Small-Diameter Synthetic Vascular Graft Immobilized with the REDV Peptide Reduces Early-Stage Fibrin Clot Deposition and Results in Graft Patency in Rats

Pro-endothelialization of nitinol alloy cardiovascular stents enhanced by the programmed assembly of exosomes and endothelial affinity peptide

Stent implantation is one of the most effective methods for the treatment of atherosclerosis. Nitinol stent is a type of stent with good biocompatibility and relatively mature development; however, it cannot effectively achieve long-term anticoagulation and early endothelialization. In this study, nitinol surfaces with the programmed assembly of heparin, exosomes from endothelial cells, and endothelial affinity peptide (REDV) were fabricated through layer-by-layer assembly technology and click-chemistry, and then exosomes/REDV-modified nitinol interface (ACC-Exo-REDV) was prepared. ACC-Exo-REDV could promote the rapid proliferation and adhesion of endothelial cells and achieve anticoagulant function in the blood. Besides, ACC-Exo-REDV had excellent anti-inflammatory properties and played a positive role in the transformation of macrophage from the pro-inflammatory to anti-inflammatory phenotype. Ex vivo and in vivo experiments demonstrated the effectiveness of ACC-Exo-REDV in preventing thrombosis and hyperplasia formation. Hence, the programmed assembly of exosome interface could contribute to endothelialization and have potential application on the cardiovascular surface modification to prevent stent thrombosis and restenosis.

Characterization and promotion of endothelialization of Bombyx mori silk fibroin functionalized with REDV peptide

In the development of small-diameter vascular grafts, it is crucial to achieve early-stage endothelialization to prevent thrombus formation and intimal hyperplasia. Silk fibroin (SF) from Bombyx mori is commonly used for such grafts. However, there is a need to expedite endothelialization post-implantation. In this study, we functionalized SF with Arg-Glu-Asp-Val (REDV) (SF + REDV) using cyanuric chloride to enhance endothelialization. The immobilization of REDV onto SF was confirmed and the amount of immobilized REDV could be calculated by 1H NMR. Furthermore, the conformational changes in Tyr, Ser, and Ala residues in [3-13C]Tyr- and [3-13C]Ser-SF due to REDV immobilization were monitored using 13C solid-state NMR. The REDV immobilized onto the SF film was found to be exposed on the film's surface, as confirmed by biotin-avidin system. Cell culture experiments, including adhesiveness, proliferation, and extensibility, were conducted using normal human umbilical vein endothelial cells (HUVEC) and normal human aortic smooth muscle cells (HAoSMC) on both SF and SF + REDV films to evaluate the impact of REDV on endothelialization. The results indicated a trend towards promoting HUVEC proliferation while inhibiting HAoSMC proliferation. Therefore, these findings suggest that SF + REDV may be more suitable than SF alone for coating small-diameter SF knitted tubes made of SF threads.

Vascular tissue reconstruction by monocyte subpopulations on small-diameter acellular grafts via integrin activation

Although the clinical application of cell-free tissue-engineered vascular grafts (TEVGs) has been proposed, vascular tissue regeneration mechanisms have not been fully clarified. Here, we report that monocyte subpopulations reconstruct vascular-like tissues through integrin signaling. An Arg-Glu-Asp-Val peptide-modified acellular long-bypass graft was used as the TEVG, and tissue regeneration in the graft was evaluated using a cardiopulmonary pump system and porcine transplantation model. In 1 day, the luminal surface of the graft was covered with cells that expressed CD163, CD14, and CD16, which represented the monocyte subpopulation, and they exhibited proliferative and migratory abilities. RNA sequencing showed that captured cells had an immune-related phenotype similar to that of monocytes and strongly expressed cell adhesion-related genes. In vitro angiogenesis assay showed that tube formation of the captured cells occurred via integrin signal activation. After medium- and long-term graft transplantation, the captured cells infiltrated the tunica media layer and constructed vascular with a CD31/CD105-positive layer and an αSMA-positive structure after 3 months. This finding, including multiple early-time observations provides clear evidence that blood-circulating monocytes are directly involved in vascular remodeling.

Double-layered blood vessels over 3 mm in diameter extruded by the inverse-gravity technique

One of the most promising techniques for treating severe peripheral artery disease is the use of cellular tissue-engineered vascular grafts (TEVGs). This study proposes an inverse-gravity (IG) extrusion technique for creating long double-layered cellular TEVGs with diameters over 3 mm. A three-layered coaxial laminar hydrogel flow in an 8 mm-diameter pipe was realised simply by changing the extrusion direction of the hydrogel from being aligned with the direction of gravity to against it. This technique produced an extruded mixture of human aortic smooth muscle cells (HASMCs) and type-I collagen as a tubular structure with an inner diameter of 3.5 mm. After a 21 day maturation period, the maximal burst pressure, longitudinal breaking force, and circumferential breaking force of the HASMC TEVG were 416 mmHg, 0.69 N, and 0.89 N, respectively. The HASMC TEVG was endothelialised with human umbilical vein endothelial cells to form a tunica intima that simulated human vessels. Besides subcutaneous implantability on mice, the double-layered blood vessels showed a considerably lower adherence of platelets and red blood cells once exposed to heparinised mouse blood and were considered nonhaemolytic. The proposed IG extrusion technique can be applied in various fields requiring multilayered materials with large diameters.

