Sheep Carotid Arteries Research Articles

Surgical procedure for acellular vascular xenografts testing in sheep carotid artery

Surgical procedure for acellular vascular xenografts testing in sheep carotid artery

Preventing Sheep Carotid Artery Spasm for Vascular Graft Surgery and Computed Tomography Angiography.

The development of small-diameter vascular grafts requires testing in large animal models before advancing to clinical trials. Vascular graft interposition implantation in sheep carotid arteries (CAs) is the most widely used model, but ovine CAs are prone to severe spasm following surgical manipulation, potentially impairing graft performance assessment. There is paucity in the literature on reducing sheep CA spasm using effective vasodilator therapeutic protocols. In this study, four healthy Merino cross White Suffolk wethers (1-2 years, 52.1 ± 0.8 kg) underwent CT angiography and CA graft surgery. CT angiography using iodinated contrast agent was performed with innominate artery access through the CA or ascending aortic arch access through the femoral artery. Sheep then underwent right CA sham surgery or left CA vascular graft implantation. A variety of vasodilators, including papaverine, sodium nitroprusside, verapamil, and their combination, were tested for preventing or treating CA spasms intraoperatively. Blood flow was reassessed immediately after CA surgery using CT angiography. The results showed that innominate artery access through the CA for CT angiography in sheep induced presurgical CA spasm with reduced arterial flow. Conversely, ascending aortic arch access through the femoral artery for CT angiography did not cause CA spasm and maintained arterial flow. During CA graft surgery, surgical trauma induced CA spasm, which was prevented by localized intra-arterial administration of vasodilators papaverine hydrochloride and verapamil before significant surgical manipulation.

ML-driven segmentation of microvascular features during histological examination of tissue-engineered vascular grafts.

The development of next-generation tissue-engineered medical devices such as tissue-engineered vascular grafts (TEVGs) is a leading trend in translational medicine. Microscopic examination is an indispensable part of animal experimentation, and histopathological analysis of regenerated tissue is crucial for assessing the outcomes of implanted medical devices. However, the objective quantification of regenerated tissues can be challenging due to their unusual and complex architecture. To address these challenges, research and development of advanced ML-driven tools for performing adequate histological analysis appears to be an extremely promising direction. We compiled a dataset of 104 representative whole slide images (WSIs) of TEVGs which were collected after a 6-month implantation into the sheep carotid artery. The histological examination aimed to analyze the patterns of vascular tissue regeneration in TEVGs in situ. Having performed an automated slicing of these WSIs by the Entropy Masker algorithm, we filtered and then manually annotated 1,401 patches to identify 9 histological features: arteriole lumen, arteriole media, arteriole adventitia, venule lumen, venule wall, capillary lumen, capillary wall, immune cells, and nerve trunks. To segment and quantify these features, we rigorously tuned and evaluated the performance of six deep learning models (U-Net, LinkNet, FPN, PSPNet, DeepLabV3, and MA-Net). After rigorous hyperparameter optimization, all six deep learning models achieved mean Dice Similarity Coefficients (DSC) exceeding 0.823. Notably, FPN and PSPNet exhibited the fastest convergence rates. MA-Net stood out with the highest mean DSC of 0.875, demonstrating superior performance in arteriole segmentation. DeepLabV3 performed well in segmenting venous and capillary structures, while FPN exhibited proficiency in identifying immune cells and nerve trunks. An ensemble of these three models attained an average DSC of 0.889, surpassing their individual performances. This study showcases the potential of ML-driven segmentation in the analysis of histological images of tissue-engineered vascular grafts. Through the creation of a unique dataset and the optimization of deep neural network hyperparameters, we developed and validated an ensemble model, establishing an effective tool for detecting key histological features essential for understanding vascular tissue regeneration. These advances herald a significant improvement in ML-assisted workflows for tissue engineering research and development.

