Mesh Filaments Research Articles

Blooming of insecticides from polyethylene mesh and film

Malaria remains a public health concern with vector control still the vital component of disease prevention, control, and elimination strategies. Recent years has seen a “stalling” in the progress made towards the reduction in the global malaria burden, highlighting the need to develop new, innovative, and safe alternative tools and delivery systems to achieve global malaria elimination. Interventions based on the use of indoor residual spraying (IRS) and long-life insecticidal bed nets (LLINs), i.e. insecticide-containing wall linings (IWLs), can contribute towards the reduction of malaria. Both LLINs and IWLs rely on the presence of insecticides on the fibre or filament surfaces. However, materials directly incorporating the insecticides into the polymer melt during extrusion, allows for effective killing of the mosquitoes when they come into contact with the surface of the material, only if there is insecticide present there. This means that the insecticide must migrate to the surface and precipitate there (bloom). Over time the internal concentration of insecticide will decay. This investigation was done using Fourier transform infrared spectroscopy (FTIR) in both the transmission and attenuated total reflection (ATR) modes to better understand the blooming of three World Health Organization-approved contact insecticides, i.e. alphacypermethrin, fipronil and chlorfenapyr, from mesh or film to better understand the likeliness of insecticides within the materials to migrate to the surface. Film-based samples were prepared in addition to wall lining mesh, because of their easier characterisation than the irregular shaped mesh filaments. FTIR, in ATR and in transmission modes, enabled the tracking of the migration of the three insecticides, over time to the surface of polyethylene mesh or film. This made it possible to estimate the apparent solubility of the insecticides in the polymer matrix. However, scanning electron microscopy (SEM) revealed that a portion of the insecticide is trapped, in a crystalline state, inside the polymer matrix. These results suggest the possibility of developing products-based insecticides for protection against infective mosquito bites in malaria-endemic regions.

Tissue response to collagen containing polypropylene meshes in an ovine vaginal repair model

Pelvic Organ Prolapse (POP) is the herniation of pelvic organs into the vagina. Despite broad acceptance of mesh use in POP surgical repair, the complication rate is unacceptable. We hypothesized that collagen-containing polypropylene (PP) mesh types could modulate mesh-tissue integration and reduce long-term inflammation, thereby reducing mesh-associated complications. This study compared the long-term tissue response to an unmodified PP mesh and two collagen containing meshes in an ovine model which has similar pelvic anatomy and vaginal size to human. Three commercially available macroporous PP meshes, uncoated PP mesh (Avaulta Solo) (PP), the same textile PP mesh layered with a sheet of cross-linked porcine acellular matrix (Avaulta Plus) (PP-ACM) and a different yet also macroporous PP (Sofradim) mesh coated with solubilized atelocollagen (Ugytex) (PP-sCOL) were implanted in the ovine vagina and tissue explanted after 60 and 180days. The macrophage phenotype and response to implanted meshes, and vascularity were quantified by immunostaining and morphometry. We quantified changes in extracellular matrix composition biochemically and collagen organisation and percentage area around the interface of the mesh implants by Sirius Red birefringence and morphometry. PP-ACM induced a more sustained inflammatory response, indicated by similar CD45+ leukocytes but reduced CD163+ M2 macrophages at 60days (P<0.05). PP-sCOL increased Von Willebrand Factor (vWF)-immunoreactive vessel profiles after 60days. At the micro-molecular level, collagen birefringence quantification revealed significantly fewer mature collagen fibrils (red, thick fibrils) at the mesh-tissue interface than control tissue for all mesh types (P<0.001) but still significantly greater than the proportion of immature (green thin fibrils) at 60days (P<0.05). The proportion of mature collagen fibrils increased with time around the mesh filaments, particularly those containing collagen. The total collagen percent area at the mesh interface was greatest around the PP-ACM mesh at 60days (P<0.05). By 180days the total mature and immature collagen fibres at the interface of the mesh filaments resembled that of native tissue. In particular, these results suggest that both meshes containing collagen evoke different types of tissue responses at different times during the healing response yet both ultimately lead to physiological tissue formation approaching that of normal tissue. Statement of SignificancePelvic organ prolapse (POP) is the descent of the pelvic organs to the vagina. POP affects more than 25% of all women and the lifetime risk of undergoing POP surgery is 19%. Although synthetic polypropylene (PP) meshes have improved the outcome of the surgical treatment for POP, there was an unacceptable rate of adverse events including mesh exposure and contracture. It is hypothesized that coating the PP meshes with collagen would provide a protective effect by preventing severe mesh adhesions to the wound, resulting in a better controlled initial inflammatory response, and diminished risk of exposure. In this study we assessed the effect of two collagen-containing PP meshes on the long-term vaginal tissue response using new techniques to quantify these tissue responses.

