Integration of biomaterials implanted into abdominal wall: process of scar formation and macrophage response

3D-Printed Medical-Grade Polycaprolactone (mPCL) Scaffold for the Surgical Treatment of Vaginal Prolapse and Abdominal Hernias

The expected outcome after a scaffold augmented hernia repair is the regeneration of a tissue composition strong enough to sustain biomechanical function over long periods. It is hypothesised that melt electrowriting (MEW) medical-grade polycaprolactone (mPCL) scaffolds loaded with platelet-rich plasma (PRP) will enhance soft tissue regeneration in fascial defects in abdominal and vaginal sheep models. A pre-clinical evaluation of vaginal and abdominal hernia reconstruction using mPCL mesh scaffolds and polypropylene (PP) meshes was undertaken using an ovine model. Each sheep was implanted with both a PP mesh (control group), and a mPCL mesh loaded with PRP (experimental group) in both abdominal and vaginal sites. Mechanical properties of the tissue-mesh complexes were assessed with plunger tests. Tissue responses to the implanted meshes were evaluated via histology, immunohistochemistry and histomorphometry. At 6 months post-surgery, the mPCL mesh was less stiff than the PP mesh, but stiffer than the native tissue, while showing equitable collagen and vascular ingrowth when compared to PP mesh. The results of this pilot study were supportive of mPCL as a safe and effective biodegradable scaffold for hernia and vaginal prolapse repair, hence a full-scale long-term study (over 24-36 months) with an adequate sample size is recommended.

Biosynthetic meshes in contaminated fields: where are we now? A systematic review and meta-analysis in humans

PURPOSE

Selection of an appropriate mesh reinforcement for hernia repair in contaminated fields is a significant problem for surgeons. To date the proper mesh for contaminated fields has not been found. Biosynthetic meshes have emerged as new treatment option in contaminated fields. This study aims to evaluate the postoperative outcomes of biosynthetic meshes in contaminated fields.

METHODS

Systematic electronic search (PubMed, Medline, Embase, Scopus), according to PRISMA criteria, was performed. A literature search of scientific papers was performed by two reviewers until April 2021. Articles were chosen based on reference to biosynthetic meshes, their use in infected fields, and in human subjects. GRADE methodology and the modified Newcastle-Ottawa scale were used to assess the quality of studies. According to CDC-Centers for Disease Control classes patients were divided into two subgroups, group 1 (CDC class 2) and group 2 (CDC classes 3-4).

RESULTS

The research included 21 articles and 1619 patients were analyzed. Long-term follow-up showed a significant higher recurrence rate than short-term follow-up. P < 0.001. Meta-analysis of these studies showed that the SSI were significantly higher in CDC classes 3-4 than CDC class 2 (P < 0.01). No differences were found in SSO (P = 0.06) and recurrence (P = 0.37) rate among the two groups. Phasix™ was the most common mesh in 15 studies. The mean follow-up was 23.0 months. The surgical site infection (SSI) rate was 17.3%. The surgical site occurrence (SSO) rate was 32.4%. Recurrence rate was 11.5%.

CONCLUSION

This is the first systematic review and meta-analysis on the clinical outcomes of abdominal wall repair using biosynthetic mesh in contaminated-infected settings. The results show good results in patients at high risk of postoperative wound complications. The aim of this study is to add to the growing literature on biosynthetic mesh a picture of current literature evidence to help future researchers performing further studies on this topic.

Polymer Hernia Repair Materials: Adapting to Patient Needs and Surgical Techniques

Biomaterials and their applications are perhaps among the most dynamic areas of research within the field of biomedicine. Any advance in this topic translates to an improved quality of life for recipient patients. One application of a biomaterial is the repair of an abdominal wall defect whether congenital or acquired. In the great majority of cases requiring surgery, the defect takes the form of a hernia. Over the past few years, biomaterials designed with this purpose in mind have been gradually evolving in parallel with new developments in the different surgical techniques. In consequence, the classic polymer prosthetic materials have been the starting point for structural modifications or new prototypes that have always strived to accommodate patients’ needs. This evolving process has pursued both improvements in the wound repair process depending on the implant interface in the host and in the material’s mechanical properties at the repair site. This last factor is important considering that this site—the abdominal wall—is a dynamic structure subjected to considerable mechanical demands. This review aims to provide a narrative overview of the different biomaterials that have been gradually introduced over the years, along with their modifications as new surgical techniques have unfolded.