Exploring the effects of Nano-liposomal TGF-β1 on induced pluripotent stem Cell-Derived vascular smooth muscle cells in Tissue-Engineered vascular graft; an in vivo study

This study explores the impact of liposomal Transforming Growth Factor β1 (TGF-β1) on phenotypic switching in Vascular Smooth Muscle Cells (VSMCs) derived from induced pluripotent stem cells (iPSCs) for arterial tissue engineering. We present an innovative approach to reducing graft waiting periods effectively. Using a biomimetic perfusion system, biological scaffolds were developed from sheep's carotid artery to create Tissue-Engineered Vessels (TEVs). VSMCs derived from rabbit iPSCs were reseeded onto these TEVs to promote proliferation. TGF-β1 was encapsulated in liposomes using the thin-film hydration method to enhance VSMC growth. The controlled release of TGF-β1 from these liposomes was quantified through enzyme-linked immunosorbent assay (ELISA). Nano-liposomal TGF-β1 was loaded into the scaffolds at a concentration of 50 ng/mL, with the release monitored through ELISA. The proliferative activity of VSMCs was evaluated using the CCK8 kit. Techniques such as real-time PCR, Western blot, Immunohistochemistry, and Flowcytometry were employed to assess VSMC phenotypic switching. Liposomal TGF-β1 treatment led to a 122.30 % increase in cell proliferation rate in TEVs compared to the control group, indicating no cytotoxicity. ELISA results confirmed a controlled and sustained release of liposomal TGF-β1. Furthermore, we demonstrated the efficacy of liposomal TGF-β1 for sustained delivery over an extended period by implanting the grafts in rabbit aortas and monitoring their performance for four weeks. Our findings highlight the role of Nano-liposomal TGF-β1 in inducing phenotypic transformation within TEVs. This research underscores the promising therapeutic potential of Nano-liposomal TGF-β1 in advancing blood vessel tissue engineering, offering novel pathways for clinical application and addressing the critical need for improved vascular graft outcomes. In conclusion, our study showcases the synergy between a biomimetic environment and Nano-liposomal TGF-β1 on rabbit induced pluripotent stem cell-derived VSMCs, emphasizing the significant increase in SMC proliferation, controlled release of TGF-β1, successful graft implantation, and the pioneering approach in arterial tissue engineering through the development of TEVs from sheep carotid arteries.

Histologic and genetic features of remodeling of tissue-engineered small-diameter vascular grafts: outcomes of six-month implantation in a sheep model

Surface modification of polymeric scaffolds with drugs to avoid thrombus formation and infection is a promising area in tissue engineering, which also makes it possible to accelerate the remodeling of such scaffolds and improve long-term patency.The objective of this paper is to study the histologic and genetic features of remodeling of tissue-engineered small-diameter vascular grafts (SDVGs) with antithrombogenic drug-coated and reinforced external scaffolds, implanted into a sheep carotid artery.Materials and methods. Poly(ε-caprolactone) (PCL) matrices, ∅4 mm in diameter, were fabricated via electrospinning, followed by creation of a reinforcing spiral PCL scaffold on their outer surface by extrusion. To prevent thrombus formation and infection, the fabricated grafts were modified with iloprost and cationic amphiphile by complexation through polyvinylpyrrolidone (PVP). The work was carried out to evaluate, by infrared spectroscopy, the formation of PVP-based coating, to study the physical and mechanical properties of the grafts in longitudinal and transverse directions, and to implant the vascular grafts (VGs) into a sheep carotid artery. To assess and control the patency of the implanted grafts, Doppler ultrasound was performed at days 1 and 5, then at 1, 3 and 6 months. The explanted samples were studied via histological and immunofluorescent analyses; gene expression profile was evaluated.Results. Ultrasound on days 1 and 5 after implantation showed the patency of vascular grafts to be 100%. At 1 month, the patency decreased to 83.3%; patency was 50% by the end of the implantation period (6 months), without aneurysm formation and detachment of the reinforcing scaffold. Histological and immunofluorescence studies of patent grafts showed the formation of a newly formed three-layer vascular tissue structure on their basis, without signs of inflammation and calcification. However, despite the structural similarity between the newly formed vascular tissue and the native tissue of a sheep carotid artery, analysis of the gene expression profile revealed some differences in terms of genetic profile: CNN and SNA12 expression levels in the neotissue decreased, and those of CTSB, TNFa, and TGFb increased.Conclusion. Modified polymeric vascular scaffolds showed good remodeling of the prosthetic wall, without aneurysm formation. The identified genetic differences between newly formed tissue and native tissue are logical in view of formation on the basis of the artificial polymeric scaffold. Further research on reinforced polymeric scaffolds will be aimed at improving the inner surface in order to improve their thromboresistance.

