacks, such as biological inertness, low cell adhesion, and low degradation rate, and the efforts conducted to address these challenges toward the design of new enhanced alternative biomaterials.

The Application of Porous Scaffolds for Cardiovascular Tissues

As the number of arteriosclerotic diseases continues to increase, much improvement is still needed with treatments for cardiovascular diseases. This is mainly due to the limitations of currently existing treatment options, including the limited number of donor organs available or the long-term durability of the artificial organs. Therefore, tissue engineering has attracted significant attention as a tissue regeneration therapy in this area. Porous scaffolds are one of the effective methods for tissue engineering. However, it could be better, and its effectiveness varies depending on the tissue application. This paper will address the challenges presented by various materials and their combinations. We will also describe some of the latest methods for tissue engineering.

Fibrinogen-based cell and spheroid sheets manipulating and delivery for mouse hindlimb ischemia

In this research, we introduced a novel strategy for fabricating cell sheets (CSs) prepared by simply adding a fibrinogen solution to growth medium without using any synthetic polymers or chemical agents. We confirmed that the fibrinogen-based CS could be modified for target tissue regardless of size, shape, and cell types. Also, fibrinogen-based CSs were versatile and could be used to form three-dimensional (3D) CSs such as multi-layered CSs and those mimicking native blood vessels. We also prepared fibrinogen-based spheroid sheets for the treatment of ischemic disease. The fibrinogen-based spheroid sheets had much higherin vitrotubule formation and released more angiogenic factors compared to other types of platform in this research. We transplanted fibrinogen-based spheroid sheets into a mouse hindlimb ischemia model and found that fibrinogen-based spheroid sheets showed significantly improved physiological function and blood perfusion rates compared to the other types of platform in this research.

3D-bioprinted, phototunable hydrogel models for studying adventitial fibroblast activation in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease of the lung vasculature, characterized by elevated pulmonary blood pressure, remodeling of the pulmonary arteries, and ultimately right ventricular failure. Therapeutic interventions for PAH are limited in part by the lack ofin vitroscreening platforms that accurately reproduce dynamic arterial wall mechanical properties. Here we present a 3D-bioprinted model of the pulmonary arterial adventitia comprised of a phototunable poly(ethylene glycol) alpha methacrylate (PEG-αMA)-based hydrogel and primary human pulmonary artery adventitia fibroblasts (HPAAFs). This unique biomaterial emulates PAH pathogenesisin vitrothrough a two-step polymerization reaction. First, PEG-αMA macromer was crosslinked off-stoichiometry by 3D bioprinting an acidic bioink solution into a basic gelatin support bath initiating a base-catalyzed thiol-ene reaction with synthetic and biodegradable crosslinkers. Then, matrix stiffening was induced by photoinitiated homopolymerization of unreacted αMA end groups. A design of experiments approach produced a hydrogel platform that exhibited an initial elastic modulus (E) within the range of healthy pulmonary arterial tissue (E= 4.7 ± 0.09 kPa) that was stiffened to the pathologic range of hypertensive tissue (E= 12.8 ± 0.47 kPa) and supported cellular proliferation over time. A higher percentage of HPAAFs cultured in stiffened hydrogels expressed the fibrotic marker alpha-smooth muscle actin than cells in soft hydrogels (88 ± 2% versus 65 ± 4%). Likewise, a greater percentage of HPAAFs were positive for the proliferation marker 5-ethynyl-2'-deoxyuridine (EdU) in stiffened models (66 ± 6%) compared to soft (39 ± 6%). These results demonstrate that 3D-bioprinted, phototunable models of pulmonary artery adventitia are a tool that enable investigation of fibrotic pathogenesisin vitro.

Advances in the development of tubular structures using extrusion-based 3D cell-printing technology for vascular tissue regenerative applications

Until recent, there are no ideal small diameter vascular grafts available on the market. Most of the commercialized vascular grafts are used for medium to large-sized blood vessels. As a solution, vascular tissue engineering has been introduced and shown promising outcomes. Despite these optimistic results, there are limitations to commercialization. This review will cover the need for extrusion-based 3D cell-printing technique capable of mimicking the natural structure of the blood vessel. First, we will highlight the physiological structure of the blood vessel as well as the requirements for an ideal vascular graft. Then, the essential factors of 3D cell-printing including bioink, and cell-printing system will be discussed. Afterwards, we will mention their applications in the fabrication of tissue engineered vascular grafts. Finally, conclusions and future perspectives will be discussed.

In Vitro Differentiation of Myoblast Cell Lines on Spider Silk Scaffolds in a Rotating Bioreactor for Vascular Tissue Engineering

Functional construction of tissue-engineered vessels as an alternative to autologous vascular grafts has been shown to be feasible, however the proliferation of seeded smooth-muscle cells remains a limiting factor. We employed a rotating bioreactor system to improve myoblast cell differentiation on a spider silk scaffold for tissue-engineered vessel construction. C2C12 myofibroblast cells were seeded on the surface of spider silk scaffold constructs and cultivated in a rotating bioreactor system with a continuous rotation speed (1 rpm). Cell function, cell growth and morphological structure and expression of biomarkers were analyzed using scanning electron microscopy, the LIVE/DEAD^® assay, Western blot and quantitative real-time PCR analyses. A dense myofibroblast cell sheet could be developed which resembled native blood vessel muscular tissue in morphological structure and in function. Bioreactor perfusion positively affected cell morphology, and increased cell viability and cell differentiation. The expression of desmin, MYF5 and MEF2D surged as an indication of myoblast differentiation. Cell-seeded scaffolds showed a tear-down at 18 N when strained at a set speed (20 mm min^-1). Spider silk scaffolds appear to offer a reliable basis for engineered vascular constructs and rotating bioreactor cultivation may be considered an effective alternative to complex bioreactor setups to improve cell viability and biology.

