On-demand antimicrobial release from a temperature-sensitive polymer — Comparison with ad libitum release from central venous catheters

Antibacterial Activity of Inverse Vulcanized Polymers

Inverse vulcanization is a bulk polymerization method for synthesizing high sulfur content polymers from elemental sulfur, a byproduct of the petrochemical industry, with vinylic comonomers. There is growing interest in polysulfides as novel antimicrobial agents due to the antimicrobial activity of natural polysulfides found in garlic and onions (Tsao et al. J. Antimicrob. Chemother. 2001, 47, 665-670). Herein, we report the antibacterial properties of several inverse vulcanized polymers against Gram-positive Staphylococcus aureus and Gram-negative Pseudomonas aeruginosa, two common causes of nosocomial infection and pathogens identified by the World Health Organization as priorities for antimicrobial development. High sulfur content polymers were synthesized with different divinyl comonomers and at different sulfur/comonomer ratios, to determine the effect of such variables on the antibacterial properties of the resulting materials. Furthermore, polymers were tested for their potential as antibacterial materials at different temperatures. It was found that the test temperature influenced the antibacterial efficacy of the polymers and could be related to the glass transition temperature of the polymer. These findings provide further understanding of the antibacterial properties of inverse vulcanized polymers and show that such polymers have the potential to be used as antibacterial surfaces.

On-demand pulling-off of magnetic nanoparticles from biomaterial surfaces through implant-associated infectious biofilms for enhanced antibiotic efficacy

Biomaterial-associated infections can occur any time after surgical implantation of biomaterial implants and limit their success rates. On-demand, antimicrobial release coatings have been designed, but in vivo release triggers uniquely relating with infection do not exist, while inadvertent leakage of antimicrobials can cause exhaustion of a coating prior to need. Here, we attach magnetic-nanoparticles to a biomaterial surface, that can be pulled-off in a magnetic field through an adhering, infectious biofilm. Magnetic-nanoparticles remained stably attached to a surface upon exposure to PBS for at least 50 days, did not promote bacterial adhesion or negatively affect interaction with adhering tissue cells. Nanoparticles could be magnetically pulled-off from a surface through an adhering biofilm, creating artificial water channels in the biofilm. At a magnetic-nanoparticle coating concentration of 0.64 mg cm^-2, these by-pass channels increased the penetrability of Staphylococcus aureus and Pseudomonas aeruginosa biofilms towards different antibiotics, yielding 10-fold more antibiotic killing of biofilm inhabitants than in absence of artificial channels. This innovative use of magnetic-nanoparticles for the eradication of biomaterial-associated infections requires no precise targeting of magnetic-nanoparticles and allows more effective use of existing antibiotics by breaking the penetration barrier of an infectious biofilm adhering to a biomaterial implant surface on-demand.

Methodologies for in vitro and in vivo evaluation of efficacy of antifungal and antibiofilm agents and surface coatings against fungal biofilms

Unlike superficial fungal infections of the skin and nails, which are the most common fungal diseases in humans, invasive fungal infections carry high morbidity and mortality, particularly those associated with biofilm formation on indwelling medical devices. Therapeutic management of these complex diseases is often complicated by the rise in resistance to the commonly used antifungal agents. Therefore, the availability of accurate susceptibility testing methods for determining antifungal resistance, as well as discovery of novel antifungal and antibiofilm agents, are key priorities in medical mycology research. To direct advancements in this field, here we present an overview of the methods currently available for determining (i) the susceptibility or resistance of fungal isolates or biofilms to antifungal or antibiofilm compounds and compound combinations; (ii) the in vivo efficacy of antifungal and antibiofilm compounds and compound combinations; and (iii) the in vitro and in vivo performance of anti-infective coatings and materials to prevent fungal biofilm-based infections.

One-step grafting of temperature-and pH-sensitive (N-vinylcaprolactam-co-4-vinylpyridine) onto silicone rubber for drug delivery

A one-step method was implemented to graft N-vinylcaprolactam (NVCL) and 4-vinylpyridine (4VP) onto silicone rubber (SR) films using gamma radiation in order to endow the silicone surface with temperature- and pH-responsiveness, and give it the ability to host and release diclofenac in a controlled manner and thus prevent bacterial adhesion. The effects of radiation conditions (e.g., dose and monomers concentration) on the grafting percentage were evaluated, and the modified films were characterized by means of FTIR-ATR, Raman spectroscopy, calorimetry techniques (DSC and TGA) and contact angle measurements. The films responsiveness to stimuli was evaluated by recording the swelling degree of pristine and modified SR in buffer solutions (critical pH point) and as a function of changes in temperature (Upper Critical Solution Temperature, UCST). The graft copolymers of SR-g-(NVCL-co-4VP) showed good cytocompatibility against fibroblast cells for prolonged times, could host diclofenac and release it in a sustained manner for up to 24 h, and exhibited bacteriostatic activity when challenged against Escherichia coli.

Stimuli-responsive polymers for antimicrobial therapy: drug targeting, contact-killing surfaces and competitive release

INTRODUCTION

Polymers can be designed to modify their features as a function of the level and nature of the surrounding microorganisms. Such responsive polymers can endow drug delivery systems and drug-medical device combination products with improved performance against intracellular infections and biofilms.

AREAS COVERED

Knowledge on microorganism growth environment outside and inside cells and formation of biofilm communities on biological and synthetic surfaces, together with advances in materials science and drug delivery are prompting strategies with improved efficacy and safety compared to traditional systemic administration of antimicrobial agents. This review deals with antimicrobial strategies that rely on: (i) polymers that disintegrate or undergo phase-transitions in response to changes in enzymes, pH and pO2 associated to microorganism growth; (ii) stimuli-responsive polymers that expose contact-killing groups when microorganisms try to adhere; and (iii) bioinspired polymers that recognize microorganisms for triggered (competitive/affinity-driven) drug release.

EXPERT OPINION

Prophylaxis and treatment of infections may benefit from polymers that are responsive to the unique changes that microbial growth causes in the surrounding environment or that even recognize the microorganism itself or its quorum sensing signals. These polymers may offer novel tools for the design of macrophage-, bacteria- and/or biofilm-targeted nanocarriers as well as of medical devices with switchable antibiofouling properties.

Antimicrobial polymers

Better health is basic requirement of human being, but the rapid growth of harmful pathogens and their serious health effects pose a significant challenge to modern science. Infections by pathogenic microorganisms are of great concern in many fields such as medical devices, drugs, hospital surfaces/furniture, dental restoration, surgery equipment, health care products, and hygienic applications (e.g., water purification systems, textiles, food packaging and storage, major or domestic appliances etc.) Antimicrobial polymers are the materials having the capability to kill/inhibit the growth of microbes on their surface or surrounding environment. Recently, they gained considerable interest for both academic research and industry and were found to be better than their small molecular counterparts in terms of enhanced efficacy, reduced toxicity, minimized environmental problems, resistance, and prolonged lifetime. Hence, efforts have focused on the development of antimicrobial polymers with all desired characters for optimum activity. In this Review, an overview of different antimicrobial polymers, their mechanism of action, factors affecting antimicrobial activity, and application in various fields are given. Recent advances and the current clinical status of these polymers are also discussed.