Morphological features of biological and tissue-engineered vascular patches remodeling: results of tests on a sheep model

One of the ways to reconstruct the arterial wall is endarterectomy with a vascular patch. The use of vascular wall prostheses made from existing materials can lead to complications with the need for reoperation. The search for new materials for the manufacture of vascular patches that have optimal compatibility with the vessel wall is still relevant.Aim: To study the dynamics and compare the morphological features of remodeling of tissue-engineered vascular patches from silk fibroin (SF) and biological xenopericardium (XP) flaps implanted into the wall of the sheep carotid artery.Material and Methods. Matrices from a 15% SF solution (n = 2) were prepared by electrospinning. For comparison, bovine pericardial flaps were used (n = 2). Vascular patches were implanted into the wall of the carotid artery in sheep for 2 and 6 months. A histological examination of explanted samples of vascular patches, scanning electron microscopy and confocal microscopy with specific immunofluorescent staining of the preparations were performed.Results. Based on the implanted SF-patch, neointima and neoadventitia were formed. After 2 months of implantation, the SFmatrix retained its structure; after 6 months, there were signs of moderate biodegradation of the material with the replacement of the vessel wall with its own tissue. There were no areas of calcification or massive inflammation. After 6 months, neointimal hyperplasia was detected in the projection of the implanted SF-patch. Based on the implanted XP-flap, neointima and neoadventitia were also formed. After 2 months, delamination of the implanted XP was revealed. After 6 months, neointimal hyperplasia was found in the projection of the XP-patch.Conclusion. Remodeling of the SF-patches and XP-flaps implanted into the wall of the sheep carotid artery followed the formation of a three-layer structure resembling the architecture of the vessel’s own wall, with signs of moderate biodegradation of the material. Neointimal hyperplasia is explained by insufficient compliance of the arterial wall and the patch and requires improvement in the composition of the implanted matrix.

FEATURES OF POLYURETHANE MATRIX REMODELING IN SHEEP MODEL EXPERIMENTS

HighlightsThe article describes the features of remodeling of polyurethane matrices during long-term implantation into the vascular bed of sheep. The results indicate high biocompatibility of polyurethane and resistance to bioresorption. The obtained data are significant for the development of medical products for cardiovascular surgery, in particular, biodegradable vascular prostheses. AbstractAim. To evaluate the features of polyurethane remodeling in a long-term experiment on a large animal model.Methods. Matrices made of 12% polyurethane solution in chloroform were manufactured by electrospinning at the Nanon-01A nanofiber electrospinning system (MIC, Japan). Matrix samples in the form of patches were implanted into the carotid arteries of sheep (n = 3) for a period of 6 months. The patency of vessels with implanted matrices was assessed after 2, 4 and 6 months using a portable hand-carried color Doppler - M7 Premium Ultrasound Machine (Mindray, China). The structure of the matrix surface before and after implantation was studied using an S-3400N scanning electron microscope (Hitachi, Japan). Histological examination of the explanted samples was carried out using an AXIO Imager A1 microscope (Carl Zeiss, Oberkochen, Germany) with previous staining of matrix sections with hematoxylin-eosin, Van Gieson and alizarin red C. Data processing was performed using the Statistica 6.0 software.Results. After 2, 4 and 6 months of implantation of polyurethane matrices into the carotid artery of sheep, complete patency of the carotid arteries was revealed. Macroscopically, after 6 months of implantation, the matrix completely resembled the carotid artery wall due to the full consolidation of the matrix with the artery wall and remodeling. Layers of newly formed vascular tissue – neointima and neoadventitia – were formed on the basis of the matrix. Histological examination revealed the structural integrity of the matrix without signs of inflammation and calcification both in the matrix structure and adjacent tissues.Conclusion. The biological inertia of polyurethane matrices with signs of remodeling was noted, which indicates a high biocompatibility of the material. Resistance to bioresorption and the ability to keep the frame of the product for a long time allows us to consider polyurethane as a suitable material for the formation of anti-aneurysmal protection of biodegradable vascular prostheses.