An Investigation of the Constructional Design Components Affecting the Mechanical Response and Cellular Activity of Electrospun Vascular Grafts

Cardiovascular disease is anticipated to remain the leading cause of death globally. Due to the current problems connected with using autologous arteries for bypass surgery, researchers are developing tissue-engineered vascular grafts (TEVGs). The major goal of vascular tissue engineering is to construct prostheses that closely resemble native blood vessels in terms of morphological, mechanical, and biological features so that these scaffolds can satisfy the functional requirements of the native tissue. In this setting, morphology and cellular investigation are usually prioritized, while mechanical qualities are generally addressed superficially. However, producing grafts with good mechanical properties similar to native vessels is crucial for enhancing the clinical performance of vascular grafts, exposing physiological forces, and preventing graft failure caused by intimal hyperplasia, thrombosis, aneurysm, blood leakage, and occlusion. The scaffold's design and composition play a significant role in determining its mechanical characteristics, including suturability, compliance, tensile strength, burst pressure, and blood permeability. Electrospun prostheses offer various models that can be customized to resemble the extracellular matrix. This review aims to provide a comprehensive and comparative review of recent studies on the mechanical properties of fibrous vascular grafts, emphasizing the influence of structural parameters on mechanical behavior. Additionally, this review provides an overview of permeability and cell growth in electrospun membranes for vascular grafts. This work intends to shed light on the design parameters required to maintain the mechanical stability of vascular grafts placed in the body to produce a temporary backbone and to be biodegraded when necessary, allowing an autologous vessel to take its place.

Evaluation of perfusion-driven cell seeding of small diameter engineered tissue vascular grafts with a custom-designed seed-and-culture bioreactor

Tissue engineering commonly entails combining autologous cell sources with biocompatible scaffolds for the replacement of damaged tissues in the body. Scaffolds provide functional support while also providing an ideal environment for the growth of new tissues until host integration is complete. To expedite tissue development, cells need to be distributed evenly within the scaffold. For scaffolds with a small diameter tubular geometry, like those used for vascular tissue engineering, seeding cells evenly along the luminal surface can be especially challenging. Perfusion-based cell seeding methods have been shown to promote increased uniformity in initial cell distribution onto porous scaffolds for a variety of tissue engineering applications. We investigate the seeding efficiency of a custom-designed perfusion-based seed-and-culture bioreactor through comparisons to a static injection counterpart method and a more traditional drip seeding method. Murine vascular smooth muscle cells were seeded onto porous tubular electrospun polycaprolactone scaffolds, 2 mm in diameter and 30 mm in length, using the three methods, and allowed to rest for 24 hours. Once harvested, scaffolds were evaluated longitudinally and circumferentially to assess the presence of viable cells using alamarBlue and live/dead cell assays and their distribution with immunohistochemistry and scanning electron microscopy. On average, bioreactor-mediated perfusion seeding achieved 35% more luminal surface coverage when compared to static methods. Viability assessment demonstrated that the total number of viable cells achieved across methods was comparable with slight advantage to the bioreactor-mediated perfusion-seeding method. The method described is a simple, low-cost method to consistently obtain even distribution of seeded cells onto the luminal surfaces of small diameter tubular scaffolds.

Biofabrication of Collagen Tissue-Engineered Blood Vessels with Direct Co-Axial Extrusion

Cardiovascular diseases are considered one of the worldwide causes of death, with atherosclerosis being the most predominant. Nowadays, the gold standard treatment is blood vessel replacement by bypass surgery; however, autologous source is not always possible. Thereby, tissue-engineered blood vessels (TEBVs) are emerging as a potential alternative source. In terms of composition, collagen has been selected in many occasions to develop TEBVs as it is one of the main extracellular matrix components of arteries. However, it requires specific support or additional processing to maintain the tubular structure and appropriate mechanical properties. Here, we present a method to develop support-free collagen TEBVs with co-axial extrusion in a one-step procedure with high concentrated collagen. The highest concentration of collagen of 20 mg/mL presented a burst pressure of 619.55 ± 48.77 mmHg, being able to withstand perfusion of 10 dynes/cm². Viability results showed a high percentage of viability (86.1 and 85.8% with 10 and 20 mg/mL, respectively) of human aortic smooth muscle cells (HASMCs) and human umbilical vein endothelial cells (HUVEC) after 24 h extrusion. Additionally, HUVEC and HASMCs were mainly localized in their respective layers, mimicking the native distribution. All in all, this approach allows the direct extrusion of collagen TEBVs in a one-step procedure with enough mechanical properties to be perfused.

