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

Mechanical and microstructural analysis of a radially expandable vascular conduit for neonatal and pediatric cardiovascular surgery

In pediatric cardiovascular surgery, there is a significant need for vascular prostheses that have the potential to grow with the patient following implantation. Current clinical options consist of nonexpanding conduits, requiring repeat surgeries as the patient outgrows the device. To address this issue, PECA Labs has developed a novel ePTFE vascular conduit with the capability of being radially expanded via balloon catheterization. In the described study, a systematic characterization and comparison of two proprietary ePTFE expandable conduits was conducted. Conduit sizes of 8 and 16 mm inner diameters for both conduits were evaluated before and after expansion with a 26 mm balloon. Comprehensive mechanical testing was completed, including quantification of circumferential, and longitudinal tensile strength, suture retention strength, burst strength, water entry pressure, dynamic compliance, and kink radius. Scanning electron microscopy was used to investigate the microstructural properties. Automated extraction of the fiber architectural features for each scanning electron micrograph was achieved with an algorithm for each conduit before and after expansion. Results showed that both conduits were able to expand significantly, to as much as 2.5× their original inner diameter. All mechanical properties were within clinically acceptable values following expansion. Analysis of the microstructure properties of the conduits revealed that the circumferential main angle of orientation, orientation index, and spatial periodicity did not significantly change following expansion, whereas the node area fraction decreased post expansion. Successful proof-of-concept of this novel product represents a critical step toward clinical translation and provides hope for newborns and growing children with congenital heart disease. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 659-671, 2018.

Effects of temperature and strain level on stress relaxation behaviors of polypropylene sutures

An investigation has been conducted on stress relaxation behaviors of polypropylene sutures under different temperatures and strain levels in a temperature-controlled water bath. The study showed that the temperature and strain level significantly affected the stress relaxation behaviors of the sutures. High temperature resulted in fast stress relaxation. The stress relaxation data could be well described by two empirical formulas. For most of the test conditions, the stress relaxation tests caused limited permanent deformation in sutures. Effects of temperature on the permanent deformation may be illustrated by a power law. The tensile properties of the sutures were not affected adversely by the stress relaxation tests, indicating good properties of polypropylene sutures.

Chronic loading and extension increases the acute breaking strength of polypropylene sutures

Polypropylene sutures provide satisfactory strength for construction of vascular anastomoses, but occasionally they break. Experimental studies show that they break at reduced forces when they are subjected to chronic loads. Moreover, in patients, sutures are subject to acute loads superimposed on chronic loads. For example, an episode of hypertension applies acute load that is added to the baseline chronic load in a suture that has been used to close an arteriotomy. The purpose of the present study was to examine the breaking force of 6-0 polypropylene sutures subjected to acute loads after they had been loaded with chronic loads. One hundred sixty-five 6-0 polypropylene sutures were subjected to 50-175 g chronic loads in vitro. After 38 days they were subjected to additional increasing acute loads until they broke. Five hundred ninety other sutures were subjected to "injuries" of manipulation before chronic loading. A stray knot was simulated by placing a knot in the center of 90 sutures. Nurse's tugs used to straighten folded sutures in the operating room were simulated by applying brief loads of 75-275 g to 452 other sutures. Intraoperative injuries were simulated in 48 other sutures by pinching them with DeBakey forceps. Surprisingly, chronic loading of polypropylene sutures increased their acute breaking force. It is suggested that this may have resulted from increased orientation of crystals in the core of the filaments. By contrast, disturbing the outer surface of the filament by placing a stray knot, or pinching with forceps decreased acute breaking strength. These data suggest that if polypropylene sutures do not break soon after they have been placed in a patient, they may gain strength over time.