Mechanical Performance and Finite Element Analysis of Bi-directional Barbed Sutures.

Abstract

In the current investigation the mechanical performance of barbed sutures made from resorbable and non-resorbable polymer monofilaments were studied. The main objective was to find a method to differentiate between those polymers that form "good" barbs and those that do not. To achieve this objective a suture/tissue pull-out test was developed in which the suture was stressed in a tensile test until it was removed from a tissue simulant specimen. This test was conducted on four resorbable sutures: Biosyn, Maxon, Monocryl & PDS and on three non-resorbable sutures: Ethilon, Novafil & Prolene. Those barbed sutures giving a pull-out load in excess of 1.5 kg were considered to have "good" barbs with adequate mechanical performance. X-ray diffraction, differential scanning calorimetry and tensile testing experiments were performed on the suture polymers in an attempt to identify which microstructural characteristics of the polymer and/or mechanical properties of the monofilament are associated with "good" barb performance. It was found that Maxon, PDS, Ethilon and Prolene sutures gave superior barb performance. Small compactly arranged crystalline structures were found to be the most important factor for the formation of "good" barbs. In addition, the peak tensile elongation of the unbarbed suture was also found to correlate with superior barb performance. The peak tensile force, modulus and toughness of the monofilament appeared to have no effect. It is therefore concluded that the ability of a polymer to form good barbs depends on small crystal size and high tensile elongation. Barb failure was observed to proceed through one of two mechanism; either curling or peeling. Two dimensional finite element analysis of the barb geometry identified the stress concentrations in and near the barbs under load, which were in agreement with the mechanisms of barb failure as observed by image analysis.