Pain after Hernia Surgery Must Be Avoided and Hopefully Treated.

PAIN AFTER HERNIA SURGERY MUST BE AVOIDED AND HOPEFULLY TREATED © Springer-Verlag 2014 P5:04 QUICK HOT SPOT: SYSTEMATIC PATHOLOGICAL ASSESSMENT OF EXPLANTED HERNIA MESHES REVEALS IMPORTANT INFORMATION OF MESH-BODY INTERACTIONS V Iakovlevl , G Iakovleva2, R Bendavid3 1St, Michael's Hospital, University of Toronto, Toronto, CANADA 2Markham StoujJVille Hospital, Markham, CANADA JShouldice Hospital, Richmond Hill, CANADA Purpose: Polypropylene meshes, introduced in the late 50's, spread to other anatomical sites over the decades of use and presently are employed in millions of surgeries worldwide. Up to 10% of meshes are excised for complications or recurrence generating a large, but underutilized pool of study material. There is a surprising lack of studies based on the meshes explanted from the patients. Paradoxically, in the presence of abundant material from humans most conclusions of mesh-body interactions are based on animal studies. We aimed to standardize pathological examination of explanted meshes and correlate histological findings with clinical presentations. Methods: Consecutive specimens of explanted polypropylene hernia meshes received at the pathology department within last two years were examined according to a predefined protocol. Out of 32 available specimens 13 were ventral and 19 inguinal hernia meshes. Median age was 61 years (range 24-82), 12 female and 20 male patients. For ventral hernias 2 were removed for migration into the bladder and fallopian tube, 4 for infection and 7 for recurrence. For groin meshes 7 were excised for pain and 12 for recurrence. The following microscopic parameters were assessed: mesh deformation, extent of fibrous encapsulation, nerve density and ingrowth, degree and type of inflammation, edema, vascular thrombosis, fat necrosis, attachment to muscle, and polypropylene degradation. Subjective parameters were scored independently by two pathologists. Two-tailed T-test and Pearson correlation were calculated to assess the significance of associations. Results: In relation to reason for excision, the most significant finding was higher density of nerve branches ingrown into the meshes removed for pain compared to those removed for other complications (p < 0.001). Connection with striated muscle showed less pronounced, but significant association with pain (p = 0.05). Meshes removed for pain also showed trends of more exuberant foreign body type inflammation (p = 0.15) and edema in the scar inhabiting the mesh (p = 0.12). The amount of scarring with bridging fibrosis and the degree of foreign body reaction tended to be reduced in meshes with a longer period since implantation (correlation = -0.4 for both parameters). Polypropylene material showed a layer of degradation forming a sheath around the mesh filaments. The layer was detectable by its ability to trap histological dyes in the microcracks and become stained in the microscopic sections, however the stainable layer retained optical properties of polypropylene in polarized light. Conclusions: We observed several important findings and associations related to mesh complications. One of the main findings related to pain is innervation within the tissue ingrown into the mesh. The innervated tissue is exposed to all regular pain mechanisms including nerve entrapment, compression by edema, inflammatory and other mechanisms. Histologically, mechanical nerve irritation of entrapped nerves is likely the leading mechanism while connection to striated muscle, edema and foreign body reaction appear to contribute in the development of pain. In relation to the body reaction to the mesh, the extent of scarring and foreign body inflammation tend to become reduced over time, however the change is mild. Knitted polypropylene meshes remain encapsulated in scar and retain the ability to trigger foreign body reaction many years after implantation. We also found that polypropylene used in mesh manufacturing degrades while exposed to the body environment and the clinical impact of polypropylene degradation needs to be studied further. Overall, the explant specimens, mostly neglected over the decades contain primary information of the mesh-body interactions. A standardized systematic examination of explanted mesh specimens can help our understanding of the mechanisms of complications and build a body of knowledge needed for further technical developments and treatment strategies in the field of hernia repair.