Experimental Study Comparing Structural Changes Induced by Biologic Versus Synthetic Mesh Implants in Nephropexy

Background: The study suggests that the use of the extracellular bovine-derived peritoneum matrix as a new biological implant opens up new prospects for nephropexy. Materials and Methods: Experimental nephropexy was performed in 64 white shorthaired adult rats, divided for 2 groups: extracellular bovine-derived peritoneum matrix, UltraPro mesh. Implants were 1,5*1,5cm per one animal. Observation periods were 7, 21, 30 and 180 days. The tissue was stain with H&E, Van Gieson’s with pikro-fuchin. Cellular infiltrate was evaluated by counting granulocytes, mononuclear cells, and foreign-body giant cells on five high-magnification images for each stained section (×400). Results: The use of the extracellular bovine-derived peritoneum matrix induced less intense and less prolonged chronic inflammatory response, as well as intense production of new collagen fibers more similar to the native connective tissue in terms of their histologic structure. The UltraPro mesh induced moderately persistent chronic inflammatory response throughout the 6- month study period. Conclusion: Histologic evaluation demonstrates high biocompatibility of both the extracellular bovine-derived peritoneum matrix, and the UltraPro mesh implants.The results of using  new biological material are not worse than synthetic mesh. The data obtained justify further research of the extracellular bovine-derived peritoneum matrix as a plastic material for nephropexy.

Long term comparative evaluation of two types of absorbable meshes in partial abdominal wall defects: an experimental study in rabbits

PURPOSE

Synthetic prosthetic materials that are fully absorbable seek to reduce the host foreign body reaction and promote host tissue regeneration. This preclinical trial was designed to analyse, in the long term, the behaviour of two prosthetic meshes, one synthetic and one composed of porcine collagen, in abdominal wall reconstruction.

METHODS

Partial defects were created in the abdominal walls of New Zealand rabbits and repaired using a synthetic absorbable mesh (Phasix™) or a non-crosslinked collagen bioprosthesis (Protexa™). After 3, 6, 12 and 18 months, specimens were recovered for light microscopy and collagen expression analysis to examine new host tissue incorporation, macrophage response and biomechanical strength.

RESULTS

Both materials showed good host tissue incorporation in line with their spatial structure. At 18 months postimplant, Protexa™ was highly reabsorbed while the biodegradation of Phasix™ was still incomplete. Collagenization of both materials was good. Macrophage counts steadily decreased over time in response to Phasix™, yet persisted in the collagen meshes. At 18 months, zones of loose tissue were observed at the implant site in the absence of herniation in both implant types. The stress-stretch behaviour of Phasix™ implants decreased over time, being more pronounced during the period of 12-18 months. Nevertheless, the abdominal wall repaired with Protexa™ became stiffer over time.

CONCLUSION

Eighteen months after the implant both materials showed good compatibility but the biodegradation of Phasix™ and Protexa™ was incomplete. No signs of hernia were observed at 18 months with the stress-stretch relations being similar for both implants, regardless of the more compliant abdominal wall repaired with Protexa™ at short term.

Surgical perspectives regarding application of biomaterials for the management of large congenital diaphragmatic hernia defects

This review focuses on the surgical viewpoints on patch repairs in neonates with large congenital diaphragmatic hernia defects. The main focus  is on the various biomaterials that have been employed to date with regard to their source of origins, degradation properties as well as tissue integration characteristics. Further focus  is on the present knowledge on patch integration when biomaterials are placed in the diaphragmatic defect. The review will also look at the present evidence on the biomechanical characteristics of the most commonly used biomaterials and compares these materials to diaphragmatic tissue to offer more  insight on the present practice of patch repairs in large defects. Since tissue engineering and regenerative medicine has offered another dimension to diaphragmatic replacement, a detailed overview of this technology will be undertaken with regard to cell sourcing, scaffolds, in vitro versus in vivo implants as well as quality of tissue produced, to explore the limitations and the feasibility facing the scientific community in its clinical implementation of skeletal muscle-engineered tissue beyond laboratory research for diaphragmatic replacement.

The foreign body response and morphometric changes associated with mesh-style peripheral nerve cuffs

Nerve cuffs have been used to anchor and protect penetrating electrodes in peripheral nerves and have been used as non-penetrating electrodes for neural recording and nerve stimulation. The material of choice for such applications is silicone, an inert synthetic biomaterial which elicits a minimal chronic foreign body response (FBR). While histological studies of solid silicone cuffs are available, to the best of our knowledge a comparison to other cuff designs is not well documented. Here, we describe the FBR and morphological changes that accompany nerve cuff implantation in the rat sciatic nerve by comparing a metallic mesh with and without a parylene coating to one made of silicone. Two months after implantation, we observed that such implants, irrespective of the cuff type, were associated with a persistent inflammatory response consisting of activated macrophages attached to the implant surfaces, which extended into the endoneurial space of the encapsulated nerve. We also observed foreign body giant cells in the epineurial space that were more prevalent in the mesh cohorts. The mesh cuff groups showed significant changes in several morphometric parameters that were not seen in the silicon group including reductions in nerve fiber packing density and a greater reduction of large diameter fibers. High magnification microscopy also showed greater evidence of foamy macrophages in the endoneurial space of the mesh implanted cohorts. Although the precise mechanisms are unknown, the results showed that mesh style nerve cuffs show a greater inflammatory response and had greater reductions in morphometric changes in the underlying nerve compared to silicone in the absence of a penetrating injury.

