Affinity of Staphylococcus epidermidis to various prosthetic graft materials

Meshing around: high-risk hernias and infected mesh

Open laparotomy carries a risk up to 20% for an incisional hernia, making repair one of the most common operations performed by general surgeons in the USA. Despite a multitude of mesh appliances and techniques, no size fits all, and there is continued debate on what is the best mesh type, especially in high-risk patients with contaminated hernias. Infected mesh carries a significant burden to the patient, the surgeon and overall healthcare costs with medical legal implications. A stepwise approach that involves optimization of patient comorbidities, patient selective choice of mesh and technique is imperative in mitigating outcomes and recurrence rates. This review will focus on the avoidance of mesh infection and the selection of mesh in patients with contaminated wounds.

Antimicrobial Meshes for Hernia Repair: Current Progress and Perspectives

Recent advances in the development of biomaterials have given rise to new options for surgery. New-generation medical devices can control chemical breakdown and resorption, prevent post-operative adhesion, and stimulate tissue regeneration. For the fabrication of medical devices, numerous biomaterials can be employed, including non-degradable biomaterials (silicone, polypropylene, expanded polytetrafluoroethylene) or biodegradable polymers, including implants and three-dimensional scaffolds for tissue engineering, which require particular physicochemical and biological properties. Based on the combination of new generation technologies and cell-based therapies, the biocompatible and bioactive properties of some of these medical products can lead to progress in the repair of injured or harmed tissue and in tissue regeneration. An important aspect in the use of these prosthetic devices is the associated infection risk, due to the medical complications and socio-economic impact. This paper provides the latest achievements in the field of antimicrobial surgical meshes for hernia repair and discusses the perspectives in the development of these innovative biomaterials.

A critical review of the in vitro and in vivo models for the evaluation of anti-infective meshes

BACKGROUND

Infectious complications following mesh implantation for abdominal wall repair appear in 0.7 up to 26.6% of hernia repairs and can have a detrimental impact for the patient. To prevent or to treat mesh-related infection, the scientific community is currently developing a veritable arsenal of antibacterial meshes. The numerous and increasing reports published every year describing new technologies indicate a clear clinical need, and an academic interest in solving this problem. Nevertheless, to really appreciate, to challenge, to compare and to optimize the antibacterial properties of next generation meshes, it is important to know which models are available and to understand them.

PURPOSE

We proposed for the first time, a complete overview focusing only on the in vitro and in vivo models which have been employed specifically in the field of antibacterial meshes for hernia repair.

RESULTS AND CONCLUSION

From this investigation, it is clear that there has been vast progress and breadth in new technologies and models to test them. However, it also shows that standardization or adoption of a more restricted number of models would improve comparability and be a benefit to the field of study.

Evaluation of a fully absorbable poly-4-hydroxybutyrate/absorbable barrier composite mesh in a porcine model of ventral hernia repair

Background

The objective of this study was to evaluate the mechanical and histological properties of a fully absorbable poly-4-hydroxybutyrate/absorbable barrier composite mesh (Phasix™ ST) compared to partially absorbable (Ventralight™ ST), fully absorbable (Phasix™), and biologically derived (Strattice™) meshes in a porcine model of ventral hernia repair.

Methods

Bilateral abdominal surgical defects were created in twenty-four Yucatan pigs, repaired with intraperitoneal (Phasix™ ST, Ventralight™ ST) or retromuscular (Phasix™, Strattice™) mesh, and evaluated at 12 and 24 weeks (n = 6 mesh/group/time point).

Results

Prior to implantation, Strattice™ demonstrated significantly higher (p < 0.001) strength (636.6 ± 192.1 N) compared to Ventralight™ ST (324.3 ± 37.1 N), Phasix™ ST (206.9 ± 11.3 N), and Phasix™ (200.6 ± 25.2 N). At 12 and 24 weeks, mesh/repair strength was significantly greater than NAW (p < 0.01 in all cases), and no significant changes in strength were observed for any meshes between 12 and 24 weeks (p > 0.05). Phasix™ mesh/repair strength was significantly greater than Strattice™ (p < 0.001) at 12 and 24 weeks, and Ventralight™ ST mesh/repair strength was significantly greater than Phasix™ ST mesh (p < 0.05) at 24 weeks. At 12 and 24 weeks, Phasix™ ST and Ventralight™ ST were associated with mild inflammation and minimal–mild fibrosis/neovascularization, with no significant differences between groups. At both time points, Phasix™ was associated with minimal–mild inflammation/fibrosis and mild neovascularization. Strattice™ was associated with minimal inflammation/fibrosis, with minimal neovascularization at 12 weeks, which increased to mild by 24 weeks. Strattice™ exhibited significantly less neovascularization than Phasix™ at 12 weeks and significantly greater inflammation at 24 weeks due to remodeling.

