Effect of implantation site on outcome of tissue-engineered vascular grafts

BALANCING SCAFFOLD DEGRADATION AND NEO-TISSUE FORMATION IN IN-SITU TISSUE ENGINEERED VASCULAR GRAFTS

An essential aspect of cardiovascular in situ tissue engineering (TE) is to ensure balance between scaffold degradation and neo-tissue formation. We evaluated the degradation velocity and neo-tissue formation of three electrospun supramolecular bisurea-based biodegradable scaffolds that differ in their soft-block backbone compositions only. Scaffolds were implanted as interposition grafts in the abdominal aorta in rats, and evaluated at different time points (t = 1, 6, 12, 24 and 40 weeks) on function, tissue formation, strength and scaffold degradation. The fully carbonate-based biomaterial showed minor degradation after 40 weeks in vivo, while the other two ester-containing biomaterials showed (near) complete degradation within 6 to 12 weeks. Local dilatation was only observed in these faster degrading scaffolds. All materials showed to some extent calcifications, at early as well as late time points. Histological evaluation showed equal and non-native like neo-tissue formation after total degradation. The fully carbonate based scaffolds lagged in neo-tissue formation, presumably as its degradation was (far from) complete at 40 weeks. A significant difference in vessel wall contrast enhancement was observed by MRI between grafts with total compared to minimal degraded scaffolds.

Functional regeneration at the blood-biomaterial interface

The use of cardiovascular implants is commonplace in clinical practice. However, reproducing the key bioactive and adaptive properties of native cardiovascular tissues with an artificial replacement is highly challenging. Exciting new treatment strategies are under development to regenerate (parts of) cardiovascular tissues directly in situ using immunomodulatory biomaterials. Direct exposure to the bloodstream and hemodynamic loads is a particular challenge, given the risk of thrombosis and adverse remodeling that it brings. However, the blood is also a source of (immune) cells and proteins that dominantly contribute to functional tissue regeneration. This review explores the potential of the blood as a source for the complete or partial in situ regeneration of cardiovascular tissues, with a particular focus on the endothelium, being the natural blood-tissue barrier. We pinpoint the current scientific challenges to enable rational engineering and testing of blood-contacting implants to leverage the regenerative potential of the blood.

Construction of PCL-collagen@PCL@PCL-gelatin three-layer small diameter artificial vascular grafts by electrospinning

The demand for artificial vascular grafts in clinical applications is increasing, and it is urgent to design a tissue-engineered vascular graft with good biocompatibility and sufficient mechanical strength. In this study, three-layer small diameter artificial vascular grafts were constructed by electrospinning. Polycaprolactone (PCL) and collagen (COL) were used as the inner layer to provide good biocompatibility and cell adhesion, the middle layer was PCL to improve the mechanical properties, and gelatin (GEL) and PCL were used to construct the outer layer for further improving the mechanical properties and biocompatibility of the vascular grafts in the human body environment. The electrospun artificial vascular graft had good biocompatibility and mechanical properties. Its longitudinal maximum stress reached 2.63 ± 0.12 MPa, which exceeded the maximum stress that many natural blood vessels could withstand. The fiber diameter of the vascular grafts was related to the proportion of components that made up the vascular grafts. In the inner structure of the vascular grafts, the hydrophilicity of the vascular grafts was enhanced by the addition of COL to the PCL, and human umbilical vein endothelial cells (HUVECs) adhered more easily to the vascular grafts. In particular, the cytocompatibility and proliferation of HUVECs on the scaffold with an inner structure PCL:COL = 2:1 was superior to other ratios of vascular grafts. The vascular grafts did not cause hemolysis of red blood cells. Thus, the bionic PCL-COL@PCL@PCL-GEL composite graft is a promising material for vascular tissue engineering.

Animal studies for the evaluation of in situ tissue-engineered vascular grafts - a systematic review, evidence map, and meta-analysis

Vascular in situ tissue engineering (TE) is an approach that uses bioresorbable grafts to induce endogenous regeneration of damaged blood vessels. The evaluation of newly developed in situ TE vascular grafts heavily relies on animal experiments. However, no standard for in vivo models or study design has been defined, hampering inter-study comparisons and translational efficiency. To provide input for formulating such standard, the goal of this study was to map all animal experiments for vascular in situ TE using off-the-shelf available, resorbable synthetic vascular grafts. A literature search (PubMed, Embase) yielded 15,896 studies, of which 182 studies met the inclusion criteria (n = 5,101 animals). The reports displayed a wide variety of study designs, animal models, and biomaterials. Meta-analysis on graft patency with subgroup analysis for species, age, sex, implantation site, and follow-up time demonstrated model-specific variations. This study identifies possibilities for improved design and reporting of animal experiments to increase translational value.

Decellularized Scaffold-based Poly(ethylene glycol) Biomimetic Vascular Patches Modified with Polyelectrolyte Multilayer of Heparin and Chitosan: Preparation and Vascular Tissue Engineering Applications in a Porcine Model

The mechanical property mismatch between vascular patches and native blood vessels can result in post-operation failure, so it is important to develop vascular patches that mimic the biomechanical properties of...