A critical review of fibrous polyurethane-based vascular tissue engineering scaffolds

Certain polymeric materials such as polyurethanes (PUs) are the most prevalent class of used biomaterials in regenerative medicine and have been widely explored as vascular substitutes in several animal models. It is thought that PU-based biomaterials possess suitable hemo-compatibility with comparable performance related to the normal blood vessels. Despite these advantages, the possibility of thrombus formation and restenosis limits their application as artificial functional vessels. In this regard, various surface modification approaches have been developed to enhance both hemo-compatibility and prolong patency. While critically reviewing the recent advances in vascular tissue engineering, mainly PU grafts, this paper summarizes the application of preferred cell sources to vascular regeneration, physicochemical properties, and some possible degradation mechanisms of PU to provide a more extensive perspective for future research.

Current Progress in Vascular Engineering and Its Clinical Applications

Coronary heart disease (CHD) is caused by narrowing or blockage of coronary arteries due to atherosclerosis. Coronary artery bypass grafting (CABG) is widely used for the treatment of severe CHD cases. Although autologous vessels are a preferred choice, healthy autologous vessels are not always available; hence there is a demand for tissue engineered vascular grafts (TEVGs) to be used as alternatives. However, producing clinical grade implantable TEVGs that could healthily survive in the host with long-term patency is still a great challenge. There are additional difficulties in producing small diameter (<6 mm) vascular conduits. As a result, there have not been TEVGs that are commercially available. Properties of vascular scaffolds such as tensile strength, thrombogenicity and immunogenicity are key factors that determine the biocompatibility of TEVGs. The source of vascular cells employed to produce TEVGs is a limiting factor for large-scale productions. Advanced technologies including the combined use of natural and biodegradable synthetic materials for scaffolds in conjunction with the use of mesenchyme stem cells or induced pluripotent stem cells (iPSCs) provide promising solutions for vascular tissue engineering. The aim of this review is to provide an update on various aspects in this field and the current status of TEVG clinical applications.

Quantification of adhesion of mesenchymal stem cells spread on decellularized vein scaffold

Purpose:

To evaluate methods that improve adipose-derived stem cells (ASCs) population in decellularized biological venous scaffold for tissue engineering in blood vessels, a model in rabbits.

Methods:

The ASC was expanded until the third passage. Inferior vena cava (IVC) was submitted to the decellularization process using 1% sodium dodecyl sulfate (SDS) or 2% sodium deoxycholate (SD) to compose 12 study groups (G): pure SD or SDS, exposed or not to 1% TritonX-100 (TX-100) and exposed or not to poly-l’lysine and laminin (PL). Scaffolds were covered with 1 × 10⁵ or 1 × 10⁶ ASCs diluted in 10 μL Puramatrix™. The histological analysis was done by cell counting in hematoxylin and eosin (HE) and nuclei count in immunofluorescence (IF) with 4’,6-Diamidine-2’-phenylindole dihydrochloride (DAPI).

Results:

The study of groups in HE and IF showed similar results. For both analyses,IVC-SD-1 × 10⁶ ASC and IVC-SD-PL-1 × 10⁶ ASC provided the best results. The IF technique showed better sensitivity than HE, with a weak agreement between them.

Conclusions:

Decellularizing agent and the number of ASC influence scaffolds cellularization response and the best protocols as those ones using SD with or without the addition of PL.

Bioprinting Scaffolds for Vascular Tissues and Tissue Vascularization

In recent years, tissue engineering has achieved significant advancements towards the repair of damaged tissues. Until this day, the vascularization of engineered tissues remains a challenge to the development of large-scale artificial tissue. Recent breakthroughs in biomaterials and three-dimensional (3D) printing have made it possible to manipulate two or more biomaterials with complementary mechanical and/or biological properties to create hybrid scaffolds that imitate natural tissues. Hydrogels have become essential biomaterials due to their tissue-like physical properties and their ability to include living cells and/or biological molecules. Furthermore, 3D printing, such as dispensing-based bioprinting, has progressed to the point where it can now be utilized to construct hybrid scaffolds with intricate structures. Current bioprinting approaches are still challenged by the need for the necessary biomimetic nano-resolution in combination with bioactive spatiotemporal signals. Moreover, the intricacies of multi-material bioprinting and hydrogel synthesis also pose a challenge to the construction of hybrid scaffolds. This manuscript presents a brief review of scaffold bioprinting to create vascularized tissues, covering the key features of vascular systems, scaffold-based bioprinting methods, and the materials and cell sources used. We will also present examples and discuss current limitations and potential future directions of the technology.

A rapid quantitation of cell attachment and spreading based on digital image analysis: Application for cell affinity and compatibility assessment of synthetic polymers

Accurate and rapid quantitation of cell attachment, spreading, and growth on a polymer thin film coated glass cover slide was developed by analyzing the digital images of cells stained with dyes. A biodegradable block copolymer poly(ethylene glycol)-block-poly(l-lactide-co-2-methyl-2-carboxyl-propylene carbonate) [PEG-b-P(LA-co-MCC)] was synthesized as model polymer with poly(L-lactic acid) [PLLA] as a control polymer. Only a small quantity of polymer (~5 mg) was needed in this method through dissolving in a solvent and casting on cover slides which were previously modified with dimethyl dichlorosilane (DMDC). Then it was seeded with cells and taken pictures with a digital camera under an optical microscope and analyzed with ImageJ software. Cell number and a series of morphological data were obtained, including cell area, circularity, perimeter and Feret's diameter, etc. The quantitative analysis results indicated that cells preferred to attach and spread on the surface of the copolymer PEG-b-P(LA-co-MCC) compared to PLLA during 24 h of cell culture. This efficient procedure provides a series of convincing statistical data to evaluate the direct interaction between cells and polymers with only an optical microscope, a digital camera and ImageJ software. It's a rapid, economic way for assessing cell affinity and compatibility of novel synthetic polymers by cell culture in vitro.

