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

An antibacterial biologic patch based on bacterial cellulose for repair of infected hernias

Infection-associated complications and repair failures and antibiotic resistance have emerged as a formidable challenge in hernia repair surgery. Consequently, the development of antibiotic-free antibacterial patches for hernia repair has become an exigent clinical necessity. Herein, a GBC/Gel/LL37 biological patch (biopatch) with exceptional antibacterial properties is fabricated by grafting 2-Methacryloyloxyethyl trimethylammonium chloride (METAC), a unique quaternary ammonium salt with vinyl, onto bacterial cellulose (GBC), followed by compounding with gelatin (Gel) and LL37. The GBC/Gel/LL37 biopatch exhibits stable swelling capacity, remarkable mechanical properties, flexibility, and favorable biocompatibility. The synergistic effect of METAC and LL37 confers upon the GBC/Gel/LL37 biopatch excellent antibacterial efficacy against Staphylococcus aureus and Escherichia coli, effectively eliminating invading bacteria without the aid of exogenous antibiotics in vivo while significantly reducing local acute inflammation caused by infection. Furthermore, the practical efficacy of the GBC/Gel/LL37 biopatch is evaluated in an infected ventral hernia model, revealing that the GBC/Gel/LL37 biopatch can prevent the formation of visceral adhesions, facilitate the repair of infected ventral hernia, and effectively mitigate chronic inflammation. The prepared antibacterial GBC/Gel/LL37 biopatch is very effective in dealing with the risk of infection in hernia repair surgery and offers potential clinical opportunities for other soft injuries, exhibiting considerable clinical application prospects.

Abdominal wall hernia repair: from prosthetic meshes to smart materials

Hernia reconstruction is one of the most frequently practiced surgical procedures worldwide. Plastic surgery plays a pivotal role in reestablishing desired abdominal wall structure and function without the drawbacks traditionally associated with general surgery as excessive tension, postoperative pain, poor repair outcomes, and frequent recurrence. Surgical meshes have been the preferential choice for abdominal wall hernia repair to achieve the physical integrity and equivalent components of musculofascial layers. Despite the relevant progress in recent years, there are still unsolved challenges in surgical mesh design and complication settlement. This review provides a systemic summary of the hernia surgical mesh development deeply related to abdominal wall hernia pathology and classification. Commercial meshes, the first-generation prosthetic materials, and the most commonly used repair materials in the clinic are described in detail, addressing constrain side effects and rational strategies to establish characteristics of ideal hernia repair meshes. The engineered prosthetics are defined as a transit to the biomimetic smart hernia repair scaffolds with specific advantages and disadvantages, including hydrogel scaffolds, electrospinning membranes, and three-dimensional patches. Lastly, this review critically outlines the future research direction for successful hernia repair solutions by combing state-of-the-art techniques and materials.

Dual-jet electrospun PDLGA/PCU nonwovens as promising mesh implant materials with controlled release of sirolimus and diclofenac

Dual-jet electrospinning was employed to produce two-component, partially degradable drug releasing nonwovens with interlacing of poly(D,L-lactide-co-glycolide) (PDLGA) and different poly(carbonate urethanes) (PCUs). Diclofenac sodium and sirolimus were released simultaneously from the copolyester carrier. The research focused on determining of release profiles of drugs, depending on the hydrophilicity of introduced PCU nanofibers. The influence of drugs incorporation on the hydrolytic degradation of the PDLGA and mechanical properties of nonwovens was also studied. Evaluation for interaction with cells in vitro was investigated on a fibroblast cell line in cytotoxicity and surface adhesion tests. Significant changes in drugs release rate, depending on the applied PCU were observed. It was also noticed, that hydrophilicity of drugs significantly influenced the hydrolytic degradation mechanism and surface erosion of the PDLGA, as well as the tensile strength of nonwovens. Tests carried out on cells in an in vitro experiment showed that introduction of sirolimus caused a slight reduction in the viability of fibroblasts as well as a strong limitation in their capability to colonize the surface of fibers. Due to improvement of mechanical strength and the ability to controlled drugs release, the obtained material may be considered as prospect surgical mesh implant in the treatment of hernia.