STATEMENT OF SIGNIFICANCE

While traditional silicone cuffs have been in use for decades, the inflammatory and morphometric effects of these cuffs on the underlying nerve have not been deeply studied. Further, manipulation of the foreign body response to nerve cuffs by using various materials and/or designs has not been well reported. Therefore, we report the inflammatory response around nerve cuffs of various materials and designs, as well as report morphometric parameters of the underlying nerve. These data provide important information regarding the potential for quantitative morphometric changes associated with the use of nerve cuffs, and, importantly, suggests that these changes are associated with the degree of inflammation associated with the cuff.

Mesh materials and hernia repair

Hernia incidence has been observed since ancient time. Advancement in the medical textile industry came up with the variety of mesh materials to repair hernia, but none of them are without complications including recurrence of hernia. Therefore individuals once developed with the hernia could not lead a healthy and comfortable life. This drawn attention of surgeons, patients, researchers and industry to know the exact mechanism behind its development, complications and recurrence. Recent investigations highlighted the role of genetic factors and connective tissue disorders being the reason for the development of hernia apart from the abnormal pressure that is known to develop during other disease conditions. This review discusses different mesh materials, their advantages and disadvantages and their biological response after its implantation.

Bioprosthetic mesh of bacterial cellulose for treatment of abdominal muscle aponeurotic defect in rat model

The use of meshes for treatment of hernias continues to draw attention of surgeons and the industry in the search of an ideal prosthesis. The purpose of this work is to use meshes manufactured from bacterial cellulose, evaluate their organic tissue interaction and compare with an expanded polytetrafluorethylene (ePTFE's) prosthesis used to repair acute defect of muscle aponeurotic induced in rats. Forty-five male Wistar rats were classified using the following criteria: (1) surgical repair of acute muscle aponeurotic defect with perforated bacterial cellulose film (PBC; n = 18); (2) compact bacterial cellulose film (CBC; n = 12) and (3) ePTFE; (n = 15). After postoperative period, rectangles (2 × 3 cm) including prosthesis, muscles and peritoneum were collected for biomechanical, histological and stereological analysis. In all cases, the maximum acceptable error probability for rejecting the null hypothesis was 5 %. Between PBC and CBC samples, the variables of strain (P = 0.011) and elasticity (P = 0.035) were statistically different. The same was found between CBC and ePTFE (elasticity, P = 0.000; strain, P = 0.009). PBC differed from CBC for giant cells (P = 0.001) and new blood vessels (P = 0.000). In conclusion, there was biological integration and biomechanical elasticity of PBC; therefore, we think this option should be considered as a new alternative biomaterial for use as a bio prosthesis.

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 72 h. 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.

Quantitative multispectral imaging of Herovici's polychrome for the assessment of collagen content and tissue remodelling

Bioprosthetic devices, constructed from a variety of materials, are routinely implanted in a variety of anatomical locations. Essential to their success is the formation of a non-destructive interface with the host tissue and appropriate tissue remodelling. Traditionally, the main method of assessing the host-material interface has been qualitative histological evaluation, using pattern recognition and comparative assessment to identify changes in the normal tissue architecture that are characteristic of scar tissue. In the present study, the recently developed technique of multispectral imaging was used to revisit a little-described histological stain, Herovici's polychrome, which is capable of distinguishing between types I and III collagen. Combined, these techniques allowed quantification of collagen content and distribution of collagen types within a tissue sample. Samples of rat tail and human scar tissue were used to optimize the staining, while comparison with immunolabelled samples was used to develop a reproducible quantification system, based on the specific colour profiles for types I and III collagen. Finally the remodelling of rat abdominal wall defects repaired with crosslinked or non-crosslinked extracellular matrix scaffolds derived from porcine urinary bladder was assessed with this technique. Compared to standard histological assessment, the combination of multispectral imaging and Herovici's polychrome staining presents a quick, simple, reliable technique that can provide accurate quantification of tissue remodelling and specifically identify the expression and distribution of types I and III collagen.

New antibiotic-eluting mesh used for soft tissue reinforcement

The surgical implantation of prostheses for soft tissue repair may be followed by post-operative mesh-related infection, a significant and dramatic complication, that is treated by mesh removal. A new antibiotic-eluting mesh has been manufactured on pre-existing polypropylene prostheses using an airbrush spraying technology. Among the degradable polymers tested as coating agents and drug reservoirs, poly(ε-caprolactone) (PCL), which is deposited after heating, provides a homogeneous, regular and smooth shell around the polypropylene filaments of the mesh without dramatically altering the biomechanical properties of the new modified mesh. An anti-infective drug (e.g. ofloxacin) is incorporated into this polymeric coating giving a limited burst effect followed by sustained drug diffusion for several days. An ofloxacin-eluting mesh has demonstrated excellent antibacterial activity in vitro on Escherichia coli adherence, biofilm formation and inhibitory diameter, even with low drug loads. Although further in vivo investigations are required to draw conclusions on the anti-infective effectiveness of the coated mesh, the airbrush coating of ofloxacin-PCL on existing prostheses is already potentially appealing in an effort to decrease post-operative infection.

