Wojciech Mrówczyński

Long term performance of polycaprolactone vascular grafts in a rat abdominal aorta replacement model

In the active field of vascular graft research, polycaprolactone is often used because of its good mechanical strength and its biocompatibility. It is easily processed into micro and nano-fibers by electrospinning to form a porous, cell-friendly scaffold. However, long term in vivo performance of polycaprolactone vascular grafts had yet to be investigated. In this study, polycaprolactone micro and nano-fiber based vascular grafts were evaluated in the rat abdominal aorta replacement model for 1.5, 3, 6, 12, and 18 months (n = 3 for each time point). The grafts were evaluated for patency, thrombosis, compliance, tissue regeneration, and material degradation. Results show excellent structural integrity throughout the study, with no aneurysmal dilation, and perfect patency with no thrombosis and limited intimal hyperplasia. Endothelialization, cell invasion, and neovascularization of the graft wall rapidly increased until 6 months, but at 12 and 18 months, a cellular regression is observed. On the medium term, chondroid metaplasia takes place in the intimal hyperplasia layers, which contributes to calcification of the grafts. This study presents issues with degradable vascular grafts that cannot be identified with short implantation times or in vitro studies. Such findings should allow for better design of next generation vascular grafts.

Advantages of bilayered vascular grafts for surgical applicability and tissue regeneration

Nanofibrous scaffolds are part of an intense research effort to design the next generation of vascular grafts. With electrospinning, the production of micro- and nano-fiber-based prostheses is simple and cost effective. An important parameter for tissue regeneration in such scaffolds is pore size. Too small pores will impede cell infiltration, but too large pores can lead to problems such as blood leakage. In this study, bilayered grafts were made by electrospinning a high-porosity graft with a low-porosity layer on either the luminal or the adventitial side. Grafts were characterized in vitro for fiber size, pore size, total porosity, water and blood leakage, mechanical strength, burst pressure and suture retention strength, and were evaluated in vivo in the rat abdominal aorta replacement model for 3 and 12 weeks. In vitro blood leakage through these bilayered grafts was significantly reduced compared with a high-porosity graft. All grafts had an excellent in vivo outcome, with perfect patency and no thrombosis. Cell invasion and neovascularization were significantly reduced in the grafts with a low-porosity layer on the adventitial side, and there was no significant difference between the grafts in endothelialization rate or intimal hyperplasia. By tailoring the microarchitecture of biodegradable vascular prostheses, it is therefore possible to optimize the scaffold for tissue regeneration while preventing blood leakage, and thus facilitating applicability in the clinic.

Porcine carotid artery replacement with biodegradable electrospun poly-e-caprolactone vascular prosthesis

OBJECTIVE There is a continuous search for shelf-ready small-caliber vascular prostheses with satisfactory early and late results. Biodegradable scaffolds, repopulated by recipients cells regenerating a neovessel, can be a suitable option for adult and pediatric, urgent and elective cardiovascular procedures. METHODS This was a short-term experimental assessment of a new biodegradable vascular prosthesis for arterial replacement in the pig. Eleven pigs underwent bilateral carotid artery replacement with biodegradable electrospun poly-ε-caprolactone (PCL) nanofiber prostheses (internal diameter, 4 mm; length, 5 cm); or expanded polytetrafluoroethylene (ePTFE) prostheses as control. Perioperative anticoagulation was achieved with intravenous heparin (double baseline activated clotting time). Postoperatively, until conclusion of the study at 1 month, animals received aspirin and clopidogrel daily. Transit time flow was measured intraoperatively and at sacrifice. Doppler ultrasound (1 and 4 weeks) and a selective carotid angiography (4 weeks) were performed to assess patency. All explanted grafts were analyzed by histology, morphometry, and scanning electron microscopy in order to study graft-host interaction. RESULTS Surgical handling and hemostasis of the new prostheses were excellent. Patency rate was 78% (7/9) for PCL grafts, compared with 67% (4/6) for ePTFE grafts. Transit time flow and Doppler ultrasound showed no significant changes in flow and velocity or diameter over time in both groups. Both prostheses showed no detectable in vivo compliance as compared with native carotid artery. Percent neoendothelialization was 86% for PCL and 58% for ePTFE grafts (P = .008). Neointima formation was equal in both grafts. More adventitial infiltration of macrophages, myofibroblasts, and capillaries was seen in PCL grafts with a milder foreign-body reaction when compared with ePTFE implants. Both grafts showed similar endoluminal thrombus formation. CONCLUSIONS Biodegradable, electrospun PCL grafts showed good surgical and mechanical properties, no aneurysm formation, and similar short-term patency compared with ePTFE grafts. Rapid endothelialization and cell ingrowth confirms favorable PCL graft-recipient biological interaction. Despite good early results, long-term follow-up is required before clinical application.