Multifunctional nanoparticle-VEGF modification for tissue-engineered vascular graft to promote sustained anti-thrombosis and rapid endothelialization

Purpose: The absence of a complete endothelial cell layer is a well-recognized reason leading to small-diameter tissue-engineered vascular graft failure. Here we reported a multifunctional system consisting of chitosan (CS), Arg-Glu-Asp-Val (REDV) peptide, heparin, and vascular endothelial growth factor (VEGF) to achieve sustained anti-thrombosis and rapid endothelialization for decellularized and photo-oxidized bovine internal mammary arteries (DP-BIMA). Methods: CS-REDV copolymers were synthesized via a transglutaminase (TGase) catalyzed reaction. CS_-REDV-Hep nanoparticles were formed by electrostatic self-assembly and loaded on the DP-BIMA. The quantification of released heparin and vascular endothelial growth factor was detected. Hemolysis rate, platelets adhesion, endothelial cell (EC) adhesion and proliferation, and MTT assay were performed in vitro. The grafts were then tested in a rabbit abdominal aorta interposition model for 3 months. The patency rates were calculated and the ECs regeneration was investigated by immunofluorescence staining of CD31, CD144, and eNOS antibodies. Results: The nanoparticle-VEGF system (particle size: 61.8 ± 18.3 nm, zeta-potential: +13.2 mV, PDI: .108) showed a sustained and controlled release of heparin and VEGF for as long as 1 month and exhibited good biocompatibility, a lower affinity for platelets, and a higher affinity for ECs in vitro. The nanoparticle-VEGF immobilized BIMA achieved 100% and 83.3% patency in a rabbit abdominal interposition model during 1 and 3 months, respectively, without any thrombogenicity and showed CD31, CD144, eNOS positive cell adhesion as early as 1 day. After 3 months, CD31, CD144, and eNOS positive cells covered almost the whole luminal surface of the grafts. Conclusion: The results demonstrated that the multifunctional nanoparticle-VEGF system can enhance the anti-thrombosis property and promote rapid endothelialization of small-diameter tissue-engineered vascular grafts. Utilizing nanoparticles to combine different kinds of biomolecules is an appropriate technology to improve the long-term patency of small-diameter tissue-engineered vascular grafts.

Heparin/Collagen-REDV Modification of Expanded Polytetrafluoroethylene Improves Regional Anti-thrombosis and Reduces Foreign Body Reactions in Local Tissues

Prosthetic implants of expanded polytetrafluoroethylene (ePTFE) in the cardiovascular system have a high failure rate over the long term because of thrombosis and intimal hyperplasia. Although multiple surface modification methods have been applied to improve the anti-thrombotic and in situ endothelialization abilities of ePTFE, none have delivered outstanding results in vivo. Our previous study combined heparin/collagen multilayers and REDV peptides to modify ePTFE, and the in-vitro results showed that modification ePTFE with heparin/collagen-REDV can promote the cytocompatibility and antiplatelet property. This study illustrated the physical change, selective endothelial cells capture ability, and in vivo performance in further. The physical test demonstrated that this modification improved the hydrophilicity, flexibility and strength of ePTFE. A competition experiment of co-cultured endothelial cells and vascular smooth muscle cells verified that the heparin/collagen-REDV modification had high specificity for endothelial cell capture. A rabbit animal model was constructed to evaluate the in vivo performance of modified ePTFE implanted in the right ventricular outflow tract. The results showed that heparin/collagen-REDV modification was safe, promoted endothelialization, and successfully achieved regional anti-thrombosis without influencing body-wide coagulation function. The pathologic manifestations and mRNA expression pattern in tissues in contact with modified ePTFE indicated that this modification method may reduce M2-type macrophage infiltration and the expression of genes related to immune and inflammatory responses. The heparin/collagen-REDV modification may lower the incidence of complications related to ePTFE implantation and has good prospects for clinical use.