Conclusions

Phasix™ ST demonstrated mechanical and histological properties comparable to partially absorbable (Ventralight™ ST) and fully resorbable (Phasix™) meshes at 12 and 24 weeks in this model. Data also suggest that fully absorbable meshes with longer-term resorption profiles may provide improved mechanical and histological properties compared to biologically derived scaffolds.

Evaluation of the Antimicrobial Efficacy of a Novel Rifampin/Minocycline-Coated, Noncrosslinked Porcine Acellular Dermal Matrix Compared With Uncoated Scaffolds for Soft Tissue Repair

Background Despite meticulous aseptic technique and systemic antibiotics, bacterial colonization of mesh remains a critical issue in hernia repair. A novel minocycline/rifampin tyrosine-coated, noncrosslinked porcine acellular dermal matrix (XenMatrix AB) was developed to protect the device from microbial colonization for up to 7 days. The objective of this study was to evaluate the in vitro and in vivo antimicrobial efficacy of this device against clinically isolated methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli. Methods XenMatrix AB was compared with 5 existing uncoated soft tissue repair devices using in vitro methods of zone of inhibition (ZOI) and scanning electron microscopy (SEM) at 24 hours following inoculation with MRSA or E coli These devices were also evaluated at 7 days following dorsal implantation and inoculation with MRSA or E coli (60 male New Zealand white rabbits, n = 10 per group) for viable colony-forming units (CFU), abscess formation and histopathologic response, respectively. Results In vitro studies demonstrated a median ZOI of 36 mm for MRSA and 16 mm for E coli for XenMatrix AB, while all uncoated devices showed no inhibition of bacterial growth (0 mm). SEM also demonstrated no visual evidence of MRSA or E coli colonization on the surface of XenMatrix AB compared with colonization of all other uncoated devices. In vivo XenMatrix AB demonstrated complete inhibition of bacterial colonization, no abscess formation, and a reduced inflammatory response compared with uncoated devices. Conclusion We demonstrated that XenMatrix AB possesses potent in vitro and in vivo antimicrobial efficacy against clinically isolated MRSA and E coli compared with uncoated devices.

Mesh Infection and Hernia Repair: A Review

BACKGROUND

The use of a prosthetic mesh to repair a tissue defect may produce a series of post-operative complications, among which infection is the most feared and one of the most devastating. When occurring, bacterial adherence and biofilm formation on the mesh surface affect the implant's tissue integration and host tissue regeneration, making preventive measures to control prosthetic infection a major goal of prosthetic mesh improvement.

METHODS

This article reviews the literature on the infection of prosthetic meshes used in hernia repair to describe the in vitro and in vivo models used to examine bacterial adherence and biofilm formation on the surface of different biomaterials. Also discussed are the prophylactic measures used to control implant infection ranging from meshes soaked in antibiotics to mesh coatings that release antimicrobial agents in a controlled manner.

RESULTS

Prosthetic architecture has a direct effect on bacterial adherence and biofilm formation. Absorbable synthetic materials are more prone to bacterial colonization than non-absorbable materials. The reported behavior of collagen biomeshes, also called xenografts, in a contaminated environment has been contradictory, and their use in this setting needs further clinical investigation. New prophylactic mesh designs include surface modifications with an anti-adhesive substance or pre-treatment with antibacterial agents or metal coatings.

CONCLUSIONS

The use of polymer coatings that slowly release non-antibiotic drugs seems to be a good strategy to prevent implant contamination and reduce the onset of resistant bacterial strains. Even though the prophylactic designs described in this review are mainly focused on hernia repair meshes, these strategies can be extrapolated to other implantable devices, regardless of their design, shape or dimension.

