Prototyping and finite element analysis of tissue specific barbed sutures

The project titled 'Prototyping and Finite Element Analysis of Tissue Specific Barbed Sutures' is focussed on understanding the relationship between barb geometry and mechanical behavior of barbed sutures. In this study size '0' polypropylene monofilament sutures of diameter 0.4mm were used for creating barbs at 150°, 160° and 170° cut angles and 0.07, 0.12 and 0.18mm cut depths. A new prototyping method was developed to create barbed sutures with precisely controlled geometries whichd used tMTS tensile testing machine to control cut depth. The cut samples were then characterized by image analysis to assess the reproducibility and the variability associated with the barbs geometric dimensions. Tensile testing and stress and bulk relaxation experiments were performed to obtain viscoelastic constants for finite element modeling. An experiment was run to quantify the peeling properties of a barb under point-pressure load by attaching a metal wire to the end of the barb. Suture/tissue pullout experiments were also performed using bovine tendon and porcine skin tissues. The finite element simulation of the point-pressure loading of a barb tip in ANSYS was validated by experimental results of the same materials by a margin of only 4%. Three sets of FEA simulations were then performed for each of the nine blocks of combination of barb geometries. The same three levels of cut angle and three levels of cut depth were selected. In addition point-pressure loading simulations were run and experimental suture/tissue pullout tests were performed on tendon and skin tissues. The experimental results revealed that since tendon tissue has a higher modulus than skin it needs a more rigid barb to penetrate and anchor into the surrounding tissue. A cut angle of 150° and 0.18mm cut depth are recommended. On the other hand for the softer skin tissue a cut angle of 170 degrees and 0.18 mm cut depth provided a more flexible barb that gives superior skin tissue anchoring. The simulations helped identify the areas of stress concentration. The cut line at the base of the cut appears to be the weakest part of the barb. So the geometry or design should be modified so that the stresses generated are lower. A new design with a circular cut line has been virtually prototyped and tested in ANSYS. This new and improved design helps to redistribute the stresses along the barb and its cut line so that peeling is initiated at higher stresses and improved anchoring performance.