Infection Risk Factors in Pediatric Cardiac Surgery

Cardiac operations were preformed in 499 children from January 1998 through December 1999. Their median age was 263 days. A positive culture from blood, bronchoalveolar lavage, wound, or central catheter was obtained in 110 patients (22%). Age, sex, presence of pulmonary hypertension, body surface area, ratio of body surface area to oxygenator surface area, whether heart surgery was open or closed, and the duration of the operation, cardiopulmonary bypass, intubation, and intensive care were analyzed. Patients who developed infections were significantly younger, with smaller body surface areas and disparity with the oxygenator surface area, longer operative and bypass times, extended intubation, and prolonged intensive care. There was a significant correlation between infection and pulmonary hypertension. Sex and type of operation were not predictors of infection.

Thyroid hormones levels in infants during and after cardiopulmonary bypass with ultrafiltration

OBJECTIVE The aim of this study was to find out if infants after cardiopulmonary bypass develop non-thyroidal illness and if illness severity after cardiopulmonary bypass depends on hormone concentration in ultrafiltrate. METHODS Thyroid hormone status was assessed in 20 infants with congenital heart defects undergoing cardiac surgery (age range 7 days-11 months). Blood samples were collected preoperatively, during cardiopulmonary bypass, after cardiopulmonary bypass, and also postoperatively in 1, 2, 3, and 8 day after cardiac surgery. Plasma thyrotropin, thyroxine, free thyroxine, triiodothyronine, free triiodothyronine and reverse triiodothyronine were measured in blood samples and also in ultrafiltrate. RESULTS All patients had reduction in serum thyrotropin, thyroxine, free thyroxine, triiodothyronine, free triiodothyronine, and elevation of reverse triiodothyronine after cardiac surgery. In all patients we performed ultrafiltration. Patients were divided in to two groups. (with and without prolonged recovery). In the group of patients with prolonged recovery we noticed significantly higher amount of triiodothyronine per kilogram body weight. One of these patients died. The average level of total thyroxine decreased from the level 126 nmol/l before bypass to the minimal level 73 nmol/l after bypass, free thyroxine from the level 18 pmol/l before bypass to the minimal level 12 pmol/l after bypass. The average level of total triiodothyronine decreased from the level 1.54 nmol/l before bypass to the minimal level 0.42 nmol/l after bypass, free triiodothyronine from the level 6.12 pmol/l before bypass to the minimal level 3.21 pmol/l after bypass. The average level of TSH decreased from the level 4.31 mU/l before bypass to the level 0.64 mU/l after bypass. The average level of reverse-triiodothyronine increase from the level 0.83 nmol/l before bypass to the maximal level 1.94 nmol/l after bypass. CONCLUSIONS We conclude that non-thyroidal illness occurs in all infants after cardiopulmonary bypass. The amount of free triiodothyronine that is filtrated during cardiopulmonary bypass may influence postoperative recovery.

Does contegra xenograft implantation evoke cellular immunity in children

The aim of the study was to search for changes in subpopulations of peripheral blood lymphocytes and in their activation as the manifestation of cellular immunity against xenograft in recipients of bovine valved conduit used for right ventricle outflow tract reconstruction. Between 24-06-1999 and 19-10-2000 35 children were operated in ECC, 19 had a xenograft implanted, the rest entered the control group. Immunophenotype of lymphoid cells and T cells activation was evaluated with use of flow cytometer: preoperatively and 3, 6 and 12 months after the operation in both groups. There were no differences in numbers of CD3+, CD4+, CD8+ and natural killer cells between groups. A significant rise of B-cells percentages (from 15.5% to 23%) between 3rd and 6th month was noted. The T-lymphocyte activation study revealed higher numbers of CD69+ (0.17 vs. 0.09 G/l) and CD71+ (0.23 vs. 0.11 G/l) cells one year after the implantation in xenograft recipients. Difference between groups in number of CD69+ and CD71+ cells in 12th month may suggest mild activation (<10%) of these subgroups in xenograft recipients. This data may hint the presence of cellular reactivity. Changes in numbers of B-cells may evidence humoral immunity activation. Influence of these phenomena on graft survival remains to be established.

Experimental noninferiority trial of synthetic small-caliber biodegradable versus stable vascular grafts

OBJECTIVE Long-term evolution of polycaprolactone vascular prostheses has been investigated recently. The goal of this study was to evidence a noninferiority of such grafts compared with expanded polytetrafluoroethylene (ePTFE) implants in an aortic replacement model in the rat. METHODS Fourteen anesthetized Sprague-Dawley rats received an infrarenal aortic graft (biodegradable, n = 8; expanded polytetrafluoroethylene, n = 6) replacement (end to end; inner diameter, 2 mm). Biodegradable grafts (polycaprolactone) were produced by random micro-/nanofiber electrospinning. After a median survival of 16.5 months, in vivo ultrasonography and angiography as well as postexplantation microcomputed tomography, histomorphometry, immunohistochemistry, and scanning electron microscopy were performed. RESULTS Patency was 100% for polycaprolactone and 67% for ePTFE. No aneurysmal dilatation or stenoses were found in either group. Compliance was significantly higher for polycaprolactone compared with ePTFE (8.2 ± 1.0%/100 mm Hg vs 5.7 ± 0.7%/100 mm Hg; P < .01), but markedly reduced compared with adjacent native aortas and the control group. Histologically, low cellular in-growth was found in ePTFE whereas polycaprolactone showed significantly greater homogenous cellularity, producing an autologous extracellular matrix (10.8% ± 4.0% vs 32.1% ± 9.2%, P < .0001). Morphometry showed 100% neo-endothelialization for both grafts with a totally confluent endothelial coverage for polycaprolactone grafts by scanning electron microscope. More intimal hyperplasia was found in ePTFE compared with polycaprolactone grafts. Calcification was higher in ePTFE than in polycaprolactone grafts (15.8% vs 7.0%, P = .04) and was absent in controls. CONCLUSIONS Outcomes of synthetic biodegradable nanofiber polycaprolactone grafts are not inferior compared with the clinically used expanded polytetrafluoroethylene grafts after long-term implantation in the rat aorta. Moreover, these implants show better patency, compliance, endothelialization, and cell in-growth, and less intimal hyperplasia and calcification than their counterparts.