Gelatin-Polyvinyl Alcohol Film for Tissue Engineering: A Concise Review

The field of biomaterials has been steadily expanding as a large number of pharmaceutical and manufacturing companies invest in research in order to commercialize biomaterial products. Various three-dimensional biomaterials have been explored including film, hydrogel, sponge, microspheres etc., depending on different applications. Thus, gelatin and polyvinyl alcohol (PVA) are widely used as a natural- and synthetic-based biomaterial, respectively, for tissue engineering and clinical settings. The combination of these materials has proven its synergistic effects in wound-healing applications. Therefore, this review aims to highlight the hybrid gelatin and PVA thin film development and evaluate its potential characteristics for tissue engineering applications from existing published evidence (within year 2010–2020). The primary key factor for polymers mixing technology might improve the quality and the efficacy of the intended polymers. This review provides a concise overview of the current knowledge for hybrid gelatin and PVA with the method of fabricating and mixing technology into thin films. Additionally, the findings guided to an optimal fabrication method and scrutinised characterisation parameters of fabricated gelatin-PVA thin film. In conclusion, hybrid gelatin-PVA thin film has higher potential as a treatment for various biomedical and clinical applications.

Recent advancements in the bioprinting of vascular grafts

Recent advancements in the bioinks and three-dimensional (3D) bioprinting methods used to fabricate vascular constructs are summarized herein. Critical biomechanical properties required to fabricate an ideal vascular graft are highlighted, as well as various testing methods have been outlined to evaluate the bio-fabricated grafts as per the Food and Drug Administration (FDA) and International Organization for Standardization (ISO) guidelines. Occlusive artery disease and cardiovascular disease are the major causes of death globally. These diseases are caused by the blockage in the arteries, which results in a decreased blood flow to the tissues of major organs in the body, such as the heart. Bypass surgery is often performed using a vascular graft to re-route the blood flow. Autologous grafts represent a gold standard for such bypass surgeries; however, these grafts may be unavailable due to the previous harvesting or possess a poor quality. Synthetic grafts serve well for medium to large-sized vessels, but they fail when used to replace small-diameter vessels, generally smaller than 6 mm. Various tissue engineering approaches have been used to address the urgent need for vascular graft that can withstand hemodynamic blood pressure and has the ability to grow and remodel. Among these approaches, 3D bioprinting offers an attractive solution to construct patient-specific vessel grafts with layered biomimetic structures.

4D Printing of Shape Memory Vascular Stent Based on βCD-g-Polycaprolactone

The 4D-printing technology is applied to fabricate a shape memory peripheral stent with good biocompatibility, which sustains long-term drug release. The star polymer s-PCL is prepared by ring opening polymerization of ε-caprolactone with the -OH of β-cyclodextrin (βCD) as initiator, and then the s-PCL is modified with acrylate endgroup which allows the polymerization under UV light to form the crosslinking network c-PCL. Attributed to the feature of the high crosslinked structure and chemical nature of polycaprolactone (PCL) and βCD, the composite exhibits appropriate tensile strength and sufficient elasticity and bursting pressure, and it is comparable with great saphenous vein in human body. The radial support of the 4D-printed stent is 0.56 ± 0.11 N and is equivalent to that of commercial stent. The cell adhesion and proliferation results show a good biocompatibility of the stent with human umbilical vein endothelial cells. Due to the presence of βCD, the wettability and biocompatibility of the materials are improved, and the sustained paclitaxel release based on the host-guest complexion shows the potential of the drug-loaded stent for long-term release. This study provides a new strategy to solve the urgent need of small-diameter scaffolds to treat critical limb ischemia.

Use of the ligamentum teres hepatis for outflow reconstruction during ex vivo liver resection and autotransplantation in patients with hepatic alveolar echinococcosis: A case series of 24 patients

BACKGROUND

Patients with extensive hepatic alveolar echinococcosis might require ex vivo liver resection and autotransplantation to remove the lesion. Patients with extensive vascular invasion will need reconstruction, but the selection of the proper graft is complicated. This study aimed to investigate the effectiveness and adverse events of using the ligamentum teres hepatis as a vascular replacement graft in ex vivo liver resection and autotransplantation.

METHODS

This was a retrospective case series of patients with hepatic alveolar echinococcosis who underwent ex vivo liver resection and autotransplantation between August 2010 and October 2018 and in whom the ligamentum teres hepatis was used to repair the remnant liver. The operative outcomes, recurrence, and survival were examined.