Lysostaphin-Coated Mesh Prevents Staphylococcal Infection and Significantly Improves Survival in a Contaminated Surgical Field

Mesh and wound infections during hernia repair are predominantly caused by Staphylococcus aureus. Human acellular dermis (HAD) is known to lose its integrity in the face of large bacterial loads. The goal of this study was to determine if lysostaphin (LS), a naturally occurring anti-Staphylococcal protein, can protect HAD mesh from S. aureus infection. HAD samples, 3 cm X 3 cm, were implanted in the onlay fashion on the anterior abdominal wall of rats (n = 75). Subjects were grouped based on presence of antimicrobial bound to HAD (none or LS) and presence of S. aureus inoculum (sterile, 106, 108 CFU). At 60 days, meshes were explanted, and bacterial growth, histology, and mesh tensile strength were examined. None of the controls receiving bacterial inoculation without LS survived to 60 days. All LS-HAD sterile and LS-106 animals survived to explantation. The LS-HAD 108 group had a mortality rate of 50 per cent. All surviving LS-treated animals (n = 25) had negative wound and mesh cultures. Blinded gross and histologic evaluation and measured tensile strengths between all LS groups were comparable. Animals implanted with LS-HAD had a dramatically improved rate of survival. All animals surviving to 60 days had completely cleared S. aureus from their wounds with maintenance of mesh integrity and tensile strength. These findings strongly suggest the clinical use of LS-treated mesh in contaminated fields may translate into a more durable hernia repair.

Structural characteristics of small intestinal submucosa constructs dictate in vivo incorporation and angiogenic response

The rate of angiogenesis and cellular infiltration into degradable biomaterials determines scaffold persistence in vivo. The ability to tune the degradation properties of naturally derived biomaterials has been a popular goal in tissue engineering, yet has often depended on chemical crosslinking. Small intestinal submucosa (SIS) is a naturally derived, collagen-based, bioactive scaffold that has broad clinical success in many therapeutic applications. Two methods for producing multilayer, non-crosslinked SIS constructs were compared in vitro and in vivo. Traditional and cryo SEM, mercury intrusion porosimetry, and a novel enzymatic degradation assay determined that lyophilization produced an open, porous scaffold, in contrast to the collapsed, denser structure of SIS constructs produced using a vacuum press process. The angiogenic responses to lyophilized and vacuum-pressed SIS constructs were evaluated in vivo using a subcutaneous implant assay in mice. Explanted samples were compared after 7 and 21 days using fluorescence microangiography and light microscopy. Capacity of the implant neovasculature was also determined. These experiments revealed that the lyophilized SIS was infiltrated and vascularized more rapidly than the vacuum pressed. These data demonstrate the tunable incorporation of a non-crosslinked ECM-based biomaterial, which may have implications for the persistence of this degradable scaffold in tissue engineering.

Fibroplasia after polypropylene mesh implantation for abdominal wall hernia repair 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 III collagen increased progressively from the 3rd to the 21st days, when it reached its highest percentage (p<0.001); on the 30th day, it decreased significantly (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.

Use of hyaluronidase cream to prevent peritoneal adhesions in laparoscopic ventral hernia repair by means of intraperitoneal mesh fixation using spiral tacks

BACKGROUND

The aim of this study was to investigate the effects of hyaluronidase gel on the prevention of post-operative peritoneal adhesions to prosthetic materials used in laparosopic ventral hernia repair.

METHODS

Ten pigs were included in this study. The animals were anesthetized using Na-penthotal for induction and isofluorane for maintenance. The abdomen was opened and, using helical fasteners, four implantations were performed (squares of 4 x 4 cm). Two of the implants, placed in an upper location, were in polypropylene mesh, and two of the implants, placed in a lower area, were in polytetrafluoroethylene (PTFE-e, Dualmesh Plus Corduroy). The implants located in the right side of animals were painted with hyaluronidase gel. Two helical fasteners, painted and unpainted, were implanted in a medial location. After a five-week period the pigs were operated on again, intraperitoneal adhesion ratios and grades were determined, and the pigs later sacrificed. Specimens having abdominal wall implants were taken for histological studies.

RESULTS

Intraperitoneal adhesions decreased in implants painted with hyaluronidase gel in a comparative study with implants located in the left side of animals (not painted). On the other hand the polypropylene mesh, said typically to produce intraperitoneal adhesions, produced almost no adhesion in many animals.

CONCLUSIONS

Hyaluronidase gel reduces post-operative peritoneal adhesions ratio and grades including in the presence of polypropylene mesh.

Sixty-month follow-up after endoscopic inguinal hernia repair with three types of mesh: a prospective randomized trial

BACKGROUND

This prospective, clinical, randomized, double-blind study was intended to investigate the impact of the structure and the amount of polypropylene (PP) mesh used in laparoscopic transabdominal preperitoneal hernioplastic (TAPP) on physical function and life quality.

