Recent advancements in the bioprinting of vascular grafts

Development and deployment of a functional 3D-bioprinted blood vessel

Creating vascular structures in vitro via bioprinting to replace damaged or missing vasculature has significant advantages over current surgical methods of vessel replacement. Using rat fibroblasts and smooth muscle cells, we have bioprinted a rat aorta using a rotating mandrel method to create the tubular replacement structure. Then, the 3D-bioprinted aortas were implanted into rats to determine their functionality long-term in vivo. The implanted vascular conduits were well-tolerated, well-incorporated into native vasculature, and showed the physiological behavior of a native vessel. The development and deployment of 3D-bioprinted vessels for repair of large vessels in an animal model paves the way for advancements in the treatment of vascular disease in humans.

A coaxial 3D bioprinted hybrid vascular scaffold based on decellularized extracellular matrix/nano clay/sodium alginate bioink

Currently, vascular grafting is the preferred option to replace or bypass the defective vascular segments, but finding materials with good biocompatibility and diversity alternative for practical clinical applications are still the challenge. The construction of tissue engineered blood vessels (TEBVs) with complex structures will be realized using 3D bioprinting technology, which provides a new idea for vascular transplantation. In this paper, the decellularized extracellular matrix (dECM)/nano clay (NC)/sodium alginate (SA) hybrid bioink was prepared to construct tubular scaffolds in vitro by coaxial 3D bioprinting. The physical properties of the tubular scaffolds showed that there were plenty of pores, of which the size was ranged from 5 μm to 100 μm. Among them, the 2d/NC/SA scaffold not only has good hydrophilicity (>300 %), good biomechanical properties (tensile strength: 0.99 ± 0.01 MPa, Young's modulus: 0.61 ± 0.02 MPa) and low hemolysis ratio (0.3 %), but also can effectively enhance cell adhesion and proliferation. Cell experiment also showed that the cell density and cell colonies were large and more on the coaxial printed tubular scaffolds compare to those on the 3D printed lamellar scaffolds, and the 2d/NC/SA tubular scaffold has the best bioactivity of tunica intima model. Overall, the advanced dECM/NC/SA tubular scaffold has a considerable potential to be applied in vascular tissue engineering.

Leveraging printability and biocompatibility in materials for printing implantable vessel scaffolds

Vessel scaffolds are crucial for treating cardiovascular diseases (CVDs). It is currently feasible to fabricate vessel scaffolds from a variety of materials using traditional fabrication methods, but the risks of thrombus formation, chronic inflammation, and atherosclerosis associated with these scaffolds have led to significant limitations in the clinical usages. Bioprinting, as an emerging technology, has great potential in constructing implantable vessel scaffolds. During the fabrication of the constructs, the biomaterials used for bioprinting have offered significant contributions for the successful fabrications of the vessel scaffolds. Herein, we review recent advances in biomaterials for bioprinting implantable vessel scaffolds. First, we briefly introduce the requirements for implantable vessel scaffolds and its conventional manufacturing methods. Next, a brief overview of the classic methods for bioprinting vessel scaffolds is presented. Subsequently, we provide an in-depth analysis of the properties of the representative natural, synthetic, composite and hybrid biomaterials that can be used for bioprinting implantable vessel scaffolds. Ultimately, we underscore the necessity of leveraging biocompatibility and printability for biomaterials, and explore the unmet needs and potential applications of these biomaterials in the field of bioprinted implantable vessel scaffolds.

Light-based 3D bioprinting techniques for illuminating the advances of vascular tissue engineering

Vascular tissue engineering faces significant challenges in creating in vitro vascular disease models, implantable vascular grafts, and vascularized tissue/organ constructs due to limitations in manufacturing precision, structural complexity, replicating the composited architecture, and mimicking the mechanical properties of natural vessels. Light-based 3D bioprinting, leveraging the unique advantages of light including high resolution, rapid curing, multi-material adaptability, and tunable photochemistry, offers transformative solutions to these obstacles. With the emergence of diverse light-based 3D bioprinting techniques and innovative strategies, the advances in vascular tissue engineering have been significantly accelerated. This review provides an overview of the human vascular system and its physiological functions, followed by an in-depth discussion of advancements in light-based 3D bioprinting, including light-dominated and light-assisted techniques. We explore the application of these technologies in vascular tissue engineering for creating in vitro vascular disease models recapitulating key pathological features, implantable blood vessel grafts, and tissue analogs with the integration of capillary-like vasculatures. Finally, we provide readers with insights into the future perspectives of light-based 3D bioprinting to revolutionize vascular tissue engineering.

Bioprinting of Cells, Organoids and Organs-on-a-Chip Together with Hydrogels Improves Structural and Mechanical Cues

The 3D bioprinting technique has made enormous progress in tissue engineering, regenerative medicine and research into diseases such as cancer. Apart from individual cells, a collection of cells, such as organoids, can be printed in combination with various hydrogels. It can be hypothesized that 3D bioprinting will even become a promising tool for mechanobiological analyses of cells, organoids and their matrix environments in highly defined and precisely structured 3D environments, in which the mechanical properties of the cell environment can be individually adjusted. Mechanical obstacles or bead markers can be integrated into bioprinted samples to analyze mechanical deformations and forces within these bioprinted constructs, such as 3D organoids, and to perform biophysical analysis in complex 3D systems, which are still not standard techniques. The review highlights the advances of 3D and 4D printing technologies in integrating mechanobiological cues so that the next step will be a detailed analysis of key future biophysical research directions in organoid generation for the development of disease model systems, tissue regeneration and drug testing from a biophysical perspective. Finally, the review highlights the combination of bioprinted hydrogels, such as pure natural or synthetic hydrogels and mixtures, with organoids, organoid-cell co-cultures, organ-on-a-chip systems and organoid-organ-on-a chip combinations and introduces the use of assembloids to determine the mutual interactions of different cell types and cell-matrix interferences in specific biological and mechanical environments.

