Safety and Efficacy of Electrospun Polycarbonate-Urethane Vascular Graft for Early Hemodialysis Access: First Clinical Results in Man

Bio-Based Electrospun Fibers for Wound Healing

Being designated to protect other tissues, skin is the first and largest human body organ to be injured and for this reason, it is accredited with a high capacity for self-repairing. However, in the case of profound lesions or large surface loss, the natural wound healing process may be ineffective or insufficient, leading to detrimental and painful conditions that require repair adjuvants and tissue substitutes. In addition to the conventional wound care options, biodegradable polymers, both synthetic and biologic origin, are gaining increased importance for their high biocompatibility, biodegradation, and bioactive properties, such as antimicrobial, immunomodulatory, cell proliferative, and angiogenic. To create a microenvironment suitable for the healing process, a key property is the ability of a polymer to be spun into submicrometric fibers (e.g., via electrospinning), since they mimic the fibrous extracellular matrix and can support neo- tissue growth. A number of biodegradable polymers used in the biomedical sector comply with the definition of bio-based polymers (known also as biopolymers), which are recently being used in other industrial sectors for reducing the material and energy impact on the environment, as they are derived from renewable biological resources. In this review, after a description of the fundamental concepts of wound healing, with emphasis on advanced wound dressings, the recent developments of bio-based natural and synthetic electrospun structures for efficient wound healing applications are highlighted and discussed. This review aims to improve awareness on the use of bio-based polymers in medical devices.

Determining the incidence of needle-related complications in hemodialysis access: We need a better system

INTRODUCTION

Hemodialysis access complications are common. We hypothesize that many of these complications can be traced back to needle-related injury from routine cannulation practices or inadvertent cannulation injuries. We set out to compare the rates of hemodialysis access complications under prior and current diagnosis coding systems, determine the incidence of needle-related complications for hemodialysis access, and describe the association of needle-related complications and resulting interventions.

METHODS

Arteriovenous graft and arteriovenous fistula placements occurring in the first 6 months of 2014 and 2016 were identified in the United States Renal Data System Medicare claims data. Placements were followed until end of hemodialysis access life or end of the calendar year. Diagnoses and resulting interventions occurring during placement life were identified and mapped to needle-related complication terms.

RESULTS

Almost 30,000 placements for 27,000 patients were followed in each year, with 67% of all accesses placed being arteriovenous fistula and 33% arteriovenous graft. In both years, 75% of arteriovenous fistulae and arteriovenous grafts required one or more interventions. Stenosis and thrombosis were the most common complications diagnosed and treated (41% and 16%, respectively); however, potential needle-related complications accounted for 6% of this dataset.

DISCUSSION

International Classification of Diseases, 9th Revision, was inadequate for determining the incidence of specific hemodialysis access complications or needle-related complications. International Classification of Diseases, 10th Revision, introduced several more hemodialysis access diagnoses but is still subject to coding confusion and catch-all coding for a variety of common and otherwise well-defined complications, suggesting that the true incidence of needle-related complications is buried in the non-specific diagnosis codes. These findings mark the clear need for an improved diagnosis coding system that consistently represents all common hemodialysis access complications.

Computational study on the haemodynamic and mechanical performance of electrospun polyurethane dialysis grafts

Compliance mismatch between an arteriovenous dialysis graft (AVG) and the connected vein is believed to result in disturbed haemodynamics around the graft–vein anastomosis and increased mechanical loading of the vein. Both phenomena are associated with neointimal hyperplasia development, which is the main reason for AVG patency loss. In this study, we use a patient-specific fluid structure interaction AVG model to assess whether AVG haemodynamics and mechanical loading can be optimised by using novel electrospun polyurethane (ePU) grafts, since their compliance can be better tuned to match that of the native veins, compared to gold standard, expanded polytetrafluoroethylene (ePTFE) grafts. It was observed that the magnitude of flow disturbances in the vein and the size of anastomotic areas exposed to highly oscillatory shear (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {OSI} >0.25$$\end{document}OSI>0.25) and very high wall shear stress (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$>40 \hbox { Pa}$$\end{document}>40Pa) were largest for the ePTFE graft. Median strain and von Mises stress in the vein were similar for both graft types, whereas highest stress and strain were observed in the anastomosis of the ePU graft. Since haemodynamics were most favourable for the ePU graft simulation, AVG longevity might be improved by the use of ePU grafts.

An immediate access dialysis graft designed to prevent needle-related complications: Results from the initial pre-clinical studies

INTRODUCTION

No technology has been specifically developed with the intent to reduce needle-related vascular access injuries; a significant source of complications and abandonment. We present the initial pre-clinical study results of a novel, self-sealing, immediate cannulation dialysis graft that aims to prevent needle-related complications; to promote safe, reliable needle access; to reduce catheter use; and could facilitate home hemodialyisis.