RESULTS

Twenty-four patients were included (10 men, 14 women). The anhepatic period was 290 to 672 minutes (median of 450 minutes). The ratio of the remnant liver volume to the standard liver volume was 0.43 to 0.97 (median of 0.71). The blood loss was 1,000 (500-5,000) mL. The postoperative hospital stay was 23 (1-85) days. Of the 24 patients, 3 died after the operation, but those deaths were unrelated to liver vascular complications.

CONCLUSION

The ligamentum teres hepatis could be used as a vascular replacement graft in ex vivo liver resection and autotransplantation. It has the advantages of convenient specimen extraction, no donor site injury, and no immunological rejection, which has promising clinical application prospects.

Rebuilding the Vascular Network: In vivo and in vitro Approaches

As the material transportation system of the human body, the vascular network carries the transportation of materials and nutrients. Currently, the construction of functional microvascular networks is an urgent requirement for the development of regenerative medicine and in vitro drug screening systems. How to construct organs with functional blood vessels is the focus and challenge of tissue engineering research. Here in this review article, we first introduced the basic characteristics of blood vessels in the body and the mechanism of angiogenesis in vivo, summarized the current methods of constructing tissue blood vessels in vitro and in vivo, and focused on comparing the functions, applications and advantages of constructing different types of vascular chips to generate blood vessels. Finally, the challenges and opportunities faced by the development of this field were discussed.

Applications of Biocompatible Scaffold Materials in Stem Cell-Based Cartilage Tissue Engineering

Cartilage, especially articular cartilage, is a unique connective tissue consisting of chondrocytes and cartilage matrix that covers the surface of joints. It plays a critical role in maintaining joint durability and mobility by providing nearly frictionless articulation for mechanical load transmission between joints. Damage to the articular cartilage frequently results from sport-related injuries, systemic diseases, degeneration, trauma, or tumors. Failure to treat impaired cartilage may lead to osteoarthritis, affecting more than 25% of the adult population globally. Articular cartilage has a very low intrinsic self-repair capacity due to the limited proliferative ability of adult chondrocytes, lack of vascularization and innervation, slow matrix turnover, and low supply of progenitor cells. Furthermore, articular chondrocytes are encapsulated in low-nutrient, low-oxygen environment. While cartilage restoration techniques such as osteochondral transplantation, autologous chondrocyte implantation (ACI), and microfracture have been used to repair certain cartilage defects, the clinical outcomes are often mixed and undesirable. Cartilage tissue engineering (CTE) may hold promise to facilitate cartilage repair. Ideally, the prerequisites for successful CTE should include the use of effective chondrogenic factors, an ample supply of chondrogenic progenitors, and the employment of cell-friendly, biocompatible scaffold materials. Significant progress has been made on the above three fronts in past decade, which has been further facilitated by the advent of 3D bio-printing. In this review, we briefly discuss potential sources of chondrogenic progenitors. We then primarily focus on currently available chondrocyte-friendly scaffold materials, along with 3D bioprinting techniques, for their potential roles in effective CTE. It is hoped that this review will serve as a primer to bring cartilage biologists, synthetic chemists, biomechanical engineers, and 3D-bioprinting technologists together to expedite CTE process for eventual clinical applications.

Healthy and diseased in vitro models of vascular systems

Irregular hemodynamics affects the progression of various vascular diseases, such atherosclerosis or aneurysms. Despite the extensive hemodynamics studies on animal models, the inter-species differences between humans and animals hamper the translation of such findings. Recent advances in vascular tissue engineering and the suitability of in vitro models for interim analysis have increased the use of in vitro human vascular tissue models. Although the effect of flow on endothelial cell (EC) pathophysiology and EC-flow interactions have been vastly studied in two-dimensional systems, they cannot be used to understand the effect of other micro- and macro-environmental parameters associated with vessel wall diseases. To generate an ideal in vitro model of the vascular system, essential criteria should be included: 1) the presence of smooth muscle cells or perivascular cells underneath an EC monolayer, 2) an elastic mechanical response of tissue to pulsatile flow pressure, 3) flow conditions that accurately mimic the hemodynamics of diseases, and 4) geometrical features required for pathophysiological flow. In this paper, we review currently available in vitro models that include flow dynamics and discuss studies that have tried to address the criteria mentioned above. Finally, we critically review in vitro fluidic models of atherosclerosis, aneurysm, and thrombosis.

Lymphatic Tissue Engineering: A Further Step for Successful Lymphedema Treatment

BACKGROUND

 Secondary lymphedema, caused by oncologic surgery, radiation, and chemotherapy, is one of the most relevant, nononcological complications affecting cancer survivors. Severe functional deficits can result in impairing quality of life and a societal burden related to increased treatment costs. Often, conservative treatments are not sufficient to alleviate lymphedema or to prevent stage progression of the disease, as they do not address the underlying etiology that is the disruption of lymphatic pathways. In recent years, lymphatic surgery approaches were revolutionized by advances in microsurgical technique. Currently, lymphedema can effectively be treated by procedures such as lymphovenous anastomosis (LVA) and lymph node transfer (LNT). However, not all patients have suitable lymphatic vessels, and lymph node harvesting is associated with risks. In addition, some data have revealed nonresponders to the microsurgical techniques.

METHODS

 A literature review was performed to evaluate the value of lymphatic tissue engineering for plastic surgeons and to give an overview of the achievements, challenges, and goals of the field.