Hybrid biofabricated blood vessel for medical devices testing

Current in vitro and in vivo tests applied to assess the safety of medical devices retain several limitations, such as an incomplete ability to faithfully recapitulate human features, and to predict the response of human tissues together with non-trivial ethical aspects. We here challenged a new hybrid biofabrication technique that combines bioprinting and Fast Diffusion-induced Gelation strategy to generate a vessel-like structure with the attempt to spatially organize fibroblasts, smooth-muscle cells, and endothelial cells. The introduction of Fast Diffusion-induced Gelation minimizes the endothelial cell mortality during biofabrication and produce a thin endothelial layer with tunable thickness. Cell viability, Von Willebrand factor, and CD31 expression were evaluated on biofabricated tissues, showing how bioprinting and Fast Diffusion-induced Gelation can replicate human vessels architecture and complexity. We then applied biofabricated tissue to study the cytotoxicity of a carbothane catheter under static condition, and to better recapitulate the effect of blood flow, a novel bioreactor named CuBiBox (Customized Biological Box) was developed and introduced in a dynamic modality. Collectively, we propose a novel bioprinted platform for human in vitro biocompatibility testing, predicting the impact of medical devices and their materials on vascular systems, reducing animal experimentation and, ultimately, accelerating time to market.

Endothelial progenitor cells for fabrication of engineered vascular units and angiogenesis induction

The promotion of vascularization and angiogenesis in the grafts is a crucial phenomenon in the healing process and tissue engineering. It has been shown that stem cells, especially endothelial progenitor cells (EPCs), can stimulate blood vessel formation inside the engineered hydrogels after being transplanted into the target sites. The incorporation of EPCs into the hydrogel can last the retention time, long-term survival, on-target delivery effects, migration and differentiation into mature endothelial cells. Despite these advantages, further modifications are mandatory to increase the dynamic growth and angiogenesis potential of EPCs in in vitro and in vivo conditions. Chemical modifications of distinct composites with distinct physical properties can yield better regenerative potential and angiogenesis during several pathologies. Here, we aimed to collect recent findings related to the application of EPCs in engineered vascular grafts and/or hydrogels for improving vascularization in the grafts. Data from the present article can help us in the application of EPCs as valid cell sources in the tissue engineering of several ischemic tissues.

Penile Replantation: A Review of Microsurgical Techniques, Patient Outcomes, and Solutions to Complex Reconstructive Challenges

Introduction: Penile amputation is a rare urological emergency with varying etiologies, ranging from psychiatric disorders to traumatic injuries, and requires precise microsurgical replantation techniques to restore function and appearance. The popularization of microsurgery has greatly improved outcomes by enabling accurate vascular and nerve reattachments, which are crucial for erectile function and sensation. This comprehensive study reviews advancements in microsurgical penile replantation, perioperative, and postoperative care, focusing on the nuances of surgical interventions and potential complications such as ischemia and necrosis. Methods: The PubMed, EMBASE, and Cochrane databases, were queried for studies published between 2015 and 2023 that discussed preoperative conditions, surgical techniques, and postoperative outcomes in penile replantation cases. Resulting studies that reported preoperative and postoperative outcomes of at least one case of penile replantation after amputation were included. Case parameters of interest were then extracted and categorized to determine the most common complications as well as solutions utilized in penile replantation. Results: Our findings from 46 cases across 37 studies revealed a common occurrence of postoperative necrosis (56.5%) and highlighted the importance of timely vascular reconnection and innovative surgical strategies to manage complications. Three cases were complicated by scrotal hematomas and 23 cases reported at least one psychiatric comorbidity. Some innovative solutions mentioned include hyperbaric oxygen therapy, laser angiography, leech therapy, PDE inhibitors, and penile splints. Conclusion: The outcomes suggest a critical need for standardized protocols and further research into optimizing techniques and therapies to enhance the success rates as well as quality of life post-replantation. This review aims to guide future practices and encourage collaborative efforts to refine the complex microsurgical procedures involved in penile replantation.

The Past, Present, and Future of Tubular Melt Electrowritten Constructs to Mimic Small Diameter Blood Vessels - A Stable Process?

Melt Electrowriting (MEW) is a continuously growing manufacturing platform. Its advantage is the consistent production of micro- to nanometer fibers, that stack intricately, forming complex geometrical shapes. MEW allows tuning of the mechanical properties of constructs via the geometry of deposited fibers. Due to this, MEW can create complex mechanics only seen in multi-material compounds and serve as guiding structures for cellular alignment. The advantage of MEW is also shown in combination with other biotechnological manufacturing methods to create multilayered constructs that increase mechanical approximation to native tissues, biocompatibility, and cellular response. These features make MEW constructs a perfect candidate for small-diameter vascular graft structures. Recently, studies have presented fascinating results in this regard, but is this truly the direction that tubular MEW will follow or are there also other options on the horizon? This perspective will explore the origins and developments of tubular MEW and present its growing importance in the field of artificial small-diameter vascular grafts with mechanical modulation and improved biomimicry and the impact of it in convergence with other manufacturing methods and how future technologies like AI may influence its progress.

Design-encoded dual shape-morphing and shape-memory in 4D printed polymer parts toward cellularized vascular grafts

Current additive manufacturing technologies wherein as-printed simple two-dimensional (2D) structures morph into complex tissue mimetic three-dimensional (3D) shapes are limited to multi-material hydrogel systems, which necessitates multiple fabrication steps and specific materials. This work utilizes a single shape memory thermoplastic polymer (SMP), PLMC (polylactide-co-trimethylene carbonate), to achieve programmable shape deformation through anisotropic design and infill angles encoded during 3D printing. The shape changes were first computationally predicted through finite element analysis (FEA) simulations and then experimentally validated through quantitative correlation. Rectangular 2D sheets could self-roll into complete hollow tubes of specific diameters (ranging from ≈6 mm to ≈10 mm) and lengths (as long as 40 mm), as quantitatively predicted from FEA simulations within one minute at relatively lower temperatures (≈80 °C). Furthermore, shape memory properties were demonstrated post-shape change to exhibit dual shape morphing at temperatures close to physiological levels. The tubes (retained as the permanent shape) were deformed into flat sheets (temporary shape), seeded with endothelial cells (at T < Tg), and thereafter triggered at ≈37 °C back into tubes (permanent shape), utilizing the shape memory properties to yield bioresorbable tubes with cellularized lumens for potential use as vascular grafts with improved long-term patency. Additionally, out-of-plane bending and twisting deformation were demonstrated in complex structures by careful control of infill angles that can unprecedently expand the scope of cellularized biomimetic 3D shapes. This work demonstrates the potential of the combination of shape morphing and SMP behaviors at physiological temperatures to yield next-generation smart implants with precise control over dimensions for tissue repair and regeneration.