A case report on management of synergistic gangrene following an incisional abdominal hernia repair in an immunocompromised obese patient

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Synergistic gangrene is generated from bacterial colonies present in necrotic tissues. Within our case, continual removal of the necrotic burden was essential in wound bed preparation, reducing contamination and tissue destruction.

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In surgery, wide necrotic wound debridement, early and repetitive wound drainages with the use of a large pore polypropylene mesh with a detailed surgical follow up is recommended.

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This case has demonstrated how a planned multidisciplinary action can produce prosperous results in a severely obese immunocompromised patient with an SSI, following an incisional hernia repair.

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Our selective case is unique within current literature, being the first to illustrate mesh salvage in a morbid obese patient with chronic lymphoblastic leukaemia.

Introduction

We present a case on conservative management of salvaging the mesh in an immunocompromised morbidly obese patient, who developed a synergistic gangrene infection following a primary open mesh repair of an incisional hernia.

Presentation of case

Our patient presented with a surgical wound infection, comorbidities were Chronic Lymphoblastic Leukemia (CLL), Body Mass Index (BMI) of 50, hypertension and diet controlled type-2 diabetes. In surgery, wide necrotic wound debridement, early and repetitive wound drainages with the use of a large pore polypropylene mesh and a detailed surgical follow up was required. High dose intravenous broad-spectrum antibiotic treatment and Negative Pressure Wound Therapy (NPWT) was administrated in combination with adopting a multidisciplinary approach was key to our success.

Discussion

Stoppa Re et al. complied a series of 360 ventral hernia mesh repairs reporting an infection rate of 12% that were managed conservatively. However, our selective case is unique within current literature, being the first to illustrate mesh salvage in a morbid obese patient with CLL. Recent modifications in mesh morphology, such as lower density, wide pores, and lighter weight has led to considerable improvements regarding infection avoidance.

Conclusion

This case has demonstrated how a planned multidisciplinary action can produce prosperous results in a severely obese immunocompromised patient with an SSI, following an incisional hernia repair.

Bacterial adhesion to biological versus polymer prosthetic materials used in abdominal wall defect repair: do these meshes show any differences in vitro?

PURPOSE

Although clinical data suggest the similar performance of collagen-based biological prosthetic materials to some polymer materials, the use of a biomesh for abdominal hernia repair in a setting of infection is controversial. This in vitro study compares the adhesion of two Staphylococcus strains to polymer and biological meshes.

METHODS

Sterile fragments of Optilene(®) (Op), Surgipro™ (Surg), Preclude(®) (Precl), TIGR(®) (TIGR), Bio-A(®) (BioA), Permacol™ (Perm), Surgisis(®) (SIS), and Tutomesh(®) (Tuto) were inoculated with 10(6) CFU of S. aureus (Sa) or S. epidermidis (Se) (n = 18 per strain per mesh). The first five meshes are polymer materials while Perm, SIS and Tuto are biomeshes. After 24/48 h of incubation, bacterial adhesion was examined by sonication, scanning electron microscopy (SEM) and light microscopy.

RESULTS

Sa and Se showed a high affinity for the absorbable meshes (TIGR, BioA, Perm, SIS, Tuto) (p < 0.001). Precl yielded the lowest bacterial loads (p < 0.001). Surg, Precl and BioA underwent no substantial change over time, while Op (p < 0.001) and TIGR (p < 0.05) showed decreasing bacterial loads during incubation. The Sa-contaminated biomeshes behaved similarly while biomeshes inoculated with Se returned higher bacterial yields at 48 h, especially SIS (p < 0.001). SEM and light microscopy observations revealed planktonic bacteria and biofilms on the polymer surface and bacterial niches in biomesh pores.

CONCLUSIONS

Within 48 h of contamination, the absorbable polymer and biological meshes exhibited high bacterial loads. Given their lower affinity for both bacterial strains, the conventional non-absorbable polymer materials could be better candidates for use in contaminated surgical fields.

Conservative management of mesh-site infection in hernia repair surgery: a case series

PURPOSE

The aim of this study is to assess the outcome of conservative management of infected mesh grafts following abdominal wall hernia repair.

