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PURPOSE The development of biologic graft products has been a significant advance in General and Plastic Surgery by providing materials to reinforce or bridge abdominal closures in contaminated cases. The utility of these products in hernia repair and abdominal wall reconstruction lies in their ability to provide a scaffold for the rapid in-growth of host cells, collagen, and blood vessels despite the possible presence of infection. This study investigates the physical properties of a novel bioprosthetic graft to determine efficacy for clinical use.
METHODS A prospective evaluation of graft properties prior to implantation and following explantation in a rodent model was performed. XenMatrix, XM, (Bard Davol Inc., Warwick, RI) was compared to two xenograft controls: Permacol, PC, (Covidien Inc., Mansfield, MA) and Strattice, ST, (LifeCell, Inc., Branchburg, NJ). Each graft product was evaluated in 30 male Lewis rats (n=90 total). End points included observation for post-surgical complications. Following sacrifice at 2, 4, and 8 weeks after implantation, the graft-abdominal wall complexes were assessed for clinical appearance in vivo and then excised for mechanical testing. The maximum force required to separate grafts from the abdominal wall tissues (shear force) and the force required to rupture the grafts (burst force) were measured. Data was reported as means with standard deviations, and experimental groups were compared with appropriate statistical testing. A p<0.05 indicated significance.
RESULTS Measurement of initial burst force at baseline revealed that XM had a stronger baseline tensile strength when compared to PC (676.8N vs. 303.7N, p<0.001); however, there was no difference when compared to ST (546.7N). At two weeks, ST had a higher burst force compared to XM (538.7N vs. 288.4N, p=0.04). ST had greater burst pressures than PC (p<0.05) at all time points except for 4 weeks. There were no statistical differences in shear forces between groups. Twenty-nine of the 30 (97%) XM animals developed seromas compared to 7/30 (23%) of the ST group and none of the PC group (XM vs. PC and XM vs. ST, p<0.001; ST vs. PC, p=0.005). One animal in both the XM and PC groups was euthanized for wound complications. At procurement, 13/29 (45%) XM grafts had undergone partial or complete degradation; whereas, all PC (29/29) and ST (30/30) grafts remained intact (XM vs. PC and XM vs. ST, p<0.001). Explanted grafts that had a clinical suspicion of infection were cultured and shown to have bacterial growth in 20% of rodents containing XM; no bacterial growth was observed in the other two groups (XM vs. PC and XM vs. ST, p=0.01).
CONCLUSIONS Ninety-seven percent of animals implanted with XM developed seromas. Forty-five percent of the XM grafts had undergone such degradation in vivo that they could not be evaluated by standard mechanical testing. ST had higher burst pressures than PC. The results in the XM group appear to be related to poor tissue interaction resulting in seroma formation and, possibly, a higher bacterial load in this group.