Advantages of Fibrin Polymerization Method without the Use of Exogenous Thrombin for Vascular Tissue Engineering Applications

Fibrin is widely used in vascular tissue engineering. Typically, fibrin polymerization is initiated by adding exogenous thrombin. In this study, we proposed a protocol for the preparation of completely autologous fibrin without the use of endogenous thrombin and compared the properties of the prepared fibrin matrix with that obtained by the traditional method. Fibrinogen was obtained by ethanol precipitation followed by fibrin polymerization by adding either exogenous thrombin and calcium chloride (ExThr), or only calcium chloride (EnThr). We examined the structure, mechanical properties, thrombogenicity, degradation rate and cytocompatibility of fibrin matrices. Factor XIII (FXIII) quantitative assay was performed by ELISA, and FXIII activity was assessed by SDS-PAGE detection of γ-γ cross-links. The results show that network structure of EnThr fibrin was characterized by thinner fibers. The EnThr fibrin matrices had higher strength, stiffness and resistance to proteolytic degradation compared to ExThr fibrin. EnThr fibrin matrices exhibited less thrombogenicity in vitro than ExThr, and retained high cytocompatibility. Thus, the proposed approach has several advantages over the traditional method, namely the fabrication of a completely autologous coating material that has better mechanical properties, higher resistance to proteolysis and lower thrombogenicity.

A nitric oxide-eluting and REDV peptide-conjugated coating promotes vascular healing

Drug-eluting stents (DESs) placement remarkably reduces the over-proliferation of smooth muscle cells (SMCs) and thus neointimal hyperplasia. However, the pharmacological agent also slows down the re-endothelization, delays injury vascular healing and increases the risk of in-stent restenosis (ISR). Here, inspired by mussel foot proteins (Mfps), a mimicking endothelium functional stent coating was efficiently fabricated by thiol-ene "click" reaction, consisting of catechol grafted chitosan (CS-C), zinc sulfate, and Arg-Glu-Asp-Val (REDV) peptide. The mimicking endothelium coating could continuously catalyze endogenous nitric oxide (NO) gas and maintain the bioactivity of REDV peptide. Compared with bare stents, the mimicking coatings significantly inhibited the acute thrombosis for the first 1-week, accelerated re-endothelization and decreased in-stent restenosis for 1- and 3-month after implantation. In addition, the synergistic effect of NO and REDV peptide also regulated inflammation response and promoted the expression of muscle fiber.

Vascular transplantation with dual-biofunctional ePTFE vascular grafts in a porcine model

Cardiovascular disease (CVD) poses serious health concerns worldwide. The lack of transplantable vascular grafts is an unmet clinical need in the surgical treatment of CVD. Although expanded polytetrafluoroethylene (ePTFE) vascular grafts have been used in clinical practice, a low long-term patency rate in small-diameter transplantation application is still the biggest challenge. Thus, surface modification of ePTFE is sought after. In this study, polydopamine (PDA) was used to improve the hydrophilia and provide immobilization sites in ePTFE. Bivalirudin (BVLD), a direct thrombin inhibitor, was used to enhance the anti-thrombotic activity of ePTFE. The peptides derived from extracellular matrix proteins were used to elevate the bioactivity of ePTFE. The morphology, chemical composition, peptide modified strength, wettability, and hemocompatibility of modified ePTFE vascular grafts were investigated. Then, an endothelial cell proliferation assay was used to evaluate the best co-modification strategy of the ePTFE vascular graft in vitro. Since a large animal could relatively better mimic human physiology, we chose a porcine carotid artery replacement model in the current study. The results showed that the BVLD/REDV co-modified ePTFE vascular grafts had a satisfactory patency rate (66.7%) and a higher endothelial cell coverage ratio (70%) at 12 weeks after implantation. This may offer an opportunity to produce a multi-biofunctional ePTFE vascular graft, thereby yielding a potent product to meet the clinical needs.

Identification of circulating cells interacted with integrin α4β1 ligand peptides REDV or HGGVRLY

Recently, artificial blood vessels modified by integrin α4β1 ligand, such as REDV, showed endothelialization improvement and antithrombotic properties have been reported. Early endothelialization was affected by the type of circulating cells captured by the peptide in the initial transplantation state, however, it is still not clarified. In this study, we identified in vitro circulating cells bound with the peptides arginine-glutamic acid-aspartic acid-valine (REDV) or histidine-glycine-glycine-valine-arginine-leucine-tyrosine (HGGVRLY). The effect of free C- or N-terminal of HGGVRLY on the type of peptide-binding cells was also studied. The rat circulating cells were isolated from blood and incubated with 5(6)-carboxyfluorescein (5/6-FAM, F) labeled F-REDV (C-terminal free), F-HGGVRLY (C-terminal free), or HGGVRLY-F (N-terminal free). Furthermore, peptide-binding cells were identified by co-staining with various antibodies labeled with PE, PerCP/Cy5.5, or APC. N-terminal free HGGVRLY-F was found to bind to more circulating cells than C-terminal free F-REDV and F-HGGVRLY. The ratio of integrin α4β1 positive cell bound with F-REDV, F-HGGVRLY, or HGGVRLY-F reached over 90 %, demonstrating that HGGVRLY is also a ligand of integrin α4β1. Among identified cell types, we found that F-REDV mainly bounds with EPC and BMSC, while F-HGGVRLY with BMSC. HGGVRLY-F bounds with EPC and BMSC, exhibiting a higher EPC binding ratio than F-REDV and F-HGGVRLY.