Bypass Surgery in Limb Salvage: Polytetrafluoroethylene Prosthetic Bypass

Abstract

Polytetrafluoroethylene (PTFE) grafts have proven to be an adequate alternative conduit for peripheral bypass operations. Whether or not one uses PTFE depends on several factors: surgeon preference, individual patient circumstances, or when autologous greater saphenous vein is not available or adequate. These conventional grafts have evolved and undergone modification. The intraluminal surface has been coated with carbon or bonded with heparin. The structure of grafts has been modified with the creation of a hood or cuff, with the incorporation of a stent-graft segment for a sutureless anastomosis, or the fusion of PTFE with an outer polyester layer to minimize suture hole bleeding. This evolution intends to limit graft thrombogenicity, ameliorate the formation of intimal hyperplasia, decrease complications, and improve overall graft patency.

Polymers in Cardiology

“…observed for PA and PET) or oxidation (e.g. observed for PUR) [86]. Furthermore, vascular grafts based on ePTFE have proven to be an adequate biostable conduit for bypass surgery [87,88].…”

“…In this context, the integration of hydrolytically cleavable bonds is a conventional method to realize degradable polymeric materials synthetically. The hydrolytic degradation has the advantage that the degradation rate is at most independent from the position of implantation due to the fact that in all regions of the human organism water is present [86]. In contrast, the concentration of enzymes, which can catalyze the hydrolysis of bonds and therefore can cause an increase of cleavage velocity, is locally different.…”

“…In contrast, the concentration of enzymes, which can catalyze the hydrolysis of bonds and therefore can cause an increase of cleavage velocity, is locally different. The list of factors that influence the degradation behavior of biodegradable polymers is long and ranges exemplarily from their chemical structure, their molecular weight and distribution, their crystallinity and the existence of ionic groups (polymer-dependent) over the sample geometry, the surface morphology and thus the surface-volume ratio, the sterilization and storage conditions (sample-dependent) to the kind of their implantation, the pH and enzymatic conditions, as well as the physisorption of proteins and as a result the fibrotic encapsulation which can possibly accelerate the degradation by autocatalytic action of degradation products (implantation-dependent) [86]. Two mechanisms are described for the biodegradation process: (1) the bulk degradation, where the degradation is favored in the polymer bulk material due to the fact that water can diffuse faster into the bulk than the polymer can degrade and (2) the surface erosion, where the diffusion velocity of water is slower than the degradation rate of the polymer.…”

“…During the third step polymer fragmentation can be observed and thus mass loss of the test samples can be measured. The degradation of such implanted polymers are completed when the formed low-molecular fragments including the free hydroxycarboxylic acids are dissolved in the surrounding physiologic medium and then metabolized in the citric acid cycle (Krebs cycle) [86,93].…”

“…An additional increase of hydrophobicity could be achieved by integration of aliphatic diacids with long hydrocarbon chains (dimers of unsaturated fatty acids) or by aromatic monomer units [86]. Another interesting group of surface erodible polymers are poly(ortho esters) which were focused investigated regarding their potential as drug delivery systems [94][95][96].…”