METHODS

This study retrospectively examined the charts of patients who developed mesh-site infection following surgery for abdominal hernia repair to determine how effective conservative management in the form of antibiotics and wound management was on the resolution of infection and wound healing.

RESULTS

Over a period of 30 months, 13 patients developed infected mesh grafts post-hernia repair surgery. Twelve patients were successfully treated conservatively with local wound care and antibiotics if clinically indicated. One patient returned to theatre to have the infected mesh removed. Of the patients that healed eleven were treated with negative pressure wound therapy (VAC(®)).

CONCLUSION

This series of case studies indicate that conservative management of abdominal wall-infected hernia mesh cases is likely to be successful.

Comparison of infectious complications with synthetic mesh in ventral hernia repair

BACKGROUND

Infection can be a devastating complication associated with prosthetic incisional hernia repair. It is unclear whether the type of mesh used affects the risk of infection.

METHODS

A retrospective review was performed of all patients who underwent elective incisional hernia repair with permanent prosthetic mesh between January 1, 2000, and August 1, 2007.

RESULTS

A total of 176 patients underwent elective incisional hernia repair with mesh. The overall infection rate with the use of goretex (Flagstaff, AZ, USA) was 12 of 86 (14%) and 2 of 90 (2.2%) in cases in which nongoretex material was used (P = .016). In the goretex group, infection rates were significantly higher in open versus laparoscopic cases (26.5% vs 5.8%, P = .030). Methicillin-resistant Staphylococcus aureus was the most common organism recovered.

CONCLUSIONS

The risk of mesh infection with the use of goretex was found to be higher than with the use of nongoretex mesh. Laparoscopic placement of goretex reduces this risk of infection. No significant differences in recurrence rates were found.

History of methicillin-resistant Staphylococcus aureus (MRSA) surgical site infection may not be a contraindication to ventral hernia repair with synthetic mesh: a preliminary report

PURPOSE

A history of methicillin-resistant Staphylococcus aureus (MRSA) surgical site infection presents a significant surgical dilemma as to the risk of subsequent mesh infection, even if no active infection is present. We investigated the outcomes of ventral hernia repair with synthetic mesh in patients with prior MRSA surgical site infections (SSIs).

METHODS

All patients with a clean wound but prior MRSA SSI undergoing open ventral hernia repair with mesh by a single surgeon over a 3-year period were reviewed for the development of any major (need for readmission, operative debridement, or mesh removal) or minor SSI. All patients received peri-operative intravenous vancomycin and prolonged suppressive oral trimethoprim/sulfamethoxazole or doxycycline.

RESULTS

Ten patients (male = 7, female = 3) with clean wounds and a history of MRSA SSI underwent open ventral hernia repair with retrorectus synthetic mesh placement. Mean follow-up was 13.5 ± 3.3 months. Overall, two patients (20 %) developed SSIs (minor = 2, major = 0). Both SSIs were successfully managed with therapeutic oral antibiotics and local wound care without need for surgical debridement or mesh removal. There have been no hernia recurrences in any of the patients.

CONCLUSIONS

Preliminary results suggest that history of MRSA infection may not be a contraindication to the use of synthetic mesh for ventral hernia repair. Macroporous lightweight meshes, combined with use of prolonged suppressive antibiotics and sublay retromuscular mesh placement that provides complete tissue coverage, should be further investigated as an acceptable prosthetic choice when planning a complex ventral hernia repair in the setting of prior MRSA SSI.

Use of autologous renal capsule grafts for venous repair

OBJECTIVE

To evaluate the efficacy of the renal capsule for reconstruction of the inferior vena cava in a canine model.

MATERIALS AND METHODS

The present study was conducted on 10 dogs; an oval window (2-8 cm long, mean 6.5 cm) was made in the inferior vena cava and then repaired using the autologous renal capsule patch. The patency and functionality of the graft were assessed macroscopically and microscopically 3 months postoperatively.

RESULTS

All the dogs were killed at 3 months, showing excellent patency of the vena cava macroscopically and in the venography. In the microscopic examination, all the patches were completely endothelialized. No evidence of infection or thrombosis was noted.

CONCLUSION

A renal capsule patch can be used for reconstruction of the inferior vena cava. Patency appears to be good, and the risk of infection is low. Moreover, this is an accessible material.

