Vascular Bioreactor Research Articles

Flexible Transient Bioelectronic System Enables Multifunctional Active‐Controlled Drug Delivery

AbstractOn‐demand drug delivery systems (DDSs) have tremendous promise for clinical in vivo personalized drug delivery. However, the current DDSs are monofunctional and unable to meet the individualized needs of patients. Herein, a biodegradable multifunctional active‐controlled drug delivery system (ADDS) is reported. The device can be implanted in various tissues with valves controlled by the deactivation of magnesium (Mg) for rapid drug release from drug reservoirs and long‐term drug delivery with the biodegradation of the ADDS. Multiple chambers are constructed by designing a structure with tandem Mg valves and aligning them in the z‐axis direction, allowing the system to deliver drugs in a pulsatile or sequential manner. The biodegradability of the entire system minimizes the potential side effects of the ADDS. The application of the device for drug delivery in rats confirmed its ability to perform pulsatile delivery in vivo. The excellent biocompatibility and dual timeline drug delivery capability of this system are demonstrated with cellular and in vitro vascular bioreactors. This multifunctional ADDS will play an important role in precise drug delivery in the treatment of chronic diseases and diseases with complications.

Engineering Vascular Bioreactor Systems to Closely Mimic Physiological Forces In Vitro.

In vitro models of the vasculature play an important role in biomedical discovery research, with diverse applications in vascular biology, drug discovery, and tissue engineering. These models aim to replicate the conditions of the human vasculature including physical geometry, employing appropriate vascular cells exposed to physiological forces. However, vessel biology is complex, with multiple relevant cell types, precise three-dimensional (3D) architectural arrangement, an array of biological cues and pressure, flow rate, and shear stress stimulation that are difficult to replicate outside of the body. Vessel bioreactors typically comprise core modules, common to most systems: a 3D tubular scaffold to support cells, media and nutrient exchange for cell viability, a pumping module, and sensor arrays for monitoring. In our comprehensive review of the literature, foundational elements such as maintenance of cell viability, nutrient exchange with flow, use of 3D scaffolds, and basic sensing capabilities are well established. However, most bioreactor systems fail to adequately replicate combinations of physiologically relevant stimuli-including pressure, shear stress, and flow rate-independently, as system input parameters. At the root of this deficiency is the field's reliance on simple pumping systems designed for other applications, making it necessary to add resistors and compliance chambers to even approach human vascular conditions. As vascular biology research rapidly progressed it became increasingly clear that combinations of physical forces strongly influence cell phenotype, gene expression, and in turn can be drivers of pathology. We highlight the need for renewed innovation in vascular bioreactor development with a focus on the importance of providing appropriate physiological forces in the same system. Impact statement In vitro systems modeling aspects of the human vasculature are increasingly important in tissue engineering and biomedical research. Current systems maintain basic cell viability and facilitate nutrient exchange but poorly replicate physiological forces, reliant on simplistic pumping systems. Our review highlights the need to more accurately mimic arterial pressure, flow rate, and shear stress in the same system. Innovation in this area would improve in vitro modeling of the vasculature, significantly impacting tissue engineering and vascular biology in this area.

Abstract 14766: Development of an Ex-Vivo Vascular Bioreactor to Investigate Viability of Coronary Arteries