Mid-term experience with valved bovine jugular vein conduits.

From June 1999 to January 2004, 43 children underwent implantation of a valved bovine jugular vein conduit and correction of complex congenital heart defects. Median age was 1.98 years (range, 11 days – 13.3 years). There were 7 early deaths (16.3%) unrelated to conduit failure or thrombosis. Median follow-up of 36 survivors was 24 months (range, 1–48 months, quartile range, 12–48 months), total follow-up was 78 patient-years. There were 3 late deaths (8.3%) due to infection, pulmonary thromboembolism, and sudden cardiac arrest after re-operation to repair a right ventricular outflow tract aneurysm. There were 2 conduit explantations due to dysfunction and suspected endocarditis. Three patients underwent balloon dilatation of distal stenoses. The mean peak gradient through the pulmonary anastomosis was 15 mm Hg (range, 3–42 mm Hg) among patients free from re-intervention. No severe valve regurgitation was observed. Freedom from re-intervention was 72% at 48 months. This conduit remains a good alternative to homografts. Causes of distal stenosis must be clarified, guidelines for prophylactic anticoagulation must be created, and the role of percutaneous balloon dilatation established.

Application of the CardioCel bovine pericardial patch – a preliminary report

Introduction Animal pericardial patches are widely used in adult and pediatric cardiac surgery. A search is ongoing for a new material with optimal surgical properties that will reduce intraoperative bleeding and the occurrence of restenosis, calcification, and pseudoaneurysms in long-term observation. One product of interest is the CardioCel bovine pericardial patch. Aim Evaluation of the short-term results of CardioCel bovine pericardial patch implantation during pediatric cardiac surgery. Material and methods The study included 8 patients who underwent surgical correction of congenital cardiac defects between January 2015 and February 2016. Pericardial patches were used to repair supravalvular aortic stenosis and reconstruct the aortic arch and pulmonary arteries. The age of the patients ranged from 10 days to 14 years. Results There were no hospital deaths. The new material exhibited satisfactory durability and elasticity during surgery, facilitating optimal adaptation of the patch to the patients tissues. No significant bleeding was reported from the suture site. The median duration of follow-up was 58 days. During the follow-up, there were no symptoms of pseudoaneurysm formation, patch thickening, or calcification in the areas where the pericardial patches were implanted. No clinical or laboratory symptoms of infection were observed in locations where the new material was applied. Conclusions Satisfactory surgical properties of the patch were observed intraoperatively. Positive results using the new pericardial patch were obtained in short-term follow-up.

Biological effects of anti-CD34-coated ePTFE vascular grafts. Early in vivo experimental results.

Aim of the study To assess the biological activity of anti-CD34 antibody-coated ePTFE vascular prostheses. Material and methods Indium111-labeled autologous thrombocytes were administered to 5 anesthetized pigs after the placement of femoral arterial and venous catheters. An arterio-venous fistula, created by the random interposition of 4 different ePTFE grafts (A = dry control, B = dry anti-CD34, C = wet control, D = wet anti-CD34), was blood perfused for 0, 10, 30, 60 and 120 minutes. Radioactivity of each graft was measured and expressed in cpm/mg. Morphological studies were performed to assess intraluminal deposition. Results The median radioactivity of graft B was significantly higher than that of graft A after 60 min (1074 vs. 18; p = 0.021) and 120 min (1990 vs. 25; p = 0.043) of perfusion. Similarly, graft D was significantly more active than graft C (60 min: 1388 vs. 26; p = 0.021 and 120 min: 2780 vs. 23; p = 0.021). Histological and SEM results confirmed the radio-labeling in-vivo studies by showing significantly more protein/cell and platelet depositions (p = 0.012). Conclusions Anti-CD34-coated ePTFE grafts bound significantly more platelets/cells and proteins than their uncoated counterparts, confirming the bioactivity of the antibody. This process is time-dependent and matches the morphological results. The anti-CD34 coating may enhance temporal and spatial endothelialization of vascular grafts and, thus, possibly improve clinical results by providing direct endothelial progenitor cell (EPC) adhesion/entrapment or by creating a biocompatible protein-thrombocyte/cell layer that indirectly enhances migration and further proliferation of EPCs.