Temporal changes in the biomechanical properties of endometrial mesenchymal stem cell seeded scaffolds in a rat model

Use of synthetic clinical meshes in pelvic organ prolapse (POP) repair can lead to poor mechanical compliance in vivo, as a result of a foreign body reaction leading to excessive scar tissue formation. Seeding mesh with mesenchymal stem cells (MSCs) prior to implantation may reduce the foreign body reaction and lead to improved biomechanical properties of the mesh–tissue complex. This study investigates the influence of seeding human endometrial mesenchymal stem cells (eMSCs) on novel gelatin-coated polyamide scaffolds, to identify differences in scaffold/tissue biomechanical properties and new tissue growth following up to 90days’ implantation, in a subcutaneous rat model of wound repair. Scaffolds were subcutaneously implanted, either with or without eMSCs, in immunocompromised rats and following 7, 30, 60 and 90days were removed and assessed for their biomechanical properties using uniaxial tensile testing. Following 7, 30 and 90days’ implantation scaffolds were assessed for tissue ingrowth and organization using histological staining and scanning electron microscopy. The eMSCs were associated with altered collagen growth and organization around the mesh filaments of the scaffold, affecting the physiologically relevant tensile properties of the scaffold–tissue complex, in the toe region of the load–elongation curve. Scaffolds seeded with eMSCs were significantly less stiff on initial stretching than scaffolds implanted without eMSCs. Collagen growth and organization were enhanced in the long-term in eMSC-seeded scaffolds, with improved fascicle formation and crimp configuration. Results suggest that neo-tissue formation and remodelling may be enhanced through seeding scaffolds with eMSCs.

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

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. On 55 meshes explanted from humans, we characterised the cells in the inflammatory infiltrate of the granuloma by immunohistochemistry using 10 cellular markers: CD3+ lymphocytes, CD4+ T helper cells, CD8+ cytotoxic T cells, CD20+ B lymphocytes, CD34+ stem cells, CD45R0+ leucocytes, CD68+ macrophages, Mib1 for proliferation, Vimentin for mesenchymal origin, and Desmin for myocytes. Collagen deposits were analysed after staining with Sirius Red. More than 80 % of the cells in the infiltrate showed a positive expression of CD68, CD8, CD45R0 and Vimentin. CD4 and Desmin were seen in 30-80 % of the cells, unaffected by material or time. A score summarising the expression of all markers positively correlated significantly with an increased percentage of collagen type III (green) in the mesh wound. The analysis of collagen deposits was only affected to a small degree by size of area for investigation. At the vicinity of the mesh filaments, the accumulated inflammatory cells represent a mixture of cells of various origins. The high expression of at least four markers requires co-expression of different surface markers and thus confirms the existence of multiple transition forms instead of dominance of just macrophages. This offers new options for interventions to attenuate the inflammatory reaction of mesh implants.

Multilayer, degradable coating as a carrier for the sustained release of antibiotics: Preparation and antimicrobial efficacy in vitro

One of the most critical post-surgical complications is mesh-related infection. This paper describes how a commercially available polypropylene (PP) mesh was modified to minimize the risk of post-implantation infection. A dual drug-release coating was created around mesh filaments using an airbrush spray system. This coating was composed of three layers containing ofloxacin and rifampicin dispersed in a degradable polymer reservoir made up of [poly(ε-caprolactone) (PCL) and poly(dl-lactic acid) (PLA)]. Drug release kinetics were managed by varying the structure of the degradable polymer and the multilayer coating. In vitro, this new drug delivery polymer system was seen to be more rapidly invaded by fibroblasts than was the initial PP mesh. Active mesh showed excellent antibacterial properties with regard to microorganism adhesion, biofilm formation and the periprosthetic inhibition of bacterial growth. Sustained release of the two antibiotics from the coated mesh prevented mesh contamination for at least 72h. This triple-layer coating technology is potentially of great interest for it can be easily extrapolated to other medical devices and drug combinations for the prevention or treatment of other diseases.

Comparative study between polypropylene and polypropylene/poliglecaprone meshes used in the correction of abdominal wall defect in rats

To evaluate the healing process of a defect in the ventral abdominal wall of rats, comparing the polypropylene and polypropylene/poliglecaprone meshes on the 30(th) and 60(th) postoperative day. Thirty two Wistar rats were submitted to a ventral abdominal wall defect, with integrity of the parietal peritoneum. In the repair, were used polypropylene (group A) and polypropylene/poliglecaprone (group B) meshes. The groups were subdivided into four subgroups of eight animals euthanized on the 30(th) (A30 and B30) and 60(th) postoperative day (A60 and B60). Fragments of the abdominal wall of the animals were submitted to macroscopic, tensiometric and histological evaluations. The tensiometry on subgroup A30 showed a mean average break point of 0.78 MPa and in A60, 0.66 Mpa. In subgroup B30 it was 0.84 MPa and in B60, 1.27 Mpa. The score of the inflammatory process showed subacute phase on A30 and B30 sub-groups and chronic inflammatory process in subgroups A30 and 60B. The tensile strength was higher on the wall repaired by polypropylene/poliglecaprone mesh in the 60(th) post-operative day. Histology showed higher concentration of fibrosis on the surface of the polypropylene mesh with a tendency to encapsulation. In polypropylene/poliglecaprone subgroups the histology showed higher concentration of fibrosis on the surface of mesh filaments.