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.

Advancements in tissue engineering for cardiovascular health: a biomedical engineering perspective

Myocardial infarction (MI) stands as a prominent contributor to global cardiovascular disease (CVD) mortality rates. Acute MI (AMI) can result in the loss of a large number of cardiomyocytes (CMs), which the adult heart struggles to replenish due to its limited regenerative capacity. Consequently, this deficit in CMs often precipitates severe complications such as heart failure (HF), with whole heart transplantation remaining the sole definitive treatment option, albeit constrained by inherent limitations. In response to these challenges, the integration of bio-functional materials within cardiac tissue engineering has emerged as a groundbreaking approach with significant potential for cardiac tissue replacement. Bioengineering strategies entail fortifying or substituting biological tissues through the orchestrated interplay of cells, engineering methodologies, and innovative materials. Biomaterial scaffolds, crucial in this paradigm, provide the essential microenvironment conducive to the assembly of functional cardiac tissue by encapsulating contracting cells. Indeed, the field of cardiac tissue engineering has witnessed remarkable strides, largely owing to the application of biomaterial scaffolds. However, inherent complexities persist, necessitating further exploration and innovation. This review delves into the pivotal role of biomaterial scaffolds in cardiac tissue engineering, shedding light on their utilization, challenges encountered, and promising avenues for future advancement. By critically examining the current landscape, we aim to catalyze progress toward more effective solutions for cardiac tissue regeneration and ultimately, improved outcomes for patients grappling with cardiovascular ailments.

Long-term observation of polycaprolactone small-diameter vascular grafts with thickened outer layer and heparinized inner layer in rabbit carotid arteries

In our previous study, the pristine bilayer small-diameterin situtissue engineered vascular grafts (pTEVGs) were electrospun from a heparinized polycaprolactone (PCL45k) as an inner layer and a non-heparinized PCL80k as an outer layer in the thickness of about 131 μm and 202 μm, respectively. However, the hydrophilic enhancement of inner layer stemmed from the heparinization accelerated the degradation of grafts leading to the early formation of arterial aneurysms in a period of 3 months, severely hindering the perennial observation of the neo-tissue regeneration, host cell infiltration and graft remodeling in those implanted pTEVGs. Herein to address this drawback, the thickness of the outer layers was increased with PCL80k to around 268 μm, while the inner layer remained unchangeable. The thickened TEVGs named as tTEVGs were evaluated in six rabbits via a carotid artery interpositional model for a period of 9 months. All the animals kept alive and the grafts remained patent until explantation except for one whose one side of arterial blood vessels was occluded after an aneurysm occurred at 6 months. Although a significant degradation was observed in the implanted grafts at 9 month, the occurrence of aneurysms was obviously delayed compared to pTEVGs. The tissue stainings indicated that the endothelial cell remodeling was substantially completed by 3 months, while the regeneration of elastin and collagen remained smaller and unevenly distributed in comparison to autologous vessels. Additionally, the proliferation of macrophages and smooth muscle cells reached the maximum by 3 months. These tTEVGs possessing a heparinized inner layer and a thickened outer layer exhibited good patency and significantly delayed onset time of aneurysms.

Understanding genomic medicine for thoracic aortic disease through the lens of induced pluripotent stem cells

Thoracic aortic disease (TAD) is often silent until a life-threatening complication occurs. However, genetic information can inform both identification and treatment at an early stage. Indeed, a diagnosis is important for personalised surveillance and intervention plans, as well as cascade screening of family members. Currently, only 20% of heritable TAD patients have a causative mutation identified and, consequently, further advances in genetic coverage are required to define the remaining molecular landscape. The rapid expansion of next generation sequencing technologies is providing a huge resource of genetic data, but a critical issue remains in functionally validating these findings. Induced pluripotent stem cells (iPSCs) are patient-derived, reprogrammed cell lines which allow mechanistic insights, complex modelling of genetic disease and a platform to study aortic genetic variants. This review will address the need for iPSCs as a frontline diagnostic tool to evaluate variants identified by genomic discovery studies and explore their evolving role in biological insight through to drug discovery.

Sacrificial-Rotating Rod-Based 3D Bioprinting Technique for the Development of an In Vitro Cardiovascular Model

Several studies have attempted to develop complex cardiovascular models, but the use of multiple cell types and poor cell alignments after fabrication have limited the practical application of these models. Among various bioprinting methods, extrusion-based bioprinting is the most widely used in the bioengineering field. This method not only has the potential to construct complex 3D biological structures but it also enables the alignment of cells in the printing direction owing to the application of shear stress to the cells during the printing process. Therefore, this study developed an in vitro cardiovascular model using an extrusion-based bioprinting method that utilizes a rotating rod as a printing platform. The rotating rod was made of polyvinyl alcohol (PVA) and used as a sacrificial rod. This rotating platform approach enabled the printing of longer tubular-vascular structures of multiple shapes, including disease models, and the water-soluble properties of PVA facilitated the isolation of the printed vascular models. In addition, this method enabled the printing of the endothelial cells in the bloodstream direction and smooth muscle cells in the circumferential direction to better mimic the anatomy of real blood vessels. Consequently, a cardiovascular model was successfully printed using a gelatin methacryloyl bioink with cells. In conclusion, the proposed fabrication method can facilitate the fabrication of various cardiovascular models that mimic the alignment of real blood vessels.

