Improvements in GORE-TEX vascular graft performance by Carmeda BioActive surface heparin immobilization

Improving the hemocompatibility of a porohyperelastic layered vascular graft using luminal reversal microflows

Vascular graft thrombosis is a long-standing clinical problem. A myriad of efforts have been devoted to reducing thrombus formation following bypass surgery. Researchers have primarily taken a chemical approach to engineer and modify surfaces, seeking to make them more suitable for blood contacting applications. Using mechanical forces and surface topology to prevent thrombus formation has recently gained more attention. In this study, we have designed a bilayered porous vascular graft capable of repelling platelets and destabilizing absorbed protein layers from the luminal surface. During systole, fluid penetrates through the graft wall and is subsequently ejected from the wall into the luminal space (Luminal Reversal Flow - LRF), pushing platelets away from the surface during diastole. In-vitro hemocompatibility tests were conducted to compare platelet deposition in high LRF grafts with low LRF grafts. Graft material properties were determined and utilized in a porohyperelastic (PHE) finite element model to computationally predict the LRF generation in each graft type. Hemocompatibility testing showed significantly lower platelet deposition values in high versus low LRF generating grafts (median±IQR = 5,708 ± 987 and 23,039 ± 3,310 platelets per mm2, respectively, p=0.032). SEM imaging of the luminal surface of both graft types confirmed the quantitative blood test results. The computational simulations of high and low LRF generating grafts resulted in LRF values of -10.06 μm/s and -2.87 μm/s, respectively. These analyses show that a 250% increase in LRF is associated with a 75.2% decrease in platelet deposition. PHE vascular grafts with high LRF have the potential to improve anti-thrombogenicity and reduce thrombus-related post-procedure complications. Additional research is required to overcome the limitations of current graft fabrication technologies that further enhance LRF generation.

Photoresponsive heparin ionic complexes toward controllable therapeutic efficacy of anticoagulation

Controllable heparin-release is of great importance and necessity for the precise anticoagulant regulation. Efforts have been made on designing heparin-releasing systems, while, it remains a great challenge for gaining the external-stimuli responsive heparin-release in either intravenous or catheter delivery. In this study, an azobenzene-containing ammonium surfactant is designed and synthesized for the fabrication of photoresponsive heparin ionic complexes through the electrostatic complexation with heparin. Under the assistance of photoinduced trans-cis isomerization of azobenzene, the obtained heparin materials perform reversible athermal phase transition between ordered crystalline and isotropic liquid state at room temperature. Compared to the ordered state, the formation of isotropic state can effectively improve the dissolving of heparin from ionic materials in aqueous condition, which realizes the photo-modulation on the concentration of free heparin molecules. With good biocompatibility, such a heparin-releasing system addresses photoresponsive anticoagulation in both in vitro and in vivo biological studies, confirming its great potential clinical values. This work provides a new designing strategy for gaining anticoagulant regulation by light, also opening new opportunities for the development of photoresponsive drugs and biomedical materials based on biomolecules.

Long-term outcomes of below-the-knee bypass surgery using heparin-bonded expanded polytetrafluoroethylene grafts

PURPOSE

To report the outcomes of below-the-knee (BK) bypass surgery using heparin-bonded expanded polytetrafluoroethylene (ePTFE) grafts, performed in two centers since its launch in Japan.

METHODS

We conducted a retrospective analysis of databases from two medical centers, evaluating 51 limbs in 42 consecutive patients with peripheral arterial disease (PAD), who underwent BK bypass surgery using heparin-bonded ePTFE grafts between October, 2013 and April, 2023.

RESULTS

Thirty-three limbs (64.7%) were classified as Rutherford category 4-6 and 33 limbs (64.7%) had a history of ipsilateral revascularization. Technical success was achieved in 98% of the patients. The 30 day mortality rate was 2.4% (n = 1) and the overall 30 day complication rate was 9.5% (n = 4). The median follow-up period was 38 (interquartile range 13-67) months. Three patients required major amputation and 14 died during follow-up. Primary patency rates at 1, 3, and 5 years were 67.8%, 57.5%, and 46.5%, respectively, while secondary patency rates for these periods were 84.6%, 70.0%, and 66.0%, respectively. Overall survival rates at 1, 3, and 5 years were 90.1%, 74.5%, and 70.9%, respectively.

CONCLUSIONS

BK bypass surgery using heparin-bonded ePTFE graft is a viable and durable option for patients with PAD, who are deemed unsuitable for autologous vein bypass surgery.

Improving hemocompatibility of decellularized vascular tissue by structural modification of collagen fiber

Decellularized vascular tissue has high potential as a tissue-engineered vascular graft because of its similarity to native vessels in terms of mechanical strength. However, exposed collagen on the tissue induces blood coagulation, and low hemocompatibility is a major obstacle to its vascular application. Here we report that freeze-drying and ethanol treatment effectively modify collagen fiber structure and drastically reduce blood coagulation on the graft surface without exogenous chemical modification. Decellularized carotid artery of ostrich was treated with freeze-drying and ethanol solution at concentrations ranging between 5 and 99.5 %. Collagen fiber distance in the graft was narrowed by freeze-drying, and the non-helical region increased by ethanol treatment. Although in vitro blood coagulation pattern was similar on the grafts, platelet adhesion on the grafts was largely suppressed by freeze-drying and ethanol treatments. Ex vivo blood circulation tests also indicated that the adsorption of platelets and Von Willebrand Factor was largely reduced to approximately 80 % by ethanol treatment. These results indicate that structural modification of collagen fibers in decellularized tissue reduces blood coagulation on the surface by inhibiting platelet adhesion.

Dragging 3D printing technique controls pore sizes of tissue engineered blood vessels to induce spontaneous cellular assembly

To date, several off-the-shelf products such as artificial blood vessel grafts have been reported and clinically tested for small diameter vessel (SDV) replacement. However, conventional artificial blood vessel grafts lack endothelium and, thus, are not ideal for SDV transplantation as they can cause thrombosis. In addition, a successful artificial blood vessel graft for SDV must have sufficient mechanical properties to withstand various external stresses. Here, we developed a spontaneous cellular assembly SDV (S-SDV) that develops without additional intervention. By improving the dragging 3D printing technique, SDV constructs with free-form, multilayers and controllable pore size can be fabricated at once. Then, The S-SDV filled in the natural polymer bioink containing human umbilical vein endothelial cells (HUVECs) and human aorta smooth muscle cells (HAoSMCs). The endothelium can be induced by migration and self-assembly of endothelial cells through pores of the SDV construct. The antiplatelet adhesion of the formed endothelium on the luminal surface was also confirmed. In addition, this S-SDV had sufficient mechanical properties (burst pressure, suture retention, leakage test) for transplantation. We believe that the S-SDV could address the challenges of conventional SDVs: notably, endothelial formation and mechanical properties. In particular, the S-SDV can be designed simply as a free-form structure with a desired pore size. Since endothelial formation through the pore is easy even in free-form constructs, it is expected to be useful for endothelial formation in vascular structures with branch or curve shapes, and in other tubular tissues such as the esophagus.