Abdominal ventral hernia repair with current biological prostheses: an experimental large animal model

Biologic prostheses have emerged to address the limitations of synthetic materials for ventral hernia repairs; however, they lack experimental comparative data. Fifteen swine were randomly assigned to 1 of 3 bioprosthetic groups (DermaMatrix, AlloDerm, and Permacol) after creation of a full thickness ventral fascial defect. At 15 weeks, host incorporation, hernia recurrence, adhesion formation, neovascularization, inflammation, and biomechanical properties were assessed. No animals had hernia recurrence or eventration. DermaMatrix and Alloderm implants demonstrated more adhesions, greater inflammatory infiltration, and more longitudinal laxity, but near identical neovascularization and tensile strength to Permacol. We found that porcine acellular dermal products (Permacol) contain following essential properties of an ideal ventral hernia repair material: low inflammation, less elastin and stretch, lower adhesion rates and cost, and more contracture. The addition of lower cost xenogeneic acellular dermal products to the repertoire of available acellular dermal products demonstrates promise, but requires long-term clinical studies to verify advantages and efficacy.

Conservative management of mesh-site infection in hernia repair

BACKGROUND

Mesh hernioplasty is the preferred surgical procedure for large abdominal wall hernias. Infection remains one of the most challenging complications of this operation. Salvaging infected prosthetic material after ventral hernia repair is rarely successful. Most cases require mesh excision and complex abdominal wall reconstruction, with variable success rates. In this article, we report 3 cases of mesh salvage after laparoscopic ventral herniorrhapy with a novel use of percutaneous drainage and antibiotic irrigation.

RESULTS

Three patients developed infected seromas after laparoscopic ventral hernia repair. The fascial defect of the first patient was repaired with a commercially available 20 x 18 cm polytetrafluoroethylene (PTFE) mesh. A complex fluid collection developed the following month in the anterior abdominal wall overlying the patient's mesh. The cultures grew Staphylococcus aureus. The second patient had a 30 x 20 cm PTFE mesh placed, which developed a fluid collection with Enterococcus faecalis and Escherichia coli. The third case underwent repair, using a another commercially available 22 x 28 cm PTFE mesh. A fluid collection measuring 20 x 10 cm in the anterior abdominal wall developed, growing Staphylococcus lugdunensis. In all 3 cases, a percutaneous drain was placed within the fluid collection and long-term intravenous (i.v.) access was obtained. I.v. antibiotics were initiated. In addition, gentamicin (80 mg) with 20 mL of saline was infused through the drain 3 times a day. All patients have remained free of clinical signs of infection following the completion of therapy.

CONCLUSIONS

Infected mesh after laparoscopic ventral herniorrhapy without systemic sepsis may be amenable to nonoperative treatment. A conservative approach that includes percutaneous drainage followed by antibiotic irrigation is a potential alternative to prosthetic removal in carefully selected patients. Further evaluation of this technique is warranted to define the most appropriate management strategies for these patients.

Comparison of the adherence of E.Coli and S. Aureus to ten different prosthetic mesh grafts: In vitro experimental study

BACKGROUND

The prosthetic mesh grafts used to repair the abdominal wall may become infected, primarily by S. aureus and E. coli. This study sought to provide a rational basis for the choice of mesh used to repair a hernia when there is a likelihood of infection or contamination.

METHODS

S. aureus and E. coli were incubated with ten types of prosthetic mesh graft (Table 1) in liquid growth medium. After sequential dilution of samples from the prosthetic mesh grafts, the colony forming units of adherent S. aureus and E. coli were counted.

RESULTS

There was no significant difference in the numbers of E. coli and S. aureus adherent to simple polypropylene mesh grafts. Significantly more of both species were adherent to the polyester, expanded polytetrafluoroethylene (ePTFE), and composite prosthetic mesh grafts, except for E. coli on graft 5. Significantly fewer E. coli were adherent to composite mesh grafts 5, 8, and 10 than S. aureus.

CONCLUSION

S. aureus and E. coli adhere to polypropylene similarly. In vitro, fewer S. aureus and E. coli adhere to simple polypropylene mesh grafts than to polyester, ePTFE, or composite prosthetic mesh grafts.

