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.

Polyester Mesh Functionalization with Nitric Oxide-Releasing Silica Nanoparticles Reduces Early Methicillin-Resistant Staphylococcus aureus Contamination

Background: Infected hernia mesh is a cause of post-operative morbidity. Nitric oxide (NO) plays a key role in the endogenous immune response to infection. We sought to study the efficacy of a NO-releasing mesh against methicillin-resistant Staphylococcus aureus (MRSA). We hypothesized that a NO-releasing polyester mesh would decrease MRSA colonization and proliferation. Materials and Methods: A composite polyester mesh functionalized with N-diazeniumdiolate silica nanoparticles was synthesized and characterized. N-diazeniumdiolate silica parietex composite (NOSi) was inoculated with 10⁴,10⁶, or 10⁸ colony forming units (CFUs) of MRSA and a dose response was quantified in a soy tryptic broth assay. Utilizing a rat model of contaminated hernia repair, implanted mesh was inoculated with MRSA, recovered, and CFUs were quantified. Clinical metrics of erythema, mesh contracture, and adhesion severity were then characterized. Results: Methicillin-resistant Staphylococcus aureus CFUs demonstrated a dose-dependent response to NOSi in vitro. In vivo, quantified CFUs showed a dose-dependent response to NOSi-PCO. Treated rats had fewer severe adhesions, less erythema, and reduced mesh contracture. Conclusions: We demonstrate the efficacy of a NO-releasing mesh to treat MRSA in vitro and in vivo. Creation of a novel class of antimicrobial prosthetics offers new strategies for reconstructing contaminated abdominal wall defects and other procedures that benefit from deploying synthetic prostheses in contaminated environments.

Functionalized Strategies and Mechanisms of the Emerging Mesh for Abdominal Wall Repair and Regeneration

Meshes have been the overwhelmingly popular choice for the repair of abdominal wall defects to retrieve the bodily integrity of musculofascial layer. Broadly, they are classified into synthetic, biological and composite mesh based on their mechanical and biocompatible features. With the development of anatomical repair techniques and the increasing requirements of constructive remodeling, however, none of these options satisfactorily manages the conditional repair. In both preclinical and clinical studies, materials/agents equipped with distinct functions have been characterized and applied to improve mesh-aided repair, with the importance of mesh functionalization being highlighted. However, limited information exists on systemic comparisons of the underlying mechanisms with respect to functionalized strategies, which are fundamental throughout repair and regeneration. Herein, we address this topic and summarize the current literature by subdividing common functions of the mesh into biomechanics-matched, macrophage-mediated, integration-enhanced, anti-infective and antiadhesive characteristics for a comprehensive overview. In particular, we elaborate their effects separately with respect to host response and integration and discuss their respective advances, challenges and future directions toward a clinical alternative. From the vastly different approaches, we provide insight into the mechanisms involved and offer suggestions for personalized modifications of these emerging meshes.

Thermo-Responsive Antimicrobial Hydrogel for the In-Situ Coating of Mesh Materials for Hernia Repair

The prophylactic coating of prosthetic mesh materials for hernia repair with antimicrobial compounds is commonly performed before implantation of the mesh in the abdominal wall. We propose a novel alternative, which is a rifampicin-loaded thermo-responsive hydrogel formulation, to be applied on the mesh after its implantation. This formulation becomes a gel in-situ once reached body temperature, allowing an optimal coating of the mesh along with the surrounding tissues. In vitro, the hydrogel cytotoxicity was assessed using rabbit fibroblasts and antimicrobial efficacy was determined against Staphylococcus aureus. An in vivo rabbit model of hernia repair was performed; implanted polypropylene meshes (5 × 2 cm) were challenged with S. aureus (10⁶ CFU), for two study groups—unloaded (n = 4) and 0.1 mg/cm² rifampicin-loaded hydrogel (n = 8). In vitro, antibacterial activity of the hydrogel lasted for 5 days, without sign of cytotoxicity. Fourteen days after implantation, meshes coated with drug-free hydrogel developed a strong infection and resulted in poor tissue integration. Coating meshes with the rifampicin-loaded hydrogel fully prevented implant infection and permitted an optimal tissue integration. Due to its great performance, this, degradable, thermo-responsive antimicrobial hydrogel could potentially be a strong prophylactic armamentarium to be combined with prosthesis in the surgical field.