Introduction: The cardiovascular disease that causes most of the deaths is atherosclerosis. The current research to assess efficacy of treatments is based on animal models, but these present several limitations related to time and costs associated. Ex-vivo systems represent useful models to study vascular biology and to test medical devices. The main goal of this research was to culture coronary arteries in an ex-vivo vascular bioreactor in order to maintain them alive and functional by mimicking physiological conditions. Methods: Culture experiments were performed on porcine right coronary arteries (RCA). Duration was set to 2 (n=3), 4 (n=3), and 9 days (n=3). The RCAs were dissected from hearts harvested from a local slaughterhouse. The bioreactor containing the dissected RCA was placed in a 38°C incubator. The RCA was cultured in a blood-mimicking culture medium. To assess RCA morphology and diameter, ultrasound imaging was performed. Pressure and flow rate were monitored daily. The flow rate was set to ensure a physiological peak endothelial shear stress of around 0.8-1.8 Pa. After 2, 4 or 9 days of culture, the RCA was embedded in paraffin and cut into 4 μm sections. Histological stainings (H&E and RF) were performed on the sections. Results: During RCA cultures, the mean pressure was 60-100 mmHg, and the peak flow rate was around 60 ml/min. Ultrasound imaging showed that the morphology and structure of cultured arteries was maintained during the culture. Histological analyses showed preserved endothelium and extracellular matrix. After 2 days of culture, endothelial coverage was not complete while after 4 days it was completely restored. After 9 days of culture, a layer of newly formed neointima was visible. Conclusions: The cultured RCAs maintained their physiological morphology up to 9 days of culture. The investigated model represents a useful tool for testing vascular therapies and devices, supporting the translational phase between in-vitro and in-vivo studies.

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.

The Development of an ex vivo Flow System to Assess Acute Arterial Drug Retention of Cardiovascular Intravascular Devices.

Purpose: The goal of this study was to develop an ex vivo system capable of rapidly evaluating arterial drug levels in living, isolated porcine carotid arteries.Methods: A vascular bioreactor system was developed that housed a native porcine carotid artery under physiological flow conditions. The ex vivo bioreactor system was designed to quantify the acute drug transfer of catheter-based drug delivery devices into explanted carotid arteries. To evaluate our ex vivo system, a paclitaxel-coated balloon and a perfusion catheter device delivering liquid paclitaxel were utilized. At 1-h post-drug delivery, arteries were removed, and paclitaxel drug levels measured using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Parallel experiments were performed in a pig model to validate ex vivo measurements.Results: LC-MS/MS analysis demonstrated arterial paclitaxel levels of the drug-coated balloon-treated arteries to be 48.49 ± 24.09 ng/mg and the perfusion catheter-treated arteries to be 25.42 ± 9.74 ng/mg at 1 h in the ex vivo system. Similar results were measured in vivo, as arterial paclitaxel concentrations were measured at 59.23 ± 41.27 ng/mg for the drug-coated balloon-treated arteries and 23.43 ± 20.23 ng/mg for the perfusion catheter-treated arteries. Overall, no significant differences were observed between paclitaxel measurements of arteries treated ex vivo vs. in vivo.Conclusion: This system represents the first validated ex vivo pulsatile system to determine pharmacokinetics in a native blood vessel. This work provides proof-of-concept of a quick, inexpensive, preclinical tool to study acute drug tissue concentration kinetics of drug-releasing interventional vascular devices.

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

Conventional in vitro methods for biological evaluation of intra-arterial devices such as stents fail to accurately predict cytotoxicity and remodeling events. An ex vivo flow-tunable vascular bioreactor system (VesselBRx), comprising intra- and extra-luminal monitoring capabilities, addresses these limitations. VesselBRx mimics the in vivo physiological, hyperplastic, and cytocompatibility events of absorbable magnesium (Mg)-based stents in ex vivo stent-treated porcine and human coronary arteries, with in-situ and real-time monitoring of local stent degradation effects. Unlike conventional, static cell culture, the VesselBRx perfusion system eliminates unphysiologically high intracellular Mg2+ concentrations and localized O2 consumption resulting from stent degradation. Whereas static stented arteries exhibited only 20.1% cell viability and upregulated apoptosis, necrosis, metallic ion, and hypoxia-related gene signatures, stented arteries in VesselBRx showed almost identical cell viability to in vivo rabbit models (~94.0%). Hyperplastic intimal remodeling developed in unstented arteries subjected to low shear stress, but was inhibited by Mg-based stents in VesselBRx, similarly to in vivo. VesselBRx represents a critical advance from the current static culture standard of testing absorbable vascular implants.