Potentiation of active force by cyclic strain in sheep carotid arterial smooth muscle.

The ability to generate force in large arteries is known to be augmented by cyclic strain that mimics the mechanically dynamic in vivo environment associated with blood pressure fluctuation experienced by these arteries. Cyclic strain does not induce a contractile response, like that observed in the myogenic response seen in small arteries, but prompts a substantial increase in the response to electrical stimulation. We coined this phenomenon "force potentiation." Because protein kinase C (PKC) and rho-kinase (ROCK) are known to play a role in increasing contractility of arterial smooth muscle by inhibition of myosin light chain phosphatase, and integrin-link kinase (ILK) is crucial in mechanotransduction, we examined how inhibition of these kinases affected force potentiation in sheep carotid artery. We found that phosphorylation of the regulatory myosin light chain was enhanced by cyclic strain, but the enhancement was observed only in activated, not in relaxed muscle. Inhibition of ROCK diminished force potentiation and active isometric force, likely due to the disinhibition of myosin light chain phosphatase. Inhibition of PKC abolished force potentiation without an effect on active force, suggesting a more exclusive role of PKC (compared with ROCK) in mediating force potentiation. Inhibition of ILK had a similar effect as PKC inhibition, suggesting that ILK may be an upstream kinase for PKC activation by mechanical stimuli. Taken together, the findings suggest that ILK, PKC, and ROCK are important kinases in the signal transduction pathway that mediate the effect of mechanical strain on force potentiation.NEW & NOTEWORTHY When subjected to mechanical strain, smooth muscle from large arteries has the ability to increase its force generation (force potentiation), which could be important in autoregulation of blood pressure. This phenomenon, however, does not involve a myogenic response, such as the one seen in small arteries and arterioles. Our work shows the involvement of ILK, PKC, and ROCK in the signal transduction pathway that mediates the force-potentiating effect of mechanical strain in large arteries.

Function Assessment of a Fabricated Artificial Vascular Graft in Sheep Carotid Artery

Function Assessment of a Fabricated Artificial Vascular Graft in Sheep Carotid Artery

Comparison of the Patency and Regenerative Potential of Biodegradable Vascular Prostheses of Different Polymer Compositions in an Ovine Model.