Infections associated with mesh repairs of abdominal wall hernias: Are antimicrobial biomaterials the longed-for solution?

The incidence of mesh-related infection after abdominal wall hernia repair is low, generally between 1 and 4%; however, worldwide, this corresponds to tens of thousands of difficult cases to treat annually. Adopting best practices in prevention is one of the keys to reduce the incidence of mesh-related infection. Once the infection is established, however, only a limited number of options are available that provides an efficient and successful treatment outcome. Over the past few years, there has been a tremendous amount of research dedicated to the functionalization of prosthetic meshes with antimicrobial properties, with some receiving regulatory approval and are currently available for clinical use. In this context, it is important to review the clinical importance of mesh infection, its risk factors, prophylaxis and pathogenicity. In addition, we give an overview of the main functionalization approaches that have been applied on meshes to confer anti-bacterial protection, the respective benefits and limitations, and finally some relevant future directions.

Infection prevention using affinity polymer-coated, synthetic meshes in a pig hernia model

BACKGROUND

Given concern for hernia mesh infection, surgeons often use biologic mesh which may provide reduced risk of infection but at the cost of decreased repair durability. We evaluated mesh coating to provide sustained release of antibiotics to prevent prosthetic mesh infection and also allow a durable repair.

MATERIALS AND METHODS

Cyclodextrin-based polymer was crosslinked onto multifilament polyester mesh and loaded with vancomycin (1.75 mg/cm²). Pigs received modified meshes (n = 6) or normal, untreated meshes (n = 4), which were implanted into acute 10 × 5 cm ventral hernia, then directly inoculated with 10⁶ colony-forming unit (CFU) of methicillin-resistant Staphylococcus aureus (MRSA). These were compared to animals receiving normal, uninfected mesh. All mesh was secured in an underlay bridge manner, and after 30 d, the abdominal wall was removed for quantitative bacterial culture and biomechanical analysis.

RESULTS

All animals survived 30 d. All six animals with coated mesh cleared MRSA infection. The four control animals did not clear MRSA (P = 0.005). Quantitative bacterial load was higher in standard mesh versus drug-delivery mesh group (2.34 × 10⁴versus 80.9 CFU/gm). These data were log₁₀-transformed and analyzed by Welch's t-test (P = 0.001). Minimum number of CFUs detectable by assay (300) was used instead of zero. Biomechanical analysis of controls (1.82 N/mm infected; 1.71 N/mm uninfected) showed no difference to the modified meshes (1.31 N/mm) in tissue integration (P = 0.15).

CONCLUSIONS

We successfully prevented synthetic mesh infection in a pig model using a cyclodextrin-based polymer to locally deliver vancomycin to the hernia repair site and clearing antibiotic-resistant bacteria. Polymer coating did not impact the strength of the hernia repair.

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.

Emerging Trends in Abdominal Wall Reinforcement: Bringing Bio-Functionality to Meshes

Abdominal wall hernia is a recurrent issue world-wide and requires the implantation of over 1 million meshes per year. Because permanent meshes such as polypropylene and polyester are not free of complications after implantation, many mesh modifications and new functionalities have been investigated over the last decade. Indeed, mesh optimization is the focus of intense development and the biomaterials utilized are now envisioned as being bioactive substrates that trigger various physiological processes in order to prevent complications and to promote tissue integration. In this context, it is of paramount interest to review the most relevant bio-functionalities being brought to new meshes and to open new avenues for the innovative development of the next generation of meshes with enhanced properties for functional abdominal wall hernia repair.

Fever after redo Nissen fundoplication with hiatal hernia repair

BACKGROUND

Fevers often arise after redo fundoplication with hiatal hernia repair. We reviewed our experience to evaluate the yield of a fever work-up in this population.

METHODS

We performed a retrospective review of children undergoing redo Nissen fundoplication with hiatal hernia repair between December 2001 and September 2012. Temperatures and fever evaluations of those children receiving a mesh repair were compared with those without mesh. A fever defined as temperature ≥38.4°C.