Poly(ethylene glycol) Hydrogels with the Sustained Release of Hepatocyte Growth Factor for Enhancing Vascular Regeneration

The surface modification of biologically active factors on tissue-engineering vascular scaffold fails to fulfill the mechanical property and bioactive compounds' sustained release in vivo and results in the inhibition of tissue regeneration of small-diameter vascular grafts in vascular replacement therapies. In this study, biodegradable poly(ε-caprolactone) (PCL) was applied for scaffold preparation, and poly(ethylene glycol) (PG) hydrogel was used to load heparin and hepatocyte growth factor (HGF). In vitro analysis demonstrated that the PCL scaffold could inhibit the heparin release from the PG hydrogel, and the PG hydrogel could inhibit heparin release during the process of PCL degradation. Finally, it results in sustained release of HGF and heparin from the PCL-PG-HGF scaffold. The mechanical property of this hybrid scaffold improved after being coated with the PG hydrogel. In addition, the PCL-PG-HGF scaffold illustrated no inflammatory lesions, organ damage, or biological toxicity in all primary organs, with rapid organization of the endothelial cell layer, smooth muscle regeneration, and extracellular matrix formation. These results indicated that the PCL-PG-HGF scaffold is biocompatible and provides a microenvironment in which a tissue-engineered vascular graft with anticoagulant properties allows regeneration of vascular tissue (Scheme 1). Such findings confirm the feasibility of creating hydrogel scaffolds coated with bioactive factors to prepare novel vascular grafts.

Challenges and advances in materials and fabrication technologies of small-diameter vascular grafts

The arterial occlusive disease is one of the leading causes of cardiovascular diseases, often requiring revascularization. Lack of suitable small-diameter vascular grafts (SDVGs), infection, thrombosis, and intimal hyperplasia associated with synthetic vascular grafts lead to a low success rate of SDVGs (< 6 mm) transplantation in the clinical treatment of cardiovascular diseases. The development of fabrication technology along with vascular tissue engineering and regenerative medicine technology allows biological tissue-engineered vascular grafts to become living grafts, which can integrate, remodel, and repair the host vessels as well as respond to the surrounding mechanical and biochemical stimuli. Hence, they potentially alleviate the shortage of existing vascular grafts. This paper evaluates the current advanced fabrication technologies for SDVGs, including electrospinning, molding, 3D printing, decellularization, and so on. Various characteristics of synthetic polymers and surface modification methods are also introduced. In addition, it also provides interdisciplinary insights into the future of small-diameter prostheses and discusses vital factors and perspectives for developing such prostheses in clinical applications. We propose that the performance of SDVGs can be improved by integrating various technologies in the near future.

Strategies for surface coatings of implantable cardiac medical devices

Cardiac medical devices (CMDs) are required when the patient's cardiac capacity or activity is compromised. To guarantee its correct functionality, the building materials in the development of CMDs must focus on several fundamental properties such as strength, stiffness, rigidity, corrosion resistance, etc. The challenge is more significant because CMDs are generally built with at least one metallic and one polymeric part. However, not only the properties of the materials need to be taken into consideration. The biocompatibility of the materials represents one of the major causes of the success of CMDs in the short and long term. Otherwise, the material will lead to several problems of hemocompatibility (e.g., protein adsorption, platelet aggregation, thrombus formation, bacterial infection, and finally, the rejection of the CMDs). To enhance the hemocompatibility of selected materials, surface modification represents a suitable solution. The surface modification involves the attachment of chemical compounds or bioactive compounds to the surface of the material. These coatings interact with the blood and avoid hemocompatibility and infection issues. This work reviews two main topics: 1) the materials employed in developing CMDs and their key characteristics, and 2) the surface modifications reported in the literature, clinical trials, and those that have reached the market. With the aim of providing to the research community, considerations regarding the choice of materials for CMDs, together with the advantages and disadvantages of the surface modifications and the limitations of the studies performed.

Design of an Ultralow Molecular Weight Heparin That Resists Heparanase Biodegradation

Heparanase, an endo-β-d-glucuronidase produced by a variety of cells and tissues, cleaves the glycosidic linkage between glucuronic acid (GlcA) and a 3-O- or 6-O-sulfated glucosamine, typified by the disaccharide -[GlcA-GlcNS3S6S]-, which is found within the antithrombin-binding domain of heparan sulfate or heparin. As such, all current forms of heparin are susceptible to degradation by heparanase with neutralization of anticoagulant properties. Here, we have designed a heparanase-resistant, ultralow molecular weight heparin as the structural analogue of fondaparinux that does not contain an internal GlcA residue but otherwise displays potent anticoagulant activity. This heparin oligosaccharide was synthesized following a chemoenzymatic scheme and displays nanomolar anti-FXa activity yet is resistant to heparanase digestion. Inhibition of thrombus formation was further demonstrated after subcutaneous administration of this compound in a murine model of venous thrombosis. Thrombus inhibition was comparable to that observed for enoxaparin with a similar effect on bleeding time.

Advances in the development of tubular structures using extrusion-based 3D cell-printing technology for vascular tissue regenerative applications

Until recent, there are no ideal small diameter vascular grafts available on the market. Most of the commercialized vascular grafts are used for medium to large-sized blood vessels. As a solution, vascular tissue engineering has been introduced and shown promising outcomes. Despite these optimistic results, there are limitations to commercialization. This review will cover the need for extrusion-based 3D cell-printing technique capable of mimicking the natural structure of the blood vessel. First, we will highlight the physiological structure of the blood vessel as well as the requirements for an ideal vascular graft. Then, the essential factors of 3D cell-printing including bioink, and cell-printing system will be discussed. Afterwards, we will mention their applications in the fabrication of tissue engineered vascular grafts. Finally, conclusions and future perspectives will be discussed.

Acellular Tissue-Engineered Vascular Grafts from Polymers: Methods, Achievements, Characterization, and Challenges

Extensive and permanent damage to the vasculature leading to different pathogenesis calls for developing innovative therapeutics, including drugs, medical devices, and cell therapies. Innovative strategies to engineer bioartificial/biomimetic vessels have been extensively exploited as an effective replacement for vessels that have seriously malfunctioned. However, further studies in polymer chemistry, additive manufacturing, and rapid prototyping are required to generate highly engineered vascular segments that can be effectively integrated into the existing vasculature of patients. One recently developed approach involves designing and fabricating acellular vessel equivalents from novel polymeric materials. This review aims to assess the design criteria, engineering factors, and innovative approaches for the fabrication and characterization of biomimetic macro- and micro-scale vessels. At the same time, the engineering correlation between the physical properties of the polymer and biological functionalities of multiscale acellular vascular segments are thoroughly elucidated. Moreover, several emerging characterization techniques for probing the mechanical properties of tissue-engineered vascular grafts are revealed. Finally, significant challenges to the clinical transformation of the highly promising engineered vessels derived from polymers are identified, and unique perspectives on future research directions are presented.

