Neo-endothelialisation of PTFE microvascular grafts: a five-year experience

In vivo self-assembly of small diameter pulmonary visceral pleura artery graft

BACKGROUND

There is a significant clinical need for small vascular grafts <1 mm in diameter.

MATERIALS AND METHODS

The structure and composition of swine pulmonary visceral pleura (PVP) were investigated. Two processes, glutaraldehyde (GA) crosslink and decellularization (dc) plus GA crosslink, were used to inhibit the immune response. The thrombosis-resistance of the GA-crosslinked PVP (GA-PVP) was determined with in vitro and in vivo studies. Small vessel grafts with 0.7 diameter mm were constructed using the GA-PVP and surgically interposed in the femoral artery of rats for up to 24 weeks. Blood flow in the GA-PVP grafts were measured and ex vivo vascular reactivity of the prostheses were evaluated along with immuno-histological analysis.

RESULTS

The GA-PVP mesothelium contains abundant glycocalyx-like substance and a smooth surface. The mechanical properties of the GA-PVP were similar to the femoral artery of rat in the range of physiological pressures. The in vitro and in vivo studies confirmed poor platelet adhesion on the GA-PVP mesothelial surface in comparison with dc processed PVP (dc-PVP). Patency of the GA-PVP prostheses in femoral arteries of rats was 86% in the 24 weeks postoperative period while patency of dc-PVP in femoral arteries of rats was 33% at 1 week postoperative period. Blood flow in the GA-PVP prostheses were not statistically different than the contralateral femoral artery. Biomarkers of neo-endothelial cells, neo-media smooth muscle cells, and extracellular matrices were observed in the GA-PVP prostheses. The significant agonists-induced vasoconstriction and endothelium-dependent vasodilation were apparent at 12 weeks and further amplified in the 24 weeks postoperative, which suggests self-assembly of functional neo-endothelium and neo-media.

CONCLUSIONS

The high patency and functionality of the small grafts suggest that the GA-PVP is a promising prosthetic biomaterial for vascular reconstructions.

STATEMENT OF SIGNIFICANCE

Small artery graft (diameter <1 mm) in the peripheral circulation that functionally arterializes has not been possible primarily due to thrombosis. Our findings indicate that lung visceral pleura may address thrombogenicity as the major pitfall in small diameter grafts. Here, grafts of 0.7 mm diameter were constructed from swine pulmonary visceral pleura (PVP) and implanted into femoral artery position of rats up to 24 weeks. The total patency of grafts in femoral arteries of rats was 86% in the 24-week period. The neo-endothelial and -medial layers were assembled in the grafts as evidenced by robust biomarkers of endothelial cells, smooth muscle cells, and extracellular matrices observed in the grafts. Agonists-induced vasoconstriction and endothelium-dependent vasodilation were apparent at 12 weeks and were amplified at 24 weeks. The high patency of the small grafts suggests that the PVP is a promising prosthetic biomaterial for vascular reconstructions.

[Huge periprosthetic (peritransplant) seroma of a femoropopliteal bypass graft]

Presented herein is a clinical case report of a huge periprosthetic seroma of a femoropopliteal bypass graft made of polytetrafluoroethylene with a follow-up period and unsuccessful conservative management of more than one year. At 15 months after the primary operation, the bypass graft was retrieved and replaced by a knitted vascular graft made of polyester and impregnated with absorbable modified gelatine to decrease porosity, without relapse of the process of transudation into the periprosthetic space. Histological study of the retrieved conduit demonstrated the absence of formation of the intimal layer on the inner surface of the graft and fibrous capsule on the external surface of the main part of the length of the prosthesis, which, apparently, had provided a possibility of long-term preservation of porosity of the material.

Preclinical evaluation of hydrogel sealed fluropassivated indigenous vascular prosthesis

Background & objectives:

Polyethylene terephthalate (PET) graft, designed and developed at our institute for vascular reconstruction, is porous to promote optimal incorporation and neointima formation, requiring pre-clotting or biomodification by sealing the pores before implantation. The objective of this study was to characterize, test and perform preclinical evaluation of hydrogel (alginate dialdehyde cross-linked gelatin) sealed fluoropassivated PET vascular prosthesis in pig model, so as to avoid pre-clotting, for its safety and efficacy before employing the indigenous and less expensive graft for clinical use.