In Vitro Cytotoxicity, Colonisation by Fibroblasts and Antimicrobial Properties of Surgical Meshes Coated with Bacterial Cellulose

Hernia repairs are the most common abdominal wall elective procedures performed by general surgeons. Hernia-related postoperative infective complications occur with 10% frequency. To counteract the risk of infection emergence, the development of effective, biocompatible and antimicrobial mesh adjuvants is required. Therefore, the aim of our in vitro investigation was to evaluate the suitability of bacterial cellulose (BC) polymer coupled with gentamicin (GM) antibiotic as an absorbent layer of surgical mesh. Our research included the assessment of GM-BC-modified meshes’ cytotoxicity against fibroblasts ATCC CCL-1 and a 60-day duration cell colonisation measurement. The obtained results showed no cytotoxic effect of modified meshes. The quantified fibroblast cells levels resembled a bimodal distribution depending on the time of culturing and the type of mesh applied. The measured GM minimal inhibitory concentration was 0.47 µg/mL. Results obtained in the modified disc-diffusion method showed that GM-BC-modified meshes inhibited bacterial growth more effectively than non-coated meshes. The results of our study indicate that BC-modified hernia meshes, fortified with appropriate antimicrobial, may be applied as effective implants in hernia surgery, preventing risk of infection occurrence and providing a high level of biocompatibility with regard to fibroblast cells.

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.

Characterization of Inflammatory and Fibrotic Encapsulation Responses of Implanted Materials with Bacterial Infection

Medical device infections are costly, while preclinical assessment of antimicrobial properties for new materials is time intensive and imperfect at capturing the interrelated aspects of infection response and wound resolution. Herein, we developed an in vivo model for quantification of inflammatory and biocompatibility responses in the presence of a sustained implant-associated infection. The antimicrobial effectiveness of commercially available polymer materials was compared to that of thermoplastic polyurethane (TPU) materials modified with putative antimicrobial strategies as example test materials. Materials were incubated with bioluminescent Escherichia coli prior to implantation in a dorsal subcutaneous pocket in rats with an additional intraluminal bolus of bacteria. Infection kinetics were monitored with bioluminescence, and inflammatory infiltrate and fibrous capsule thickness were determined from stained histological sections. Our model resulted in a persistent infection, sensitive to antimicrobial effects, as the materials modified with a putative antimicrobial surface were able to significantly reduce the level of infection in animals at day 4 postimplantation with efficacy similar to that of commercially available antimicrobial drug-eluting polymers (positive controls). At day 30 postimplantation, the antimicrobial surface modified TPU tubing was found to promote complete elimination of intraluminal bacteria in the absence of antibiotics. Differences were also measurable in acute inflammation, as Wright-Giemsa staining demonstrated reduced inflammatory cell infiltration at day 4 postimplantation for antimicrobial TPU materials. Additionally, antimicrobial materials exhibited reduced fibrous capsule thickness coinciding with infection resolution, as compared to unmodified TPU controls. The developed model can be utilized for testing antimicrobial polymers in the context of a prolonged infection while also revealing concurrent differences in the infiltrating immune cell profiles and fibrous capsule thickness, thus improving the relevance of preclinical medical device material testing.

Prosthetic meshes for hernia repair: State of art, classification, biomaterials, antimicrobial approaches, and fabrication methods

Worldwide, hernia repair represents one of the most frequent surgical procedures encompassing a global market valued at several billion dollars. This type of surgery usually requires the implantation of a mesh that needs the appropriate chemical, physical and biological properties for the type of repair. This review thus presents a description of the types of hernias, current hernia repair methods, and the state of the art of prosthetic meshes for hernia repair providing the most important meshes used in clinical practice by surgeons working in this area classified according to their biological or chemical nature, morphology and whether bioabsorbable or not. We emphasise the importance of surgical site infection in herniatology, how to deal with this microbial problem, and we go further into the future research lines on the production of advanced antimicrobial meshes to improve hernia repair and prevent microbial infections, including multidrug-resistant strains. A great deal of progress has been made in this biomedical field in the last decade. However, we are still far from an ideal antimicrobial mesh that can also provide excellent integration to the abdominal wall, mechanical performance, low visceral adhesion and minimal inflammatory or foreign body reactions, among many other problems.

Nonthermal Plasma Treatment Improves Uniformity and Adherence of Cyclodextrin-Based Coatings on Hydrophobic Polymer Substrates

Low surface energy substrates, which include many plastics and polymers, present challenges toward achieving uniform, adherent coatings, thus limiting intended coating function. These inert materials are common in various applications due to favorable bulk, despite suboptimal surface, properties. The ability to functionally coat low surface energy substrates holds broad value for uses across medicine and industry. Cyclodextrin-based materials represent an emerging, widely useful class of coatings, which have previously been explored for numerous purposes involving sustained release, enhanced sorption, and reversible reuse thereof. In this study, substrate exposure to nonthermal plasma was explored as a novel means to improve uniformity and adherence of cyclodextrin-based polyurethane coatings upon unreceptive polypropylene substrates. Plasma effects on substrates were investigated using contact angle goniometry and X-ray photoelectron spectroscopy (XPS). Plasma impact on coating uniformity was assessed through visualization directly and microscopically. Plasma effects on coating adhesion and bonding were studied with mechanical lap-shear testing and XPS, respectively. Substrate surface wettability and oxygen content increased with plasma exposure, and these modifications were associated with improved coating uniformity, adhesion, and interfacial covalent bonding. Findings demonstrate utility of, and elucidate mechanisms behind, plasma-based surface activation for improving coating uniformity, adherence, and performance on inert polymeric substrates.

