24: Histological and biomechanical characteristics of permanent and absorbable sling mesh in a rabbit model: 3-month time point

Abstract

To compare histological and biomechanical properties of a permanent sling mesh to 2 differently woven delayed absorbable mesh in a rabbit model. A permanent polypropylene (PP) mesh, delayed absorbable poly-4-hydroxybutyrate (P4HB) crochet-weave (CW) mesh, and delayed absorbable P4HB net-weave (NW) mesh were used. 3 rabbits were implanted with the 3 different mesh types abdominally, measuring 8.0x1.1 cm, and anterior and posterior vagina with a different mesh type, measuring 1.5x1.1 cm. At 3 months, implants were harvested and underwent histological and biomechanical testing. Two blinded pathologists graded histological samples on a scale of 0 to 3 for inflammation, collagen deposition, and elastic composition. Collagen I/III ratio was also calculated. An Instron machine (Model #5566) was used to perform load to failure biomechanical testing to assess ultimate tensile strength (UTS) and stiffness. Descriptive statistics were used for all variables. All rabbits tolerated implantation well. No mesh exposures were noted. Vaginally, CW decreased most in length and width by 32.8% and 37%, respectively. NW decreased in length by 27.3% and width by 16.6%. PP decreased in length by 11.1% and width by 2.6%. Results were similar abdominally; CW had the most tissue contraction with change in length and width by 23.9% and 21.1%, respectively. NW decreased in length by 26.3% and width by 4.4%. PP decreased in length by 15.1% with no change in width. Histological evaluation of vaginal samples showed no acute inflammation (Score=0) and scant chronic inflammation (Score=1). CW had the least inflammatory cells (Score=1), while NW and PP showed slightly more inflammation (Score=1.5). Abdominal samples revealed similar results, with all mesh-tissue specimens noted to have chronic inflammation (Score=1.5). No neovascularization was seen in vaginal and abdominal samples. Collagen deposition was noted in the vaginal NW and PP samples (Score=1.5), CW had scant collagen deposition (Score=1). Abdominally, moderate collagen deposition was noted in all mesh-tissue samples (Score=2). Elastin was not seen in CW and NW abdominally and vaginally (Score=0), but scant was noted in PP vaginally (Score=1). Type I collagen was the predominant collagen vaginally and abdominally. Biomechanical testing was successful for both vaginal and abdominal samples. Vaginally, the UTS of PP was 0.2 Mpa, while NW was 0.1 Mpa and CW was 0.4 Mpa. PP had the most stiffness at 3.9 N/mm, while NW and CW was 2.8 N/mm and 2.2 N/mm, respectively. Overall, the 3 meshes exhibited similar histologic responses, but CW exhibited the most tissue contraction with the least inflammatory reaction and collagen deposition. CW had the highest UTS while PP had the highest stiffness. Future time points can provide more information regarding the tissue response to the PP and different P4HB weaves.