Highly compliant biomimetic scaffolds for small diameter tissue-engineered vascular grafts (TEVGs) produced via melt electrowriting (MEW)

Biofabrication approaches toward the development of tissue-engineered vascular grafts (TEVGs) have been widely investigated. However, successful translation has been limited to large diameter applications, with small diameter grafts frequently failing due to poor mechanical performance, in particular mismatched radial compliance. Herein, melt electrowriting (MEW) of poly(ϵ-caprolactone) has enabled the manufacture of highly porous, biocompatible microfibre scaffolds with physiological anisotropic mechanical properties, as substrates for the biofabrication of small diameter TEVGs. Highly reproducible scaffolds with internal diameter of 4.0 mm were designed with 500 and 250µm pore sizes, demonstrating minimal deviation of less than 4% from the intended architecture, with consistent fibre diameter of 15 ± 2µm across groups. Scaffolds were designed with straight or sinusoidal circumferential microfibre architecture respectively, to investigate the influence of biomimetic fibre straightening on radial compliance. The results demonstrate that scaffolds with wave-like circumferential microfibre laydown patterns mimicking the architectural arrangement of collagen fibres in arteries, exhibit physiological compliance (12.9 ± 0.6% per 100 mmHg), while equivalent control geometries with straight fibres exhibit significantly reduced compliance (5.5 ± 0.1% per 100 mmHg). Further mechanical characterisation revealed the sinusoidal scaffolds designed with 250µm pores exhibited physiologically relevant burst pressures of 1078 ± 236 mmHg, compared to 631 ± 105 mmHg for corresponding 500µm controls. Similar trends were observed for strength and failure, indicating enhanced mechanical performance of scaffolds with reduced pore spacing. Preliminaryin vitroculture of human mesenchymal stem cells validated the MEW scaffolds as suitable substrates for cellular growth and proliferation, with high cell viability (>90%) and coverage (>85%), with subsequent seeding of vascular endothelial cells indicating successful attachment and preliminary endothelialisation of tissue-cultured constructs. These findings support further investigation into long-term tissue culture methodologies for enhanced production of vascular extracellular matrix components, toward the development of the next generation of small diameter TEVGs.

Microtube embedded hydrogel bioprinting for vascularization of tissue-engineered scaffolds

Vascular tissue engineering has been considered promising as one of the alternatives for viable artificial tissues and organs. Macro- and microscale hollow tubes fabricated with various techniques have been widely studied to mimic blood vessels. To date, the fabrication of biomimetic capillary vessels with sizes ranging from 1 to 10 µm is still challenging. In this paper, core-sheath microtubes were electrospun to mimic capillary vessels and were embedded in carboxymethyl cellulose/sodium alginate hydrogel for bioprinting. The results showed improved printing fidelity and promoted cell attachment. The tube concentration and tube length both had significant influences on filament size and merging area. Printed groups with higher microtube concentration showed higher microtube density, with filament/nozzle size ratio, and printed/designed grid area ratio closer to 100%. In the in vitro experiments, microtubes were not only compatible with human umbilical vein endothelial cells but also provided microtopographical cues to promote cell proliferation and morphogenesis in three-dimensional space. In summary, the microtubes fabricated by our groups have the potential for the bioprinting of vascularized soft tissue scaffolds.

Bioprinted vascular tissue: Assessing functions from cellular, tissue to organ levels

3D bioprinting technology is widely used to fabricate various tissue structures. However, the absence of vessels hampers the ability of bioprinted tissues to receive oxygen and nutrients as well as to remove wastes, leading to a significant reduction in their survival rate. Despite the advancements in bioinks and bioprinting technologies, bioprinted vascular structures continue to be unsuitable for transplantation compared to natural blood vessels. In addition, a complete assessment index system for evaluating the structure and function of bioprinted vessels in vitro has not yet been established. Therefore, in this review, we firstly highlight the significance of selecting suitable bioinks and bioprinting techniques as they two synergize with each other. Subsequently, focusing on both vascular-associated cells and vascular tissues, we provide a relatively thorough assessment of the functions of bioprinted vascular tissue based on the physiological functions that natural blood vessels possess. We end with a review of the applications of vascular models, such as vessel-on-a-chip, in simulating pathological processes and conducting drug screening at the organ level. We believe that the development of fully functional blood vessels will soon make great contributions to tissue engineering and regenerative medicine.

Programmable DNA hydrogel provides suitable microenvironment for enhancing autophagy-based therapies in intervertebral disc degeneration treatment

The pathogenesis of intervertebral disc degeneration (IVDD) is attributed to metabolic dysregulation within the extracellular matrix and heightened apoptosis of nucleus pulposus cells (NPC). Therefore, a potential therapeutic strategy for managing IVDD involves the reestablishment of metabolic equilibrium within the extracellular matrix and the suppression of excessive myeloid cell apoptosis. The microRNA, miR-5590, displays marked differential expression in degenerative nucleus pulposus (NP) tissues and exerts a direct influence on the regulation of DDX5 expression. This, in turn, modulates mammalian target of rapamycin (mTOR) phosphorylation, thereby impacting autophagy and apoptosis. However, ensuring the smooth delivery of miRNA to a specific injury site poses a significant challenge. To address this issue, a multifunctional DNA hydrogel was developed and subsequently loaded with miR-5590 via spherical nucleic acids (SNAs) for the treatment of IVDD. The hydrogel, which exhibits versatility, has the potential to be administered through injection at the site of injury, resulting in a consistent and prolonged release of miR-5590. This leads to the creation of a genetic microenvironment within the NP, which triggers the onset of autophagy in NPCs and subsequently suppresses apoptosis. As a result, this process regulates the metabolic equilibrium within the extracellular matrix, thereby impeding the in vitro and in vivo progression of IVDD. The amalgamation of miRNAs and biomaterials offers a promising therapeutic strategy for the management of IVDD in clinical settings.

Biological Materials for Tissue-Engineered Vascular Grafts: Overview of Recent Advancements

The clinical demand for tissue-engineered vascular grafts is still rising, and there are many challenges that need to be overcome, in particular, to obtain functional small-diameter grafts. The many advances made in cell culture, biomaterials, manufacturing techniques, and tissue engineering methods have led to various promising solutions for vascular graft production, with available options able to recapitulate both biological and mechanical properties of native blood vessels. Due to the rising interest in materials with bioactive potentials, materials from natural sources have also recently gained more attention for vascular tissue engineering, and new strategies have been developed to solve the disadvantages related to their use. In this review, the progress made in tissue-engineered vascular graft production is discussed. We highlight, in particular, the use of natural materials as scaffolds for vascular tissue engineering.