RESULTS

Fifty one children received 46 laparoscopic, 4 open, and 1 laparoscopic converted to open procedures. Biosynthetic mesh was used in 25 children whereas 26 underwent repair without mesh. A fever occurred in 56% of those repaired with mesh compared with 23.1% without mesh (P = 0.02). A fever evaluation was conducted in 32% of those with mesh compared with 11.5% without mesh (P = 0.52). A urinary tract infection was identified in one child after mesh use and an infection was identified in two children without mesh, one pneumonia and one wound infection (P = 1). In those repaired with mesh, there was no significant difference in maximum temperature.

CONCLUSIONS

Fever is common after redo Nissen fundoplication with hiatal hernia repair and occurs more frequently, and with higher temperatures in those with mesh. Fever work-up in these patients is unlikely to yield an infectious source and is attributed to the extensive dissection during the redo procedure.

Does presoaking synthetic mesh in antibiotic solution reduce mesh infections? An experimental study

BACKGROUND

Prosthetic mesh infection is one of the most challenging complications after hernia repair. We evaluate the efficacy of soaking mesh in antibiotics to prevent prosthetic infection in an animal model of clean-contaminated ventral hernia repair (VHR).

MATERIAL AND METHODS

Rats underwent an acute VHR with one of four synthetic meshes (composite multifilament polyester (Parietex PCO), multifilament polyester (Parietex TET), composite monofilament polypropylene (Ventralight), or monofilament polypropylene (SoftMesh)). Prior to implantation, mesh was soaked in saline or 10 mg/ml of vancomycin for 15 min. Following implantation, meshes were contaminated with 10(4) CFU of methicillin-resistant Staphylococcus aureus (MRSA) bacteria. Thirty days after implantation, mesh samples were cultured and evaluated under scanning electron microscope for biofilm formation.

RESULTS

Presoaking meshes significantly improves bacterial clearance in composite meshes and multifilament polyester mesh. MRSA clearance was as follows for all meshes (saline-soaked vs. vanco-soaked): Parietex PCO (0 vs. 56 %, p = 0.006), Parietex TET (0 vs. 50 %, p = 0.01), Ventralight (20 vs. 78 %, p = 0.012), and SoftMesh (70 vs. 80 %, p = 0.6). MRSA biofilm formation was consistent with bacterial growth.

CONCLUSION

Presoaking multifilament and composite mesh in vancomycin solution reduces MRSA bacterial growth. Its implementation may reduce the risk of mesh infection in clean-contaminated cases, although further investigation with human trials should be performed.

Risk factors for mesh-related infections after hernia repair surgery: a meta-analysis of cohort studies

Mesh infection, although infrequent, is a devastating complication of mesh hernioplasties. The aim of this study was to systematically review and synthesize the available evidence on risk factors for synthetic mesh infection after hernioplasty. A systematic search was performed in PubMed and Scopus databases. The extracted data were synthesized with the methodology of meta-analysis. We identified six eligible studies that reported on 2,418 mesh hernioplasties. The crude mesh infection rate was 5%. Statistically significant risk factors were smoking (risk ratio [RR] = 1.36 [95% confidence interval (CI): 1.07, 1.73]; 1,171 hernioplasties), American Society of Anesthesiologists (ASA) score ≥3 (RR = 1.40 [1.15, 1.70]; 1,682 hernioplasties), and emergency operation (RR = 2.46 [1.56, 3.91]; 1,561 hernioplasties). Also, mesh infections were significantly correlated with patient age (weighted mean difference [WMD] = 2.63 [0.22, 5.04]; 2,364 hernioplasties), ASA score (WMD = 0.23 [0.08, 0.38]; 1,682 hernioplasties), and the duration of the hernioplasty (WMD = 44.92 [25.66, 64.18]; 833 hernioplasties). A trend toward higher mesh infection rates was observed in obese patients (RR = 1.41 [0.94, 2.11]; 2,243 hernioplasties) and in patients operated on by a resident (in contrast to a consultant; RR = 1.18 [0.99, 1.40]; 982 hernioplasties). Mesh infections usually resulted in mesh removal, and common pathogens included Staphylococcus spp., Enterococcus spp., and gram-negative bacteria. Patient age, ASA score, smoking, and the duration and emergency setting of the operation were found to be associated with the development of synthetic mesh infection. The heterogeneity of the available evidence should be taken under consideration. Prospective studies with a meticulous follow-up are warranted to further investigate mesh-related infections.