Comparison of in Vascular Bioreactors and In Vivo Models of Degradation and Cellular Response of Mg-Zn-Mn Stents.

Traditional in vitro evaluation criteria of magnesium (Mg)-based stents cannot reflect the degradation process in vivo, due to the interdependence and interference between biodegradable properties and bioenvironment. The current direct and indirect evaluation approaches of in vitro biocompatibility do not have a hydrodynamic environment and vascular biological structure existing in vivo. Herein, we designed a vascular bioreactor to provide an ex vivo culture environment for vessels, which reveals the degradation behavior of Mg-Zn-Mn stent and the effect of its degradation on cells. We reported that rabbit carotid arteries could maintain native morphology and viability in the bioreactor under the best condition within a flow rate of 5.4 mL min-1 and a culture time of one week. With this culture condition, Mg-Zn-Mn stents were implanted into the arteries in the bioreactors and compared with in vivo rabbit models. The arteries maintained cell survival in the bioreactor, but the cell attachment was absent on the stent struts, associated with a fast degradation. Conversely, the stents achieved a rapid and complete endothelialization in vivo for two weeks. This study could provide a correlation and difference of the degradation behavior and cellular response to the degradation of Mg-based stent between ex vivo and in vivo approaches.

An Innovative Ex Vivo Vascular Bioreactor as Comprehensive Tool to Study the Behavior of Native Blood Vessels Under Physiologically Relevant Conditions

Abstract Ex vivo systems represent important models to study vascular biology and to test medical devices, combining the advantages of in vitro and in vivo models such as controllability of parameters and the presence of biological response, respectively. The aim of this study was to develop a comprehensive ex vivo vascular bioreactor to long-term culture and study the behavior of native blood vessels under physiologically relevant conditions. The system was designed to allow for physiological mechanical loading in terms of pulsatile hemodynamics, shear stress, and longitudinal prestretch and ultrasound imaging for vessel diameter and morphology evaluation. In this first experience, porcine carotid arteries (n = 4) from slaughterhouse animals were cultured in the platform for 10 days at physiological temperature, CO2 and humidity using medium with blood-mimicking viscosity, components, and stability of composition. As expected, a significant increase in vessel diameter was observed during culture. Flow rate was adjusted according to diameter values to reproduce and maintain physiological shear stress, while pressure was kept physiological. Ultrasound imaging showed that the morphology and structure of cultured arteries were comparable to in vivo. Histological analyses showed preserved endothelium and extracellular matrix and neointimal tissue growth over 10 days of culture. In conclusion, we have developed a comprehensive pulsatile system in which a native blood vessel can be cultured under physiological conditions. The present model represents a significant step toward ex vivo testing of vascular therapies, devices, drug interaction, and as basis for further model developments.

Characterization of Endothelial and Smooth Muscle Cells From Different Canine Vessels.

Vasculature performs a critical function in tissue homeostasis, supply of oxygen and nutrients, and the removal of metabolic waste products. Vascular problems are implicated in a large variety of pathologies and accurate in vitro models resembling native vasculature are of great importance. Unfortunately, existing in vitro models do not sufficiently reflect their in vivo counterpart. The complexity of vasculature requires the examination of multiple cell types including endothelial cells (ECs) and vascular smooth muscle cells (VSMCs), as well as vessel location in the body from which they originate. The use of canine blood vessels provides a way to study vasculature with similar vessel size and physiology compared to human vasculature. We report an isolation procedure that provides the possibility to isolate both the endothelial and smooth muscle cells from the same vessels simultaneously, enabling new opportunities in investigating vasculature behavior. Canine primary ECs and VSMCs were isolated from the vena cava, vena porta and aorta. All tissue sources were derived from three donors for accurate comparison and to reduce inter-animal variation. The isolation and purification of the two distinct cell types was confirmed by morphology, gene- and protein-expression and function. As both cell types can be derived from the same vessel, this approach allows accurate modeling of vascular diseases and can also be used more widely, for example, in vascular bioreactors and tissue engineering designs. Additionally, we identified several new genes that were highly expressed in canine ECs, which may become candidate genes for novel EC markers. In addition, we observed transcriptional and functional differences between arterial- and venous-derived endothelium. Further exploration of the transcriptome and physiology of arteriovenous differentiation of primary cells may have important implications for a better understanding of the fundamental behavior of the vasculature and pathogenesis of vascular disease.