Stable and direct coating of fibronectin-derived Leu-Asp-Val peptide on ePTFE using one-pot tyrosine oxidation for endothelial cell adhesion

Expanded polytetrafluoroethylene (ePTFE) is widely used in clinical applications, such as in the manufacture of blood-contacting implantable devices, owing to its flexibility, biostability, and non-adhesiveness. Modification with peptides is an effective strategy to further improve the ePTFE function. However, the chemical stability of PTFE makes it difficult to modify with peptides. In this study, we reported a simple method for the dense and stable coating of biofunctional peptides on the ePTFE surface through the anchor sequence, Tyr-Lys-Tyr-Lys-Tyr-Lys (YK3). A peptide (YK3-LDV) incorporating the YK3 anchor and a ligand sequence for α₄β₁ integrin, Leu-Asp-Val (LDV), was successfully coated on ePTFE grafts through one-pot oxidation. The peptide layer constructed via YK3-LDV coating on ePTFE was stable and resistant to extensive washing by aqueous solutions of highly concentrated salts and surfactants. YK3-LDV coating promoted the in vitro adhesion of endothelial cells to ePTFE. Furthermore, YK3-LDV coating accelerated the in vivo formation of neointima-like tissue in a rat model with an ePTFE patch implanted into the carotid artery.

Medical Applications of Porous Biomaterials: Features of Porosity and Tissue-Specific Implications for Biocompatibility

Porosity is an important material feature commonly employed in implants and tissue scaffolds. The presence of material voids permits the infiltration of cells, mechanical compliance, and outward diffusion of pharmaceutical agents. Various studies have confirmed that porosity indeed promotes favorable tissue responses, including minimal fibrous encapsulation during the foreign body reaction (FBR). However, increased biofilm formation and calcification is also described to arise due to biomaterial porosity. Additionally, the relevance of host responses like the FBR, infection, calcification, and thrombosis are dependent on tissue location and specific tissue microenvironment. In this review, the features of porous materials and the implications of porosity in the context of medical devices is discussed. Common methods to create porous materials are also discussed, as well as the parameters that are used to tune pore features. Responses toward porous biomaterials are also reviewed, including the various stages of the FBR, hemocompatibility, biofilm formation, and calcification. Finally, these host responses are considered in tissue specific locations including the subcutis, bone, cardiovascular system, brain, eye, and female reproductive tract. The effects of porosity across the various tissues of the body is highlighted and the need to consider the tissue context when engineering biomaterials is emphasized.

A novel small diameter nanotextile arterial graft is associated with surgical feasibility and safety and increased transmural endothelial ingrowth in pig

Globally, millions of patients are affected by myocardial infarction or lower limb gangrene/amputation due to atherosclerosis. Available surgical treatment based on vein and synthetic grafts provides sub-optimal benefits. We engineered a highly flexible and mechanically robust nanotextile-based vascular graft (NanoGraft) by interweaving nanofibrous threads of poly-L-lactic acid to address the unmet need. The NanoGrafts were rendered impervious with selective fibrin deposition in the micropores by pre-clotting. The pre-clotted NanoGrafts (4 mm diameter) and ePTFE were implanted in a porcine carotid artery replacement model. The fibrin-laden porous milieu facilitated rapid endothelization by the transmural angiogenesis in the NanoGraft. In-vivo patency of NanoGrafts was 100% at 2- and 4-weeks, with no changes over time in lumen size, flow velocities, and minimal foreign-body inflammatory reaction. However, the patency of ePTFE at 2-week was 66% and showed marked infiltration, neointimal thickening, and poor host tissue integration. The study demonstrates the in-vivo feasibility and safety of a thin-layered vascular prosthesis, viz., NanoGraft, and its potential superiority over the commercial ePTFE.

End-Point Immobilization of Heparin on Electrospun Polycarbonate-Urethane Vascular Graft

There is a tremendous clinical need for synthetic vascular grafts either for bypass procedure or vascular access during hemodialysis. However, currently, there is no small-diameter vascular graft commercially available to meet long-term patency requirement due to frequent thrombus formation and intimal hyperplasia. This chapter describes the fabrication of electrospun small-diameter polycarbonate-urethane (PCU) vascular graft with a biomimetic fibrous structure. Additionally, the surface of the vascular graft is aminated via plasma treatment for the subsequently end-point heparin immobilization to enhance antithrombosis property.

Sulfated Alginate Hydrogels Prolong the Therapeutic Potential of MSC Spheroids by Sequestering the Secretome

Cell-based approaches to tissue repair suffer from rapid cell death upon implantation, limiting the window for therapeutic intervention. Despite robust lineage-specific differentiation potential in vitro, the function of transplanted mesenchymal stromal cells (MSCs) in vivo is largely attributed to their potent secretome comprising a variety of growth factors (GFs). Furthermore, GF secretion is markedly increased when MSCs are formed into spheroids. Native GFs are sequestered within the extracellular matrix (ECM) via sulfated glycosaminoglycans, increasing the potency of GF signaling compared to their unbound form. To address the critical need to prolong the efficacy of transplanted cells, alginate hydrogels are modified with sulfate groups to sequester endogenous heparin-binding GFs secreted by MSC spheroids. The influence of crosslinking method and alginate modification is assessed on mechanical properties, degradation rate, and degree of sulfate modification. Sulfated alginate hydrogels sequester a mixture of MSC-secreted endogenous biomolecules, thereby prolonging the therapeutic effect of MSC spheroids for tissue regeneration. GFs are sequestered for longer durations within sulfated hydrogels and retain their bioactivity to regulate endothelial cell tubulogenesis and myoblast infiltration. This platform has the potential to prolong the therapeutic benefit of the MSC secretome and serve as a valuable tool for investigating GF sequestration.

Distinct Effects of Heparin and Interleukin-4 Functionalization on Macrophage Polarization and In Situ Arterial Tissue Regeneration Using Resorbable Supramolecular Vascular Grafts in Rats

Two of the greatest challenges for successful application of small-diameter in situ tissue-engineered vascular grafts are 1) preventing thrombus formation and 2) harnessing the inflammatory response to the graft to guide functional tissue regeneration. This study evaluates the in vivo performance of electrospun resorbable elastomeric vascular grafts, dual-functionalized with anti-thrombogenic heparin (hep) and anti-inflammatory interleukin 4 (IL-4) using a supramolecular approach. The regenerative capacity of IL-4/hep, hep-only, and bare grafts is investigated as interposition graft in the rat abdominal aorta, with follow-up at key timepoints in the healing cascade (1, 3, 7 days, and 3 months). Routine analyses are augmented with Raman microspectroscopy, in order to acquire the local molecular fingerprints of the resorbing scaffold and developing tissue. Thrombosis is found not to be a confounding factor in any of the groups. Hep-only-functionalized grafts resulted in adverse tissue remodeling, with cases of local intimal hyperplasia. This is negated with the addition of IL-4, which promoted M2 macrophage polarization and more mature neotissue formation. This study shows that with bioactive functionalization, the early inflammatory response can be modulated and affect the composition of neotissue. Nevertheless, variability between graft outcomes is observed within each group, warranting further evaluation in light of clinical translation.

A heparin-functionalized covered stent prepared by plasma technology

In this study, the surface of the covered stent was treated by plasma technology to introduce amino functional groups, and glutaraldehyde and heparin were successfully grafted to prepare a heparin-functionalized covered stent (HPLCS). The preparation parameters such as plasma treatment power, plasma treatment time, concentration of glutaraldehyde and heparin, and pH of heparin solution were studied in detail. The functionalized heparin covered stent can make the titer of heparin reach 1.23 ± 0.03 IU/cm². In animal experiments, after implantation in pigs for 6 months, the titer of heparin can still reach 0.93 ± 0.05 IU/cm². This work provides a good method for preparing heparin covered stent.