The lack of suitable autologous grafts and the impossibility of using synthetic prostheses for small artery reconstruction make it necessary to develop alternative efficient vascular grafts. In this study, we fabricated an electrospun biodegradable poly(ε-caprolactone) (PCL) prosthesis and poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/poly(ε-caprolactone) (PHBV/PCL) prosthesis loaded with iloprost (a prostacyclin analog) as an antithrombotic drug and cationic amphiphile with antibacterial activity. The prostheses were characterized in terms of their drug release, mechanical properties, and hemocompatibility. We then compared the long-term patency and remodeling features of PCL and PHBV/PCL prostheses in a sheep carotid artery interposition model. The research findings verified that the drug coating of both types of prostheses improved their hemocompatibility and tensile strength. The 6-month primary patency of the PCL/Ilo/A prostheses was 50%, while all PHBV/PCL/Ilo/A implants were occluded at the same time point. The PCL/Ilo/A prostheses were completely endothelialized, in contrast to the PHBV/PCL/Ilo/A conduits, which had no endothelial cells on the inner layer. The polymeric material of both prostheses degraded and was replaced with neotissue containing smooth-muscle cells; macrophages; proteins of the extracellular matrix such as type I, III, and IV collagens; and vasa vasorum. Thus, the biodegradable PCL/Ilo/A prostheses demonstrate better regenerative potential than PHBV/PCL-based implants and are more suitable for clinical use.

Features of remodeling of newly formed vascular tissue based on biodegradable vascular prostheses implanted in the carotid artery of sheep: morphogenetic analysis

Tissue-engineered vascular prostheses developed for prosthesis of small-diameter arteries have high biocompatibility and coverage of their patency after implantation into the vascular bed, and should also show a high probability of forming on their basis a newly formed tissue that is largely susceptible to native vascular tissue.Aim: To evaluate the expected patency of biodegradable vascular prostheses with athrombogenic drug coating in large laboratory animal models.Material and Methods. Vascular prostheses Ø 4 mm were fabricated by electrospinning from a polymer composition of 5% polyhydrosibutyrate/valeriate (PHBV) and 10% polycaprolactone (PCL) and a complex of proangiogenic tissues (GFmix): vascular endothelial growth (VEGF), rare fibroblast growth (bFGF) and chemoattractant molecule (SDF-1α). To induce thromboresistant properties of grafts, an athrombogenic modification of the surface of parts of the fabricated prostheses with heparin and iloprost was carried out. Modified prostheses were implanted in the carotid artery for a period of 12 months. The group with autoarterial implantation acted as a control.Results. In 12 months after implantation, the patency of auto-arterial grafts was 87.5%. The patency of PHBV/PCL/GFmix with heparin and iloprost reached 50% at the time of implantation. The biodegradable frame made of reinforced prostheses was almost completely resorbed with the formation of aneurysms throughout. In the modified prostheses, the main elements of the newly formed vascular tissue are present. There is no formation in the walls of the prostheses.Conclusion. The results showed that biodegradable vascular prostheses PHBV/PCL/GFmixHep/Ilo have a high final patency, which allows us to consider them suitable for the formation of newly formed vascular tissue on their basis. However, due to the aneurysm formation, a long-term execution of the bone tissue of the prosthesis and the thrombogenic properties of the inner surface are required.

The effect of Nano-liposomal sodium nitrite on smooth muscle cell growth in a tissue-engineered small-diameter vascular graft.

Nitric oxide is a chemical agent produced by endothelial cells in a healthy blood vessel, inhibiting the overgrowth of vascular smooth muscle cells and regulating vessel tone. Liposomes are biocompatible and biodegradable drug carriers with a similar structure to cell bilayer phospholipid membrane that can be used as useful nitric oxide carriers in vascular grafts. Using a custom-designed apparatus, the sheep carotid arteries were decellularized while still maintaining important components of the vascular extracellular matrix (ECM), allowing them to be used as small-diameter vascular grafts. A chemical signal of sodium nitrite was applied to control smooth muscle cells' behavior under static and dynamic cell culture conditions. The thin film hydration approach was used to create nano-liposomes, which were then used as sodium nitrite carriers to control the drug release rate and enhance the amount of drug loaded into the liposomes. The ratio of 80:20:2 for DPPC: Cholesterol: PEG was determined as the optimum formulation of the liposome structure with high drug encapsulation efficiency (98%) and optimum drug release rate (the drug release rate was 40%, 65%, and 83% after 24, 48, and 72h, respectively). MTT assay results showed an improvement in endothelial cell proliferation in the presence of nano-liposomal sodium nitrite (LNS) at the concentration of 0.5μg/mL. Using a suitable concentration of liposomal sodium nitrite (0.5μg/mL) put onto the constructed scaffold resulted in the controllable development of smooth muscle cells in the experiment. The culture of smooth muscle cells in a pulsatile perfusion bioreactor indicated that in the presence of synthesized liposomal sodium nitrite, the overgrowth of smooth muscle cells was inhibited in dynamic cell culture conditions. The mechanical properties of ECM graft were measured, and a multi-scale model with an accuracy of 83% was proposed to predict mechanical properties successfully. The liposomal drug-loaded small-diameter vascular graft can prevent the overgrowth of SMCs and the formation of intimal hyperplasia in the graft. Aside from that, the effect of LNS on endothelial has the potential to stimulate endothelial cell proliferation and re-endothelialization.