Peritoneal Effects of Prosthetic Meshes Used to Repair Abdominal Wall Defects: Monitoring Adhesions by Sequential Laparoscopy

The prosthetic materials currently used to repair abdominal wall defects sometimes have to be placed in contact with the visceral peritoneum. This interface is often a site of complications such as intestinal obstruction or fistulas due to adhesions. The aim of this study was to follow the process of adhesion formation in several prosthetic materials by sequential laparoscopy. Defects (7 x 5 cm) were created in the abdominal wall of 30 New Zealand White rabbits and repaired using Surgipro polypropylene mesh (PP), Ultrapro monocryl-prolene mesh (UP), Dual Mesh expanded polytetrafluoroethylene (ePTFE), Composix (PP-ePTFE), Parietex Composite (polyester with collagen-polyethylene glycol-glycerol coating [PO-gl]), or PL-PU99 (PP-polyurethane) patches fixed to the edges of the defect by running polypropylene suture. Adhesions to the implants were laparoscopically determined at 3, 7, and 14 days after surgery. Percentage adhesion scores were significantly lower for ePTFE, PP-ePTFE, PO-gl, and PP-PU, compared to PP or UP. No differences were observed in adhesion scores recorded at 3, 7, and 14 days postimplant. Reticular prostheses were infiltrated by disorganized scar tissue with fibers concentric to the mesh filaments. In contrast, ePTFE implants were encapsulated by organized tissue, with fibers running parallel to the surface of biomaterial. All three composites achieved good recipient tissue integration and a homogeneous, organized, and well-vascularized neoperitoneum. At 14 days postimplant, laminar prostheses and composites showed similar results in terms of adhesion formation and integration within host tissue. Our findings suggest that both the composite prostheses and the laminar ePTFE performed very well in terms of reduced adhesion formation at the peritoneal interface.

Polymeric meshes induce zonal regulation of matrix metalloproteinase‐2 gene expression by macrophages and fibroblasts

Matrix metalloproteinase-2 (MMP-2) is a key regulator in wound healing that orchestrates tissue remodeling. In the present study the spatial and temporal distribution of MMP-2 gene transcription, protein synthesis, and enzymatic activity were analyzed following polymeric mesh (polyglactin, polypropylene) implantation in transgenic reporter mice harboring MMP-2 regulatory sequences -1686/+423 or -1241/+423. Polymers induced MMP-2 promoter activity in macrophages within the foreign body granuloma via sequences -1686/+423 with concomitantly up-regulated protein synthesis and enzymatic activity. Macrophages distant from mesh filaments exhibited low MMP-2 expression levels. Fibroblasts surrounding mesh material displayed strong MMP-2 gene transcription independent of the included promoter sequences, whereas fibroblasts without close contact to mesh material had low MMP-2 synthesis rates due to silencing activity of sequences -1686/-1241. In vitro studies support a cellular crosstalk concept, as macrophages trans-repressed MMP-2 gene transcription in fibroblasts. The zonal and cell-specific regulation of MMP-2 gene transcription illuminates an intimate cellular crosstalk in foreign body reaction that may provide a new approach for mesh modification.

Midline Abdominal Wall Closure: A New Prophylactic Mesh Concept

Despite intense research efforts, incisional hernias continue to be a problem in patients who undergo laparotomy. This study was designed to reinforce the midline laparotomy closure by including a new prosthetic design between the edges of the surgical wound. A midline incision was made in New Zealand white rabbits and closed by inserting a polypropylene strip, T-shaped in cross-section, between the incisional borders. The T was placed upside down such that the horizontal arm of the T, whose surface is coated with extra-low pore size expanded polytetrafluoroethylene, made contact with the visceral peritoneum. The mesh was secured by a mass polypropylene 3/0 running suture. Surgery outcomes in these animals were compared with those in which the surgical wound was closed by simple suture and with control, nonoperated animals. The T-mesh induced an increased amount of scar tissue at the midline, where neoformed recipient tissue appeared around the polypropylene mesh filaments. The expanded polytetrafluoroethylene lamina became appropriately mesothelialized. Compared with the simple suture, the T-mesh provided a significant gain in biomechanical strength at postoperative week 6 (43.99+/-4.17 Newtons and 56.96+/-10.94 Newtons, respectively, p < 0.05). At 6 months, the strength of the reinforced wound even surpassed, although not significantly, that of the control intact abdominal wall (82.25+/-7.60 Newtons versus 79.55+/-11.46 Newtons). Data were expressed as mean +/- standard deviation. The use of a nonabsorbable biomaterial for midline laparotomy closure significantly improves its biomechanical resistance. Used in high-risk patients or even prophylactically, this technique could reduce the incidence of incisional hernia.