Characterization of a Water-Dispersed Biodegradable Polyurethane-Silk Composite Sponge Using 13C Solid-State Nuclear Magnetic Resonance as Coating Material for Silk Vascular Grafts with Small Diameters

Recently, Bombyx mori silk fibroin (SF) has been shown to be a suitable material for vascular prostheses for small arteries. In this study, we developed a softer SF graft by coating water-dispersed biodegradable polyurethane (PU) based on polycaprolactone and an SF composite sponge on the knitted SF vascular graft. Three kinds of 13C solid-state nuclear magnetic resonance (NMR), namely carbon-13 (13C) cross-polarization/magic angle spinning (MAS), 13C dipolar decoupled MAS, and 13C refocused insensitive nuclei enhanced by polarization transfer (r-INEPT) NMR, were used to characterize the PU-SF coating sponge. Especially the 13C r-INEPT NMR spectrum of water-dispersed biodegradable PU showed that both main components of the non-crystalline domain of PU and amorphous domain of SF were highly mobile in the hydrated state. Then, the small-diameter SF artificial vascular grafts coated with this sponge were evaluated through implantation experiments with rats. The implanted PU-SF-coated SF grafts showed a high patency rate. It was confirmed that the inside of the SF grafts was covered with vascular endothelial cells 4 weeks after implantation. These results showed that the water-dispersed biodegradable PU-SF-coated SF graft created in this study could be a strong candidate for small-diameter artificial vascular graft.

A rechargeable anti-thrombotic coating for blood-contacting devices

Despite the potential of anti-thrombogenic coatings, including heparinized surfaces, to improve the performance of blood-contacting devices, the inevitable deterioration of bioactivity remains an important factor in device failure and related thrombotic complications. As a consequence, the ability to restore the bioactivity of a surface coating after implantation of a blood-contacting device provides a potentially important strategy to enhance its clinical performance. Here, we report the regeneration of a multicomponent anti-thrombogenic coating through use of an evolved sortase A to mediate reversible transpeptidation. Both recombinant thrombomodulin and a chemoenzymatically synthesized ultra-low molecular weight heparin were repeatedly and selectively immobilized or removed in a sequential, alternating, or simultaneous manner. The generation of activated protein C (aPC) and inhibition of activated factor X (FXa) was consistent with the molecular composition of the surface. The fabrication of a rechargeable anti-thrombogenic surface was demonstrated on an expanded polytetrafluoroethylene (ePTFE) vascular graft with reconstitution of the surface bound coating 4 weeks after in vivo implantation in a rat model.

Comparative assessment of different versions of axial and centrifugal LVADs: A review

Continuous-flow left ventricular assist devices (LVADs) have gained tremendous acceptance for the treatment of end-stage heart failure patients. Among different versions, axial flow and centrifugal flow LVADs have shown remarkable potential for clinical implants. It is also very crucial to know which device serves its purpose better to treat heart failure patients. A thorough comparison of axial and centrifugal LVADs, which may guide doctors in deciding before the implant, still lacks in the literature. In this work, an assessment of axial and centrifugal LVADs has been made to suggest a better device by comparing their engineering, clinical, and technological development of design aspects. Hydrodynamic and hemodynamic aspects for both types of pumps are discussed along with their biocompatibility, bearing types, and sizes. It has been observed numerically that centrifugal LVADs perform better over axial LVADs in every engineering aspect like higher hydraulic efficiency, better characteristics curve, lesser power intake, and also lesser blood damage. However, the clinical outcomes suggest that centrifugal LVADs experience higher events of infections, renal, and respiratory dysfunction. In contrast, axial LVADs encountered higher bleeding and cardiac arrhythmia. Moreover, recent technological developments suggested that magnetic type bearings along with biocompatible coating improve the life of LVADs.

Evaluation of heparin-bonded ePTFE grafts for forearm loop vascular access: Comparison between Gore® PROPATEN vascular graft and ACUSEAL vascular graft

BACKGROUND

This retrospective study evaluates the clinical outcomes of two heparin-bonded expanded polytetrafluoroethylene grafts, PROPATEN and ACUSEAL (W. L. Gore & Associates, Flagstaff, AZ, USA), for forearm loop vascular access.

METHODS

We prospectively collected data on 60 patients who had undergone arteriovenous graft of the forearm loop type between January 2015 and December 2019. The primary endpoints were graft primary, assisted primary, and secondary patency rates. Secondary endpoints were time to first cannulation and postoperative complications.

RESULTS

We enrolled 36 patients in the PROPATEN group (Group P) and 24 in the ACUSEAL group (Group A). All procedures were successful without any 30-day mortality. The median times to first cannulation were 16.5 days and 3 days in Groups P and A, respectively (p < 0.001). Mean follow-up periods were 13.4 ± 14.5 and 17.3 ± 9.3 months, respectively. Primary patency rates were 81% and 64%, respectively, at 6 months, and 60% and 40%, respectively, at 12 months (p = 0.008). Assisted primary patency rates were 96% and 83% at 6 months, 91% and 73% at 12 months, and 81% and 35% at 24 months (p = 0.044). Secondary patency rates were 96% and 81% at 12 months, and 87% and 62% at 24 months (p = 0.207). As a remote-period complication, disruption of the luminal layer of the graft was observed in two patients (4.2%) in Group A due to puncture and thrombectomy.

CONCLUSIONS

Although the ACUSEAL graft offers the advantage of early cannulation, its primary and assisted primary patency outcomes were inferior to those of the PROPATEN graft. It is important for physicians to be aware of the different characteristics of each graft to select the best option for each patient.

Development of Small-Diameter Elastin-Silk Fibroin Vascular Grafts

Globally, increasing mortality from cardiovascular disease has become a problem in recent years. Vascular replacement has been used as a treatment for these diseases, but with blood vessels <6 mm in diameter, existing vascular grafts made of synthetic polymers can be occluded by thrombus formation or intimal hyperplasia. Therefore, the development of new artificial vascular grafts is desirable. In this study, we developed an elastin (EL)-silk fibroin (SF) double-raschel knitted vascular graft 1.5 mm in diameter. Water-soluble EL was prepared from insoluble EL by hydrolysis with oxalic acid. Compared to SF, EL was less likely to adhere to platelets, while vascular endothelial cells were three times more likely to adhere. SF artificial blood vessels densely packed with porous EL were fabricated, and these prevented the leakage of blood from the graft during implantation, while the migration of cells after implantation was promoted. Several kinds of ¹³C solid-state NMR spectra were observed with the EL-SF grafts in dry and hydrated states. It was noted that the EL molecules in the graft had very high mobility in the hydrated state. The EL-SF grafts were implanted into the abdominal aorta of rats to evaluate their patency and remodeling ability. No adverse reactions, such as bleeding at the time of implantation or disconnection of the sutured ends, were observed in the implanted grafts, and all were patent at the time of extraction. In addition, vascular endothelial cells were present on the graft's luminal surface 2 weeks after implantation. Therefore, we conclude that EL-SF artificial vascular grafts may be useful where small-diameter grafts are required.

Outcome of GORE® ACUSEAL graft for brachial-axillary vascular access in chronic haemodialysis patients: Cohort retrospective single-centre study

Background

The aim of this study was to evaluate the midterm results of a brachio-axillary arteriovenous graft (BA-AVG) for the provision of vascular access haemodialysis patients.