Development of an ex vivo aneurysm model for vascular devices testing_suppl

An ex vivo aneurysm model that closely resembles the in vivo situation can provide an important tool to test therapeutic approaches while avoiding animal experimentation. The model should mimic a variety of conditions, such as in vivo hemodynamics and native arterial structure and characteristics. The aim of this study was to develop an ex vivo aneurysm model by stiffening vessel walls to be used to assess treatment strategies. Porcine carotid arteries from slaughterhouse animals were used to evaluate the acute effect of different concentrations of Rose Bengal on vessel distensibility. Rose Bengal is a sono-sensitive compound that is activated by several ultrasound frequencies, resulting in stiffening of the treated arteries; the most effective combination of concentration and frequency was determined. In a pulsatile ex vivo vascular bioreactor, treated and control porcine carotid arteries were subjected to physiological conditions for 10 days. Treated arteries showed increased mean pressure and decreased pulsatility compared to controls. Changes in vessel morphology and a significant increase of distal diameter were observed in the treated arteries but not in the controls. His­tology revealed distal dissection-like lesions and proximal aneurysm-like structure in the treated arteries. Finally, a stent graft was deployed and cultured in one treated artery, demonstrating the feasibility of testing endovascular devices in the model. In conclusion, we developed an ex vivo model reproducing the onset of aneurysm formation. This represents a promising tool for early stage device testing, thereby reducing the need for animal studies.

Development of an ex vivo aneurysm model for vascular devices testing

An ex vivo aneurysm model that closely resembles the in vivo situation can provide an important tool for testing therapies. The model should mimic a variety of conditions, such as in vivo hemodynamics and native arterial structure and characteristics, avoiding animal experimentation. Therefore, the aim of this study is to develop an ex vivo aneurysm model by vessel wall stiffening to be used to assess treatment strategies. Porcine carotid arteries from slaughterhouse animals were used to evaluate the acute effect of different concentrations of Rose Bengal on distensibility. This sono-sensitive compound was activated by several ultrasound frequencies, resulting in stiffening of the treated arteries of which the most effective combination was selected. In a pulsatile ex vivo vascular bioreactor treated and control porcine carotid arteries were subjected to physiological conditions for 10 days. During culture, hemodynamics showed increased mean pressure and decreased pulsatility in treated arteries compared to controls. Change in vessel morphology and significant increase of distal diameter was observed in the treated arteries but not in the controls. Histology of treated arteries revealed dissection-like lesions distally and aneurysm-like structure proximally. Finally, a stent graft was deployed in one treated artery and cultured demonstrating the feasibility of testing endovascular devices in the model. In conclusion, we developed an ex vivo model reproducing the onset of aneurysm formation. This could represent a promising tool for early stage device testing thereby reducing the need for animal studies.

Development and in vivo validation of tissue-engineered, small-diameter vascular grafts from decellularized aortae of fetal pigs and canine vascular endothelial cells

