The aims of this study were to evaluate the feasibility of the New Zealand White (NZW) rabbit for studying implanted biomaterials in pelvic reconstructive surgery; and to compare the biological properties of a commercial polypropylene (PP) mesh and a new developed human acellular dermal matrix (hADM) implanted at vaginal and abdominal level.

20 NZW rabbits were randomized into 2 groups: 10 received hADM grafts and 10 were implanted with PP grafts. Each rabbit had 4 segments implanted: 2 into the abdomen and 2 in the vagina, in the submucosal layer. The graft segments were removed 180 days later. Rabbits were monitored for 180 days and euthanasia was performed. After sacrifice, grafts were explanted and analyzed by macroscopic, biomechanical, immunohistochemical and histological characteristics. Comparisons between categorical variables were performed by chi-square test with the approximation of likelihood ratio. The comparison between groups was made with the Mann-Whitney nonparametric test. In all cases the level of significance was set at 5% (alpha = 0.05). All analysis were performed with the IBM-SPSS (V25) statistical package.

Rabbits were successfully followed up until euthanasia. One animal died due to causes other than surgery or implant placement complications. The main surgical challenges during graft implantation were: a) an adequate vaginal exposure while maintaining the integrity of the vaginal mucosa layer; b) to keep aseptic conditions; c) to locate and dissect the breast vein abdominal surgery; and d) to collect blood samples from the ear artery. The most abnormal findings during the explant surgery were found in the PP group (33% of vaginal mesh extrusion) in comparison with the hADM group (0% of vaginal graft extrusion) ( p=0.015). The macroscopic observation also showed that full integration of the vaginal grafts was more common in the hADM group (40% resulting in difficult macroscopic recognition of the graft) than in the PP group, in which the vaginal mesh was identified in 100% of the animals (p=0.014). Both PP and hADM showed cellular infiltrates corresponding to an inflammatory foreign body response. hADM integration was complete, especially in the vaginal location. Biomechanical analysis of explants showed that hADM had lower resistance to stress in the traction trial than the PP mesh. Moreover, the results showed that PP mesh stiffness and elasticity were superior to those of hADM. The analysis of resistance of the hADM after implantation showed a decrease in all the mechanical properties when compared with the hADM before implantation which agrees with the degradation observed in the macroscopic findings.

This project could provide potential therapeutic, scientific and technical benefits that would have relevance and applicability in the field of regenerative medicine, and specifically in the field of urogynecology. These results offer effective therapeutic options based on the use of human tissues in clinical practice to improve current therapies, which are suboptimal. We demonstrate a need for optimization of explant collection and processing protocols, an improved knowledge of their characteristics, behavior and properties to be applied to reconstructive and therapeutic purposes. Finally our results can be shared with the field of urogynecology.

The NZW rabbit is a good model for assessing materials to be used as grafts for pelvic reconstructive surgery and vaginal surgery. Animals are easily managed during the procedures, including surgical intervention and vaginal mucosa approach. Finally, hADM implantation is associated with fewer clinical complications, as well as better macroscopic tissue integration, but with poorer biomechanical properties 6 months after implantation in the vagina, compared to PP mesh.