Materials and methods

A cohort retrospective consecutive single-centre study of 46 patients undergoing BA-AVG using the Gore Acuseal, from November 2015 to October 2019 was conducted. Data on patient demographics, comorbidities, medical therapy, and complications were collated for the initial endpoints of primary patency, primary assisted patency, and secondary patency. A subgroup analysis included outcomes in patients over 70 years old and events (complications) per AVG per year. Data were subjected to Kaplan-Meier survival estimator with log-rank analysis and test of probability.

Results

The mean age of the cohort was 63.5 years with male predominance (male, n = 27, 59%). A total of 37 (80%) patient procedures were conducted with elective settings as well as on an emergency basis with a 91.3% technical success rate. The most common complication was grade I steal syndrome (8.7%), followed by graft infections (4.3%), median nerve neuropraxia (4.3%), and postoperative bleeding (2%), demonstrating a 0.1 per AVG complication per 2 years. Median primary patency, primary assisted patency, and secondary patency over a mean follow-up period of 28 months was 5.5, 12.5, and 18 months, respectively, with no associated 30-day mortality.

Conclusion

BA-AVG with midterm longevity and low complications may serve as an alternative access type when a suitable site is not identified. The AVG patency rate in the elderly or patients with limited life expectancy is promising. However, more robust data are needed to confirm the benefit of AVG in this cohort.

•

This series showed that Gore® Acuseal graft can be used as vascular access option in ESRD patients on chronic haemodialysis.

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It has reasonable technical success rate comparable to other synthetic access grafts and low complications rates in mid to long-term follow up.

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Sub-groups analysis included outcome in patients over 70 years old and events (complications) per AVG per year.

•

AVG patency rate in elderly or patients with limited life expectancy is promising. However, more robust data needed.

Recent Update on Peripheral Arterial Endovascular Therapy for Peripheral Arterial Occlusive Disease

Endovascular treatment is effective for symptomatic peripheral arterial disease (PAD). Following recent device improvements, favorable long-term outcomes have been achieved in iliac arteries as well as small arteries such as the femoral and popliteal arteries. This paper outlines the history and recent advances in endovascular treatment of peripheral vascular diseases as well as the characteristics and usage of devices. The history and the advances in endovascular treatment of peripheral vascular disease have been parallel, with the development of devices such as catheters and stents. Accordingly, endovascular treatment is now recommended in guidelines as the first-line for PAD.

The effect of pore diameter on neo-tissue formation in electrospun biodegradable tissue-engineered arterial grafts in a large animal model

To date, there has been little investigation of biodegradable tissue engineered arterial grafts (TEAG) using clinically relevant large animal models. The purpose of this study is to explore how pore size of electrospun scaffolds can be used to balance neoarterial tissue formation with graft structural integrity under arterial environmental conditions throughout the remodeling process. TEAGs were created with an outer poly-ε-caprolactone (PCL) electrospun layer and an inner sponge layer composed of heparin conjugated 50:50 poly (l-lactide-co-ε-caprolactone) copolymer (PLCL). Outer electrospun layers were created with four different pore diameters (4, 7, 10, and 15 µm). Fourteen adult female sheep underwent bilateral carotid artery interposition grafting (n = 3-4 /group). Our heparin-eluting TEAG was implanted on one side (n = 14) and ePTFE graft (n = 3) or non-heparin-eluting TEAG (n = 5) on the other side. Twelve of the fourteen animals survived to the designated endpoint at 8 weeks, and one animal with 4 µm pore diameter graft was followed to 1 year. All heparin-eluting TEAGs were patent, but those with pore diameters larger than 4 µm began to dilate at week 4. Only scaffolds with a pore diameter of 4 µm resisted dilation and could do so for up to 1 year. At 8 weeks, the 10 µm pore graft had the highest density of cells in the electrospun layer and macrophages were the primary cell type present. This study highlights challenges in designing bioabsorbable TEAGs for the arterial environment in a large animal model. While larger pore diameter TEAGs promoted cell infiltration, neotissue could not regenerate rapidly enough to provide sufficient mechanical strength required to resist dilation. Future studies will be focused on evaluating a smaller pore design to better understand long-term remodeling and determine feasibility for clinical use. STATEMENT OF SIGNIFICANCE: In situ vascular tissue engineering relies on a biodegradable scaffold that encourages tissue regeneration and maintains mechanical integrity until the neotissue can bear the load. Species-specific differences in tissue regeneration and larger mechanical forces often result in graft failure when scaling up from small to large animal models. This study utilizes a slow-degrading electrospun PCL sheath to reinforce a tissue engineered arterials graft. Pore size, a property critical to tissue regeneration, was controlled by changing PCL fiber diameter and the resulting effects of these properties on neotissue formation and graft durability was evaluated. This study is among few to report the effect of pore size on vascular neotissue formation in a large animal arterial model and also demonstrate robust neotissue formation.

Surface Zwitterionization of Expanded Poly(tetrafluoroethylene) via Dopamine-Assisted Consecutive Immersion Coating

Expanded polytetrafluoroethylene (ePTFE) is one of the materials widely used in the biomedical field, yet its application is being limited by adverse reactions such as thrombosis when it comes in contact with blood. Thus, a simple and robust way to modify ePTFE to be biologically inert is sought after. Modification of ePTFE without high-energy pretreatment, such as immersion coating, has been of interest to researchers for its straightforward process and ease in scaling up. In this study, we utilized a two-step immersion coating to zwitterionize ePTFE membranes. The first coating consists of the co-deposition of polyethylenimine (PEI) and polydopamine (PDA) to produce amine groups in the surface of the ePTFE for further functionalization. These amine groups from PEI will be coupled with the epoxide group of the zwitterionic copolymer, poly(GMA-co-SBMA) (PGS), via a ring-opening reaction in the second coating. The coated ePTFE membranes were physically and chemically characterized to ensure that each step of the coating is successful. The membranes were also tested for their thrombogenicity via quantification of the blood cells attached to it during contact with biological solutions. The coated membranes exhibited around 90% reduction in attachment with respect to the uncoated ePTFE for both Gram-positive and Gram-negative strains of bacteria (Staphylococcus aureus and Escherichia coli). The coating was also able to resist blood cell attachment from human whole blood by 81.57% and resist red blood cell attachment from red blood cell concentrate by 93.4%. These ePTFE membranes, which are coated by a simple immersion coating, show significant enhancement of the biocompatibility of the membranes, which shows promise for future use in biological devices.

Heparin-bonded versus standard polytetrafluoroethylene arteriovenous grafts: A Bayesian perspective on a randomized controlled trial for comparative effectiveness

BACKGROUND

Heparin-bonded polytetrafluoroethylene grafts were marketed to improve hemodialysis access outcomes but are twice the cost of standard polytetrafluoroethylene. We launched a randomized trial of heparin-bonded polytetrafluoroethylene versus standard polytetrafluoroethylene for hemodialysis access to compare patency. Since the trial began, additional studies were published with heterogeneous findings. We performed an interim analysis by Bayesian methods using prior probability from meta-analysis of existing literature.