RESULTS

 While certain challenges exist, including cell harvesting, nutrient supply, biocompatibility, and hydrostatic properties, it is possible and desirable to engineer lymph nodes and lymphatic vessels. The path toward clinical translation is considered more complex for LNTs secondary to the complex microarchitecture and pending final mechanistic clarification, while LVA is more straight forward.

CONCLUSION

 Lymphatic tissue engineering has the potential to be the next step for microsurgical treatment of secondary lymphedema. Current and future researches are necessary to optimize this clinical paradigm shift for improved surgical treatment of lymphedema.

Designed and fabrication of triple-layered vascular scaffold with microchannels

Currently, one of the best preparation strategies for the triple-layered vascular scaffold is to imitate the three-layer structure of natural blood vessels to achieve the biofunctional characteristics of vascular transplantation. Here, we developed a combinatorial method to fabricate triple-layered vascular scaffold (TVS) by using electrospinning and coaxial 3 D printing. First, Polycaprolactone-collagen (PCL-Col) was applied to prepared the inner layer of TVS by electrospinning. Second, egg white/sodium alginate (EW/SA) blend hydrogel was extruded to form hollow filaments by coaxial 3 D printing and crosslinking mechanism, which enwound around the surface of the inner layer in a circumferential direction as the intermediate layer of TVS. Finally, electrospun PCL-Col nanofibers were wrapped on the surface of hydrogel layer as the outer layer of TVS. The morphological characterization and mechanical strength of the fabricated TVS were measured. Compared with natural blood vessels, results shown that ultimate tensile stress (UTS), strain to failure (STF), the estimated burst strength and the suture retention strength (SRS) of TVS were superior. Also, the fabricated TVS exhibits good hydrophilicity and excellent flexibility. Moreover, the biocompatibility of TVS was investigated through human umbilical vein endothelial cells (HUVECs), the results demonstrated that cells can successfully attach the surface of graft and maintain high viability. In summary, all of results demonstrated that this method could fabricate a novel triple-layered vascular scaffold, possessing appropriate mechanical properties and good biological properties, which has the potential to be used in tissue engineered vascular grafts applications.

3D printing of tissue engineering scaffolds: a focus on vascular regeneration

Tissue engineering is an emerging means for resolving the problems of tissue repair and organ replacement in regenerative medicine. Insufficient supply of nutrients and oxygen to cells in large-scale tissues has led to the demand to prepare blood vessels. Scaffold-based tissue engineering approaches are effective methods to form new blood vessel tissues. The demand for blood vessels prompts systematic research on fabrication strategies of vascular scaffolds for tissue engineering. Recent advances in 3D printing have facilitated fabrication of vascular scaffolds, contributing to broad prospects for tissue vascularization. This review presents state of the art on modeling methods, print materials and preparation processes for fabrication of vascular scaffolds, and discusses the advantages and application fields of each method. Specially, significance and importance of scaffold-based tissue engineering for vascular regeneration are emphasized. Print materials and preparation processes are discussed in detail. And a focus is placed on preparation processes based on 3D printing technologies and traditional manufacturing technologies including casting, electrospinning, and Lego-like construction. And related studies are exemplified. Transformation of vascular scaffolds to clinical application is discussed. Also, four trends of 3D printing of tissue engineering vascular scaffolds are presented, including machine learning, near-infrared photopolymerization, 4D printing, and combination of self-assembly and 3D printing-based methods.

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

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

Future Perspectives in Small-Diameter Vascular Graft Engineering

The increased demands of small-diameter vascular grafts (SDVGs) globally has forced the scientific society to explore alternative strategies utilizing the tissue engineering approaches. Cardiovascular disease (CVD) comprises one of the most lethal groups of non-communicable disorders worldwide. It has been estimated that in Europe, the healthcare cost for the administration of CVD is more than 169 billion €. Common manifestations involve the narrowing or occlusion of blood vessels. The replacement of damaged vessels with autologous grafts represents one of the applied therapeutic approaches in CVD. However, significant drawbacks are accompanying the above procedure; therefore, the exploration of alternative vessel sources must be performed. Engineered SDVGs can be produced through the utilization of non-degradable/degradable and naturally derived materials. Decellularized vessels represent also an alternative valuable source for the development of SDVGs. In this review, a great number of SDVG engineering approaches will be highlighted. Importantly, the state-of-the-art methodologies, which are currently employed, will be comprehensively presented. A discussion summarizing the key marks and the future perspectives of SDVG engineering will be included in this review. Taking into consideration the increased number of patients with CVD, SDVG engineering may assist significantly in cardiovascular reconstructive surgery and, therefore, the overall improvement of patients' life.

Endothelial progenitor/stem cells in engineered vessels for vascular transplantation

BACKGROUND

Dysfunction of blood vessel leads to aneurysms, myocardial infarction and other thrombosis conditions. Current treatment strategies are transplantation of blood vessels from one part of the body to other dysfunction area, or allogenic, synthetic. Due to shortage of the donor, painful dissection, and lack of efficacy in synthetic, there is a need for alternative to native blood vessels for transplantation.