Systematic Review of Tissue-Engineered Vascular Grafts

Pathologies related to the cardiovascular system are the leading causes of death worldwide. One of the main treatments is conventional surgery with autologous transplants. Although donor grafts are often unavailable, tissue-engineered vascular grafts (TEVGs) show promise for clinical treatments. A systematic review of the recent scientific literature was performed using PubMed (Medline) and Web of Science databases to provide an overview of the state-of-the-art in TEVG development. The use of TEVG in human patients remains quite restricted owing to the presence of vascular stenosis, existence of thrombi, and poor graft patency. A total of 92 original articles involving human patients and animal models were analyzed. A meta-analysis of the influence of the vascular graft diameter on the occurrence of thrombosis and graft patency was performed for the different models analyzed. Although there is no ideal animal model for TEVG research, the murine model is the most extensively used. Hybrid grafting, electrospinning, and cell seeding are currently the most promising technologies. The results showed that there is a tendency for thrombosis and non-patency in small-diameter grafts. TEVGs are under constant development, and research is oriented towards the search for safe devices.

Functionalized Silk Vascular Grafts with Decellularized Human Wharton's Jelly Improves Remodeling via Immunomodulation in Rabbit Jugular Vein

Cell-free polymeric tissue-engineered vascular grafts (TEVGs) have shown great promise towards clinical translation; however, their limited bioactivity and remodeling ability challenge this cause. Here, a novel cell-free bioresorbable small diameter silk TEVG system functionalized with decellularized human Wharton's jelly (dWJ) matrix is developed and successfully implanted as interposition grafts into rabbit jugular vein. Implanted TEVGs remain patent for two months and integrate with host tissue, demonstrating neo-tissue formation and constructive remodeling. Mechanistic analysis reveals that dWJ matrix is a reservoir of various immunomodulatory cytokines (Interleukin-8, 6, 10, 4 and tumor necrosis factor alpha (TNF-α)), which aids in upregulating M2 macrophage-associated genes facilitating pro-remodeling behavior. Besides, dWJ treatment to human endothelial cells upregulates the expression of functional genes (cluster of differentiation 31 (CD31), endothelial nitric oxide synthase (eNOS), and vascular endothelial (VE)-cadherin), enables faster cell migration, and elevates nitric oxide (NO) production leading to the in situ development of endothelium. The dWJ functionalized silk TEVGs support increased host cell recruitment than control, including macrophages and vascular cells. It endows superior graft remodeling in terms of a dense medial layer comprising smooth muscle cells and elevates the production of extracellular matrix proteins (collagen and elastin). Altogether, these findings suggest that dWJ functionalization imitates the usefulness of cell seeding and enables graft remodeling.

Small diameter polycaprolactone vascular grafts are patent in sheep carotid bypass but require antithrombotic therapy

Background: Polycaprolactone (PCL) scaffolds exhibit high biocompatibility and are attractive as vascular conduits. Materials & methods: PCL tubes were cultivated in bioreactor with human adipose regenerative cells to assess ex vivo cytocompatibility, whereas in vivo PCL tube patency was evaluated in sheep carotid bypass with and without antithrombotic treatment. Results: Ex vivo results revealed increasing adipose regenerative cells on PCL using dynamic bioreactor culturing. In vivo data showed that 67% (2/3) of grafts in the antithrombotic group were patent at day 28, while 100% (3/3) of control grafts were occluded already during the first week due to thrombosis. Histology showed that patent PCL grafts were recellularized by host cells. Conclusion: PCL tubes may work as small diameter vascular scaffolds under antithrombotic treatment.

Evaluation of remodeling and regeneration of electrospun PCL/fibrin vascular grafts in vivo

The success of artificial vascular graft in the host to obtain functional tissue regeneration and remodeling is a great challenge in the field of small diameter tissue engineering blood vessels. In our previous work, poly(ε-caprolactone) (PCL)/fibrin vascular grafts were fabricated by electrospinning. It was proved that the PCL/fibrin vascular graft was a suitable small diameter tissue engineering vascular scaffold with good biomechanical properties and cell compatibility. Here we mainly examined the performance of PCL/fibrin vascular graft in vivo. The graft showed randomly arranged nanofiber structure, excellent mechanical strength, higher compliance and degradation properties. At 9 months after implantation in the rat abdominal aorta, the graft induced the regeneration of neoarteries, and promoted ECM deposition and rapid endothelialization. More importantly, the PCL/fibrin vascular graft showed more microvessels density and fewer calcification areas at 3 months, which was beneficial to improve cell infiltration and proliferation. Moreover, the ratio of M2/M1macrophage in PCL/fibrin graft had a higher expression level and the secretion amount of pro-inflammatory cytokines started to increase, and then decreased to similar to the native artery. Thus, the electrospun PCL/fibrin tubular vascular graft had great potential to become a new type of artificial blood vessel scaffold that can be implanted in vivo for long term.

Arteriovenous access in hemodialysis: A multidisciplinary perspective for future solutions

In hemodialysis, vascular access is a key issue. The preferred access is an arteriovenous fistula on the non-dominant lower arm. If the natural vessels are insufficient for such access, the insertion of a synthetic vascular graft between artery and vein is an option to construct an arteriovenous shunt for punctures. In emergency situations and especially in elderly with narrow and atherosclerotic vessels, a cuffed double-lumen catheter is placed in a larger vein for chronic use. The latter option constitutes a greater risk for infections while arteriovenous fistula and arteriovenous shunt can fail due to stenosis, thrombosis, or infections. This review will recapitulate the vast and interdisciplinary scenario that characterizes hemodialysis vascular access creation and function, since adequate access management must be based on knowledge of the state of the art and on future perspectives. We also discuss recent developments to improve arteriovenous fistula creation and patency, the blood compatibility of arteriovenous shunt, needs to avoid infections, and potential development of tissue engineering applications in hemodialysis vascular access. The ultimate goal is to spread more knowledge in a critical area of medicine that is importantly affecting medical costs of renal replacement therapies and patients’ quality of life.