Methods:

Hydrogel sealed, fluoropassivated PET vascular prosthesis were tested for haemocompatibility and toxicity followed by small animal toxicology tests and in vivo experiments in pigs receiving implantation at thoracic aorta. All 33 animals received test as well as control grafts with a plan for phased explantation at 2, 12 and 26 weeks. All animals underwent completion angiogram at the end of procedure as well as before graft explantation.

Results:

Haemocompatibility tests for haemolysis and toxicity tests showed no adverse events in tested mice and rabbits. Completion angiogram showed intact anastamosis and patent graft in each animal in post-operative period and at explantation. Gross and histopathological examination showed well-encapsulated grafts, clean glistening neointima and no evidence of thrombus in both test and control grafts.

Interpretation & conclusions:

Hydrogel sealed, fluoropassivated PET vascular prosthesis was found non-toxic, haemocompatible and remained patent in in vivo studies at planned intervals.

Bacterial signatures in thrombus aspirates of patients with lower limb arterial and venous thrombosis

OBJECTIVE

Increasing data supports the role of bacterial inflammation in adverse events of cardiovascular and cerebrovascular diseases. In our previous research, DNA of bacterial species found in coronary artery thrombus aspirates and ruptured cerebral aneurysms were mostly of endodontic and periodontal origin, where Streptococcus mitis group DNA was the most common. We hypothesized that the genomes of S mitis group could be identified in thrombus aspirates of patients with lower limb arterial and deep venous thrombosis.

METHODS

Thrombus aspirates and control blood samples taken from 42 patients with acute or acute-on-chronic lower limb ischemia (Rutherford I-IIb) owing to arterial or graft thrombosis (n = 31) or lower limb deep venous thrombosis (n = 11) were examined using a quantitative real-time polymerase chain reaction to detect all possible bacterial DNA and DNA of S mitis group in particular. The samples were considered positive, if the amount of bacterial DNA in the thrombus aspirates was 2-fold or greater in comparison with control blood samples.

RESULTS

In the positive samples the mean difference for the total bacterial DNA was 12.1-fold (median, 7.1), whereas the differences for S mitis group DNA were a mean of 29.1 and a median of 5.2-fold. Of the arterial thrombus aspirates, 57.9% were positive for bacterial DNA, whereas bacterial genomes were found in 75% of bypass graft thrombosis with 77.8% of the prosthetic grafts being positive. Of the deep vein thrombus aspirates, 45.5% contained bacterial genomes. Most (80%) of bacterial DNA-positive cases contained DNA from the S mitis group. Previous arterial interventions were significantly associated with the occurrence of S mitis group DNA (P = .049, Fisher's exact test).

CONCLUSIONS

This is the first study to report the presence of bacterial DNA, predominantly of S mitis group origin, in the thrombus aspirates of surgical patients with lower limb arterial and deep venous thrombosis, suggesting their possible role in the pathogenesis of thrombotic events. Additional studies will, however, be needed to reach a final conclusion.

The modulation of platelet and endothelial cell adhesion to vascular graft materials by perlecan

Controlled neo-endothelialisation is critical to the patency of small diameter vascular grafts. Endothelialisation and platelet adhesion to purified endothelial cell-derived perlecan, the major heparan sulfate (HS) proteoglycan in basement membranes, were investigated using in vivo and in vitro assays. Expanded polytetrafluoroethylene (ePTFE) vascular grafts were coated with perlecan and tested in an ovine carotid interposition model for a period of 6 weeks and assessed using light and scanning microscopy. Enhanced endothelial cell growth and reduced platelet adhesion were observed on the perlecan coated grafts when compared to uncoated controls implanted in the same sheep (n=5). Perlecan was also found to stimulate endothelial cell proliferation in vitro over a period of 6 days in the presence of plasma proteins and fibroblastic growth factor 2 (FGF-2), however in the absence of FGF-2 endothelial cell growth could not be maintained during this period. Perlecan was found to be anti-adhesive for platelets, however after removal of the HS chains attached to perlecan, platelet adhesion and aggregation were supported. These results suggest a role for HS chains of perlecan in improving graft patency by selectively promoting endothelial cell proliferation while modulating platelet adhesion.

