Fracture of polypropylene suture

BioGlue® is not associated with polypropylene suture breakage after aortic surgery

Objective

We have encountered broken or damaged polypropylene sutures (Prolene^®) at the anastomotic sites during aortic reoperations. Because a surgical sealant, bovine serum albumin-glutaraldehyde (BioGlue^®), was used in previous aortic surgery in some of these cases, we undertook this in vitro study to evaluate whether the use of BioGlue^® was associated with breakage of polypropylene sutures at the aortic anastomosis.

Materials and methods

The broken polypropylene sutures, anastomotic sites and aortic tissue at the location of suture breakage were visually inspected and evaluated intraoperatively. Six human cadaveric aortic samples were incised circumferentially and anastomosed proximally to a valved conduit with running 4–0 polypropylene sutures (Prolene^®). In the test group (n = 3), BioGlue^® was applied directly to the Prolene^® sutures at the anastomotic sites, while in the control group (n = 3) the anastomoses were not sealed with any surgical adhesive. The six samples were immersed in Dulbecco's phosphate buffered saline solution and mounted on a M-6 Six Position Heart Valve Durability Testing System and tested up to 120 million cycles for a 2-year period. During and upon completion of the testing, the integrity of Prolene^® sutures, the anastomosis and aortic tissues was regularly assessed by visual inspection.

Results

Intraoperative findings included a stretched and thin aortic wall (some with thrombus), a small cleft between the aortic tissue and the Dacron vascular graft. An excessive amount of BioGlue^® was often found around the anastomosis, with cracking material, but no signs of mechanical damage were observed in these cases. Upon visual inspection during and after in vitro testing, there was no apparent damage to the polypropylene sutures on the interior or exterior of the aortic anastomoses in any of the samples. No difference was observed in the physical integrity of the polypropylene sutures at anastomotic lines, the anastomoses and aortic tissues between the test and control samples.

Conclusions

The results of this study suggest that the use of BioGlue^® was not associated with breakage of the polypropylene sutures at the anastomotic sites after aortic dissection repair.

Degradation Studies of Some Polymeric Biomaterials: Polypropylene (PP) and Polyvinylidene Difluoride (PVDF)

Degradation studies of PP and PVDF monofilaments were carried out using a special chamber for several periods of time. One set of the samples was exposed to a 0.9 % NaCl solution and to ultraviolet radiation at 830 C and the other set involved the exposition in air under the same conditions of irradiation and temperature. Scanning Electron Microscopy (SEM) analysis showed direct evidence of PP degradation. Meanwhile, the PVDF monofilaments showed no apparent evidence of degradation under the same conditions. Differential Thermal Analysis (DTA) curves, FTIR spectra and Oxidation Induction Time experiments confirmed the results of SEM Analysis.

Effect of pulsatile pressure on the breaking strength and movement of Prolene sutures

PURPOSE

Most studies of sutures used in vascular surgery have used steadily applied loads. But in vivo, sutures are subject to pulsatile pressures. Pulsatile pressures could weaken sutures, or they could be beneficial by helping to slide the suture, thereby equilibrating the tension between unevenly tightened loops. This study examined the effect of pulsatile pressures on the strength and movement of polypropylene (Prolene) sutures.

METHODS

Segments of pig thoracic aorta were cannulated and studied in a tissue bath in vitro at 37 degrees C. A longitudinal arteriotomy was made and then closed with running 6-0 Prolene. Vessels were subjected to (1) no pressure; (2) 100 mm Hg steady pressure; or (3) 112/65 mm Hg pulsatile pressure. After 48 hours the sutures were studied for breaking strength. In a second, separate set of experiments, longitudinal arteriotomies were closed using running suture lines. These were constructed with either several loose loops or several overly tight loops. Fine wires were affixed to the suture loops to permit photographic recording of suture movement.

RESULTS

There was no difference in breaking force among 68 sutures that had been subjected to (1) no pressure; (2) 100 mm Hg steady pressure; or (3) 112/65 mm Hg pulsatile pressure. These also were no different than sutures that were not sewn into arteries. These findings indicate that neither steady nor pulsatile pressures weaken Prolene sutures. In the second set of experiments, it was found that pulsatile pressure did cause movement of suture lines where there were loose loops (p < 0.05). However, neither steady nor pulsatile pressures caused movement of loops in suture lines that contained normal and overly tight loops.

CONCLUSIONS

Neither steady nor pulsatile physiologic pressures weaken 6-0 Prolene sutures that have been used to close a longitudinal arteriotomy. These pressures can cause movement of loose suture lines, but do not equilibrate the tension between normal and overly tight suture loops. Overly tight loops may place excessive load on a suture line.

Polyvinylidene fluoride (PVDF) as a biomaterial: from polymeric raw material to monofilament vascular suture

This study identified the effects of various manufacturing processes on the crystalline microstructure, mechanical properties, and biocompatibility of a polyvinylidene fluoride (PVDF) suture. To achieve this, changes in the crystalline microstructure and the tensile behavior of PVDF monofilaments were monitored in vitro after different thermal processing, coloration, and sterilization treatments. In addition, the in vivo biocompatibility of the manufactured and sterilized PVDF suture was assessed by using it to anastomose a preclotted polyester vascular prosthesis as a thoracoabdominal bypass in a series of dogs. The tissue response was followed by histologic and scanning electron microscopy over implantation periods ranging from 4 h to 6 months. Differential scanning calorimetry and infrared spectroscopy (FTIR-ATR) showed that thermal processing and the addition of a coloring agent had a direct effect on modifying the crystalline microstructure and hence changing the mechanical properties. For example, thermal processing converted some of the alpha phase into the beta and gamma polymorphs, whereas coloration led only to a major increase in the beta-to-alpha ratio. The tensile properties were found to be optimized when the relative proportion of the beta and gamma phases combined compared to the alpha form gave rise to an FTIR A509/A532 absorption ratio between 4.0 and 4.5. Sterilization was found to cause some modifications to the crystalline microstructure near the surface of the monofilaments, but it did not change their mechanical properties. Pathologic examination of the anastomotic regions after different periods of implantation revealed a minimal cellular response, with no mineralization, intimal hyperplasia, or excessive fibrous tissue reaction. This good biocompatibility, together with other desirable characteristics such as ease of manipulation and satisfactory mechanical strength, makes PVDF an attractive alternative monofilament suture material for cardiovascular surgery.