METHODS

180 male patients with primary inguinal hernia undergoing TAPP were randomized for using a heavyweight (108 g/m(2)), double-filament PP mesh (Prolene, 10 x 15 cm, group A, n = 60), a multifilament, heavyweight variant (116 g/m(2)) of PP mesh (Serapren, 10 x 15 cm, group B, n = 60), or a composite mesh (polyglactin and PP) (Vypro II, 10 x 15 cm, group C, n = 60). We compared in terms of complications (seromas, recurrence rate) and life quality (pain development, physical function). The development of life quality was documented according to the SF-36 Health Survey. The follow-up period was 60 months.

RESULTS

The recurrence rate (2.2% overall) during 60-month follow-up was not significantly different between the groups. Convalescence in group A was slower than in groups B and C: mean-term values of the visual scales for pain development were significantly (p < 0.05) higher, incapacity for work was 8.2 days longer, and urological adverse effects were stronger. The mean-term development of life quality was significantly lower in group A up to 12th week postoperatively. There were no significant differences between groups B and C. Beyond the 12th postinterventional week the differences diminished.

CONCLUSIONS

The composite mesh does not provide an advantage concerning physical function or pain development in comparison to the multifilament, heavyweight, pure polypropylene mesh. Independently of which mesh was implanted 5% of patients are still suffering from discomfort after 5 years.

Role of fibrin glue in the prevention of peritoneal adhesions in ventral hernia repair

PURPOSE

The aim of this study was to investigate the effects of fibrin glue on the prevention of postoperative peritoneal adhesion to prosthetic materials used in ventral hernia repair.

METHODS

Ten pigs were included in this study. The abdomens of the animals were opened by means of a median subumbilical laparotomy to place four prostheses that were cut into square pieces of 4 x 4 cm. The two prostheses in the most cephalic position were polypropylene meshes, and the other two prostheses in a more caudal position were expanded polytetrafluoroethylene prostheses (Dualmesh Plus Corduroy). The prostheses on the right side of each animal were previously impregnated with fibrin glue. After 5 weeks, the animals were reoperated on to assess the quantity and quality (consistency) of the adhesions.

RESULTS

There were fewer intraperitoneal adhesions and they were more labile in the case of prostheses impregnated with fibrin glue. Moreover, we also observed that in many of the animals the polypropylene mesh did not show any adhesions, although polypropylene has been considered to be a typical adhesion producing material.

CONCLUSIONS

Fibrin glue reduces both the quantity and consistency of adhesions, even in the case of polypropylene meshes.

Impact of Different Texture of Polypropylene Mesh on the Inflammatory Response

Over the past decade, hernia surgery has undergone a considerable transformation with the use of prosthetic materials. The most used polypropylene meshes induce a rapid acute inflammatory response followed by chronic foreign body reaction. Many factors influence this response such as density, size, physical characteristics, different texture and porosity of each biomaterial. The aim of this study is to assess whether the implant of monofilament or multifilament meshes, in the inguinal hernioplasty, determine a different inflammatory response. Thirty-two male patients were included in the study and were randomly divided into two groups. In the first group (MO) inguinal hernioplasty was performed using monofilament polypropylene mesh, while in the second one (MU) multifilament prosthesis was used. Peripheral venous blood samples were collected 24 hours before surgery and then 6,24,48 and 168 hours posto-peratively. Modifications in leukocyte count, C-reactive protein (CRP), alpha-1 antitrypsin (α1-AT), interleukin (IL)-1, IL-6, IL-1 ra and IL-10 serum levels were recorded at all sampling times. We present evidence that serum levels of CRP, (α1-AT), leukocytes and cytokines were significantly increased post-operatively in both groups, returning to basal values 168 hours afterwards. In particular, the production of all pro-inflammatory mediators was higher in the MU group, whereas the anti-inflammatory cytokine (IL-10, IL-1ra) production was higher in MO patients. Our results indicate that polypropylene multifilament mesh allows a higher intense acute inflammatory response as compared to monofilament mesh implantation.

Postoperative intraperitoneal adhesion pathophysiology

Aside from the normal 'ad integrum' peritoneal regeneration, the postoperative intraperitoneal adhesion formation process may be considered as the pathological part of peritoneal healing following any injury, particularly a surgical one. Despite a large body of clinical and experimental studies, its pathophysiology remains controversial. Moreover, a better understanding of the pathophysiological events and of the medical and surgical factors involved in the adhesion formation process is pivotal in any attempt to control this very frequent phenomenon and its serious consequences.

Partially absorbable meshes for hernia repair offer advantages over nonabsorbable meshes

BACKGROUND

The aim of this study was to establish whether new prosthetic materials with absorbable components, designed to reduce the amount of foreign material in abdominal wall repair, offer advantages over the conventional polypropylene meshes.

METHODS

Seven x 5 cm defects created in the anterior abdominal wall of New Zealand white rabbits were repaired by using a nonabsorbable polypropylene prosthesis (Surgipro; Tyco, Barcelona, Spain) or 1 of 2 partially absorbable prostheses available on the market (Vypro II and Ultrapro; Johnson & Johnson, St. Stevens-Woluwe, Belgium). At 14 and 90 days after surgery, tissue/prosthesis specimens were subjected to histological studies, biomechanical strength tests, and shrinkage evaluation.