New experimental approach to study host tissue response to surgical mesh materials in vivo

Implantation of surgical meshes is a common procedure to increase abdominal wall stability in hernia repair. To improve biocompatibility of the implants, sophisticated in vivo animal models are needed to study inflammation and incorporation of biomaterials. Herein, we have established a new model that allows for the quantitative analysis of host tissue response and vascular ingrowth into surgical mesh materials in vivo. Ultrapro meshes were implanted into dorsal skinfold chambers of Syrian golden hamsters. Angiogenesis, microhemodynamics, microvascular permeability, and leukocyte-endothelial cell interaction of the host tissue were analyzed in response to material implantation over a 2-week period using intravital fluorescence microscopy. Mesh implantation resulted in a short-term activation of leukocytes, reflected by leukocyte accumulation and adherence in postcapillary venules. This cellular inflammatory response was accompanied by an increase of macromolecular leakage, indicating loss of integrity of venular endothelial cells. Angiogenesis started at day 3 after implantation by protrusion of capillary sprouts, originating from the host microvasculature. Until day 10, these sprouts interconnected with each other to form a new microvascular network. At day 14, the inflammatory response had disappeared and the vascular ingrowth was completed. Histology confirmed the formation of granulation tissue with adequate incorporation of the mesh filaments within the host tissue. We conclude that this novel model of surgical mesh implantation is a useful experimental approach to analyze host tissue response and vascular ingrowth of newly devised materials for hernia repair.

Modified mesh for hernia repair that is adapted to the physiology of the abdominal wall.

To develop a new mesh for hernia repair that is adapted to the physiological forces. Animal experiment. Surgical Department of the RWTH-Aachen. Wistar rats Textile analysis, tensile strength, bending stiffness, histology and morphometry. After textile analysis of commercially available meshes in clinical use we defined the physiological forces and constructed a new mesh (Soft Hernia Mesh, SHM) based on a combination of non-absorbable polypropylene and absorbable polyglactin 910. The amount of non-absorbable material could be reduced to < 30% compared with Marlex while still guaranteeing the necessary pulling force of 16 N/cm. Improvements of the hosiery structure improved the symmetrical distribution of the retaining forces in all directions. Compared with the considerable restriction of the abdominal wall mobility by Prolene (polypropylene) and Mersilene (polyester) meshes there was no increase in the bending stiffness after the implantation of the new mesh. Histological examination showed a pronounced reduction of the inflammatory reaction in the tissues, and the collagen bundles were orientated merely around the mesh filaments instead of forming a scar plate that completely embedded the mesh. Different meshes caused specific histological reactions with changes of their mechanical properties after implantation in rodents. A new mesh with a reduced amount of polypropylene showed both less inflammation and less restriction in the mobility of the abdominal wall though it exceeded the required tensile strength of 16 N/cm.

Towards retrievable vascularized bioartificial pancreas: induction and long-lasting stability of polymeric mesh implant vascularized with the help of acidic and basic fibroblast growth factors and hydrogel coating.

We seek to improve existing methodologies for allogenic grafting of pancreatic islets. The lack of success of encapsulated transplanted islets inside the peritoneal cavity is presently attributed to poor vascularization of the implant. A thick, fibrotic capsule often surrounds the graft, limiting survival. We have tested the hypothesis that neovascularization of the graft material can be induced by the addition of proper angiogenic factors embedded within a polymeric coat. Biocompatible and nonresorbable meshes coated with hydrophilic polymers were implanted in rats and harvested after 1-, 6-, and 12-week intervals. The implant response was assessed by histological observations on the degree of vascularity, fibrosis, and inflammation. Macrostructural geometry of meshes was conducive to tissue ingrowth into the interstitial space between the mesh filaments. Hydrogel coating with incorporated acidic or basic FGF in an electrostatic complex with polyelectrolytes and/or with heparin provided a sustained slow release of the angiogenic growth factor. Anti-factor VIII and anti-collagen type IV antibodies and a GSL I-B4 lectin were used to measure the extent of vascularization. Vigorous and persistent vascularization radiated several hundred microns from the implant. The level of vascularization should provide a sufficient diffusion of nutrients and oxygen to implanted islets. Based on our observations, stable vascularization may require a sustained angiogenic signal to allow for the development of a permanent implant structure.