Antibacterial mesh: a novel technique involving naturally occurring cellular proteins

BACKGROUND

Naturally occurring antimicrobial peptides are possibly the "next frontier" in infection prevention. Binding them to mesh could reduce the rate of mesh infections. This study identifies an antimicrobial agent capable of significant antibacterial activity when bound to mesh.

METHODS

Lysozyme, human beta defensin (HBD-3), human cathelicidin (LL-37), and lysostaphin were adsorbed to polypropylene mesh at various concentrations. Treated meshes were placed in a suspension of 1 × 10(6) Staphylococcus aureus. Antibacterial action was monitored by turbidimetric assay, fluorescent imaging, and a colony counting method.

RESULTS

A very high rate of lysis of S aureus cells was observed in the lysostaphin-treated group as measured by optical density; none survived as seen on colony count assays. Optical density for mesh coated with lysozyme, HBD-3, and LL-37 did not differ from untreated controls, with 100% survival rates by colony counts.

CONCLUSION

Lysostaphin had superior antibacterial activity following adsorption to mesh.

Laparoscopic ePTFE mesh repair of incisional and ventral hernias

Incisional hernia is a relatively frequent complication of abdominal surgery. The use of mesh to repair incisional and ventral hernias results in lower recurrence rates compared with primary suture techniques. The laparoscopic approach may be associated with lower postoperative morbidity compared with open procedures. Long-term recurrence rates after laparoscopic ventral and incisional hernias are not well defined. A prospective study of the initial experience of a standardized technique of laparoscopic incisional and ventral hernia repair carried out in a tertiary referral hospital was undertaken between January 2003 and February 2007. Laparoscopic hernia repair was attempted in 71 patients and was successful in 68 (conversion rate 4%). The mean age of the patients identified was 63.1 years (39 men and 31 women). Multiple hernial defects were identified in 38 patients (56%), and the mean overall size of the fascial defects was 166 cm(2). The mean mesh size used was 403 cm(2). The mean operative time was 121 minutes. There were six (9%) major complications in this series, but there were no deaths. Hernia recurrence was noted in four patients (6%) at a mean follow up of 20 months. Our preliminary experience indicates that laparoscopic incisional and ventral hernia repair is technically feasible and has acceptable postoperative morbidity and low early recurrence rates.

Development of a Functional, Internet-Accessible Department of Surgery Outcomes Database

The need for surgical outcomes data is increasing due to pressure from insurance companies, patients, and the need for surgeons to keep their own “report card”. Current data management systems are limited by inability to stratify outcomes based on patients, surgeons, and differences in surgical technique. Surgeons along with research and informatics personnel from an academic, hospital-based Department of Surgery and a state university's Department of Information Technology formed a partnership to develop a dynamic, internet-based, clinical data warehouse. A five-component model was used: data dictionary development, web application creation, participating center education and management, statistics applications, and data interpretation. A data dictionary was developed from a list of data elements to address needs of research, quality assurance, industry, and centers of excellence. A user-friendly web interface was developed with menu-driven check boxes, multiple electronic data entry points, direct downloads from hospital billing information, and web-based patient portals. Data were collected on a Health Insurance Portability and Accountability Act-compliant server with a secure firewall. Protected health information was de-identified. Data management strategies included automated auditing, on-site training, a trouble-shooting hotline, and Institutional Review Board oversight. Real-time, daily, monthly, and quarterly data reports were generated. Fifty-eight publications and 109 abstracts have been generated from the database during its development and implementation. Seven national academic departments now use the database to track patient outcomes. The development of a robust surgical outcomes database requires a combination of clinical, informatics, and research expertise. Benefits of surgeon involvement in outcomes research include: tracking individual performance, patient safety, surgical research, legal defense, and the ability to provide accurate information to patient and payers.