RESULTS

At 90 days, the absorbable filaments of Vypro II had been completely reabsorbed, whereas Ultrapro only showed signs of biodegradation in a few zones. Host tissue infiltration and collagen I deposition in the 3 reticular meshes was optimal. Macrophage counts, mesh shrinkage, and biomechanical resistance values were similar.

CONCLUSIONS

Partially absorbable prostheses perform as well as the standard polypropylene mesh and have the benefit that less foreign material remains in the recipient, without compromising mechanical resistance.

In vivo evaluation of a new composite mesh (10% polypropylene/90% poly-L-lactic acid) for hernia repair

The increasing use of mesh insertion for groin hernia repair is dashed by a worrying prevalence of chronic pain frequently related as a reaction to the biomaterial implantation. Thus, new biocompatible prosthesis, designed as a composite material associating polypropylene (PP) and long-term absorbable material, are now under development. In the present study, the typical commercially available Prolene mesh has been compared to two new meshes designed with 3-fold less PP, either alone (light PP) or associated with poly-L-lactic acid (PP-PLA) accounting for 90% of the mesh weight. These PP-mesh variants were implanted in an extraperitoneal position within the abdominal wall of 90 rats. Mesh adhesion and size were determined at autopsy 2, 4 and 8 weeks after implantation (10 animals per group) and morphometric parameters of the host tissues by light microscopy. Prolene and light PP-meshes presented intra-corporeal shrinkage and tissue adhesion, both more pronounced with light-PP, whilst PP-PLA meshes were not affected in spite of a strongest fibrosis. In contrast to Prolene and even more with light PP meshes, inflammation and cell-mediated immune responses were reduced without occurrence of angiogenesis or oedema. All these findings advocate together for a better tolerance of this new composite biomaterial, more likely due to a low macrophage response that appeared statistically correlated to the absence of mesh shrinkage and to a decreased adhesion to the tissue. On the basis of these experimental observations, it could be expected that the better tolerance of this composite biomaterial may avoid both long-term pain and recurrence when used as plug in groin hernia repair.

[Prevention of peritoneal adhesions to intraperitoneal prostheses. An experimental study in pigs]

INTRODUCTION

The aim of this study was to investigate the effect of fibrin glue and hyaluronidase gel on the prevention of postoperative peritoneal adhesions to intraperitoneal prostheses.

MATERIAL AND METHOD

Twenty pigs, divided in two groups, were included. In all animals, four implants (4 x 4 cm) were placed: two polypropylene mesh implants were placed in an upper location and two polytetrafluoroethylene (PTFE) implants (Dualmesh Plus Corduroy) were placed in a lower position. Implants located in the right side of the animals were painted with fibrin glue (group A, n = 10) or with hyaluronidase gel (group B, n = 10). After 5 weeks, the animals were sacrificed and the results (number and grade of intraperitoneal adhesions, histological data on prosthesis integration, such as mesothelialization, fibroblast infiltration, vessel neoformation, etc.) were evaluated.

RESULTS

Intraperitoneal adhesions decreased in implants painted with fibrin glue and hyaluronidase gel compared with untreated implants. When right-sided adhesions formed, they were looser and in many animals, the implants were completely peritonized. Integration of the prostheses was not affected by either fibrin glue or hyaluronidase gel.

CONCLUSIONS

Adhesion formation can be reduced after abdominal surgery. The reduction achieved in this study was greater in the quantity than in the consistency of the adhesions. The results with hyaluronidase gel were moderately superior to those obtained with fibrin glue. Hyaluronidase gel has the advantage of being inexpensive.

Histological and biomechanical evaluation of implanted graft materials in a rabbit vaginal and abdominal model

OBJECTIVE

The objective of the study was to describe the histologic and biomechanical changes of implanted dermal collagen graft materials.

STUDY DESIGN

Twenty rabbits were randomized into 2 groups (6 and 12 weeks, respectively). Each rabbit had 4 graft segments (human dermis, porcine dermis, porcine collagen-coated polypropylene mesh, and autologous fascia) randomly implanted into the abdomen and the vagina. Biomechanical testing and histologic analysis was performed after recovery of graft segments.

RESULTS

Dermal graft segments showed a marked decrease in ultimate strength (84% to 86%) and elastic modulus (73% to 82%) that was significantly different from the decrease seen in autologous fascia or coated synthetic mesh (P < .0008 and P < .0001, respectively). The decrease in ultimate strength was associated with vaginal implantation (P = .057). Dermal graft materials had moderate inflammation and minimal collagen infiltration.

CONCLUSION

The mechanical properties of dermal graft materials decline after implantation. Vaginal implantation may cause a different tissue response to graft material than abdominal implantation. Dermal graft material caused moderate inflammation and minimal collagen ingrowth remote from implantation.

