Table 2.
Design evaluation of mechanical properties for tubular vascular substitutes in accordance with ANSI/ISO 7198:2016.
| Testing method | Mechanical descriptors | Units | Sample geometry | Testing equipment | Procedure |
|---|---|---|---|---|---|
| CTS | Circumferential tensile strength | kN/mm | Tubular | Tensile testing machine with appropriately sized pins and holders over which the sample is placed | Length of the sample not less than the nominal relaxed internal diameter. Place the sample over the two pins; stretch at a steady rate between 50 and 200 mm/min (until the break point) |
| LTS | Longitudinal tensile strength | kN | Tubular | Tensile testing machine with suitable jaws to hold the sample firmly without damaging its structure | Place the ends of the sample in the jaws (initial separation between 50 and 150 mm); stretch at a steady rate between 50 and 200 mm/min (until the break point) |
| DPBSt | Burst strength | kPa | Flat | Bursting pressure tester with a clamping ring; Diaphragm able to extend beyond the failure deflection of the sample at 120 mmHg | Cut the sample longitudinally. Place the sample over the orifice of the baseplate; secure the clamping ring; increase the pressure at a uniform rate between 10 and 70 kPa/s |
| PBST | Pressurized burst pressure | kPa | Tubular | System capable of measuring and recording pressure; Apparatus capable of applying a steadily increasing rate of fluid or gas pressure to the inside of the sample; If applicable, an elastic, non-permeable liner distension apparatus of greater burst pressure than the sample | Feed fluid or gas to produce a steady rise in pressure at a controlled rate between 10 and 70 kPa/s. Measure and record the pressure inside the sample. |
| ProbeBS | Burst Pressure of an area of the sample | kN | Flat | Tensile testing machine capable of operation in the compression mode or fitted with a suitable compression cage; Sample holder with a clamping ring and a traversing probe | Cut the sample longitudinally; place the sample over the orifice of the baseplate; secure the clamping ring; align the baseplate and the probe to be concentric; traverse the probe through the sample at a constant rate of 50–200 mm/min until it bursts |
| DRC | Dynamic radial compliance | %/100 mmHg | Tubular | Machine capable of applying a dynamic pressure to the inside of a sample under constant tension or at a fixed length at 37 °C; pressure and diameter measuring device; If applicable, an elastic, non-permeable liner with diameter at 16 kPa (120 mmHg) greater than the nominal pressurized diameter of the sample | Length of the sample at least 10 times its diameter. Pressurize the sample in a cyclic fashion at a rate of 60 beats/min. To assess non-linear behavior, the tests should be conducted at 50–90 mmHg, 80–120 mmHg, and 110–150 mmHg |
| SRS | Suture retention strength | G | Flat | Tensile testing machine with a sensitive load cell (accuracy of ±5% of the measured value) and appropriate grips; A suture normally used for tubular vascular grafts | Cut the sample longitudinally, or at 45° to the long axis; Insert the suture 2 mm from the end of the stretched sample forming a half loop; pull the suture at the rate of 50 mm/min to 200 mm/min; record the force required to pull the suture and the suture size |
| SRP | Strength after repeated puncture | kPa or kN/mm | Tubular | 16-gauge dialysis needle and a tensile testing instrument or a system capable of applying a steadily increasing rate of fluid or gas pressure to the inside of the sample | Puncture 24 times per cm2 the external surface area of the sample (limited to one-third of the sample circumference); test the sample for PBSt or CTS |
| k | Kink diameter/radius | Mm | Tubular | Templates of known radii1 or cylindrical mandrels of known diameter2 |
1Place the sample in a radius template; decreases the template radius until kinking of the graft and record this radius 2Form a loop out of the test sample and pulls the ends of the sample in opposite direction until kink is observed; Measure and record the kink diameter with the appropriate mandrel |
CTS, circumferential tensile strength; LTS, longitudinal tensile strength; DPBSt, diaphragm pressurized burst strength; PBSt, pressurized burst strength; ProbeBS, probe burst strength; DRC, dynamic radial compliance; SRS, suture retention strength; SRP, strength after repeated puncture; K, kink diameter/radius.