An ex vivo physiologic and hyperplastic vessel culture model to study intra-arterial stent therapies

Development of small tissue engineered blood vessels and their clinical and research applications

Since the first tissue engineered blood vessel (TEBV) was developed, different approaches, biomaterial scaffolds and cell sources have been used to obtain an engineered vessel as much similar as native vessels in terms of structure, functionality and mechanical properties. At the same time, diverse needs to obtain a functional TEBV have emerged, such as for blood vessel replacement for cardiovascular diseases (CVDs) to be used as artery bypass, to vascularize tissue engineered constructs, or even to model vascular diseases or drug testing. In this review, after briefly describing the native structure and function of arteries, we will give an overview of different biomaterials, cells and methods that have been used during the last years for the development of small TEBV (1-6 mm diameter). The importance of perfusing the TEBV to acquire functionality and maturation will be also discussed. Finally, we will center the review on TEBV applications beyond their use as vascular graft for CVDs.

Biomechanical insights into the development and optimization of small-diameter vascular grafts

Small-diameter vascular grafts (SDVGs; inner diameter ≤6 mm) offer transformative potential for treating cardiovascular diseases, yet their clinical application remains limited due to high rates of complications such as acute thrombosis and intimal hyperplasia (IH), which compromise long-term patency. While advancements in biological and material science have driven progress, the critical role of biomechanical factors-such as hemodynamic forces and mechanical mismatch-in graft failure is often overlooked. This review presents insights from recent clinical trials of SDVG products and summarizes biomechanical contributors to failure, including disturbed flow patterns, mechanical mismatch, and insufficient mechanical strength. We outline essential mechanical performance criteria (e.g., compliance, burst pressure) and evaluation methodologies to assess SDVG performance. Furthermore, we present optimization strategies based on biomechanical principles: (1) graft morphological design optimization to improve hemodynamic stability, (2) structural, material, and fabrication innovations to achieve compliance matching with native arteries, and (3) biomimetic approaches to mimic vascular tissue and promote endothelialization. By systematically addressing these biomechanical challenges, next-generation SDVGs may achieve superior patency, accelerating their clinical translation. This review highlights the necessity of considering biomechanical compatibility in SDVG development, thereby providing initial insights for the clinical translation of SDVG. STATEMENT OF SIGNIFICANCE: Small-diameter vascular grafts (SDVGs) offer transformative potential for cardiovascular disease treatment but face clinical limitations. While significant progress has been made in biological and material innovations, the critical role of biomechanical factors in graft failure has often been underestimated. This review highlights the importance of biomechanical compatibility in SDVG design and performance, emphasizing the need to address disturbed flow patterns, mechanical mismatch, and inadequate mechanical strength. By proposing optimization strategies based on biomechanical principles, such as graft morphological design, compliance matching, and biomimetic approaches, this work provides a roadmap for developing next-generation SDVGs with improved patency. These advancements have the potential to overcome current limitations, accelerate clinical translation, ultimately benefiting patients worldwide.

Intravascular delivery of an MK2 inhibitory peptide to prevent restenosis after angioplasty

Peripheral artery disease is commonly treated with balloon angioplasty, a procedure involving minimally invasive, transluminal insertion of a catheter to the site of stenosis, where a balloon is inflated to open the blockage, restoring blood flow. However, peripheral angioplasty has a high rate of restenosis, limiting long-term patency. Therefore, angioplasty is sometimes paired with delivery of cytotoxic drugs like paclitaxel to reduce neointimal tissue formation. We pursue intravascular drug delivery strategies that target the underlying cause of restenosis - intimal hyperplasia resulting from stress-induced vascular smooth muscle cell switching from the healthy contractile into a pathological synthetic phenotype. We have established MAPKAP kinase 2 (MK2) as a driver of this phenotype switch and seek to establish convective and contact transfer (coated balloon) methods for MK2 inhibitory peptide delivery to sites of angioplasty. Using a flow loop bioreactor, we showed MK2 inhibition in ex vivo arteries suppresses smooth muscle cell phenotype switching while preserving vessel contractility. A rat carotid artery balloon injury model demonstrated inhibition of intimal hyperplasia following MK2i coated balloon treatment in vivo. These studies establish both convective and drug coated balloon strategies as promising approaches for intravascular delivery of MK2 inhibitory formulations to improve efficacy of balloon angioplasty.