METHODS

NCT01601873 is a randomized, blinded trial of heparin-bonded polytetrafluoroethylene versus standard polytetrafluoroethylene for dialysis access at 5 sites. Planned sample size was 200 with 1-year primary patency as the primary endpoint. At interim analysis (50% of sample size at 1 year), we also performed a meta-analysis for 1-year primary patency with a random effects model to compute summary rate ratio and standard-error estimates. Meta-analysis estimates formed a prior probability for a Bayesian Cox regression model, and trial data were reanalyzed to develop posterior probability of heparin-bonded polytetrafluoroethylene effectiveness at our hypothesized effect size. Futility analysis was conducted using posterior probability estimates.

RESULTS

One hundred and five patients were enrolled at the time of interim analysis. One-year primary patency was 34.9% in the heparin-bonded-polytetrafluoroethylene group vs 32.7% in the standard-polytetrafluoroethylene group (P = .884). Summary rate ratio from the meta-analysis (1,209 patients) was 0.87 favoring heparin-bonded polytetrafluoroethylene (P = .33). Posterior hazard ratio from Cox regression was 0.90 (credible interval 0.70-1.13) favoring heparin-bonded polytetrafluoroethylene, which was not significant. Bayesian posterior probability of the a priori hypothesized 20% better patency with heparin-bonded polytetrafluoroethylene was 24%. Sample size to detect superiority with the small observed effect size would require about 3,800 subjects.

CONCLUSION

Current evidence does not demonstrate sufficiently large benefit of heparin-bonded polytetrafluoroethylene over standard polytetrafluoroethylene for dialysis access to justify higher cost. Given similar 1-year patency rates, a conclusive finding of superiority was judged to be infeasible, and the trial was stopped for futility.

Single and multi-functional coating strategies for enhancing the biocompatibility and tissue integration of blood-contacting medical implants

Device-associated clot formation and poor tissue integration are ongoing problems with permanent and temporary implantable medical devices. These complications lead to increased rates of mortality and morbidity and impose a burden on healthcare systems. In this review, we outline the current approaches for developing single and multi-functional surface coating techniques that aim to circumvent the limitations associated with existing blood-contacting medical devices. We focus on surface coatings that possess dual hemocompatibility and biofunctionality features and discuss their advantages and shortcomings to providing a biocompatible and biodynamic interface between the medical implant and blood. Lastly, we outline the newly developed surface modification techniques that use lubricant-infused coatings and discuss their unique potential and limitations in mitigating medical device-associated complications.

Fucoidan functionalization on poly(vinyl alcohol) hydrogels for improved endothelialization and hemocompatibility

The performance of clinical synthetic small diameter vascular grafts remains disappointing due to the fast occlusion caused by thrombosis and intimal hyperplasia formation. Poly(vinyl alcohol) (PVA) hydrogels have tunable mechanical properties and a low thrombogenic surface, which suggests its potential value as a small diameter vascular graft material. However, PVA does not support cell adhesion and thus requires surface modification to encourage endothelialization. This study presents a modification of PVA with fucoidan. Fucoidan is a sulfated polysaccharide with anticoagulant and antithrombotic properties, which was shown to potentially increase endothelial cell adhesion and proliferation. By mixing fucoidan with PVA and co-crosslinked by sodium trimetaphosphate (STMP), the modification was achieved without sacrificing mechanical properties. Endothelial cell adhesion and monolayer function were significantly enhanced by the fucoidan modification. In vitro and ex-vivo studies showed low platelet adhesion and activation and decreased thrombin generation with fucoidan modified PVA. The modification proved to be compatible with gamma sterilization. In vivo evaluation of fucoidan modified PVA grafts in rabbits exhibited increased patency rate, endothelialization, and reduced intimal hyperplasia formation. The fucoidan modification presented here benefited the development of PVA vascular grafts and can be adapted to other blood contacting surfaces.

Small caliber heparin loaded ultrafine microfiber woven graft achieved high patency rate in a preliminary study of canine carotid artery implantation

Objective

In the past five decades, many small caliber vascular grafts have been developed as bypasses for infrapopliteal or coronary arteries. However, reliable grafts have not been obtained owing to poor patency, mainly caused by early thrombosis or neointimal hyperplasia in the intermediate period after implantation. We developed a novel small caliber heparin-loaded polyethylene terephthalate ultrafine microfiber (HL-PET) graft and evaluated the feasibility to overcome those main causes of graft failure in canine carotid artery implantation.

Methods

The HL-PET graft with a diameter of 3 mm and length of 30 mm was made with combination of three key technologies: (1) weaving with PET ultrafine microfiber with a high biological porosity allowing for cell ingrowth, (2) heparin loading on microfiber surfaces, and (3) an outer coating with a flexible bioabsorbable polymer for prevention of blood leakage and graft kinking. Kink resistance, water permeability, and loaded heparin were assessed. One HL-PET graft each was implanted into a carotid artery of six animals. Graft patency rate and healing were assessed 24 weeks after implantation.

Results

Among the six grafts, five were deemed patent (patency rate of >83%), with one occluded 20 weeks after implantation. Histopathology of the patent grafts showed neointima formation with confluent endothelial cell lining (estimated mean endothelial cell coverage area, 89 ± 18%). Intimal hyperplasia at the anastomotic sites and severe chronic inflammatory responses were not observed. Immunohistochemistry with antibodies to endothelial nitric oxide synthase, alpha 2 smooth muscle actin and calponin 1 revealed luminal surface endothelial cell layer with expression of endothelial nitric oxide synthase and vascular smooth muscle cells with contractile phenotype in the subintimal layer.

Conclusions

The HL-PET graft showed no early postoperative thrombosis and was able to demonstrate a high patency rate with no severe biological response observed after 24 weeks. These results strongly suggest the potential of the HL-PET graft to be used for distal bypasses.

The HL-PET graft achieved a high patency rate without early postoperative thrombosis or intimal hyperplasia in a small caliber artery implantation study. The histopathologic analysis demonstrated favorable healing property with a high antithrombogenicity. These results strongly suggested the possible use of the HL-PET graft as a bypass for infrapopliteal or coronary arteries.

A Novel C1-Esterase Inhibitor Oxygenator Coating Prevents FXII Activation in Human Blood

The limited hemocompatibility of currently used oxygenator membranes prevents long-term use of artificial lungs in patients with lung failure. To improve hemocompatibility, we developed a novel covalent C1-esterase inhibitor (C1-INH) coating. Besides complement inhibition, C1-INH also prevents FXII activation, a very early event of contact phase activation at the crossroads of coagulation and inflammation. Covalently coated heparin, as the current anticoagulation gold standard, served as control. Additionally, a combination of both coatings (C1-INH/heparin) was established. The coatings were tested for their hemocompatibility by dynamic incubation with freshly drawn human whole blood. The analysis of various blood and plasma parameters revealed that C1-INH-containing coatings were able to markedly reduce FXIIa activity compared to heparin coating. Combined C1-INH/heparin coatings yielded similarly low levels of thrombin-antithrombin III complex formation as heparin coating. In particular, adhesion of monocytes and platelets as well as the diminished formation of fibrin networks were observed for combined coatings. We could show for the first time that a covalent coating with complement inhibitor C1-INH was able to ameliorate hemocompatibility. Thus, the early inhibition of the coagulation cascade is likely to have far-reaching consequences for the other cross-reacting plasma protein pathways.