Affinity-Based Polymers Provide Long-Term Immunotherapeutic Drug Delivery Across Particle Size Ranges Optimal for Macrophage Targeting

Drug delivery to specific arms of the immune system can be technically challenging to provide prolonged drug release while limiting off-target toxicity given the limitations of current drug delivery systems. In this work, we test the design of a cyclodextrin (CD) polymer platform to extend immunomodulatory drug delivery via affinity interactions for sustained release at multiple size scales. The parameter space of synthesis variables influencing particle nucleation and growth (pre-incubation time and stirring speed) and post-synthesis grinding effects on resulting particle diameter were characterized. We demonstrate that polymerized CD forms exhibit size-independent release profiles of the small molecule drug lenalidomide (LND) and can provide improved drug delivery profiles versus macro-scale CD polymer disks in part due to increased loading efficiency. CD polymer microparticles and smaller, ground particles demonstrated no significant cytotoxicity as compared to the base CD monomer when co-incubated with fibroblasts. Uptake of ground CD particles was significantly higher following incubation with RAW 264.7 macrophages in culture over standard CD microparticles. Thus, the affinity/structure properties afforded by polymerized CD allow particle size to be modified to affect cellular uptake profiles independently of drug release rate for applications in cell-targeted drug delivery.

A Polymeric Delivery System Enables Controlled Release of Genipin for Spatially-Confined In Situ Crosslinking of Injured Connective Tissues

An emerging approach toward repair of connective tissues applies exogenous crosslinkers to mechanically augment injured structures in vivo. One crosslinker that has been explored for this purpose is the plant-derived small molecule genipin. However, genipin's high reactivity to primary amines in proteins, small size, and high diffusion coefficient necessitate localizing and controlling its delivery to avoid off-target or adverse effects. In this study, genipin-loaded polymers were evaluated for sustained local administration. Insoluble polymers comprising subunits of α-, β-, or γ-cyclodextrin, cyclic oligosaccharides possessing increasing cavity sizes, were compared to polymers comprising subunits of the non-cyclic polysaccharide dextran. Polymers made from β-cyclodextrin showed prolonged genipin release for over ten times longer than polymers made from α- or γ-cyclodextrins or dextran, indicating that genipin possesses molecular affinity for the β-cyclodextrin cavity. Modeling of complexation between genipin and cyclodextrin hosts supported this finding. Genipin released from all polymers was confirmed to be functional by exogenous collagen crosslinking through fluorometric and mechanical readouts. Co-incubation of genipin-loaded polymers with bovine tendon explants showed genipin crosslink-mediated coloration that was confined to the sites of exposure. Altogether, results indicate that host-guest interactions within a polymeric delivery vehicle can help to control and confine genipin release.

Development of Biocomposite Polymeric Systems Loaded with Antibacterial Nanoparticles for the Coating of Polypropylene Biomaterials

The development of a biocomposite polymeric system for the antibacterial coating of polypropylene mesh materials for hernia repair is reported. Coatings were constituted by a film of chitosan containing randomly dispersed poly(d,l-lactide-co-glycolide) (PLGA) nanoparticles loaded with chlorhexidine or rifampicin. The chlorhexidine-loaded system exhibited a burst release during the first day reaching the release of the loaded drug in three or four days, whereas rifampicin was gradually released for at least 11 days. Both antibacterial coated meshes were highly active against Staphylococcus aureus and Staphylococcus epidermidis (10⁶ CFU/mL), displaying zones of inhibition that lasted for 7 days (chlorhexidine) or 14 days (rifampicin). Apparently, both systems inhibited bacterial growth in the surrounding environment, as well as avoided bacterial adhesion to the mesh surface. These polymeric coatings loaded with biodegradable nanoparticles containing antimicrobials effectively precluded bacterial colonization of the biomaterial. Both biocomposites showed adequate performance and thus could have potential application in the design of antimicrobial coatings for the prophylactic coating of polypropylene materials for hernia repair.