Expanded polytetrafluoroethylene and polypropylene in the repairing of abdominal wall defects in Wistar rats: comparative study

PURPOSE: To compare the use of polypropylene and PTFE meshes in the treatment of incisional hernias made experimentally on Wistar rats. METHODS: The experiment used 24 Wistar rats divided into three cohorts: C-A (ressection of a segment of abdominal wall), E-A (ressection and placement of PTFEe mesh), E-B (resection and placement of polypropylene mesh). After 28 days, the mesh and the surrounding tissue were removed and submitted to macroscopic analysis (assessment of the abdominal wall for presence of abscess in the surgical wound and/or skin necrosis, and adhesions) as well as microscopic analysis (presence of fibrosis, necrosis and abscess, counting of macrophages, mononuclears and polymorphonuclears). RESULTS: Adhesions and abscesses in the surgical wound were observed more commonly associated to the group treated with PTFEe. The size of the fibrous tissue was greater in the group treated with polypropylene. Cohort E-A showed PTFEe mesh enveloped by organized fine connective tissue. No groups presented necrosis on the site of the insertion. The highest mononuclear inflammatory reaction occurred in association to PTFEe when compared to the control group, but the findings for the polypropylene mesh were also significant when compared to the control group. In the analysis of the results obtained for cohorts E-A and E-B, a minimal occurrence of polymorphonuclears was noticed in both groups, which indicates low tissue reactivity to both materials used in the present experiment. CONCLUSION: Even with epithelization and proliferation of connective tissue, anchorage between PTFEe and abdominal wall is insufficient, which can result in reherniations.

Experimental comparison of monofile light and heavy polypropylene meshes: less weight does not mean less biological response

BACKGROUND

Mesh implantation is a standard procedure in hernia repair. It provides low recurrence rate but increases complication rate due to foreign-body reaction induced by alloplastic materials in surrounding tissues. It is believed that biocompatibility of meshes may be improved by reducing their weight per meter squared (m2) and altering the implant structure.

AIM

The aim of this study was to evaluate the effect of weight and structure as determinants of mesh biocompatibility.

METHOD

Thirty-six Wistar rats were studied. In 12 animals, conventional polypropylene (heavy) meshes (HM) were implanted; in other 12, material-reduced (light) microporous polypropylene meshes (LM); and the remaining 12 served as a sham-operated control group. Meshes were explanted after 21 and 90 days (6 animals per group). All samples were examined by light and electron microscopies. Integration of meshes in surrounding tissue, inflammatory response, fibrotic reactions, and structural changes were recorded. Quantification of the inflammatory response was achieved by CD-68 marking of macrophages and counting their number per surface unit.

RESULTS

After 21 days, there was no significant difference in thickness of surrounding connective tissue between meshes in all groups studied. After 90 days, thickness of connective tissue decreased in both groups, and fibrotic reaction in the mesh bed was significantly less in the HM group. Total amount of macrophages per millimeter squared (mm2) decreased with time in HM and LM samples but was significantly lower in the HM group on day 21 (43.5%) and day 90 (46.7%).

CONCLUSION

This study found worse biocompatibility of LM compared with HM. Thus, the amount of implanted mesh was not the main determinant of biocompatibility (expressed as successful incorporation and diminished foreign-body reaction) but the size of the pores.

Influence of the structure of new generation prostheses on shrinkage after implant in the abdominal wall

When a biomaterial is used to repair an abdominal wall defect, wound contraction can cause the prosthesis to shrink, and the tension generated can provoke recurrence of the defect. This study was designed to determine whether the structure of a prosthesis can directly influence prosthetic shrinkage. Abdominal wall defects (7 x 5 cm) in rabbits were repaired using the laminar prosthesis DualMesh (DM), the composites Sepramesh (Se) and Vypro II (Vy), and the reticular prosthesis Surgipro (PP). The animals were sacrificed 14 and 90 days after surgery, at which time implant specimens were morphologically and immunohistochemically examined to establish the presence of myofibroblasts and macrophages. The size of each prosthesis was measured at the end of the study through image analysis. Morphometric measurements revealed greatest prosthesis shrinkage for Se, PP, and Vy (16.05% +/- 5.08%; 13.75% +/- 4.22%; 16.16% +/- 6.34%), while the DM prostheses only showed a 7.57% +/- 0.62% decrease in size (p < 0.05). In the DM implants, the macrophage response and myofibroblast labeling were reduced. Both biomaterial structure and the macrophage reaction induced at the implant site modulate prosthetic shrinkage, laminar prostheses of the ePTFE type undergoing less shrinkage than reticular meshes. Reduced DM shrinkage was linked to decreased myofibroblast numbers 2 weeks postimplant.

Seguimiento de la contracción de las mallas de polipropileno empleadas en la reparación de eventraciones

INTRODUCTION

Polypropylene (PP) mesh is one of the most frequently used materials in the surgical repair of ventral hernias. Despite the widely recognized ability of PP to integrate into the host tissue, these meshes may shrink during the healing process in the patient.