Evaluation of mechanical properties and biocompatibility of three-layer PCL/PLLA small-diameter vascular graft with pore diameter gradient

A three-layer small-diameter vascular graft (SDVG) of polycaprolactone (PCL) and l-polylactic acid (PLLA) with pore diameter gradient was prepared through combining variable-extrusion speed iterative electrospinning and ultrasonic reaming. The SEM results showed that the three-layer PCL/PLLA SDVG has distinct pore diameter gradient. The Young’s modulus, ultimate tensile strength (UTS), burst pressure (BP) and compliance of the vascular graft were high as 20.116 ± 0.465 MPa, 2.259 ± 0.141 MPa, 2050 ± 249 mmHg and 4.203 ± 0.330 %/100 mmHg, respectively. The UTS of the graft is similar to human coronary arteries. The BP meets the basic requirements to prevent aneurysmal dilation, and the compliance is higher than that of sheep carotid artery. The fluid–solid coupling simulation results showed that the graft had high mechanical properties to withstand the same blood flow velocity as human coronary arteries, and there was no stress concentration in the wall. Besides, it had good biocompatibility, promoting the adhesion and proliferation of rat vascular endothelial cells (ECs). The successful preparation of the small-diameter vascular graft with high mechanical properties for preventing itself from rupturing and ensuring the overall function, provides more possibilities for the clinical transplantation of small-diameter vascular grafts.

Results of preclinical trials in a sheep model of biodegradable small-diameter vascular grafts

Surface modification of polymer vascular matrices is a promising development for preventing vascular graft thrombosis, improving long-term patency and accelerating remodeling. Objective: to study the outcomes of long-term patency of PHBV/PCL/GFmix grafts with iloprost (Ilo) and heparin (Hep) implanted into the carotid artery of sheep. Materials and methods. Matrices ∅4 mm were fabricated by electrospinning from a polymer composition of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(ε-caprolactone) (PCL) with incorporation of endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF) and chemoattractant molecule (SDF-1α). The fabricated matrices were then modified with Ilo and Hep by complexation via polyvinylpyrrolidone (PVP). Synthetic Gore-Tex grafts were used as a comparison group. The physical and mechanical properties of the studied matrix groups were evaluated, the surface structure of vascular grafts before and after implantation was assessed. Vascular grafts were implanted into the carotid artery of a sheep. The explanted samples were studied via histological and immunofluorescence analysis, the elemental composition of the obtained vascular graft samples was also assessed, and the gene expression profile was evaluated. Results. One day after implantation, the patency of PHBV/PCL/GFmixHep/Ilo vascular grafts was 62.5%, whereas synthetic Gore-Tex grafts had thrombosis in 100% of cases. At the same time, after 18 months of implantation, the patency of biodegradable PHBV/PCL/GFmixHep/Ilo vascular grafts decreased to 50%. Permeable drug-coated polymer grafts were completely reabsorbed after 18 months of implantation, and aneurysmally dilated newly-formed vascular tissue was formed in their place. Conclusion. Modification of the surface of PHBV/PCL/GFmix polymer grafts with Hep + Ilo coating improved long-term patency outcomes compared to synthetic Gore-Tex grafts.

