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

**Mar Fernández-Gutiérrez 1,2 , Bárbara Pérez-Köhler 2,3,4,\* , Selma Benito-Martínez 2,4,5 , Francisca García-Moreno 2,4,5, Gemma Pascual 2,3,4,\* , Luis García-Fernández 1,2 , María Rosa Aguilar 1,2 , Blanca Vázquez-Lasa 1,2 and Juan Manuel Bellón 2,4,5**


Received: 15 July 2020; Accepted: 13 August 2020; Published: 15 August 2020

**Abstract:** 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* (10<sup>6</sup> 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.

**Keywords:** biocomposite; chitosan; chlorhexidine; coating; hernia; mesh infection; nanoparticles; PLGA; polypropylene; rifampicin

### **1. Introduction**

In hernia repair, the implantation of biomaterials constitutes the main surgical strategy aimed at reinforcing the abdominal wall, providing a tension-free repair that restores the biological, biomechanical, and functional properties of the damaged tissue [1]. Among the numerous advantages afforded by these devices, the use of hernia mesh materials allows for the reduction of recurrence rates and recovery period [2]. Nevertheless, mesh implantation is not exempt from drawbacks, being that infection is one of the most severe postoperative complications having a big impact on patients and the healthcare system [3]. Many factors influence the incidence of mesh-related infection, such as the

type of hernia pathology, the surgical procedure carried out, the prostheses implanted, and the patient co-morbidities among the most relevant [4].

Typically, biomaterial-related infections are triggered when bacteria invade the wound and adhere to the surface of the implanted mesh and surrounding tissues. Once adhered, bacteria proliferate and interact with others, forming clusters that colonize the implant [5]. Many of these bacteria secrete an extracellular polysaccharide matrix that covers the cluster and strengthen their adhesion to the surface, establishing a biofilm [6]. Protected by this barrier, bacteria are strongly attached to the substrate and exert high resistance to the action of antibiotics and host defense cells [7], events that make biofilm-based infections extremely difficult to treat. Most of these infections, either involving biofilms or not, are caused by *Staphylococcus aureus* and *S. epidermidis* [8].

Considering that bacterial adhesion to the implant surface plays a key role in the pathogenesis of mesh-related infections, there is a growing interest in developing novel surgical meshes endowed with antibacterial properties. In this sense, coating meshes with drug-loaded polymeric systems is currently one of the main approaches being evaluated by researchers [1,9]. In recent years, numerous laboratory and preclinical studies demonstrated that antimicrobial coatings could reduce mesh-related infections by inhibiting bacterial adhesion, implant colonization, and biofilm formation [3,10,11].

Different antimicrobials have been used to endow hernia mesh materials with antibacterial properties. Silver metal [12] or antibiotics such as gentamicin [13], vancomycin [14], and rifampicin–minocycline combinations [15] are among the most widely used drugs for hernia mesh coating. Although exerting a potent antibacterial activity, it is widely known that antibiotics carry the risk of provoking bacterial resistances, thus, the prophylactic use of these biocides should be reduced to a minimum. Antiseptic agents emerge as a plausible alternative to antibiotics for these purposes. From the wide variety of antiseptics available, some have been used to coat mesh materials with promising results, being a potential tool for developing antimicrobial devices. Such is the case of broad-spectrum antiseptics like triclosan [16] and chlorhexidine [17] both of which are currently being applied in the manufacturing of antimicrobial surgical devices for clinical use [11].

The simplest way to coat a mesh is via dipping or soaking the device in aqueous solutions containing the target antimicrobial immediately before its implantation. Although this strategy is often applied in human clinics [18], it fails to provide controlled levels of the drug at the surgical site. This limitation can be alleviated if the mesh is coated with a polymeric compound loaded with antimicrobials. Theoretically, antibacterial mesh polymeric coatings must provide a local, sustained, and slow drug release at the implant site, neither producing local nor systemic detrimental effects due to the diffusion of the antimicrobial [14]. Furthermore, coatings must be non-toxic and biocompatible, ensuring adequate mesh integration into the host tissue without compromising the biomechanical properties of the implant [19]. Over the last decade, many polymeric systems to be used as drug carriers were developed and applied for the prophylactic coating of hernia repair materials, with promising outcomes [11,20]. From this plethora of candidates, the polymeric systems loaded with drug releasing nanoparticles represent one of the most effective approaches to endow these devices with antibacterial activity [5].

In the present study, we developed a novel antimicrobial polymeric coating loaded with biodegradable nanoparticles containing chlorhexidine or rifampicin for hernia mesh materials. The nanoparticles were loaded with two different antimicrobials, chlorhexidine or rifampicin, as candidates for antiseptic and antibiotic agents, respectively. The former (C22H30Cl2N10) is a cationic biguanide antiseptic widely used as a preoperative skin disinfectant [21]. The latter (C43H58N4O12) is considered one of the most potent semisynthetic antibiotics to treat bacterial infections [22]. Both drugs were selected due to their antimicrobial activity as well as their promising application with biomedical devices. The morphology, drug release profile, cytocompatibility, and antimicrobial performance of coated polypropylene meshes was evaluated in vitro using a model of bacterial mesh infection caused by *S. aureus* and *S. epidermidis*.