A bioactive microparticle-loaded osteogenically enhanced bioprinted scaffold that permits sustained release of BMP-2

Extrusion-based bioprinting technology is widely used for tissue regeneration and reconstruction. However, the method that uses only hydrogel as the bioink base material exhibits limited biofunctional properties and needs improvement to achieve the desired tissue regeneration. In this study, we present a three-dimensionally printed bioactive microparticle-loaded scaffold for use in bone regeneration applications. The unique structure of the microparticles provided sustained release of growth factor for > 4 weeks without the use of toxic or harmful substances. Before and after printing, the optimal particle ratio in the bioink for cell viability demonstrated a survival rate of ≥ 85% over 7 days. Notably, osteogenic differentiation and mineralization-mediated by human periosteum-derived cells in scaffolds with bioactive microparticles-increased over a 2-week interval. Here, we present an alternative bioprinting strategy that uses the sustained release of bioactive microparticles to improve biofunctional properties in a manner that is acceptable for clinical bone regeneration applications.

Three-Dimensional Bioprinting in Cardiovascular Disease: Current Status and Future Directions

Three-dimensional (3D) printing plays an important role in cardiovascular disease through the use of personalised models that replicate the normal anatomy and its pathology with high accuracy and reliability. While 3D printed heart and vascular models have been shown to improve medical education, preoperative planning and simulation of cardiac procedures, as well as to enhance communication with patients, 3D bioprinting represents a potential advancement of 3D printing technology by allowing the printing of cellular or biological components, functional tissues and organs that can be used in a variety of applications in cardiovascular disease. Recent advances in bioprinting technology have shown the ability to support vascularisation of large-scale constructs with enhanced biocompatibility and structural stability, thus creating opportunities to replace damaged tissues or organs. In this review, we provide an overview of the use of 3D bioprinting in cardiovascular disease with a focus on technologies and applications in cardiac tissues, vascular constructs and grafts, heart valves and myocardium. Limitations and future research directions are highlighted.

Biomimetic Bilayered Scaffolds for Tissue Engineering: From Current Design Strategies to Medical Applications

Tissue damage due to cancer, congenital anomalies, and injuries needs new efficient treatments that allow tissue regeneration. In this context, tissue engineering shows a great potential to restore the native architecture and function of damaged tissues, by combining cells with specific scaffolds. Scaffolds made of natural and/or synthetic polymers and sometimes ceramics play a key role in guiding cell growth and formation of the new tissues. Monolayered scaffolds, which consist of uniform material structure, are reported as not being sufficient to mimic complex biological environment of the tissues. Osteochondral, cutaneous, vascular, and many other tissues all have multilayered structures, therefore multilayered scaffolds seem more advantageous to regenerate these tissues. In this review, recent advances in bilayered scaffolds design applied to regeneration of vascular, bone, cartilage, skin, periodontal, urinary bladder, and tracheal tissues are focused on. After a short introduction on tissue anatomy, composition and fabrication techniques of bilayered scaffolds are explained. Then, experimental results obtained in vitro and in vivo are described, and their limitations are given. Finally, difficulties in scaling up production of bilayer scaffolds and reaching the stage of clinical studies are discussed when multiple scaffold components are used.

Visualization and bibliometric analysis of 3D printing in cartilage regeneration

The self-repair ability of cartilage defects is limited, and 3D printing technology provides hope for the repair and regeneration of cartilage defects. Although 3D printing technology and cartilage repair and regeneration have been studied for decades, there are still few articles specifically describing the relationship between 3D printing and cartilage defect repair and regeneration, and a bibliometric analysis has not been completed. To supplement, sort out and summarize the content in related fields, we analyzed the research status of 3D printing technology and cartilage repair and regeneration from 2002 to 2022. According to the set search strategy, the Web of Science Core Collection was used as the data source, and the literature search was completed on December 6, 2022. CiteSpace V and VOSviewer were used as bibliometric tools to complete the analysis of the research focus and direction of the published literature. Based on the analysis results, we focus on the occurrence and development of this field of combined medical and engineering research. Moreover, the current advantages and limitations of this field as well as future development prospects are discussed in depth. It will help to shape researchers' understanding of 3D printing and cartilage repair and regeneration, inspire researchers' research ideas, guide research directions, and promote related research results to clinical application.

Additive manufacturing of sustainable biomaterials for biomedical applications

Biopolymers are promising environmentally benign materials applicable in multifarious applications. They are especially favorable in implantable biomedical devices thanks to their excellent unique properties, including bioactivity, renewability, bioresorbability, biocompatibility, biodegradability and hydrophilicity. Additive manufacturing (AM) is a flexible and intricate manufacturing technology, which is widely used to fabricate biopolymer-based customized products and structures for advanced healthcare systems. Three-dimensional (3D) printing of these sustainable materials is applied in functional clinical settings including wound dressing, drug delivery systems, medical implants and tissue engineering. The present review highlights recent advancements in different types of biopolymers, such as proteins and polysaccharides, which are employed to develop different biomedical products by using extrusion, vat polymerization, laser and inkjet 3D printing techniques in addition to normal bioprinting and four-dimensional (4D) bioprinting techniques. This review also incorporates the influence of nanoparticles on the biological and mechanical performances of 3D-printed tissue scaffolds. This work also addresses current challenges as well as future developments of environmentally friendly polymeric materials manufactured through the AM techniques. Ideally, there is a need for more focused research on the adequate blending of these biodegradable biopolymers for achieving useful results in targeted biomedical areas. We envision that biopolymer-based 3D-printed composites have the potential to revolutionize the biomedical sector in the near future.

Clinical implications of inflammation in atheroma formation and novel therapies in cardiovascular diseases

Cardiovascular diseases (CVD) are the leading causes of death and disability in the world. Among all CVD, the most common is coronary artery disease (CAD). CAD results from the complications promoted by atherosclerosis, which is characterized by the accumulation of atherosclerotic plaques that limit and block the blood flow of the arteries involved in heart oxygenation. Atherosclerotic disease is usually treated by stents implantation and angioplasty, but these surgical interventions also favour thrombosis and restenosis which often lead to device failure. Hence, efficient and long-lasting therapeutic options that are easily accessible to patients are in high demand. Advanced technologies including nanotechnology or vascular tissue engineering may provide promising solutions for CVD. Moreover, advances in the understanding of the biological processes underlying atherosclerosis can lead to a significant improvement in the management of CVD and even to the development of novel efficient drugs. To note, over the last years, the observation that inflammation leads to atherosclerosis has gained interest providing a link between atheroma formation and oncogenesis. Here, we have focused on the description of the available therapy for atherosclerosis, including surgical treatment and experimental treatment, the mechanisms of atheroma formation, and possible novel therapeutic candidates such as the use of anti-inflammatory treatments to reduce CVD.