METHODS

The innovative graft design consists of two cannulation chambers with self-sealing properties and materials that prevent side and back wall needle puncture. Study and control grafts (expanded polytetrafluoroethylene) were implanted in one pig and 10 sheep in two studies over the course of 1 year. First cannulation occurred immediately post implant for all study grafts. Post-cannulation time to hemostasis, hematoma and seroma formation, infection, and patency were recorded.

RESULTS

The two studies account for nearly 60 weeks (average 6.4 weeks/graft) of study graft follow-up. In the ovine study, average study graft time to hemostasis was 27.3 s (standard deviation = 26.3, range = 0-120), and the control averaged 177.2 s (standard deviation = 113.4, range = 60-600), p < 0.0001. Secondary patency was 75% and 67% for the study and control grafts, respectively. Neither study nor control groups experienced seroma, graft infections, or deaths.

DISCUSSION

All novel grafts in the studies were implanted successfully and functioned as intended. There were no complications related to tunneling of the study graft and the chamber prevented back/side wall needle injury. This novel technology may help to mitigate these needle-related complications, while allowing for early/immediate cannulation which could also reduce catheter contact time.

Early cannulation of bovine carotid artery grafts (Artegraft) after primary vascular access and fistula revision procedures

OBJECTIVE

Tunneled dialysis catheter (TDC) use has been associated with increased infectious complications and mortality in hemodialysis-dependent patients. Unfortunately, patients who undergo fistula revisions or creation of a new arteriovenous fistula frequently require a TDC during the postoperative period. Bovine carotid artery grafts (BCAGs) can be used as an early-access dialysis conduit to reduce TDC dependence. This study describes the performance of BCAGs that were cannulated early (<3 days) after implantation and associated clinical outcomes.

METHODS

BCAGs were implanted in 63 consecutive dialysis-dependent patients. Patients and dialysis centers were directly provided early cannulation instructions; 31 (49%) patients were cannulated early, and of the 31 patients cannulated early, 21 (68%) were cannulated during the first postoperative day. Early complications, primary patency, secondary patency, and TDC incidence were monitored through clinic visits, hospital records, and phone calls to dialysis centers.

RESULTS

The primary patency of BCAGs at 1 year in the early and late cannulation cohorts was 28% and 39%, respectively. The secondary patency of BCAGs at 1 year in the early and late cannulation cohorts was 74% and 77%, respectively. Early complications occurred in 11 (19%) patients who received a BCAG. There were no significant differences in complication rates between early and late cannulation patients. Of the 24 patients who underwent the operation without a pre-existing TDC, only three (13%) required TDC placement during the 30-day postoperative period.

CONCLUSIONS

BCAGs can be cannulated early without increased complication rates or a negative impact on midterm patency. Early cannulation of BCAGs obviates the need for a TDC postoperatively in dialysis-dependent patients undergoing primary vascular access or fistula revision procedures.

Early cannulation grafts for haemodialysis: An updated systematic review

Purpose:

Early cannulation grafts are specifically designed for dialysis, whereas standard expanded polytetrafluoroethylene grafts were not. There is developing collective experience and literature available to allow the assessment of outcomes of these early cannulation grafts. The aim of this review was to review the evidence for both short- and long-term outcomes of early cannulation grafts.

Methods:

Using standardized searches of electronic databases in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses, the primary outcomes for this study were primary and secondary patency rates for early cannulation grafts for dialysis at 12 months and beyond. Secondary outcomes were timing of first cannulation, rates of access thrombosis, steal syndrome, pseudo-aneurysm and infection.

Results:

A total of 19 studies were identified and included. These were divided into different graft types. Flixene™, Avflo™, Acuseal™ and Vectra™ grafts all showed that early cannulation within 72 h is possible. Twelve-month pooled primary and secondary patency rates were 43.3% (95% confidence interval: 31.6–55.4) and 73.4% (95% confidence interval: 63–82.7) for the Flixene graft, 58.2% (95% confidence interval: 48–68.1) and 79.2% (95% confidence interval: 68–88.7) for the Avflo graft, 43.6% (95% confidence interval: 30.7–56.9) and 70.5% (95% confidence interval: 49.7–87.8) for the Acuseal graft and 63.7% (95% confidence interval: 53.4–73.4) and 85.8% (95% confidence interval: 82.9–88.4) for the Vectra graft. Data for outcome beyond 12 months were limited to the more recent studies.

Conclusion:

This review confirms that early cannulation is not detrimental on the early outcome of early cannulation graft patencies. It has also shown that both Vectra and Avflo grafts have adequate long-term patencies. The data do not allow specific graft recommendations, as comparative trials would be required.

Early experience with a novel self-sealing nanofabric vascular graft for early hemodialysis access

Aim

To report initial experience regarding the use of novel self-sealing electrospun nanofabric graft.