METHODS

Human umbilical-cord tissue obtained from the hospital with the informed consent. Umbilical-cord blood vessels were isolated for decellularization and to establish endothelial cell culture. Cultured cells were characterized by immunophenotype, gene expression and in vitro angiogenesis assay. Decellularized blood vessels were recellularized with the endothelial progenitors and Wharton jelly, CL MSCs (1:1), which was characterized by MTT, biomechanical testing, DNA content, SEM and histologically. Bioengineered vessels were transplanted into the animal models to evaluate their effect.

RESULTS

Cultured cells express CD31 and CD14 determining endothelial progenitor cells (EPCs). EPCs expresses various factors such as angiopoitin1, VWF, RANTES, VEGF, BDNF, FGF1, FGF2, HGF, IGF, GDNF, NGF, PLGF, NT3, but fail to express NT4, EGF, and CNTF. Pro and anti-inflammatory cytokine expressions were noticed. Functionally, these EPCs elicit in vitro tube formation. Negligible DNA content and intact ECM confirms the efficient decellularization of tissue. The increased MTT activity in recellularized tissue determines proliferating cells and biocompatibility of the scaffolds. Moreover, significant (P < 0.05) increase in maximum force and tensile of recellularized biomaterial as compared to the decellularized scaffolds. Integration of graft with host tissue, suggesting biocompatible therapeutic biomaterial with cells.

CONCLUSION

EPCs with stem cells in engineered blood vessels could be therapeutically applicable in vascular surgery.

Tissue engineering: from the bedside to the bench and back to the bedside

The field of Tissue Engineering and Regenerative Medicine has evolved rapidly over the past thirty years. This review will summarize its history, current status and direction through the lens of clinical need, its progress through science in the laboratory and application back into patients. We can take pride in the fact that much effort and progress began with the surgical problems of children and that many surgeons in the pediatric surgical specialties have become pioneers and investigators in this new field of science, engineering, and medicine. Although the field has yet to fulfill its great promise, there have been several examples where a therapy has progressed from the first idea to human application within a short span of time and, in many cases, it has been applied in the surgical care of children.

Electrospun polyurethane/poly (ɛ-caprolactone) nanofibers promoted the attachment and growth of human endothelial cells in static and dynamic culture conditions

In this study, the angiogenic capacity of human endothelial cells was studied after being plated on the surface of polyurethane-poly caprolactone (PU/PCL) scaffolds for 72 h. In this study, cells were designated into five different groups, including PU, PU/PCL (2:1), PU/PCL (1:1); PU/PCL (1:2); and PCL. Data revealed that the PU/PCL (2:1) composition had a higher modulus and breakpoint in comparison with the other groups (p < 0.05). Compared to the other groups, the PU/PCL scaffold with a molar ratio of 2:1 had lower the contact angle θ and higher tensile stress (p < 0.05). The mean size of the PU nanofibers was reduced after the addition of PCL (p < 0.05). Based on our data, the culture of endothelial cells on the surface of PU/PCL (2:1) did not cause nitrosative stress and cytotoxic effects under static conditions compared to cells plated on a conventional plastic surface (p > 0.05). Based on data from the static condition, we fabricated a tubular PU/PCL (2:1) construct for six-day dynamic cell culture inside loop air-lift bioreactors. Scanning electron microscopy showed the attachment of endothelial cells to the luminal surface of the PU/PCL scaffold. Cells were flattened and aligned under the culture medium flow. Immunofluorescence imaging showed the attachment of cells to the luminal surface indicated by blue nuclei on the luminal surface. These data demonstrated that the application of PU/PCL substrate could stimulate endothelial cells activity under static and dynamic conditions.

Thoracic aortic surgery: status and upcoming novelties

Several novel technological developments and surgical approaches have characterized the field of aortic surgery in the recent decade. The progressive introduction of endovascular procedures, minimally invasive surgical techniques and hybrid approaches have changed the practice in aortic surgery and generated new trends and questions. Also, the advancements in the manufacturing of tissue engineered vascular grafts as substitutes for aortic replacements are enlightening new avenues in the treatment of aortic disease. This review will provide an overview of the current novel perspectives, debates and trends in major thoracic aortic surgery.

Artificial small-diameter blood vessels: materials, fabrication, surface modification, mechanical properties, and bioactive functionalities

Cardiovascular diseases, especially ones involving narrowed or blocked blood vessels with diameters smaller than 6 millimeters, are the leading cause of death globally. Vascular grafts have been used in bypass surgery to replace damaged native blood vessels for treating severe cardio- and peripheral vascular diseases. However, autologous replacement grafts are not often available due to prior harvesting or the patient's health. Furthermore, autologous harvesting causes secondary injury to the patient at the harvest site. Therefore, artificial blood vessels have been widely investigated in the last several decades. In this review, the progress and potential outlook of small-diameter blood vessels (SDBVs) engineered in vitro are highlighted and summarized, including material selection and development, fabrication techniques, surface modification, mechanical properties, and bioactive functionalities. Several kinds of natural and synthetic polymers for artificial SDBVs are presented here. Commonly used fabrication techniques, such as extrusion and expansion, electrospinning, thermally induced phase separation (TIPS), braiding, 3D printing, hydrogel tubing, gas foaming, and a combination of these methods, are analyzed and compared. Different surface modification methods, such as physical immobilization, surface adsorption, plasma treatment, and chemical immobilization, are investigated and are compared here as well. Mechanical requirements of SDBVs are also reviewed for long-term service. In vitro biological functions of artificial blood vessels, including oxygen consumption, nitric oxide (NO) production, shear stress response, leukocyte adhesion, and anticoagulation, are also discussed. Finally, we draw conclusions regarding current challenges and attempts to identify future directions for the optimal combination of materials, fabrication methods, surface modifications, and biofunctionalities. We hope that this review can assist with the design, fabrication, and application of SDBVs engineered in vitro and promote future advancements in this emerging research field.