Next-Generation Approaches for Biomedical Materials Evaluation: Microfluidics and Organ-on-a-Chip Technologies

Biological evaluation of biomedical materials faces constraints imposed by the limitations of traditional in vitro and animal experiments. Currently, miniaturized and biomimetic microfluidic technologies and organ-on-chip systems have garnered widespread attention in the field of drug development. However, their exploration in the context of biomedical material evaluation and medical device development remains relatively limited. In this review, a summary of existing biological evaluation methods, highlighting their respective advantages and drawbacks is provided. The application of microfluidic technologies in the evaluation of biomedical materials, emphasizing the potential of organ-on-chip systems as highly biomimetic in vitro models in material evaluation is then focused. Finally, the challenges and opportunities associated with utilizing organ-on-chip systems to evaluate biomedical materials in the field of material evaluation are discussed. In conclusion, the integration of advanced microfluidic technologies and organ-on-chip systems presents a potential paradigm shift in the biological assessment of biomedical materials, offering the prospective of more accurate and predictive in vitro models in the development of medical devices.

Synergistic coupling between 3D bioprinting and vascularization strategies

Three-dimensional (3D) bioprinting offers promising solutions to the complex challenge of vascularization in biofabrication, thereby enhancing the prospects for clinical translation of engineered tissues and organs. While existing reviews have touched upon 3D bioprinting in vascularized tissue contexts, the current review offers a more holistic perspective, encompassing recent technical advancements and spanning the entire multistage bioprinting process, with a particular emphasis on vascularization. The synergy between 3D bioprinting and vascularization strategies is crucial, as 3D bioprinting can enable the creation of personalized, tissue-specific vascular network while the vascularization enhances tissue viability and function. The review starts by providing a comprehensive overview of the entire bioprinting process, spanning from pre-bioprinting stages to post-printing processing, including perfusion and maturation. Next, recent advancements in vascularization strategies that can be seamlessly integrated with bioprinting are discussed. Further, tissue-specific examples illustrating how these vascularization approaches are customized for diverse anatomical tissues towards enhancing clinical relevance are discussed. Finally, the underexplored intraoperative bioprinting (IOB) was highlighted, which enables the direct reconstruction of tissues within defect sites, stressing on the possible synergy shaped by combining IOB with vascularization strategies for improved regeneration.

Construction of Rapid Extracellular Matrix-Deposited Small-Diameter Vascular Grafts Induced by Hypoxia in a Bioreactor

Cardiovascular disease has become one of the most globally prevalent diseases, and autologous or vascular graft transplantation has been the main treatment for the end stage of the disease. However, there are no commercialized small-diameter vascular graft (SDVG) products available. The design of SDVGs is promising in the future, and SDVG preparation using an in vitro bioreactor is a favorable method, but it faces the problem of long-term culture of >8 weeks. Herein, we used different oxygen (O₂) concentrations and mechanical stimulation to induce greater secretion of extracellular matrix (ECM) from cells in vitro to rapidly prepare SDVGs. Culturing with 2% O₂ significantly increased the production of the ECM components and growth factors of human dermal fibroblasts (hDFs). To accelerate the formation of ECM, hDFs were seeded on a polycaprolactone (PCL) scaffold and cultured in a flow culture bioreactor with 2% O₂ for only 3 weeks. After orthotopic transplantation in rat abdominal aorta, the cultured SDVGs (PCL-decellularized ECM) showed excellent endothelialization and smooth muscle regeneration. The vascular grafts cultured with hypoxia and mechanical stimulation could accelerate the reconstruction speed and obtain an improved therapeutic effect and thereby provide a new research direction for improving the production and supply of SDVGs.