Material and methods

A total of 21 patients aged between 22 and 64 (male:female ratio = 11:10) underwent AVflo vascular access graft implantation to forearm. Information for patency at 6 and 12 months after the operation was obtained. Cannulation for hemodialysis was allowed 8 h after the operation, as needed.

Results

Cannulation was performed before 12th hour of implantation in two patients, between 12th and 24th postoperative hours in 10 patients and between 12th and 24th postoperative hours in the remaining nine patients. Primary patency was 17/21 (80.9%) at 6th month and 15/21 (71.4%) at 12th month. Secondary patency was 19/21 (90.4%) at sixth month and 17/21 (80.9%) at 12th month.

Conclusion

AVflo self-sealing graft allows for early cannulation after implantation and thus may potentially eliminate the need for central venous catheters in selected patients.

Graft Modification Strategies to Improve Patency of Prosthetic Arteriovenous Grafts for Hemodialysis

Prosthetic arteriovenous grafts (AVGs) are indicated for vascular access for long-term hemodialysis in patients in whom creation or maintenance of an arteriovenous fistula (AVF) has failed or is contraindicated. AVGs have an inferior long-term patency as compared to AVFs. To ameliorate patency rates of prosthetic AVGs, different strategies have emerged to improve graft materials. This review aims to describe current strategies and future perspectives on graft modification, by graft geometry, drug coatings and graft surface technology, to improve AVG patency.

In pursuit of functional electrospun materials for clinical applications in humans

Electrospinning is a simple, low-cost and versatile approach to fabricate multifunctional materials useful in drug delivery and tissue engineering applications. Despite its emergence into other manufacturing sectors, electrospinning has not yet made a transformative impact in the clinic with a pharmaceutical product for use in humans. Why is this the current state of electrospun materials in biomedicine? Is it because electrospun materials are not yet capable of overcoming the biological safety and efficacy challenges needed in pharmaceutical products? Or, is it that technological advances in the electrospinning process are needed? This review investigates the current state of electrospun materials in medicine to identify both scientific and technological gaps that may limit clinical translation.

A two-year experience with a rapid access, self-sealing, polycarbonate urethane nanofiber vascular access graft for hemodialysis

OBJECTIVE

Evaluating the safety and efficacy of the AVflo™ graft in terms of patency and complications (early and late) over 2 years.

MATERIALS AND METHODS

Twelve end-stage renal disease (ESRD) patients (age: mean 68.5 ± 10 years) were followed up for a mean period of 946 ± 570 days after receiving an implantation of the graft for HD. The grafts were implanted at the lower arm (loop configuration), upper arm (straight configuration) and the thigh (loop configuration). First dialysis was performed at day 7 (3-21) following implantation.

RESULTS AND DISCUSSION

After a mean follow up of 24 months, the primary patency was 56% and the secondary patency was 82%. In this group, AVflo™ shows similar if not superior efficacy and safety to that of available grafts in terms of safety, complications, and long-term patency.

Early Cannulation Grafts for Haemodialysis: A Systematic Review

Purpose

Arteriovenous grafts have advantages compared with central venous catheters for dialysis access and guidelines suggest their use as second choice after arteriovenous fistulas. Standard practice with expanded polytetrafluoroethylene (ePTFE) grafts has been to avoid cannulation for 2 weeks following placement, but new generation grafts have been marketed for their early cannulation properties allowing use as an alternative to central venous catheters for prompt access. The aim of this review is to search the current literature for evidence of early cannulation of new generation grafts and to assess their patency and complication rates.

Methods

Electronic databases were searched for studies assessing the use of early cannulation grafts for dialysis in accordance with PRISMA. The primary outcomes for this study were primary patency rate, primary-assisted patency rate and secondary patency rate. Secondary outcomes were timing of first cannulation, rates of access thrombosis, steal syndrome, pseudo-aneurysm and infection.

Results

Following strict inclusion/exclusion criteria by two reviewers, 15 studies were included in our review and divided into the different types of graft. Flixene, Avflo, Rapidax and Acuseal grafts showed that early cannulation within 72 h was possible; there was no evidence of the use of Vectra within 2 weeks of placement. All grafts showed similar patency and complication rates as previously published data on standard ePTFE grafts.

Conclusion

Our review showed that early cannulation is possible without detriment, but data did not allow specific graft recommendations. Therefore, we feel that a multicentre, randomised controlled trial is necessary to compare early cannulation grafts.

The use of the early cannulation prosthetic graft (Acuseal™) for angioaccess for haemodialysis

Objectives

Autogenous arteriovenous (AV) accesses are the preferred choice for the delivery of haemodialysis (HD). With an increase in the prevalence of end-stage renal disease and in the life expectancy of these patients, the quality and availability of superficial vessels can be limited and reduced with time. The use of prosthetic AV accesses may therefore become necessary for the delivery of HD. A new early cannulation vascular prosthesis (GORE® ACUSEAL Vascular Graft) has been introduced, developed to hinder suture line and cannulation needle bleeding. The authors report their experience with this new conduit at a London teaching hospital.