BackgroundTissue engineering has emerged as a promising alternative for small-diameter vascular grafts. The aim of this study was to determine the feasibility of using decellularized aortae of fetal pigs (DAFPs) to construct tissue-engineered, small-diameter vascular grafts and to test the performance and application of DAFPs as vascular tissue-engineered scaffolds in the canine arterial system.MethodsDAFPs were prepared by continuous enzymatic digestion. Canine vascular endothelial cells (ECs) were seeded onto DAFPs in vitro and then the vascular grafts were cultured in a custom-designed vascular bioreactor system for 7 days of dynamic culture following 3 days of static culture. The grafts were then transplanted into the common carotid artery of the same seven dogs from which ECs had been derived (two grafts were prepared for each dog with one as a backup; therefore, a total of 14 tissue-engineered blood vessels were prepared). At 1, 3, and 6 months post-transplantation, ultrasonography and contrast-enhanced computed tomography (CT) were used to check the patency of the grafts. Additionally, vascular grafts were sampled for histological and electron microscopic examination.ResultsTissue-engineered, small-diameter vascular grafts can be successfully constructed using DAFPs and canine vascular ECs. Ultrasonographic and CT test results confirmed that implanted vascular grafts displayed good patency with no obvious thrombi. Six months after implantation, the grafts had been remodeled and exhibited a similar structure to normal arteries. Immunohistochemical staining showed that cells had evenly infiltrated the tunica media and were identified as muscular fibroblasts. Scanning electron microscopy showed that the graft possessed a complete cell layer, and the internal cells of the graft were confirmed to be ECs by transmission electron microscopy.ConclusionsTissue-engineered, small-diameter vascular grafts constructed using DAFPs and canine vascular ECs can be successfully transplanted to replace the canine common carotid artery. This investigation potentially paves the way for solving a problem of considerable clinical need, i.e., the requirement for small-diameter vascular grafts.

Ex vivo blood vessel bioreactor for analysis of the biodegradation of magnesium stent models with and without vessel wall integration.

Magnesium and its alloys are candidates for a new generation of biodegradable stent materials. However, the in vitro degradation of magnesium stents does not match the clinical degradation rates, corrupting the validity of conventional degradation tests. Here we report an ex vivo vascular bioreactor, which allows simulation of the microenvironment with and without blood vessel integration to study the biodegradation of magnesium implants in comparison with standard in vitro test conditions and with in vivo implantations. The bioreactor did simulate the corrosion of an intramural implant very well, but showed too high degradation for non-covered implants. It is concluded that this system is in between static incubation and animal experiments concerning the predictivity of the degradation.

A systematic comparison of biodegradation behavior of absorbable metal: in standardized immersion, arterial bioreactor and in vivo study

Event Abstract Back to Event A systematic comparison of biodegradation behavior of absorbable metal: in standardized immersion, arterial bioreactor and in vivo study Juan Wang1, 2*, Lumei Liu2*, Yeoheung Yun2* and Nan Huang1* 1 Southwest Jiaotong University, Dept. of Materials Science and Engineering, China 2 North Carolina Agricultural & Technical State University, NSF Engineering Research Center for Revolutionizing Metallic Biomaterials, United States Introduction: Absorbable metals have been widely tested in various in vitro environments to evaluate their biodegradation as vascular stent materials[1]. However, there exists a gap between in vivo and in vitro test results. A key step is to identify the relevant biochemical and biophysical microenvironments in test-systems. The purpose of this study was to establish an appropriate methodology for accurate and standardized determinations of degradation parameters in the pre- and post- endothelialization stage after stent implantation, which plays a vital part in predicting the fate of magnesium (Mg)-based stent. Materials and Methods: As-drawn Mg wires of 99.9% purity with a length of 10 mm and a diameter of 250 μm (Goodfellow, USA) were used. In the standardized immersion test, Mg wires were immersed in DMEM solution according to the standard protocol ASTM-D1141-98[2]. The LumeGen bioreactor (TGT DynaGen® Series, USA) as a vascular bioreactor was chosen to stimulate physiological aortal conditions (Fig. 1a). Each porcine abdominal aorta with a diameter of ~8 mm and a length of 5 cm was mounted into a chamber with a flow rate of 100 ml/min and a pulse pressure of 80-120 mmHg (Fig. 1b). In aortal in vivo test, rat abdominal aortas were used for implantation. Two Mg segments were symmetrically implanted into the lumen and wall of each aorta in the bioreactor or in vivo tests (Fig. 1c). Samples were analysed by X-ray computed tomography (CT). Fig. 1.(a) Photograph of bioreactor. Mg wires in the wall and lumen of a porcine aorta in the chamber (b) and rat aorta in vivo (c). Results and Discussion: One of two Mg wires exposed on the lumen and contacted the circulating medium to simulate a pre-endothelialization stage. The other Mg wire was embedded under the intima to simulate a post-endothelialization stage. The degradation product volumes, residual Mg volumes and average degradation rates were calculated utilizing the CT data. In Fig. 2, in vivo degradation was slower than in vitro degradation both in the standardized static and flow bioreactor conditions. In terms of the aortal bioreactor, flow convection on the lumen surface severely accelerated Mg degradation due to the increase of mass transfer, fluid shear stress and pulsatile stress, compared with low Mg degradation rate in the wall. In the aortal in vivo model, the degradation rate of Mg wire in the wall was faster than that in the lumen, and calcification was observed around Mg surrounding tissue. The degradation of Mg wire in the wall (diffusion limited region) was accelerated, which may result in the decrease of local pH from lysosome. Fig. 2. Volume ratios of residual Mg and corrosion products in the static no aorta, and the aortal lumen and wall of the bioreactor and in vivo conditions for 3-day. Conclusions: First-time investigation of degradation testing in the aortal bioreactor revealed that hydrodynamics plays a dominant role on the degradation. The established porcine aortal bioreactor and rat aortal in vivo model are expected to provide a better understanding of degradation mechanism of absorbable metallic stents. NIH grant (1SC3GM113728-01); NSF-ERC for revolutionizing metallic biomaterials (NSF-0812348); National Natural Science Foundation of China under Grant (81330031); Thanks Prof. Deling Kong, Dr. Zhihong Wang and Ms. Yifan Wu from Nankai University for in vivo test.