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.

Analysis of thrombin-antithrombin complex formation using microchip electrophoresis and mass spectrometry

Preterm birth (PTB) related health problems take over one million lives each year, and currently, no clinical analysis is available to determine if a fetus is at risk for PTB. Here, we describe the preparation of a key PTB risk biomarker, thrombin-antithrombin (TAT), and characterize it using dot blots, MS, and microchip electrophoresis (µCE). The pH for fluorescently labeling TAT was also optimized using spectrofluorometry and spectrophotometry. The LOD of TAT was measured in µCE. Lastly, TAT was combined with six other PTB risk biomarkers and separated in µCE. The ability to make and characterize TAT is an important step toward the development of an integrated microfluidic diagnostic for PTB risk.

Prophylactic prosthetic wrapping for vascular anastomosis in patients with Behçet's aortic aneurysms: an experience from a resource-challenged setting

BACKGROUND

The objectives of the current study were to evaluate our technical and clinical results of surgical treatment of infrarenal Behçet's abdominal aortic aneurysm (AAA). In addition to the prosthetic wrapping of the constructed anastomosis as a prophylactic measure for patients with vasculo-Behçet's disease, together with the administration of per- and postoperative immunosuppressive therapy.

METHODS

A single-center retrospective case series included 16 patients with vasculo-Behçet's AAA who treated with open surgical repair, between January 2005 and December 2013. The administration of immunosuppressive treatment was done preoperatively to achieve complete remission of the disease activity before starting the surgical repair. Patients' data were retrieved and analyzed emphasizing the diagnostic procedures, the used surgical techniques, and suitable graft selection, as well as, graft-related complications. The patients were followed up for one month to a maximum of 72 months. The median follow-up period was 24.83±9.4 months.

RESULTS

This study included 16 patients, 10 (63%) males, and 6 (37%) females, with the median age of (30.50 years, range: 21-37 years). Moreover, all patients were anticoagulated and discharged on warfarin and aspirin therapy. All surgical procedures were done on an elective basis except for only one emergency laparotomy, which was performed for a life-threatening ruptured aneurysm. The vascular anastomoses were performed using either interposition tube graft (for isolated AAA), or Y-shaped graft (for concomitant aorto-iliac aneurysms). Furthermore, prophylactic prosthetic wrapping was applied encircling the graft to the host artery. In addition, all patients received systemic immunosuppressive therapy post-surgical intervention to prevent anastomotic site complications. Technical success was obtained in 100% of cases. Moreover, the patients were followed up for a period of 12-72 months. Two anastomotic pseudoaneurysms were developed postoperatively. More interesting is that both were infected (one low-virulent that was conservatively treated and one overt that was surgically repaired). Furthermore, there was no aneurysm-related mortality.

CONCLUSIONS

Prophylactic prosthetic wrapping of vascular anastomosis in patients with Behçet's AAA in resource-challenged settings, where the proximal anastomoses were all end-to-end with wrapping, is an affordable, simple, reliable, and feasible technique, and commonly associated with a lower incidence of anastomotic site false aneurysms and different complications related to the implanted graft, where endovascular procedures might not be applicable. Moreover, the proper preoperative medical preparation for controlling the activity of Behçet's disease, with the administration of immunosuppressive agents, followed by immediate postoperative therapy, may have a good impact on the operative technical success and the prevention of the development of serious postoperative complications; especially anastomotic pseudoaneurysms (which may be complicated by fatal hemorrhage), as well as other graft-related complications.

The blood compatibility challenge. Part 4: Surface modification for hemocompatible materials: Passive and active approaches to guide blood-material interactions

Biomedical devices in the blood flow disturb the fine-tuned balance of pro- and anti-coagulant factors in blood and vessel wall. Numerous technologies have been suggested to reduce coagulant and inflammatory responses of the body towards the device material, ranging from camouflage effects to permanent activity and further to a responsive interaction with the host systems. However, not all types of modification are suitable for all types of medical products. This review has a focus on application-oriented considerations of hemocompatible surface fittings. Thus, passive versus bioactive modifications are discussed along with the control of protein adsorption, stability of the immobilization, and the type of bioactive substance, biological or synthetic. Further considerations are related to the target system, whether enzymes or cells should be addressed in arterial or venous system, or whether the blood vessel wall is addressed. Recent developments like feedback controlled or self-renewing systems for drug release or addressing cellular regulation pathways of blood platelets and endothelial cells are paradigms for a generation of blood contacting devices, which are hemocompatible by cooperation with the host system. STATEMENT OF SIGNIFICANCE: This paper is part 4 of a series of 4 reviews discussing the problem of biomaterial associated thrombogenicity. The objective was to highlight features of broad agreement and provide commentary on those aspects of the problem that were subject to dispute. We hope that future investigators will update these reviews as new scholarship resolves the uncertainties of today.

Vascular suture line wrapping for Aortoiliac anastomoses following open surgical repair of Infrarenal Behçet's Aortoiliac aneurysms

Background

This study was conducted to evaluate our local experiences of adjunctive mechanical prosthetic wrapping for aortoiliac vascular anastomoses as a prophylactic measure following surgical repair of Behçet’s aortoiliac aneurysms. The goal of prosthetic wrapping to reinforce the vascular anastomoses by mechanical protection to reduce the bleeding complications, and consequently pseudoaneurysm formation. This was aided by the administration of pre- and postoperative immunosuppressive therapy as an adjuvant treatment.

Methods

A seven-year retrospective study was conducted between January 2006 and December 2012, retrieving data of patients with Behçet’s aortoiliac aneurysms. All patients underwent open surgical repair using a heparin-bonded synthetic Dacron® graft. Data for all patients were retrieved and analyzed for diagnostic procedures, graft selection, as well as, different methods of surgical repair. Graft-related complications such as anastomotic pseudoaneurysms, occlusion, and thrombosis were also reported.

Results

Sixteen patients were recruited in this study. There were  11 (69%) males and 5 (31%) females with the male to female ratio 2:1. The patients’ age ranged between 25 and 47 years with the mean of 36.4 ± 7.3. All Behçet’s aortic/aortoiliac aneurysms were repaired by the application of heparin-bonded Dacron® tube and bifurcated grafts. The anastomotic wrapping technique was performed for both the proximal and the distal vascular anastomoses. The technical success of aortoiliac aneurysm and wrapping techniques was achieved in 100% of patients. All patients were given pre- and postoperative systemic immunosuppressive therapy. No graft-related complications were reported except for only one anastomotic pseudoaneurysm that developed at one of the right iliac anastomoses, that developed within 24 months after follow up.

Conclusions

Mechanical prosthetic wrapping for vascular anastomoses in patients with Behçet’s aortic/aortoiliac aneurysms is a feasible, simple, and reliable technique with low morbidity and mortality. It was performed as a prophylactic measure to avoid the development of postoperative anastomotic pseudoaneurysms. It must be performed for all patients with Behçet’s arterial aneurysms whenever possible. Furthermore, the supplemental administration of pre- and postoperative systemic immunosuppressive therapy should be considered as an important factor for the prophylaxis and prevention of anastomotic pseudoaneurysms and other graft-related complications.

