Performance in dynamic tests

Investigations of knot behavior have generally concentrated on the physical properties of knotted sutures subjected to static forces. In many regions of the anatomy, however, sutures are expected to maintain strength and 

The knot used throughout this study was the four-throw square, which, as shown earlier, was expected to be fully secure in both sutures under static conditions of test. The knot tying stress used was maintained at a constant level. Dynamic stress levels were denoted by time and frequency. The extension given to suture in each cycle was 25% of the rupture extension exhibited by the same suture and configuration not subjected to dynamic stress. This level was found to be just above the inflexion point of the suture stress-strain curve. In the full design, the suture size was 2/0 and the frequency was 23 cycles/min (close to that of human respiration). In the fractional design, the cycling times were 1 and 5 h, frequencies were 23 and 60, and suture sizes were 2/0 and 4/0. 

After subjecting the specimen to above treatments, tensile tests were performed on Instron with 50 mm gauge length and 20 mm/min rate of extension. 

Placing a knot in the suture produced a considerable change in properties. The values of all tensile parameters decreased significantly (Table 12.3). 

7 Second device for constructing controlled knots (a) schematic of the device and (b) the principle involved. 

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