Microvascular repair with 1-mm polytetrafluoroethylene (PTFE) grafts: effect of recombinant tissue-type plasminogen activator (rt-PA) on the patency rate and healing process

The present study assesses the effect of recombinant tissue-type plasminogen activator (rt-PA) on the patency rate and healing process of microvascular polytetrafluoroethylene (PTFE) grafts. Wistar rats were used, divided into four groups of 25 animals each. After dissection of the carotid artery a segment of the vessel, 1 cm long, was resected and replaced by equal length graft. Two different type fibril length (30- or 60-microm) grafts of the same wall thickness (0.18 mm) were used. Normal saline or 3 mg/kg of body weight of rt-PA was applied locally in each group of different fibril length grafts. Patency tests were performed at 15 min and 4 weeks after blood flow was reestablished. All grafts were harvested and examined histologically. The results showed that local application of rt-PA improves patency statistically significantly in both types of fibril length grafts. Patency in 60-microm fibril length grafts was statistically significantly higher than that of 30-microm fibril length grafts, whether rt-PA was used or not. The use of rt-PA had no influence on the healing process of either type of graft.

Fibroblast growth factor pretreatment of 1-mm PTFE grafts

When using microvascular polytetrafluoroethylene (PTFE) vascular grafts, the best results in terms of patency rate and neoendothelialization are obtained with prostheses with thin walls and long fibril length (i.e., 90 microm). A complete internal neoendothelial lining is usually achieved at 12 weeks after implantation. Clinically, this period can be too long. In this study, 1-mm internal diameter PTFE prostheses with optimal physical characteristics were pretreated with basic fibroblast growth factor in fibrin glue, a potent endothelial cell mitogen, and chemoattractant. Rate, speed, extent, quality, and origin of neoendothelium were compared with two control groups, using Evans Blue dye, immunohistochemical localization of factor VIII von Willebrand factor protein, and scanning electron microscopy. Prostheses (8 mm long) were implanted in the infrarenal rat aorta and harvested after 3 weeks. In treated grafts, the amount of endothelial regeneration was greater than in untreated grafts (75% of the internal surface compared with 30%). However, patency rate in the experimental group was lower than in the control groups. This study provides new data on neoendothelial regeneration in small-diameter PTFE grafts.

e-PTFE as scleral buckling episcleral implants: an experimental and histopathologic study

To investigate the effects of focal implantation of expanded polytetrafluoroethylene (e-PTFE) episcleral implants (i.e., explants or exoplants) on surrounding ocular tissues, an experimental and histopathological study was performed. Twenty-seven Fauve de Bourgogne rabbits eyes were implanted for a period of 3-11 months with oval-shaped e-PTFE episcleral implants. A newly formed capsule constantly encased the implants. Affected by the only two severe complications observed, 2 eyes had an endocapsular acute inflammation and could not be included in the study. Finally, 25 eyes were studied histopathologically. Neither intrusion nor extrusion of episcleral implants was observed. Other changes were related to implant characteristics. The inner surface of the capsule was often covered with numerous giant cells attesting to a foreign-body granuloma developed against the irregular outline of the episcleral implants. The porosity of the material was closely related to its surface irregularity, and also allowed its colonization by a fibrovascular and inflammatory tissue mainly in its peripheral layers. Under episcleral implants, sclera was both thinned and invaginated. Expanded PTFE hydrophobia was the other factor that might have suscitated granuloma. These microscopic changes are in contrast with an overall good apparent experimental tolerance to the material. However, additional studies on the long term behavior of this material would be helpful.

Clinical use of microvascular PTFE grafts

This paper reports on the first clinical case where a polytetrafluoroethylene (PTFE) graft of less than 3 mm in diameter was implanted in the arterial system of a patient to bridge a vascular defect. A 1.5 cm long, 1.5 mm diameter prosthesis was interposed in the superficial palmar arch of a man who sustained a laceration of the palm of his dominant hand. The graft was implanted by means of the 3M Precise Microvascular Anastomotic System on one end, and by conventional microsurgical technique on the other end. There were no postoperative complications. The patient resumed his pre-injury activities 9 weeks after trauma. Serial Doppler ultrasound examinations showed normal blood flow and complete patency of the graft. An angiogram performed 12 weeks postoperatively confirmed the patency of the prosthesis. Twelve months post-operatively the patient is free from complications. The use of small diameter PTFE prostheses may be considered when planning grafting procedures for microvascular defects.