Synthesis and Characterization of a Fluorinated S-Nitrosothiol as the Nitric Oxide Donor for Fluoropolymer-Based Biomedical Device Applications

Fluorinated polymers are widely used as biomaterials in various biomedical implant and device applications. However, thrombogenicity, surface-induced inflammation, and risk of microbial infection remain key issues that can limit their use. In this work, we describe the first nitric oxide (NO) releasing fluorinated polymer, in which a new fluorinated NO donor, S-nitroso-N-pentafluoropropionylpenicillamine (C2F5-SNAP), is incorporated within the polyvinylidene fluoride (PVDF) tubing. The synthesis, decomposition kinetics, and NO-release characteristics of the C2F5-SNAP species are described in detail. Then, using a simple solvent swelling method, we demonstrate that C2F5-SNAP can readily be doped into PVDF tubing. The resulting tubing can release NO for 11 days under physiological conditions, with an NO flux > 0.5 × 10-10 mol/cm2·min over the first 7 days. Due to fluorous-fluorous interactions, the leaching of the fluorinated NO donor and its decomposed products is shown to be very low (less than 5 nmol/mg, total). Further, the new NO-releasing PVDF tubing exhibits significant antimicrobial activity (compared to undoped PVDF tubing) against both gram positive and negative S. aureus and P. aeruginosa bacterial strains over a 7 d test period. This new NO-releasing fluorinated polymer is likely to have the potential to improve the biocompatibility and antimicrobial activity of various biomedical devices.

Experimental comparative study of thrombogenicity of two differently luminal heparinized ePTFE vascular prosthetics

Introduction

; Heparin bonded grafts have proven to improve patency, at least transiently.

Two different heparin bonded expanded polytetrafluoroethylene (ePTFE) grafts produced by different technologies are currently available.

This pilot primary goal was to test these commonly used, but differently heparinized ePTFE grafts for differences in primary patency after a 6-months follow-up in a sheep model. Secondly, the aim was to establish a large animal model to enable future translational studies and further graft development.

Method

; End-to-side bypass of the common carotid artery was performed bilaterally in sheep. Either a Gore^® Propaten heparinized graft or a Jotec^® Flowline Bipore heparinized graft was used, both 5 mm in diameter.

Following graft implantation, the sheep were kept on pasture for 6 months, with monthly duplex scans to determine patency. At termination, the grafts were duplex scanned a final time, with the animals sedated, and the grafts were removed for heparin activity analysis.

Results

; 14 sheep were operated, 11 survived total follow-up time. At final follow-up, 4 patent Gore^® grafts, and 6 Jotec^® remained. Mean patency time was 106.7 ± 21.9(SD) days and 96.2 ± 25.9(SD) days for Gore^® and Jotec^®, respectively. Log-rank test showed no significant difference at final follow-up after 6 months. Post mortem heparin analysis showed no significant difference in mean activity.

Conclusion

; Based on patency data alone, no significant difference between these grafts were found. In accordance, heparin activity analysis showed no difference between the grafts. The model itself, proved easily implementable, and provides many possibilities for future studies, though some adjustments should be made to improve survival.

•

First direct comparison of heparinized graft.

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No significant difference in patency or heparin activity concerning the two grafts.

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Animal model is easily implementable, and expandable to include numerous innovations.

Tissue Engineering at the Blood-Contacting Surface: A Review of Challenges and Strategies in Vascular Graft Development

Tissue engineered vascular grafts (TEVGs) are beginning to achieve clinical success and hold promise as a source of grafting material when donor grafts are unsuitable or unavailable. Significant technological advances have generated small-diameter TEVGs that are mechanically stable and promote functional remodeling by regenerating host cells. However, developing a biocompatible blood-contacting surface remains a major challenge. The TEVG luminal surface must avoid negative inflammatory responses and thrombogenesis immediately upon implantation and promote endothelialization. The surface has therefore become a primary focus for research and development efforts. The current state of TEVGs is herein reviewed with an emphasis on the blood-contacting surface. General vascular physiology and developmental challenges and strategies are briefly described, followed by an overview of the materials currently employed in TEVGs. The use of biodegradable materials and stem cells requires careful control of graft composition, degradation behavior, and cell recruitment ability to ensure that a physiologically relevant vessel structure is ultimately achieved. The establishment of a stable monolayer of endothelial cells and the quiescence of smooth muscle cells are critical to the maintenance of patency. Several strategies to modify blood-contacting surfaces to resist thrombosis and control cellular recruitment are reviewed, including coatings of biomimetic peptides and heparin.

Modulation of macrophage phenotype and protein secretion via heparin-IL-4 functionalized supramolecular elastomers

Hallmark of the in situ tissue engineering approach is the use of bioresorbable, synthetic, acellular scaffolds, which are designed to modulate the inflammatory response and actively trigger tissue regeneration by the body itself at the site of implantation. Much research is devoted to the design of synthetic materials modulating the polarization of macrophages, which are essential mediators of the early stages of the inflammatory response. Here, we present a novel method for the functionalization of elastomers based on synthetic peptide chemistry, supramolecular self-assembly, and immobilization of heparin and interleukin 4 (IL-4), which is known to skew the polarization of macrophages into the wound healing "M2" phenotype. Ureido-pyrimidinone (UPy)-modified chain extended polycaprolactone (CE-UPy-PCL) was mixed with a UPy-modified heparin binding peptide (UPy-HBP) to allow for immobilization of heparin, and further functionalization with IL-4 via its heparin binding domain. As a first proof of principle, CE-UPy-PCL and UPy-HBP were premixed in solution, dropcast and exposed to primary human monocyte-derived macrophages, in the presence or absence of IL-4-heparin functionalization. It was demonstrated that the supramolecular IL-4-heparin functionalization effectively promoted macrophage polarization into an anti-inflammatory phenotype, in terms of morphology, immunohistochemistry and cytokine secretion. Moreover, the supramolecular functionalization approach used was successfully translated to 3D electrospun scaffolds for in situ tissue engineering purposes, where UPy-HBP retention, and heparin and IL-4 attachment to the supramolecular scaffolds were proven over 7 days. Lastly, human monocyte-derived macrophages were cultured on 3D scaffolds, which, in case of IL-4-heparin functionalization, were proven to promote of an anti-inflammatory environment on protein level. This study presents a novel method in designing a versatile class of functionalized elastomers that effectively harness the anti-inflammatory behavior of macrophages in vitro, and as such, may be instrumental for the development of a new class of synthetic materials for in situ tissue engineering purposes.

STATEMENT OF SIGNIFICANCE

Macrophages and their phenotypic and functional plasticity play a pivotal role in metabolic homeostasis and tissue repair. Based on this notion, bioactivated materials modulating macrophage polarization were extensively investigated in the past. Here, we designed immunomodulating, synthetic materials based on supramolecular immobilization of a heparin binding peptide, and further bioactivation with heparin and IL-4, an anti-inflammatory cytokine responsible for M2 activation and polarization. Human monocyte-derived macrophages cultured on heparin-IL-4 bioactivated materials displayed an elongated morphology and an anti-inflammatory phenotype, with downregulation of pro-inflammatory cytokines and promotion of anti-inflammatory cytokines over time. This study represents the first step in designing a novel class of synthetic, bioactivated materials that harness the regenerative behavior of host macrophages towards in situ tissue regeneration.