A vertical additive-lathe printing system for the fabrication of tubular constructs using gelatin methacryloyl hydrogel

Reproducing both the mechanical and biological performance of native blood vessels remains an ongoing challenge in vascular tissue engineering. Additive-lathe printing offers an attractive method of fabricating long tubular constructs as a potential vascular graft for the treatment of cardiovascular diseases. Printing hydrogels onto rotating horizontal mandrels often leads to sagging, resulting in poor and variable mechanical properties. In this study, an additive-lathe printing system with a vertical mandrel to fabricate tubular constructs is presented. Various concentrations of gelatin methacryloyl (gelMA) hydrogel were used to print grafts on the rotating mandrel in a helical pattern. The printing parameters were selected to achieve the bonding of consecutive gelMA filaments to improve the quality of the printed graft. The hydrogel filaments were fused properly under the action of gravity on the vertical mandrel. Thus, the vertical additive-lathe printing system was used to print uniform wall thickness grafts, eliminating the hydrogel sagging problem. Tensile testing performed in both circumferential and longitudinal direction revealed that the anisotropic properties of printed gelMA constructs were similar to those observed in the native blood vessels. In addition, no leakage was detected through the walls of the gelMA grafts during burst pressure measurement. Therefore, the current printing setup could be utilized to print vascular grafts for the treatment of cardiovascular diseases.

Combined light-cured and sacrificial hydrogels for fabrication of small-diameter bionic vessels by 3D bioprinting

BACKGROUND

Bionic grafts can replace autologous tissue through tissue engineering in cases of cardiovascular disease. However, small-diameter vessel grafts remain challenging to precellularize.

OBJECTIVE

Bionic small-diameter vessels with endothelial and smooth muscle cells (SMCs) manufactured with a novel approach.

METHODS

A 1-mm-diameter bionic blood vessel was constructed by combining light-cured hydrogel gelatin-methacryloyl (GelMA) with sacrificial hydrogel Pluronic F127. Mechanical properties of GelMA (Young's modulus and tensile stress) were tested. Cell viability and proliferation were detected using Live/dead staining and CCK-8 assays, respectively. The histology and function of the vessels were observed using hematoxylin and eosin and immunofluorescence staining.

RESULTS

GelMA and Pluronic were printed together using extrusion. The temporary Pluronic support was removed by cooling during GelMA crosslinking, yielding a hollow tubular construct. A bionic bilayer vascular structure was fabricated by loading SMCs into the GelMA bioink, followed by perfusion with endothelial cells. In the structure, both cell types maintained good cell viability. The vessel showed good histological morphology and function.

CONCLUSION

Using light-cured and sacrificial hydrogels, we formed a small ca bionic vessel with a small caliber containing SMCs and endothelial cells, demonstrating an innovative approach for construction of bionic vascular tissues.

Effects of surface patterning and topography on the cellular functions of tissue engineered scaffolds with special reference to 3D bioprinting

The extracellular matrix (ECM) of the tissue organ exhibits a topography from the nano to micrometer range, and the design of scaffolds has been inspired by the host environment. Modern bioprinting aims to replicate the host tissue environment to mimic the native physiological functions. A detailed discussion on the topographical features controlling cell attachment, proliferation, migration, differentiation, and the effect of geometrical design on the wettability and mechanical properties of the scaffold are presented in this review. Moreover, geometrical pattern-mediated stiffness and pore arrangement variations for guiding cell functions have also been discussed. This review also covers the application of designed patterns, gradients, or topographic modulation on 3D bioprinted structures in fabricating the anisotropic features. Finally, this review accounts for the tissue-specific requirements that can be adopted for topography-motivated enhancement of cellular functions during the fabrication process with a special thrust on bioprinting.

Infection of Vascular Prostheses: A Comprehensive Review

Vascular graft or endograft infection (VGEI) is a complex disease that complicates vascular-surgery and endovascular-surgery procedures and determines high morbidity and mortality. This review article provides the most updated general evidence on the pathogenesis, prevention, diagnosis, and treatment of VGEI. Several microorganisms are involved in VGEI development, but the most frequent one, responsible for over 75% of infections, is Staphylococcus aureus. Specific clinical, surgical, radiologic, and laboratory criteria are pivotal for the diagnosis of VGEI. Surgery and antimicrobial therapy are cornerstones in treatment for most patients with VGEI. For patients unfit for surgery, alternative treatment is available to improve the clinical course of VGEI.

3D Bioprinting Using Hydrogels: Cell Inks and Tissue Engineering Applications

3D bioprinting is transforming tissue engineering in medicine by providing novel methods that are precise and highly customizable to create biological tissues. The selection of a "cell ink", a printable formulation, is an integral part of adapting 3D bioprinting processes to allow for process optimization and customization related to the target tissue. Bioprinting hydrogels allows for tailorable material, physical, chemical, and biological properties of the cell ink and is suited for biomedical applications. Hydrogel-based cell ink formulations are a promising option for the variety of techniques with which bioprinting can be achieved. In this review, we will examine some of the current hydrogel-based cell inks used in bioprinting, as well as their use in current and proposed future bioprinting methods. We will highlight some of the biological applications and discuss the development of new hydrogels and methods that can incorporate the completed print into the tissue or organ of interest.