Experimental evaluation of four biologic prostheses for ventral hernia repair

PURPOSE

To evaluate two bioprostheses derived from bovine pericardium, one cross-linked (Peri-Guard) and the other non-cross-linked (Veritas), and to compare them with Alloderm and Permacol for abdominal wall repair.

METHODS

The four prostheses were tested in acute and chronic hernia models. Prostheses were either sutured to the edge of the abdominal wall defect (inlay) or secured as an underlay with surgical tacks. Evaluation at 3 and 6 months included adhesion formation, defect area size and thickness, tensile strength, and histology.

RESULTS

Mean adhesion coverage area ranged from 25 to 31%. The two cross-linked materials, Permacol and Peri-Guard, showed greater tensile strength. Significant defect contraction followed repair with Veritas, whereas Alloderm stretched. All prostheses had cellular ingrowth and neovascularization by 3 months. No significant differences were found in prosthesis to abdominal wall breaking strength. Operative site infection occurred in six animals (5 Peri-Guard, 1 Veritas), and overlying skin ulceration in six others (6 Peri-Guard).

CONCLUSIONS

Permacol provided a strong and durable repair for up to six months. Peri-Guard was equally strong but prone to infection and to skin ulceration. With time, Veritas and Alloderm lost tensile strength associated with marked thinning and with hernia-like bulging in the case of Alloderm.

The analysis of infection after polypropylene mesh repair of abdominal wall hernia

AIM

The aim of the study was to evaluate the frequency of superficial and prosthetic mesh infection following polypropylene mesh repair of different abdominal wall hernia in individual patients and to analyze the manifestation, clinical process and outcomes in patients with prosthetic mesh infection.

METHODS

This was a retrospective analysis of 375 patients with 423 implanted meshes for groin, femoral, umbilical, incisional and epigastric hernias, with a mean follow-up of 15 months (range: 3-73 months).

RESULTS

The total superficial infection rate was 1.65%, and the rate of mesh infection was 0.94%. There were no statistically significant differences in prosthetic mesh infection between monofilament and multifilament meshes as well as between the different repair groups of hernias. The deep incisional surgical site infection after previous operation was established as a significant risk factor for prosthetic mesh infection in incisional hernia repair (P < 0.0001). Five cases of prosthetic mesh infection were presented and analyzed.

CONCLUSIONS

There is no correlation between the superficial and prosthetic mesh infection. There may be difficulties in determining mesh infection and to choose the right tactic. The reconvalescence in all patients with mesh infection was achieved only after removal of the infected mesh.

On the biology of saphenous vein grafts fitted with external synthetic sheaths and stents

Autologous saphenous vein is used as a conduit to bypass atherosclerotic lesions in both the coronary artery (coronary artery bypass graft surgery [CABG]) and in femoral arteries (infrainguinal bypass graft surgery [IIBS]). Despite the undoubted success and benefits of the procedures, graft failure occurs in 50% of cases within 10 years after surgery. A principal cause of late vein graft failure is intimal and medial hyperplasia and superimposed atherogenesis. Apart from lipid lowering therapy, no intervention has hitherto proved clinically effective in preventing late vein graft failure which clearly constitutes a major clinical and economic problem that needs to be urgently resolved. However, we have studied the effect of external synthetic stents and sheaths in pig models of vein into artery interposition grafting and found them to have a profound effect on vein graft remodelling and thickening. In this review, therefore, we will summarise the mechanisms underlying vein graft failure and how these stents influence these processes and the possible mechanisms involved as well as the application of these devices in preventing vein graft failure clinically.

The use of autologous rectus facia sheath for replacement of inferior caval vein defect in orthotopic liver transplantation

Occasionally, during liver transplantation, vascular reconstructions have to be performed. Donor vessels can be harvested for this purpose. However, when these are lacking, alternatives should be available. A possible alternative can be the use of autologous rectus fascia sheath, folded as a tube with the mesothelium on the inside. Earlier experimental studies from our centre showed the successful use of the rectus fascia sheath graft in vascular defects in animal experiments. This report describes the first use of this autologous tubular graft for replacement of the inferior caval vein interponate during liver transplantation in men.

Gold and gold-palladium coated polypropylene grafts in a S. epidermidis wound infection model

BACKGROUND

The use of non-absorbable mesh grafts in both abdominal wall defects and inguinal hernias are impossible in the presence of contamination. This study was conducted for evaluation of the efficiencies of polypropylene mesh grafts coated with gold and palladium-gold.