Tissue-Engineered Carotid Artery Interposition Grafts Demonstrate High Primary Patency and Promote Vascular Tissue Regeneration in the Ovine Model.

Tissue-engineered vascular graft for the reconstruction of small arteries is still an unmet clinical need, despite the fact that a number of promising prototypes have entered preclinical development. Here we test Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)Poly(ε-caprolactone) 4-mm-diameter vascular grafts equipped with vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF) and stromal cell-derived factor 1α (SDF-1α) and surface coated with heparin and iloprost (PHBV/PCL[VEGF-bFGF-SDF]Hep/Ilo, n = 8) in a sheep carotid artery interposition model, using biostable vascular prostheses of expanded poly(tetrafluoroethylene) (ePTFE, n = 5) as a control. Primary patency of PHBV/PCL[VEGF-bFGF-SDF]Hep/Ilo grafts was 62.5% (5/8) at 24 h postimplantation and 50% (4/8) at 18 months postimplantation, while all (5/5) ePTFE conduits were occluded within the 24 h after the surgery. At 18 months postimplantation, PHBV/PCL[VEGF-bFGF-SDF]Hep/Ilo grafts were completely resorbed and replaced by the vascular tissue. Regenerated arteries displayed a hierarchical three-layer structure similar to the native blood vessels, being fully endothelialised, highly vascularised and populated by vascular smooth muscle cells and macrophages. The most (4/5, 80%) of the regenerated arteries were free of calcifications but suffered from the aneurysmatic dilation. Therefore, biodegradable PHBV/PCL[VEGF-bFGF-SDF]Hep/Ilo grafts showed better short- and long-term results than bio-stable ePTFE analogues, although these scaffolds must be reinforced for the efficient prevention of aneurysms.

Long-term results of triple-layered small diameter vascular grafts in sheep carotid arteries

There is an urgent clinical for small diameter vascular grafts (SDVGs) for use in the treatment of coronary artery disease. Moreover, biodegradable SDVGs are drawing increasing attention because they have the potential to restore vascular function with the degradation of vascular graft and tissue regeneration. In this study, we designed triple-layered SDVGs to mimic the native arterial structure, with each layer contributing its unique porosity to the porous structure. We evaluated triple-layered SDVGs in a sheep carotid arterial replacement model. After implantation for 12 months, two grafts were patent and indicated the feasibility of using grafts in large animals. Nevertheless, it was determined that both grafts formed aneurysms at the proximal end. The prevention of such aneurysms remains a challenge for future investigation.

Development and in Vivo Evaluation of a Biodegradable Vascular Graft Reinforced with a Fused PCL Filament

Tissue-engineered vascular grafts developed for cardiovascular surgery must be fully functional after implantation, resistant to all types of kinks, compression and burst pressure. One of the approaches to improve mechanical properties includes the reinforcement with an outer polymeric sheath. This study was aimed at evaluating the mechanical properties of a tissue-engineered vascular graft reinforced with a fused PCL filament and in vivo testing in a carotid artery of sheep within one year.

In vivo endothelialization and neointimal hyperplasia assessment after angioplasty of sheep carotid artery with a novel polycarbonate polyurethane patch.