Numerical and Experimental Analysis of Shear Stress Influence on Cellular Viability in Serpentine Vascular Channels

3D bioprinting has emerged as a tool for developing in vitro tissue models for studying disease progression and drug development. The objective of the current study was to evaluate the influence of flow driven shear stress on the viability of cultured cells inside the luminal wall of a serpentine network. Fluid-structure interaction was modeled using COMSOL Multiphysics for representing the elasticity of the serpentine wall. Experimental analysis of the serpentine model was performed on the basis of a desirable inlet flow boundary condition for which the most homogeneously distributed wall shear stress had been obtained from numerical study. A blend of Gelatin-methacryloyl (GelMA) and PEGDA200 PhotoInk was used as a bioink for printing the serpentine network, while facilitating cell growth within the pores of the gelatin substrate. Human umbilical vein endothelial cells were seeded into the channels of the network to simulate the blood vessels. A Live-Dead assay was performed over a period of 14 days to observe the cellular viability in the printed vascular channels. It was observed that cell viability increases when the seeded cells were exposed to the evenly distributed shear stresses at an input flow rate of 4.62 mm/min of the culture media, similar to that predicted in the numerical model with the same inlet boundary condition. It leads to recruitment of a large number of focal adhesion point nodes on cellular membrane, emphasizing the influence of such phenomena on promoting cellular morphologies.

Tyramine-Functionalized Alginate-Collagen Hybrid Hydrogel Inks for 3D-Bioprinting

Extrusion-based 3D-bioprinting using hydrogels has exhibited potential in precision medicine; however, researchers are beset with several challenges. A major challenge of this technique is the production of constructs with sufficient height and fidelity to support cellular behavior in vivo. In this study, we present the 3D-bioprinting of cylindrical constructs with tunable gelation kinetics by controlling the covalent crosslinking density and gelation time of a tyramine-functionalized alginate hydrogel (ALG-TYR) via enzymatic reaction by horseradish peroxidase (HRP) and hydrogen peroxide (H₂O₂). The extruded filament was crosslinked for a second time on a support bath containing H₂O₂ to increase fidelity after printing. The resulting tubular construct, with a height of 6 mm and a wall thickness of 2 mm, retained its mechanical properties and had a maximum 2-fold swelling after 2 d. Furthermore, collagen (COL) was introduced into the ALG-TYR hydrogel network to increase the mechanical modulus and cell cytocompatibility, as the encapsulated fibroblast cells exhibited a higher cell viability in the ALG-TYR/COL construct (92.13 ± 0.70%) than in ALG-TYR alone (68.18 ± 3.73%). In summary, a vascular ECM-mimicking scaffold was 3D-bioprinted with the ALG-TYR/COL hybrid hydrogel, and this scaffold can support tissue growth for clinical translation in regenerative and personalized medicine.

Electrospun POSS integrated poly(carbonate-urea)urethane provides appropriate surface and mechanical properties for the fabrication of small-diameter vascular grafts

This study developed a platform for fabricating small-diameter vascular grafts using electrospun poly(carbonate-urea)urethane bonded with different concentrations of POSS nanocage. The characteristics of electrospun POSS-PCUUs were investigated by ATR-FTIR, 1HNMR, EDS, SEM, AFM, WCA, and DSC analyses. Besides, mechanical attributes such as tensile strength, modulus, elastic recovery, and inelastic behaviors were monitored. The survival rate and cellular attachment capacity were studied using human endothelial cells during a 7-day culture period. The results showed that electrospun nanofibers with 6 wt.% POSS-PCUU had better surface properties in terms of richness of POSS nanocage with notable improved mechanical strength and hysteresis loss properties (p < 0.05). The surface roughness of electrospun 6 wt.% POSS-PCUU reached 646 ± 10 nm with statistically significant differences compared to the control PCUU and groups containing 2, 4 wt.% POSS-PCUU (p < 0.05). The addition of 6 wt.% POSS increased the ultimate mechanical strength of nanofibers related to control PCUU and other groups (p < 0.05). The expansion of human endothelial cells on the 6 wt.% POSS-PCUU surface increased the viability reaching maximum levels on day 7 (p < 0.05). Immunofluorescence imaging using DAPI staining displayed the formation single-layer endothelial barrier at the luminal surface, indicating an appropriate cell-to-cell interaction.

Tri-Layered Vascular Grafts Guide Vascular Cells’ Native-like Arrangement

Bionic grafts hold great promise for directing tissue regeneration. In vascular tissue engineering, although a large number of synthetic grafts have been constructed, these substitutes only partially recapitulated the tri-layered structure of native arteries. Synthetic polymers such as poly(l-lactide-co-ε-caprolactone) (PLCL) possess good biocompatibility, controllable degradation, remarkable processability, and sufficient mechanical strength. These properties of PLCL show great promise for fabricating synthetic vascular substitutes. Here, tri-layered PLCL vascular grafts (TVGs) composed of a smooth inner layer, circumferentially aligned fibrous middle layer, and randomly distributed fibrous outer layer were prepared by sequentially using ink printing, wet spinning, and electrospinning techniques. TVGs possessed kink resistance and sufficient mechanical properties (tensile strength, elastic modulus, suture retention strength, and burst pressure) equivalent to the gold standard conduits of clinical application, i.e., human saphenous veins and human internal mammary arteries. The stratified structure of TVGs exhibited a visible guiding effect on specific vascular cells including enhancing endothelial cell (EC) monolayer formation, favoring vascular smooth muscle cells’ (VSMCs) arrangement and elongation, and facilitating fibroblasts’ proliferation and junction establishment. Our research provides a new avenue for designing synthetic vascular grafts with polymers.

Biofabrication of small diameter tissue-engineered vascular grafts

Current clinical treatment strategies for the bypassing of small diameter (<6 mm) blood vessels in the management of cardiovascular disease frequently fail due to a lack of suitable autologous grafts, as well as infection, thrombosis, and intimal hyperplasia associated with synthetic grafts. The rapid advancement of 3D printing and regenerative medicine technologies enabling the manufacture of biological, tissue-engineered vascular grafts (TEVGs) with the ability to integrate, remodel, and repair in vivo, promises a paradigm shift in cardiovascular disease management. This review comprehensively covers current state-of-the-art biofabrication technologies for the development of biomimetic TEVGs. Various scaffold based additive manufacturing methods used in vascular tissue engineering, including 3D printing, bioprinting, electrospinning and melt electrowriting, are discussed and assessed against the biomechanical and functional requirements of human vasculature, while the efficacy of decellularization protocols currently applied to engineered and native vessels are evaluated. Further, we provide interdisciplinary insight into the outlook of regenerative medicine for the development of vascular grafts, exploring key considerations and perspectives for the successful clinical integration of evolving technologies. It is expected that continued advancements in microscale additive manufacturing, biofabrication, tissue engineering and decellularization will culminate in the development of clinically viable, off-the-shelf TEVGs for small diameter applications in the near future. STATEMENT OF SIGNIFICANCE: Current clinical strategies for the management of cardiovascular disease using small diameter vessel bypassing procedures are inadequate, with up to 75% of synthetic grafts failing within 3 years of implantation. It is this critically important clinical problem that researchers in the field of vascular tissue engineering and regenerative medicine aim to alleviate using biofabrication methods combining additive manufacturing, biomaterials science and advanced cellular biology. While many approaches facilitate the development of bioengineered constructs which mimic the structure and function of native blood vessels, several challenges must still be overcome for clinical translation of the next generation of tissue-engineered vascular grafts.