MATERIALS AND METHODS

Ten piece of 1 x 2 cm of polypropylene mesh grafts were used in each group of naïve, gold-coated, and palladium-gold-coated. The grafts were incubated in physiological saline buffered and 0.5 McFarland slime positive Staphylococcus epidermidis for 24 h. At intervals of 6, 12, 24, 48, 72 h grafts were washed with saline and vortexed for 2 min in 2 ml of physiological saline. There were 100 microl of samples of vortexed material incubated in blood agar and 24 h later, colony numbers were assessed. In the second part of study, the grafts were implanted below the musculoaponeurotic layer at inguinal region of rats following the same procedure of incubation and washing. On the 8th day, the rats were examined for infection rate and their wound cultures were obtained.

RESULTS

The least amount of bacterial growth was detected in the samples obtained from gold-palladium coated grafts; whereas the highest rate of growth was found in samples of naive grafts. The superficial surgical site infection rate was 0% in gold-palladium coated, 30% in gold-coated and 100% in naïve polypropylene group. The bacterial growth rate from wound cultures confirmed the superficial surgical site infection rates in all groups.

CONCLUSION

Prosthetic graft infection with S. epidermidis can be prevented by coating the graft with gold-palladium or gold.

The susceptibility of prosthetic biomaterials to infection

BACKGROUND

Despite the use of a sterile technique and the administration of prophylactic antibiotics during surgical procedures, mesh infection continues to complicate the use of biomaterials. The purpose of this study was to compare the susceptibility to infection of prosthetic biomaterials in a live-animal model.

METHODS

The following seven prosthetic mesh biomaterials were used in this study. Expanded polytetrafluoroethylene (ePTFE) with silver/chlorhexidine (DM+), ePTFE (DM), porcine intestinal submucosa (S), polypropylene (M), ePTFE/polypropylene (X), hyaluronate/carboxymethylcellulose/polypropylene (SM), and human acellular dermal matrix (A). Lewis rats (n = 108) underwent creation of a single ventral hernia; 105 of them were repaired with a different mesh (2-cm2 piece). Twelve pieces of each mesh were inoculated at the time of hernia repair with 10(8) Staphylococcus aureus (n = 84). Three pieces of each mesh were placed without bacterial inoculation (n = 21). In three animals, no mesh was placed; instead, the peritoneum of the hernia defect was inoculated (n = 3). After 5 days, the animals were killed and the mesh was explanted (peritoneum for the nonmesh control). The mesh was vortex-washed and incubated in tryptic soy broth. Bacterial counts were determined using serial dilutions and spot plates and quantified in colony-forming units (CFU) per square centimeter of mesh present in the vortex wash fluid (wash count) and the soy broth (broth count). Data are presented as the mean log(10), with analysis of variance (ANOVA) and Tukey's test used to determine significance (p < 0.05).

RESULTS

The DM+ material had no detectable live bacteria in the wash or broth counts in 10 of 12 tested samples (p = 0.05). Of the samples that showed bacterial growth, the peritoneum control group had a lower wash count than A (p = 0.05) and the lowest broth count of all the materials except for DM+ (p = 0.05). In addition, SM had a significantly lower wash count than A (p = 0.05), with no broth count difference. In regard to wash and broth counts, DM, M, X, SM, S, and A were no different (p = NS).

CONCLUSIONS

The DM+ material was the least susceptible to infection. Impregnation with silver/chlorhexidine killed the inoculated bacteria, preventing their proliferation on the mesh surface. Other than DM+, native peritoneal tissue appears to be the least susceptible to infection. Silver/chlorhexidine appears to be an effective bactericidal agent for use with mesh biomaterials.

Long-term reduction of medial and intimal thickening in porcine saphenous vein grafts with a polyglactin biodegradable external sheath

OBJECTIVES

The development of neointimal hyperplasia with subsequent atherosclerotic deposition has been proposed to cause most late vein graft failures. Our unit has previously demonstrated that placement of a macroporous, loose-fitting polyester external stent prevents neointimal thickening in porcine vein grafts, and has been proposed as a therapeutic strategy to prevent late vein graft failure. To reduce any potential long-term complications of the permanent polyester stent, a study was undertaken to investigate the effect of a biodegradable external stent on porcine vein graft thickening at 1 month and to identify its longer term effects at 6 months.

