Hernia repair is one of the most frequently performed surgical interventions that use mesh implants. This article evaluates crucial mesh parameters to facilitate selection of the most appropriate mesh implant, considering raw materials, mesh composition, structure parameters and mechanical parameters. A literature review was performed using the PubMed database. The most important mesh parameters in the selection of a mesh implant are the raw material, structural parameters and mechanical parameters, which should match the physiological conditions. The structural parameters, especially the porosity, are the most important predictors of the biocompatibility performance of synthetic meshes. Meshes with large pores exhibit less inflammatory infiltrate, connective tissue and scar bridging, which allows increased soft tissue ingrowth. The raw material and combination of raw materials of the used mesh, including potential coatings and textile design, strongly impact the inflammatory reaction to the mesh. Synthetic meshes made from innovative polymers combined with surface coating have been demonstrated to exhibit advantageous behavior in specialized fields. Monofilament, large-pore synthetic meshes exhibit advantages. The value of mesh classification based on mesh weight seems to be overestimated. Mechanical properties of meshes, such as anisotropy/isotropy, elasticity and tensile strength, are crucial parameters for predicting mesh performance after implantation.

Mesh implants: An overview of crucial mesh parameters

Purpose
Incisional hernia occurs in approximately 11% of all laparotomies. Changes in collagen have been closely implicated in its pathogenesis. The high recurrence rate (45–54%) after primary suture has stimulated the development of meshes. Currently, meshes are the biomaterials implant group most used in medicine. This study aims to compare the serum and tissue inflammatory responses and collagen deposition caused by meshes made of polypropylene, polypropylene + polyglactin and polypropylene + titanium.

Experimental study comparing meshes made of polypropylene, polypropylene + polyglactin and polypropylene + titanium: inflammatory cytokines, histological changes and morphometric analysis of collagen

Purpose In this manuscript, the authors describe an animal study comparing shrinkage, inflammatory response and fibroplasia in heavyweight (HW-PP) and lightweight polypropylene (LW-PP) meshes. Methods Both meshes were fixed on abdominal fascia of 25 Wistar rats (epifascial onlay placement). They were killed at 7, 28 and 90 days to measure the prostheses. Histological analysis was performed with hematoxylin‐ eosin for cellular counting and immunohistochemistry to measure collagen types I and III. Results The authors found that the LW-PP mesh presented greater median shrinkage than HW-PP mesh at 7 (P = .036), 28 (P = .674) and 90 days (P = .038) postoperatively. There were more neutrophils on LW-PP mesh (P = .008) at 7 days, gradually diminishing in both prostheses. Lymphocytes were similar between the implants at 7 days, diminishing about 50 % on LW-PP mesh (P \ .001) at 90 days. Macrophages and giant cells diminished on LW-PP and increased on HW-PP meshes (P \ .001). Collagen I/III ratio presented a progressive, almost fivefold rise at 90 days, on both mesh types (P \ .001). The collagen I/III ratio was similar between LW-PP and HW-PP meshes at the three times studied. Conclusions It is concluded that LW-PP showed more shrinkage than HW-PP mesh at 7 and 90 days, despite the fact that HW-PP presented more lately foreign body reaction. The collagen I/III ratio was similar between the prostheses and increased during the postimplant period.

Comparative study of shrinkage, inflammatory response and fibroplasia in heavyweight and lightweight meshes

Purpose
As part of the foreign body reaction, mesh filaments are surrounded by an infiltrate of inflammatory cells. Though macrophages are considered as being predominant, little is known about the origin of other cells.

Characterisation of the cellular infiltrate in the foreign body granuloma of textile meshes with its impact on collagen deposition

Although 
meshes reduce abdominal hernia recurrence, they increase the risk of inflammatory complications. This study aimed to compare the early and late postoperative inflammation and collagen deposition responses induced by three meshes. Rats were allocated into three groups. In group I, a polypropylene (PP) mesh was implanted in the abdominal wall. In groups II and III, PP + polyglactin (PP + PG) and PP + titanium (PP + TI) meshes were employed, respectively. On the seventh (7th) postoperative day, collagen deposition and inflammation were evaluated, and immunohistochemistry was performed on abdominal wall biopsies. These data were compared with those obtained on the fortieth (40th) postoperative day in a previous study. The early inflammatory responses were the same in all groups. With time, it decreased in group I (p = 0.047) and increased in group II (p = 0.003). Group I exhibited early elevated VEGF (p < 0.001), COX2 (p < 0.001), and collagen (p = 0.023) levels, and group II exhibited the most severe inflammatory tissue response. On the 40th postoperative day, the VEGF (p < 0.001) and collagen (p < 0.005) were reduced as compared with the 7th postoperative day in all groups. Belatedly, the inflammatory reaction decreased in PP mesh group and increased in PP + PG mesh group. The PP mesh induced early great elevations in VEGF, COX2 and collagen levels, whereas the PP + PG mesh caused severe tissue inflammation with small elevation in these levels. PP + TI mesh induced inflammatory response levels between the others. In conclusion, the inflammatory response depends on the mesh density and also the mesh material with clinical implications.

Early and late postoperative inflammatory and collagen deposition responses in three different meshes: an experimental study in rats.

Purpose: This study assessed the collagen deposition and correlated it with local inflammatory responses to evaluate the length of time required for fibroplasia when polypropylene meshes are used to repair incisional abdominal wall hernias in rats. Methods: Thirty-six male Wistar rats underwent longitudinal resection of a peritoneal and musculoaponeurotic tissue segment (3x2 cm) of the abdominal wall followed by defect reconstruction with polypropylene mesh bridging over aponeurosis. The animals were divided into 6 groups according to the time points for the analysis of fibroplasia: 1, 2, 3, 7, 21 and 30 days post-implantation. Animals were sacrificed at each time point, and the site where the polypropylene mesh was implanted was evaluated histologically to assess inflammatory response and percentage of collagen using computer-assisted videomorphometry. Results: Total collagen was found at the mesh site on the 3rd day post-implantation, and increased progressively on all subsequent days up to the 21st day, when it reached its highest percentage (p 0.001). Type I collagen was first found between the 7th and 21st days; it reached its highest percentage on the 21st day and then remained stable until the 30th day. The type I to type III collagen ratio increased significantly and progressively up to the 30th day (p<0.001). Neutrophils were found at the mesh site from the 1st to the 21st day post-implantation. Macrophages, giant cells and lymphocytes were seen on the 2nd day. Thirty days after mesh implantation, neutrophils disappeared, but the percentages of macrophages, giant cells and lymphocytes remained stable (p<0.001). Conclusions: This study showed that total collagen was first seen on the 3rd day post-implantation, with a higher percentage of type I collagen at the last observational time point. The prolonged healing inflammatory response and the persistence of chronic inflammation surrounding to the mesh did not affect the length of time required for fibroplasia.

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Rodrigo Ketzer Krebs

Papers

Fibroplasia after polypropylene mesh implantation for abdominal wall hernia repair in rats