Application and development of 3D bioprinting in cartilage tissue engineering

Bioprinting technology can build complex tissue structures and has the potential to fabricate engineered cartilage with bionic structures for achieving cartilage defect repair/regeneration.

Human iPSC-derived mesodermal progenitor cells preserve their vasculogenesis potential after extrusion and form hierarchically organized blood vessels

Post-fabrication formation of a proper vasculature remains an unresolved challenge in bioprinting. Established strategies focus on the supply of the fabricated structure with nutrients and oxygen and either rely on the mere formation of a channel system using fugitive inks or additionally use mature endothelial cells and/or peri-endothelial cells such as smooth muscle cells for the formation of blood vesselsin vitro.Functional vessels, however, exhibit a hierarchical organization and multilayered wall structure that is important for their function. Human induced pluripotent stem cell-derived mesodermal progenitor cells (hiMPCs) have been shown to possess the capacity to form blood vesselsin vitro, but have so far not been assessed for their applicability in bioprinting processes. Here, we demonstrate that hiMPCs, after formulation into an alginate/collagen type I bioink and subsequent extrusion, retain their ability to give rise to the formation of complex vessels that display a hierarchical network in a process that mimics the embryonic steps of vessel formation during vasculogenesis. Histological evaluations at different time points of extrusion revealed the initial formation of spheres, followed by lumen formation and further structural maturation as evidenced by building a multilayered vessel wall and a vascular network. These findings are supported by immunostainings for endothelial and peri-endothelial cell markers as well as electron microscopic analyses at the ultrastructural level. Moreover, endothelial cells in capillary-like vessel structures deposited a basement membrane-like matrix at the basal side between the vessel wall and the alginate-collagen matrix. After transplantation of the printed constructs into the chicken chorioallantoic membrane (CAM) the printed vessels connected to the CAM blood vessels and get perfusedin vivo. These results evidence the applicability and great potential of hiMPCs for the bioprinting of vascular structures mimicking the basic morphogenetic steps ofde novovessel formation during embryogenesis.

High-resolution lithographic biofabrication of hydrogels with complex microchannels from low-temperature-soluble gelatin bioresins

Biofabrication via light-based 3D printing offers superior resolution and ability to generate free-form architectures, compared to conventional extrusion technologies. While extensive efforts in the design of new hydrogel bioinks lead to major advances in extrusion methods, the accessibility of lithographic bioprinting is still hampered by a limited choice of cell-friendly resins. Herein, we report the development of a novel set of photoresponsive bioresins derived from ichthyic-origin gelatin, designed to print high-resolution hydrogel constructs with embedded convoluted networks of vessel-mimetic channels. Unlike mammalian gelatins, these materials display thermal stability as pre-hydrogel solutions at room temperature, ideal for bioprinting on any easily-accessible lithographic printer. Norbornene- and methacryloyl-modification of the gelatin backbone, combined with a ruthenium-based visible light photoinitiator and new coccine as a cytocompatible photoabsorber, allowed to print structures resolving single-pixel features (∼50 ​μm) with high shape fidelity, even when using low stiffness gels, ideal for cell encapsulation (1-2 ​kPa). Moreover, aqueous two-phase emulsion bioresins allowed to modulate the permeability of the printed hydrogel bulk. Bioprinted mesenchymal stromal cells displayed high functionality over a month of culture, and underwent multi-lineage differentiation while colonizing the bioresin bulk with tissue-specific neo-deposited extracellular matrix. Importantly, printed hydrogels embedding complex channels with perfusable lumen (diameter <200 ​μm) were obtained, replicating anatomical 3D networks with out-of-plane branches (i.e. brain vessels) that cannot otherwise be reproduced by extrusion bioprinting. This versatile bioresin platform opens new avenues for the widespread adoption of lithographic biofabrication, and for bioprinting complex channel-laden constructs with envisioned applications in regenerative medicine and hydrogel-based organ-on-a-chip devices.

Improved Repopulation Efficacy of Decellularized Small Diameter Vascular Grafts Utilizing the Cord Blood Platelet Lysate

BACKGROUND

The development of functional bioengineered small-diameter vascular grafts (SDVGs), represents a major challenge of tissue engineering. This study aimed to evaluate the repopulation efficacy of biological vessels, utilizing the cord blood platelet lysate (CBPL).

METHODS

Human umbilical arteries (hUAs, n = 10) were submitted to decellularization. Then, an evaluation of decellularized hUAs, involving histological, biochemical and biomechanical analysis, was performed. Wharton's Jelly (WJ) Mesenchymal Stromal Cells (MSCs) were isolated and characterized for their properties. Then, WJ-MSCs (1.5 × 106 cells) were seeded on decellularized hUAs (n = 5) and cultivated with (Group A) or without the presence of the CBPL, (Group B) for 30 days. Histological analysis involving immunohistochemistry (against Ki67, for determination of cell proliferation) and indirect immunofluorescence (against activated MAP kinase, additional marker for cell growth and proliferation) was performed.

RESULTS

The decellularized hUAs retained their initial vessel's properties, in terms of key-specific proteins, the biochemical and biomechanical characteristics were preserved. The evaluation of the repopulation process indicated a more uniform distribution of WJ-MSCs in group A compared to group B. The repopulated vascular grafts of group B were characterized by greater Ki67 and MAP kinase expression compared to group A.

CONCLUSION

The results of this study indicated that the CBPL may improve the repopulation efficacy, thus bringing the biological SDVGs one step closer to clinical application.