Flow-induced corrosion of absorbable magnesium alloy: In-situ and real-time electrochemical study

An in-situ and real-time electrochemical study in a vascular bioreactor was designed to analyze corrosion mechanism of magnesium alloy (MgZnCa) under mimetic hydrodynamic conditions. Effect of hydrodynamics on corrosion kinetics, types, rates and products was analyzed. Flow-induced shear stress (FISS) accelerated mass and electron transfer, leading to an increase in uniform and localized corrosions. FISS increased the thickness of uniform corrosion layer, but filiform corrosion decreased this layer resistance at high FISS conditions. FISS also increased the removal rate of localized corrosion products. Impedance-estimated and linear polarization-measured polarization resistances provided a consistent correlation to corrosion rate calculated by computed tomography.

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

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

The Effect of Pulsatile Loading and Scaffold Structure for the Generation of a Medial Equivalent Tissue Engineered Vascular Graft

A reliable and cost-effective scaffold for tissue-engineered vascular graft that would not only support cell proliferation and growth but also maintain cell phenotype has been a long-term challenge. In this study, we propose a biodegradable and biomimetic copolymer of gelatin with vinyl acetate synthesized via a graft copolymerization technique to generate tubular scaffolds for vascular tissue engineering. Two fabrication techniques, freeze drying and electrospinning, were used to generate the differing architectures for the scaffolds and characterized. The electrospun scaffolds were found to have a faster rate of mass loss in physiological saline of 81.72% within 4 months compared with 60% mass loss for the freeze-dried samples, though the materials were more crystalline. Vascular (v) smooth muscle cells (SMCs) were seeded on these tubes, which were then subjected to dynamic pulsatile stimulation on a vascular bioreactor for a week. Gross examination of the tissue-engineered constructs revealed that the cells secreted extensive extracellular matrix, with the dynamically conditioned samples exhibiting well-orientated SMCs and collagenous fibers in comparison with growth in static conditions. In addition, the alignment of cells in the direction of strain was greater in the electrospun constructs. The electrospun scaffolds maintained the characteristic contractile phenotype of SMCs, which was confirmed by higher gene expression rates of contractile protein markers like SM22α and calponin. A significant increase in the total matrix components (collagen and elastin) in the electrospun constructs compared with the freeze-dried samples was confirmed by biochemical analysis. The results of this study indicate that a combination approach involving a biomimetic scaffold with the nanofibrillar architecture and good mechanical strength conducive to the growth of SMCs and the use of the pulsatile forces to modulate the cell morphology and phenotypic plasticity of vSMCs helps in the successful engineering of a medial layer of blood vessel.