Polyvinylidene fluoride monofilament sutures: can they be used safely for long-term anastomoses in the thoracic aorta?

Polyvinylidene fluoride (PVDF) represents an attractive alternative to polypropylene as a monofilament vascular suture because of its satisfactory physicochemical properties, it ease of handling, and its good biocompatibility. However, the polymer's ability to remain mechanically and chemically stable when exposed to a mild hydrolytic environment over the long term has yet to be demonstrated. One in vitro study involved the comparison of the long-term relative resistance of PVDF and polypropylene sutures to hydrolysis for a period of 9 years. The PVDF suture showed major molecular rearrangements from the original ratio of three crystalline structures to the single beta crystalline phase. The observation of some surface oxidation and water inhibition did not significantly modify the tensile strength of the PVDF suture, which retained 92.5% of its original value. In contrast, the polypropylene sample did not undergo any recrystallization but was associated with more oxidation byproducts and more water molecules near the surface, which contributed to a 46.6% loss in initial tensile strength. An in vivo study confirmed that PVDF sutures are biocompatible and are able to maintain satisfactory biostability when used to anastomose thoracic aortic allografts for a period of 6 months in the dog. The cellular reaction of fresh allografts as well as the control autografts to PVDF sutures was minimal. In other allografts that had been preserved in a supplemented medium for 1 week prior to implantation, the PVDF sutures healed satisfactorily with the formation of neocollagen and few macrophages surrounding the monofilament. No evidence of instability at the allograft-host artery junction was observed, confirming that the PVDF sutures were able to ensure a secure anastomosis in the thoracic aorta. PVDF sutures have demonstrated superior long-term biostability in vitro and minimal tissue response in vivo. These are two essential requirements when evaluating the use of a suture for vascular surgery in general and thoracic aortic surgery in particular.

Some mechanical properties of polypropylene sutures: relationship to the use of polypropylene in vascular surgery

This study was performed to examine some mechanical properties of Polypropylene sutures. Fifty segments of 3-0, 4-0, 5-0, 6-0, and 7-0 sutures were mounted in clamps and were subjected to stepwise elongation. Results showed that suture stiffness (elastic modulus) and breaking stress (tensile strength) correlated directly and linearly with the circumference or "skin" of the filaments and inversely with the cross-sectional area or "core" of the filaments. These data suggest that the strength of the suture may reside in the outer skin. These findings are related to the handling of Polypropylene in surgery, and to suture motion in grafts in patients.

Effect of force on anastomotic suture line disruption after carotid arteriotomy

Static and dynamic forces exerted on 6-0 polypropylene suture material after carotid arteriotomy were measured in 22 adult mongrel dogs. Force was measured in 11 normotensive animals (Group I) before and 6 weeks after carotid artery repair. Force was measured in the remaining animals during normotension and induced hypertension before and 6 weeks after operation. The tensile strength of each suture used in the study was measured by the manufacturer. The mean force required to break a 6-0 polypropylene suture measured 436.9 +/- 2 g, whereas knotting of the suture decreased the tensile strength to 316.9 +/- 3.9 g (p less than 0.001). The static and dynamic axial forces exerted on the suture after carotid arteriotomy in Group I was in the range of 26 g and decreased to 18 g at 6 weeks, whereas the 45 degree force exerted during the static dynamic phase measured in the range of 23 g and decreased to 16 g at 6 weeks (not statistically significant). The axial and 45 degree forces exerted on 6-0 polypropylene suture material in Group II under normotensive conditions were in the range of 14 g after carotid arteriotomy and ranged between 12 to 14 g at 6 weeks. Systolic hypertension did not result in a significant increase in axial or 45 degree forces during static or dynamic measurements, both in the range of 15 g after carotid arteriotomy. Measurements were similar at 6 weeks and ranged between 14 and 16 g. Our data indicate that 6-0 polypropylene suture material is an appropriate choice for repair of the carotid artery and that the suture material has sufficient inherent tensile strength to withstand forces generated in the neck region. Furthermore, our data indicate that spontaneous carotid artery suture line disruption is most likely related to damage to the suture strand during carotid artery repair rather than an inherent weakness in the suture material.

Biocompatibility of implant materials: a review and scanning electron microscopic study

The evolution of various plastic materials used in the manufacture of intraocular lenses is reviewed, with special reference to the problem of biocompatibility of lens haptic materials. To date, polypropylene has been found and continues to be a highly effective, relatively inert material, providing good surgical results. However, the present study and other morphologic and chemical studies have provided evidence that indicates long-term alteration of polypropylene may occur. For this reason we believe that further studies of this particular polymer are warranted. Also, a continuing search and trial of other plastics to discover an equivalent or even more efficacious haptic material seems desirable. There is a need for careful long-term follow-up of patients after intraocular lens implantation, particularly of young patients.