Extrusion properties of porcine intestines and surrogate materials for ventral hernia modelling

A physical model of the abdomen can be a clean and cheap surrogate environment to assess new and existing closure solutions for post-laparoscopic wound closure, but a particular challenge is finding a surrogate material to replicate intestines which may protrude through a hernia. The literature shows no focus on this topic, and this paper therefore presents an investigation of the extrusion properties of fresh porcine intestines compared to a number of potential surrogate materials: silicone, edible gelatine, dough and reconstituted powdered potatoes (RPP). An extrusion rig was developed to simulate the mechanical environment of a post-operative hernia formation. Displacement controlled extrusion tests were performed, and the force-extrusion relationships at different extrusion velocities were compared for the intestines and the surrogate materials. The intestines showed a peak extrusion force ranging from 9 N to 14.8 N when pushed through a 13 mm hole, and similar extrusion properties between cleaned and uncleaned fresh porcine intestines were observed. The tests on surrogate materials showed that the surface tension properties of silicone gel resulted in high friction, that edible gelatine extruded like a liquid and that dough is very stiff, rendering all three materials unsuitable for use as surrogates. However, the RPP mix showed very similar force-extrusion properties compared to both the cleaned and uncleaned intestines. Viscoelastic testing (7.5 mm/min, 15 mm/min and 30 mm/min) showed little rate dependency in the extrusion properties for either the porcine intestines or the RPP. Despite the complexity of intestinal tissue and the obvious physical differences between intestine and RPP, it was found that there is no statistical difference between the yield strength of intestines and RPP (P values ranged between 0.14 and 0.3) at the rates tested.