Methods

Between May 2011 and June 2013, 52 patients underwent 55 procedures where the ACUSEAL® prosthetic AV access was utilized to facilitate HD. The majority of procedures involved the placement of prosthetic brachio-axillary accesses or prosthetic axillo-axillary chest accesses.

Results

The 1-year primary and secondary patency was found to be 46% and 61%, respectively. Successful cannulation of the newly placed AV access was performed with 24 hours of surgery in 40 patients (73%). Tunnelled vascular catheters were required in only 10 (18%) patients. Six (11%) of the patients in the study suffered early complications, and 9 (16%) patients developed AV access infection.

Conclusions

These results show that, while providing patency results that compare favourably to those published for other types of regular prosthetic accesses, the conduits are amenable to very early cannulation with few cannulation-related complications. This leads to a dramatic reduction in the need for temporary or tunnelled catheters.

A Novel Electrospun Nano-fabric Graft Allows Early Cannulation Access and Reduces Exposure to Central Venous Catheters

Purpose

The use of tunneled central venous catheters (CVC) as vascular access for hemodialysis treatment is increasing worldwide. We present a novel polycarbonate urethane nano-fabric graft, produced by electrospinning technology, which has self-sealing features that avoid seroma formation and allow puncturing within 48 hours. The aim of this study was to assess its advantages in a setting where late referral is common.

Methods

A retrospective single center study assessed 24 implanted grafts in 24 patients with maximal follow-up of 18 months; patency rates, time to first cannulation and post-operative complications were assessed.

Results

Successful access was achieved in all 24 patients within 48 hours. In 50% of the patients cannulation was performed within 24 hours without increasing the complication rate. Twelve month primary and secondary patencies were 50% and 70.8%, respectively. Excluding early failures (within 30 days) because of surgical problems, 12 month primary and secondary patencies were 75% and 81.2% respectively. Complication and infection rates were 10.94 and 0.49/1000 dialysis procedures, respectively. No pseudoaneurysms or seromas were documented at 18 months.

Conclusions

Early cannulation was successful in all patients with good 12-month primary and secondary patency rates, compared to data reported by others on polytetrafluoroethylene (PTFE) grafts. The infection rate was substantially lower than in tunneled CVCs. Therefore, the AVflo graft may improve the clinical status of dialysis patients by decreasing the exposure to CVCs.

Early Experience with a Newly Developed Electrospun Polycarbonate-urethane Vascular Graft for Hemodialysis Access

Purpose

In this pilot study, we tested a newly developed electrospun multilayered, self-sealing graft, AVflo™, specifically designed for early hemodialysis access.

Methods

Ten eligible consenting patients had a polycarbonate-urethane graft (AVflo™) implanted and were followed up prospectively for at least six months. Performance measures included graft patency, complications and time to first cannulation. Mean age of the patients was 66.7 ± 10 years. Chronic glomerulonephritis was the most common cause of renal failure. A total of 70% of the patients had a history of previous vascular access and 40% history of minimally invasive radiologic procedures for patency maintenance. In 40% of the cases the need for AV graft implantation was because of recurrent infections from permanent catheter for dialysis. Seven grafts were placed in the upper arm and three in the thigh. Mean follow up was 230 ± 75 days.

Results

There were no systemic or local reactions to the graft and we did not report any graft infections. Two grafts thrombosed because of severe bleeding post-cannulation due to an incorrect needle puncture. Both grafts were successfully thrombectomized. Primary and secondary patency rates at six months were 60% and 78%, respectively. These patency rates were comparable to those reported for other polyether-urethane and ePTFE grafts. Median time to first cannulation was seven days (3-21) and all puncture sites sealed in less than five minutes.

Conclusions

This newly developed electrospun polycarbonate-urethane graft is safe in humans, permits early access obviating the need for venous catheters, and has equivalent patency as other prosthetic grafts.

Immediate use of an arteriovenous prosthetic graft for life-saving dialysis in a child

BACKGROUND

Autologous arteriovenous fistulas (AVFs) are the current gold standard for vascular access in hemodialysis (HD). However, in pediatric patients, specific clinical settings may contraindicate the procedure, thus mandating the use of a prosthetic graft (PG).

CASE-DIAGNOSIS/TREATMENT

We report a case of successful polycarbonate urethane graft implantation and subsequent resumption of HD 12 h after the procedure in a young girl with end-stage renal disease (ESRD), challenging vascular anatomy and the absence of vascular access.

CONCLUSIONS

The use of polycarbonate urethane PGs in children with ESRD and difficult vascular accesses may represent a valid alternative for early resumption of HD.