The aim of this study was to compare two variants of a novel polycarbonate polyurethane prosthesis with polyethylene terephthalate (Dacron) prosthesis in an established sheep model of carotid patch angioplasty. Two variants of the polycarbonate polyurethane prosthesis were used: (1) Polycarbonate polyurethane equal (PCU-e) prosthesis consisted of a multilayered porous structure with equal internal and external layers; (2) Polycarbonate polyurethane with more porous inner layers (PCU-mp) prosthesis had more porous inner layers than external layers. Carotid patch angioplasty was performed in 12 sheep: in six sheep, the PCU-e variant and in the other six sheep, the PCU-mp variant was implanted. Dacron patches were implanted in the contralateral carotid artery of all sheep as a control. Half of the animals with each polycarbonate polyurethane variant were euthanized after two weeks and the other half after eight weeks. Cellular infiltration, endothelialization, and neointimal hyperplasia were examined. All grafts were patent, and no thrombus was seen in any of the harvested arteries. The pores of all the three patch materials allowed infiltration of inflammatory cells, capillaries, and connective tissue. After eight weeks, a nearly complete endothelialization was visible in all patch groups without an obvious difference between the three patch materials. The neointima was thinner in the PCU patches (PCU-e: 56 ± 13 µm, PCU-mp: 119 ± 60 µm) when compared to Dacron patches (156 ± 64 µm) after two weeks. After 8 weeks, a further neointimal growth was detectable, without any significant difference of neointimal thickness between the three patch materials (Dacron: 274 ± 82 µm, PCU-e: 324 ± 98 µm, PCU-mp: 235 ± 59 µm). With the novel polycarbonate polyurethane patch materials, we achieved promising functional and morphological results with 100% patency and nearly complete endothelialization. Our findings showed at least a non-inferiority of the novel polycarbonate polyurethane patch material compared to Dacron. There were no significant differences detected between the two polycarbonate polyurethane patch variants.

Carboxymethyl kappa carrageenan-modified decellularized small-diameter vascular grafts improving thromboresistance properties.

The development of decellularized small-diameter vascular grafts is a potential solution for patients requiring vascular reconstructive procedures. However, there is a limitation for acellular scaffolds due to incomplete recellularization and exposure of extracellular matrix components to whole blood resulting in platelet adhesion. To address this issue, a perfusion decellularization method was developed using a custom-designed set up which completely removed cell nuclei and preserved three-dimensional structure and mechanical properties of native tissue (sheep carotid arteries). Afterwards, carboxymethyl kappa carrageenan (CKC) was introduced as a novel anticoagulant in vascular tissue engineering which can inhibit thrombosis formation. The method enabled uniform immobilization of CKC on decellularized arteries as a result of interaction between amine functional groups of decellularized arteries and carboxyl groups of CKC. The CKC modified graft significantly reduced platelet adhesion from 44.53 ± 2.05% (control) to 19.57 ± 1.37% (modified) and supported endothelial cells viability, proliferation, and nitric oxide production. Overall, the novel CKC modified scaffold provides a promising solution for thrombosis formation of small-diameter vessels and could be a potent graft for future in vivo applications in vascular bypass procedures. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1690-1701, 2019.

Endovascular Electrical Stimulation - A Novel Hemorrhage Control Technique.

In this study we present a novel approach for inducing vasoconstriction by pulsed electrical treatment delivered via endovascular electrodes, which can be used in cases where external access to the vessel is limited. Using computer simulations, we optimized various geometries of endovascular electrodes to maximize the induced electric field on the arterial wall. Using the optimal configuration parameters, we investigated endovascular induced vasoconstriction in both the carotid and femoral sheep arteries. Endovascular electrodes induced robust vasoconstriction in the carotid artery of sheep, showing gradual recovery following treatment. Moreover, the obtained vasoconstriction was accompanied by a sevenfold decrease in blood loss for 100% constriction, compared with no treatment (6ml vs 42ml, p<0.001). The femoral artery was less amenable to the electrical treatment, which we hypothesize results from the reduced density of the sympathetic system's innervation of the adventitia of the sheep femoral artery, as was validated by immunohistochemical analysis. Finally, treatment safety was validated through arterial histological studies, in which no adverse effect was observed, and through computer modeling, which depicted a negligible temperature increase. These results are an important step toward developing a novel approach for inducing reversible and controlled vasoconstriction in arteries that are remote from access.