METHODS

Bilateral saphenous vein to common carotid artery interposition grafting was performed in Large White pigs (25-32 kg; n = 6 per time course group) according to UK Home Office guidelines. A commercially constructed loose-fitting 8-mm-diameter polyglactin stent was placed externally around the vein graft on one side, and the contralateral side remained unstented to serve as control. The external stent was designed to biodegrade and hence disappear within 90 days. Grafts were left in situ for 1 month in 1 group of animals, and for up to 6 months in the other group, before explantation. Graft morphometric features were assessed with computer-aided planimetry.

RESULTS

At 1 month the vein grafts fitted with the polyglactin stent demonstrated a statistically significant decrease in neointimal thickening (0.038 mm; interquartile range [IQR], 0.035-0.039 mm) compared with the unstented control grafts (0.13 mm; IQR; 0.11-0.19; P = .0012), and also in medial thickening (0.09 mm; IQR, 0.086-0.093) compared with unsheathed control grafts (0.302 mm; IQR, 0.272-0.414; P = .0012). The 6-month polyglactin stented grafts also demonstrated a statistically significant reduction in neointimal thickening (0.049 mm; IQR, 0.047-0.07; P = .0012) compared with control grafts (0.178 mm; IQR, 0.164-0.19), and also in medial thickening (0.105 mm; IQR, 0.095-0.143) compared with unstented grafts (0.421 mm; IQR, 0.35-0.44; P = .0012, Mann-Whitney U test).

CONCLUSION

The loose-fitting biodegradable polyglactin external stent reduces porcine vein graft thickening at 1 month, which persists in the long term, even after degradation of the stent itself. This effective removal of the stent may therefore reduce the long-term risks for infection and mechanical complications associated with implanted prosthetic material while still eliciting the primary objective of preventing graft thickening over the long term. Biodegradable external stents therefore have potential advantages over permanent stent material in clinical application.

CLINICAL RELEVANCE

Arteriovenous bypass graft failure has a huge economic effect on health care resources, and a devastating effect o the patient. The attenuation of vein wall thickening, with subsequent luminal narrowing and occlusion, is a major goal in improving the longevity of the venous graft, to reduce secondary percutaneous and surgical interventions. The biodegradable external stent demonstrated in this study has possible clinical applications in bypass procedures with autogenous venous tissue, and represents a novel approach to ameliorating the problem of intimal hyperplasia that plagues these grafts.

A bioabsorbable (polyglactin), nonrestrictive, external sheath inhibits porcine saphenous vein graft thickening

OBJECTIVE

External, nonrestrictive, macro-porous polyester stents prevent neointima formation in porcine vein grafts and have been proposed as a therapeutic approach to the prevention of late vein graft failure. These stents are nonbiodegradable and therefore may promote long-term foreign body problems including infection and inflammation. The effect of external macro-porous biodegradable (polyglactin) sheaths on neointimal and medial thickening in porcine vein grafts was therefore investigated.

METHODS

Bilateral saphenous vein-carotid artery interposition grafting was performed in white Landrace pigs (n = 8) with external placement of polyglactin (Vicryl) sheaths (8 mm in diameter) on 1 side, with the contralateral side acting as a control. One month after surgery, grafts were explanted and wall dimensions measured on histological sections using computer-aided planimetry, and an immunocytochemical appraisal was carried out.

RESULTS

All grafts were patent at explantation. Polyglactin sheaths significantly reduced intimal thickness, medial thickness, and the percentage of proliferating cells compared with unsheathed controls. There was a pronounced accumulation of macrophages, giant cells, endothelial cells, and microvessels within and surrounding the biodegradable sheath compared with controls.

CONCLUSIONS

A nonrestrictive, biodegradable (polyglactin), external sheath reduces medial and intimal thickening in experimental saphenous vein grafts, possibly through inflammatory cell-mediated angiogenesis. If subsequent long-term studies confirm preservation of this beneficial effect, once the sheath biodegrades, this approach may have an advantage over the permanent polyester stent when applied clinically.