Elucidating the Structure-Function Relationship of Solvent and Cross-Linker on Affinity-Based Release from Cyclodextrin Hydrogels

Minocycline (MNC) is a tetracycline antibiotic capable of associating with cyclodextrin (CD), and it is a frontline drug for many instances of implant infection. Due to its broad-spectrum activity and long half-life, MNC represents an ideal drug for localized delivery; however, classic polymer formulations, particularly hydrogels, result in biphasic release less suitable for sustained anti-microbial action. A polymer delivery system capable of sustained, steady drug delivery rates poses an attractive target to maximize the antimicrobial activity of MNC. Here, we formed insoluble hydrogels of polymerized CD (pCD) with a range of crosslinking densities, and then assessed loading, release, and antimicrobial activity of MNC. MNC loads between 5-12 wt % and releases from pCD hydrogels for >14 days. pCD loaded with MNC shows extended antimicrobial activity against S. aureus for >40 days and E. coli for >70 days. We evaluated a range of water/ethanol blends to test our hypothesis that solvent polarity will impact drug-CD association as a function of hydrogel swelling and crosslinking. Increased polymer crosslinking and decreased solvent polarity both reduced MNC loading, but solvent polarity showed a dramatic reduction independent of hydrogel swelling. Due to its high solubility and excellent delivery profile, MNC represents a unique drug to probe the structure-function relationship between drug, affinity group, and polymer crosslinking ratio.

Fabrication and Characterization of Composite Meshes Loaded with Antimicrobial Peptides

Biomaterials-centered infection or implant-associated infection plays critical roles in all areas of medicine with implantable devices. The widespread over use of antibiotics has caused severe bacterial resistance and even super bugs. Therefore, the development of anti-infection implantable devices with non-antibiotic-based new antimicrobial agents is indeed a priority for all of us. In this study, antimicrobial composite meshes were fabricated with broad-spectrum antimicrobial peptides (AMPs). Macroporous polypropylene meshes with poly-caprolactone electrospun nanosheets were utilized as a substrate to load AMPs and gellan gum presented as a media to gel with AMPs. Different amounts of AMPs were loaded onto gellan gum to determine the appropriate dose. The surface morphologies, Fourier-transform infrared spectroscopy spectra, in vitro release profiles, mechanical performances, in vitro antimicrobial properties, and cytocompatibility of composite scaffolds were evaluated. Results showed that AMPs were loaded into the meshes successfully, the in vitro release of AMPs in phosphate-buffered saline was prolonged, and less than 60% peptides were released in 10 days. The mechanical properties of composite meshes were also within the scope of several commercial surgical meshes. Composite meshes with the AMP loading amount of over 3 mg/cm² showed inhibition against both Gram-negative and Gram-positive bacteria effectively, while they presented no toxicity to mammalian cells even at a loading amount of 10 mg/cm². These results demonstrate a new simple and practicable method to offer antimicrobial properties to medical devices for hernia repair.

Cyclodextrin Polymer Preserves Sirolimus Activity and Local Persistence for Antifibrotic Delivery over the Time Course of Wound Healing

Fibrosis and dysphagic stricture of the esophagus is a major unaddressed problem often accompanying endoscopic removal of esophageal cancers and precancerous lesions. While weekly injections of antiproliferative agents show potential for improved healing, repeated injections are unlikely clinically and may alternatively be replaced by creating an esophageal drug delivery system. Affinity-based polymers have previously shown success for continuous delivery of small molecules for weeks to months. Herein, we explored the potential of an affinity-based microparticle to provide long-term release of an antiproliferative drug, sirolimus. In molecular docking simulations and surface plasmon resonance experiments, sirolimus was found to have suitable affinity for beta-cyclodextrin, while dextran, as a low affinity control, was validated. Polymerized beta-cyclodextrin microparticles exhibited 30 consecutive days of delivery of sirolimus during in vitro release studies. In total, the polymerized beta-cyclodextrin microparticles released 36.9 mg of sirolimus per milligram of polymer after one month of incubation in vitro. Taking daily drug release aliquots and applying them to PT-K75 porcine mucosal fibroblasts, we observed that cyclodextrin microparticle delivery preserved bioactivity of sirolimus inhibiting proliferation by 27-67% and migration of fibroblasts by 28-100% of buffer treated controls in vitro. Testing for esophageal injection site losses, no significant loss was incurred under simulated saliva flow for 10 min, and 16.7% of fluorescently labeled polymerized cyclodextrin microparticle signal was retained at 28 days after submucosal injection in esophageal tissue ex vivo versus only 4% of the initial amount remaining for free dye molecules injected alone. By combining affinity-based drug delivery for continuous long-term release with a microparticle platform that is injectable yet remains localized in tissue interstitium, this combination platform demonstrates promise for preventing esophageal fibrosis and stricture.

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.

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.