A comparison by burst testing of three types of vascular anastomosis

Biomechanical comparison of microvascular anastomoses prepared by various suturing techniques

INTRODUCTION

The biomechanical properties of small vessels and microvascular anastomoses have not been studied completely yet. However, in case of vascular injury and various microsurgical reconstructive procedures a safe anastomosis is essential. Quick and reliable tests are needed to test various anastomoses in research and in teaching courses as well for quality control and proper feedback. We aimed to compare selected biomechanical properties of the simple interrupted, the continuous suture and the modified Lauritzen's sleeve-technique.

MATERIALS AND METHODS

Sixty femoral arteries from chicken thigh biopreparates and 12 abdominal aortas from rats were used in this study. In case of the pressure resistance test the groups were: the simple interrupted, the continuous suture and the modified Lauritzen's sleeve-technique. The tensile-strength, elongation and elasticity measurement groups were the simple interrupted and continuous sutures with 8 and 12 stitches. Furthermore the suture materials in various conditions (simple thread, knotted threads, stitch with intact and damaged threads) were also compared. The tensile-strength and the pressure probe devices were custom made in cooperation with the Faculty of Informatics.

RESULTS

The average diameter of the chicken femoral arteries was 3.25±0.38 mm. The sleeve-technique showed the biggest pressure drop (56±16.41 mmHg), however, it was the fastest method. The tensile-strength of simple interrupted suture was 4.55±0.7 Newton (N), being lower than of the intact vessel (6.8 ± 1.4 N). The tensile-strength did not differ significantly between the 12-stitch simple interrupted and continuous sutures, however, the latter was stronger. The anastomoses made on thread model were significantly stronger than the ones on vessels.

CONCLUSION

The main variables were the number of stitches and the strength of the vessel. The pressure drop was not correlated with the stitch number. One incorrect stitch can dramatically increase the leakage. Although the sleeve-technique is quick to be performed, it cannot withstand high pressure. The suture material itself is far stronger then the vessel. The vessel tensile strength was decreased in the anastomoses. For the given vessel diameter more than 8 stitches should be used.

Evaluation of an elastic decellularized tendon-derived scaffold for the vascular tissue engineering application

Due to the limited success rate of currently available vascular replacements, tissue engineering has received tremendous attention in recent years. A main challenge in the field of regenerative medicine is creating a mechanically functional tissue with a well-organized extracellular matrix, particularly of collagen and elastin. In this study, the native collagen scaffold derived from decellularized tendon sections, as a scaffold having the potential to be used for vascular tissue engineering applications, was studied. We showed that the elasticity of the scaffolds was improved when crosslinked with the bovine elastin. The effect of different concentrations of elastin on mechanical properties of the collagen scaffolds was evaluated of which 15% elastin concentration was selected for further analysis based on the results. Addition of 15% elastin to collagen scaffolds significantly decreased Young's modulus and the tensile stress at the maximum load and increased the tensile strain at the maximum load of the constructs as compared to those of the collagen scaffolds or control samples. Moreover, tubular elastin modified collagen scaffolds showed significantly higher burst pressure compared to the control samples. Smooth muscle cells and endothelial cells cultured on the elastin modified collagen scaffolds showed high viability (>80%) after 1, 3, and 7 days. Furthermore, the cells showed a high tendency to align with the collagen fibers within the scaffold and produced their own extracellular matrix over time. In conclusion, the results show that the decellularized tendon sections have a great potential to be used as scaffolds for vascular tissue engineering applications. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1225-1234, 2019.

Critical parameter of burst pressure measurement in development of bypass grafts is highly dependent on methodology used

BACKGROUND

Because of the low patency rate of currently available vascular bypass grafts, researchers are working towards the development of alternative bypass grafts, ranging from synthetic prostheses to wholly biologic living grafts. The philosophy of measurement required by regulatory agencies such as the United States Food and Drug Administration (FDA) as well as to gain the Conformité Européene (CE) mark is to test above and beyond the limits that would be expected physiologically. The critical parameter of burst pressure is needed for Conformité Européene (CE) mark or United States Food and Drug Administration (FDA) approval before clinical trials can proceed. An accurate measurement of burst pressure in potential porous vascular bypass grafts is, therefore, of utmost importance to ensure adequate strength on implantation in animals and subsequent clinical use. A wide range of methods to measure burst pressure have been used. We tested the burst pressure of a new polyurethane-based nanocomposite vascular prosthesis by using different methods to assess whether the method used affected the results.

METHODS

Water was infused at flow rates of 0.2, 50, and 100 mL/min through a syringe pump into latex sleeve-lined porous prostheses manufactured from a poly(carbonate-urea)urethane nanocomposite incorporating silsesquioxane. At the lowest infusion rate, the inflation was done with and without a nonporous inner lining sleeve. A pressure transducer was used to record the peak pressure achieved.

RESULTS

Using a nonporous sleeve resulted in a higher burst pressure (428 mm Hg vs 341 mm Hg) at a flow rate of 0.2 mL/min. A lower infusion rate (0.2 mL/min) produced a lower burst pressure than 50 mL/min (428 mm Hg vs 451 mm Hg). No significant difference was found in burst pressure using infusion rates of 50 mL/min and 100 mL/min.

CONCLUSIONS

The use of a nonporous sleeve removes the potential weakness presented by the pores themselves. A continuous high infusion rate consistently overestimates burst pressure. These methods may not reflect the physiologic state. Care needs to be taken in interpretation of methodology for burst pressure measurement, and the rate of infusion should be stated in any description of the method.

CLINICAL RELEVANCE

The poor patency of small-caliber vascular bypass prostheses has stimulated a large body of research into alternative graft materials. This includes synthetic and, more recently, tissue-engineered hybrid products. Acceptance for international standards requires demonstration of a rigorous mechanical testing regimen, including graft strength, which has on the whole involved burst strength measurement. However, the methods used to measure burst strength have varied with respect to apparatus used and rate of graft inflation. We show that these variables lead to markedly different results. In particular, fast infusion rates may overestimate the actual burst pressure, leading to a false sense of security.