A tissue‐engineered aneurysm model for evaluation of endovascular devices

Endovascular stent grafts used for treatment of arterial aneurysms require preclinical testing for investigation of biological responses following implantation. The preclinical evaluation process related to the safety and efficacy of these devices is limited by the absence of an in vitro aneurysmal blood vessel equivalent capable of providing high-throughput, cost-effective assessments. With this in mind, the focus of this work was to develop an aneurysm model consisting of human blood vessel cells. To create aneurysmal scaffolds, expanded polytetrafluoroethylene vascular grafts were dilated utilizing an angioplasty balloon. Stromal vascular fraction cells isolated from human adipose tissue were integrated with the scaffolds, and luminal flow of nutrient medium was executed for 14 days in a vascular bioreactor. Following bioreactor perfusion, histology verified that a neointimal lining of human tissue had formed. Immunohistochemistry and scanning electron microscopy revealed a flow-contacting layer of smooth muscle cells, characterizing the model as a representation of neointimal formation in an injured or diseased vessel. This study has demonstrated the engineering of a vascular construct containing an aneurysmal dilation. A tissue-engineered aneurysm model could provide an alternative to current nonbiological in vitro aneurysm models and serve as a practical tool in the progression of new devices toward in vivo studies.

Development of an In Vitro System to Assess Stent-induced Smooth Muscle Cell Proliferation: A Feasibility Study

To develop an in vitro system capable of rapidly evaluating how specific stent structures may stimulate smooth muscle cell proliferation in living isolated porcine carotid arteries. A vascular bioreactor system was developed that housed a native porcine carotid artery under physiologic pulsatile flow and pressure conditions. The bioreactor system was designed to enable vascular stent deployment into a test section of vessel that was kept alive for 1 week. The three stents tested were a Wallstent, a Cordis Smart stent, and a balloon-expandable NIR Royal stent in three different arteries. Stents were successfully deployed in the native porcine arteries within the bioreactor system. Organ bath studies demonstrated that the explanted arteries maintained 40% of their contractility. Immunohistochemical staining of the stented vessel demonstrated that smooth muscle cell proliferation was related to stent design and strut location. Specifically, smooth muscle proliferation was shown to increase with stiffer (less compliant) vascular stents and in the edge region of the stents. The system could potentially be used to assess the influence of stent design and smooth muscle cell proliferation.

Endothelial and Smooth Muscle Cell Seeding onto Processed Ex Vivo Arterial Scaffolds Using 3D Vascular Bioreactors

Biomaterials derived from ex vivo tissues offer a viable alternative to synthetic materials for organ replacement therapies. In this study, we describe the use of a tissue engineering scaffold derived from ex vivo arterial tissue to assess vascular cell adhesion within a three-dimensional perfusion bioreactor. With the aim of maximizing seeding efficiency, five methods for endothelial cell (EC) and three independent methods for vascular smooth muscle cell (VSMC) adhesion were explored. Seeded constructs were maintained in vascular bioreactors under pulsatile flow conditions, culminating at 165 ml/min at 1.33 Hz to validate cell attachment and retention over time. Progressive modification of the seeding and flow regime protocols resulted in an increased of EC retention from 5.1 to 634 cells/mm2. Seeding VSMCs as sheets rather than cell suspensions bound and stabilized surface EC matrix fibers, resulting in multiple cell layers adhered to the scaffold with cells migrating to the medial/adventitial boundary. In conjunction with the bioscaffold, the vascular perfusion system serves as a useful tool to analyze cell adhesion and retention by allowing controlled manipulation of seeding and perfusion conditions.