Analyzing the impact of pulsatile flow on drug release from a single strut of a drug-eluting stent

In this study, in-vitro experiments were performed to investigate the drug release from a single strut of a drug-eluting stent with respect to the systolic-diastolic flow and the continuous flow. Regarding, a test bench comprising a single strut and agarose gel as an arterial wall model was designed. The model chosen represents a large-scaled strut of a stent, to limit the effect of the geometrical shape of the stents on the drug release results. The comparison is carried out between two continuous flow rates and a systolic-diastolic flow pattern varying between these two flow rates, with a frequency of 70 beats per minute. The stent model is a polylactic-co-glycolic acid film (50:50) loaded with 10 % diclofenac sodium. A compartment of agarose gel (1 %) and a phosphate-buffered saline solution at 37 °C are employed to mimic the arterial wall and the blood, respectively. Our results show the importance of flow type on the drug release from the stent and distribution of drug in the hydrogel, such that the pulsatility promotes an increase in the quantity of drug absorbed into the hydrogel.

Bioprinting of 3D Adipose Tissue Models Using a GelMA-Bioink with Human Mature Adipocytes or Human Adipose-Derived Stem Cells

Adipose tissue is related to the development and manifestation of multiple diseases, demonstrating the importance of suitable in vitro models for research purposes. In this study, adipose tissue lobuli were explanted, cultured, and used as an adipose tissue control to evaluate in vitro generated adipose tissue models. During culture, lobule exhibited a stable weight, lactate dehydrogenase, and glycerol release over 15 days. For building up in vitro adipose tissue models, we adapted the biomaterial gelatin methacryloyl (GelMA) composition and handling to homogeneously mix and bioprint human primary mature adipocytes (MA) and adipose-derived stem cells (ASCs), respectively. Accelerated cooling of the bioink turned out to be essential for the homogeneous distribution of lipid-filled MAs in the hydrogel. Last, we compared manual and bioprinted GelMA hydrogels with MA or ASCs and the explanted lobules to evaluate the impact of the printing process and rate the models concerning the physiological reference. The viability analyses demonstrated no significant difference between the groups due to additive manufacturing. The staining of intracellular lipids and perilipin A suggest that GelMA is well suited for ASCs and MA. Therefore, we successfully constructed physiological in vitro models by bioprinting MA-containing GelMA bioinks.

3D Printed Bioreactor Enabling the Pulsatile Culture of Native and Angioplastied Large Arteries

Routine interventions such as balloon angioplasty, result in vascular activation and remodeling, often requiring re-intervention. 2D in vitro models and small animal experiments have enabled the discovery of important mechanisms involved in this process, however the clinical translation is often underwhelming. There is a critical need for an ex vivo model representative of the human vascular physiology and encompassing the complexity of the vascular wall and the physical forces regulating its function. Vascular bioreactors for ex vivo culture of large vessels are viable alternatives, but their custom-made design and insufficient characterization often hinders the reproducibility of the experiments. The objective of the study was to design and validate a novel 3D printed cost-efficient and versatile perfusion system, capable of sustaining the viability and functionality of large porcine arteries for 7 days and enabling early post-injury evaluations. MultiJet Fusion 3D printing was used to engineer the EasyFlow insert, converting a conventional 50 ml centrifuge tube into a mini bioreactor. Porcine carotid arteries either left untreated or injured with an angioplasty balloon, were cultured under pulsatile flow for up to 7 days. Pressure, heart rate, medium viscosity and shear conditions were adjusted to resemble arterial in vivo hemodynamics. Tissue viability, cell activation and matrix remodeling were analyzed by immunohistochemistry, and vascular function was monitored by duplex ultrasound. Culture conditions in the EasyFlow bioreactor preserved endothelial coverage and smooth muscle organization and extracellular matrix structure in the vessel wall, as compared to static culture. Injured arteries presented hallmarks of early remodeling, such as intimal denudation, smooth muscle cell disarray and media/adventitia activation in flow culture. Duplex ultrasound confirmed continuous pulsatile blood flow conditions, dose-dependent vasodilator response to nitroglycerin in untreated vessels and impaired dilator response in angioplastied vessels. The scope of this work is to validate a low-cost, robust and reproducible system to explore the culture of native and injured large arteries under pulsatile flow. While the study of vascular pathology is beyond the scope of the present paper, our system enables future investigations and provides a platform to test novel therapies and devices ex vivo, in a patient relevant system.