Pre-screening the intrinsic angiogenic capacity of biomaterials in an optimised ex ovo chorioallantoic membrane model

Biomaterial development for clinical applications is currently on the rise. This necessitates adequate in vitro testing, where the structure and composition of biomaterials must be specifically tailored to withstand in situ repair and regeneration responses for a successful clinical outcome. The chorioallantoic membrane of chicken embryos has been previously used to study angiogenesis, a prerequisite for most tissue repair and regeneration. In this study, we report an optimised ex ovo method using a glass-cling film set-up that yields increased embryo survival rates and has an improved protocol for harvesting biomaterials. Furthermore, we used this method to examine the intrinsic angiogenic capacity of a variety of biomaterials categorised as natural, synthetic, natural/synthetic and natural/natural composites with varying porosities. We detected significant differences in biomaterials' angiogenesis with natural polymers and polymers with a high overall porosity showing a greater vascularisation compared to synthetic polymers. Therefore, our proposed ex ovo chorioallantoic membrane method can be effectively used to pre-screen biomaterials intended for clinical application.

Hydrogel vehicles for sequential delivery of protein drugs to promote vascular regeneration

In recent years, as the mechanisms of vasculogenesis and angiogenesis have been uncovered, the functions of various pro-angiogenic growth factors (GFs) and cytokines have been identified. Therefore, therapeutic angiogenesis, by delivery of GFs, has been sought as a treatment for many vascular diseases. However, direct injection of these protein drugs has proven to have limited clinical success due to their short half-lives and systemic off-target effects. To overcome this, hydrogel carriers have been developed to conjugate single or multiple GFs with controllable, sustained, and localized delivery. However, these attempts have failed to account for the temporal complexity of natural angiogenic pathways, resulting in limited therapeutic effects. Recently, the emerging ideas of optimal sequential delivery of multiple GFs have been suggested to better mimic the biological processes and to enhance therapeutic angiogenesis. Incorporating sequential release into drug delivery platforms will likely promote the formation of neovasculature and generate vast therapeutic potential.

Recent advances in 3D printing: vascular network for tissue and organ regeneration

Over the past years, the fabrication of adequate vascular networks has remained the main challenge in engineering tissues due to technical difficulties, while the ultimate objective of tissue engineering is to create fully functional and sustainable organs and tissues to transplant in the human body. There have been a number of studies performed to overcome this limitation, and as a result, 3D printing has become an emerging technique to serve in a variety of applications in constructing vascular networks within tissues and organs. 3D printing incorporated technical approaches allow researchers to fabricate complex and systematic architecture of vascular networks and offer various selections for fabrication materials and printing techniques. In this review, we will discuss materials and strategies for 3D printed vascular networks as well as specific applications for certain vascularized tissue and organ regeneration. We will also address the current limitations of vascular tissue engineering and make suggestions for future directions research may take.

Collagen-Based Tissue Engineering Strategies for Vascular Medicine

Cardiovascular diseases (CVDs) account for the 31% of total death per year, making them the first cause of death in the world. Atherosclerosis is at the root of the most life-threatening CVDs. Vascular bypass/replacement surgery is the primary therapy for patients with atherosclerosis. The use of polymeric grafts for this application is still burdened by high-rate failure, mostly caused by thrombosis and neointima hyperplasia at the implantation site. As a solution for these problems, the fast re-establishment of a functional endothelial cell (EC) layer has been proposed, representing a strategy of crucial importance to reduce these adverse outcomes. Implant modifications using molecules and growth factors with the aim of speeding up the re-endothelialization process has been proposed over the last years. Collagen, by virtue of several favorable properties, has been widely studied for its application in vascular graft enrichment, mainly as a coating for vascular graft luminal surface and as a drug delivery system for the release of pro-endothelialization factors. Collagen coatings provide receptor-ligand binding sites for ECs on the graft surface and, at the same time, act as biological sealants, effectively reducing graft porosity. The development of collagen-based drug delivery systems, in which small-molecule and protein-based drugs are immobilized within a collagen scaffold in order to control their release for biomedical applications, has been widely explored. These systems help in protecting the biological activity of the loaded molecules while slowing their diffusion from collagen scaffolds, providing optimal effects on the targeted vascular cells. Moreover, collagen-based vascular tissue engineering substitutes, despite not showing yet optimal mechanical properties for their use in the therapy, have shown a high potential as physiologically relevant models for the study of cardiovascular therapeutic drugs and diseases. In this review, the current state of the art about the use of collagen-based strategies, mainly as a coating material for the functionalization of vascular graft luminal surface, as a drug delivery system for the release of pro-endothelialization factors, and as physiologically relevant in vitro vascular models, and the future trend in this field of research will be presented and discussed.