OBJECTIVE

To quantify polypropylene mesh shrinkage.

PATIENTS AND METHOD

A radiological follow-up study was performed in 23 consecutive patients who underwent surgery for midline ventral hernias with diameters of at least 5 cm. PP meshes were marked with titanium clips at the ends of their longest transverse and longitudinal axes. X-rays were performed on the first postoperative day and at 1, 3, 6 and 12 months. The distances between clips were measured and the area of the mesh was calculated.

RESULTS

Seventeen women and six men underwent surgery. In nine patients the mesh was placed on the prefascial space (onlay) and in 14 in the subfascial space (sublay). There were four seromas in patients with mesh placed with the onlay technique. The reduction in the calculated area was 12% at 1 month, 24% at 3 months, 29% at 6 months and 34% at 12 months.

CONCLUSIONS

PP mesh provided excellent clinical results. Radiological surveillance revealed substantial shrinkage, mainly in the first 3 months after implantation.

Tissue integration and tolerance to meshes used in gynecologic surgery: An experimental study

OBJECTIVE

To evaluate the tissue integration of and tolerance to five different mesh types used in genital prolapse surgery to provide mechanical support.

STUDY DESIGN

We placed five different meshes (Vicryl, Vypro, Prolene, Prolene soft, and Mersuture) on the peritoneums of 12 pigs. After 10 weeks, we used light microscopy to analyze the tissue integration of and tolerance to these meshes. We looked for inflammation, vascularization, fibroblasts, collagen fibers and the organization of connective tissue.

RESULTS

The absorbable prostheses made of polyglactin 910 (Vicryl) and the non-absorbable prostheses made of polypropylene (Prolene and Prolene soft) induced the least severe inflammatory reactions. Tissue integration was best with the polypropylene meshes, which allowed the development of a well-organized, fibrous, mature, connective tissue.

CONCLUSION

The tissue response to prosthetic meshes depends on the material used and its structure. This work highlights the feasibility of carrying out experimental studies to test the tolerance to and integration of biomaterials used in gynecology. Such studies need to be carried out whenever new prostheses become available to validate their use in common practice.

Adhesion formation and reherniation differ between meshes used for abdominal wall reconstruction

Incisional hernia is a common surgical problem, frequently requiring prosthetic mesh repair. The demands of the ideal mesh seem conflicting; ingrowth at the mesh-fascia interface, without development of adhesions at the visceral mesh surface. Various antiadhesives combined with macroporous mesh and composite meshes were studied for prevention of adhesions to mesh and ingrowth into the fascia. In 60 rats an abdominal wall defect was created and repaired with underlay mesh. Rats were divided into six groups and treated with polypropylene mesh (PPM, control), PPM with auto-cross-linked polymers (ACP) gel, PPM with fibrinogen glue (FG), polypropylene/expanded polytetrafluoroethylene (ePTFE) mesh, polypropylene/sodium hyaluronate/carboxymethylcellulose (HA/CMC) mesh, and polypropylene-collagen/polyethylene-glycol/glycerol (CPGG) mesh. Mesh infection was assessed in the postoperative period, adhesions and reherniations were scored at sacrifice 2 months after operation, and tensile strength of the mesh-tissue interface was measured. Six rats developed mesh infection, half of them were treated with PPM/ePTFE. The PPM/HA/CMC group showed a significant reduction in the amount and severity of adhesions. In animals treated with PPM/ACP and PPM/FG, severity of adhesions was reduced as well. Reherniation rate in the PPM/ACP group was 50% and significantly higher than that in other groups. Rats in the PPM/HA/CMC had the highest tensile strength. PPM/HA/CMC approaches the demands of the ideal mesh best, having superior antiadhesive properties, no reherniation and no infection in this rat model of incisional hernia.

Anti-adhesive properties of polytetrafluoroethylene (Gore-Tex) in middle ear surgery. An experimental study

CONCLUSIONS

Polytetrafluoroethylene (PTFE) may represent a material that prevents adhesions when implanted in the middle ear. This characteristic can be used to improve the design of prostheses.

OBJECTIVE

Prostheses in the middle ear have a relatively high failure rate due to extrusion, deformation and adhesion. Adhesion of prostheses to the walls of the tympanic cavity is the commonest cause of long-term hearing loss. The anti-adhesive properties of PTFE have been previously studied in abdominal and vascular surgery. To the best of our knowledge, this is the first work in which the properties of PTFE have been studied in the context of middle ear pathology.

MATERIAL AND METHODS

In order to induce otitis media with effusion, 27 Wistar rats underwent a technique based on permanent cauterization of the pharyngeal Eustachian tube. PTFE was subsequently implanted in the middle ear. Rats that underwent cauterization without implantation and cauterization with implantation of hydroxyapatite and Plastipore were included as controls.

RESULTS

Histopathological study of the tympanic bullae at 15 and 90 days after implantation demonstrated good biocompatibility of the PTFE implant under the analyzed conditions, with formation of a capsule around the material and no adhesions between the ear tissues and the prosthesis.