Many types of slippery liquid-infused porous surfaces (or ‘SLIPS’) can resist adhesion and colonization by microorganisms. These ‘slippery’ materials thus offer new approaches to prevent fouling on a range of commercial and industrial surfaces, including biomedical devices. However, while SLIPS can prevent fouling on surfaces to which they are applied, they can currently do little to prevent the proliferation of non-adherent (planktonic) organisms, stop them from colonizing other surfaces, or prevent them from engaging in other behaviors that could lead to infection and associated burdens. Here, we report an approach to the design of multi-functional SLIPS that addresses these issues and expands the potential utility of slippery surfaces in antimicrobial contexts. Our approach is based on the incorporation and controlled release of small-molecule antimicrobial agents from the porous matrices used to host infused slippery oil phases. We demonstrate that SLIPS fabricated using nanoporous polymer multilayers can prevent short- and longer-term colonization and biofilm formation by four common fungal and bacterial pathogens (Candida albicans, Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus), and that the polymer and oil phases comprising these materials can be exploited to load and sustain the release of triclosan, a model hydrophobic and broad-spectrum antimicrobial agent, into surrounding media. This approach both improves the inherent anti-fouling properties of these materials and endows them with the ability to efficiently kill planktonic pathogens. Finally, we show that this approach can be used to fabricate dual-action SLIPS on complex surfaces, including the luminal surfaces of flexible catheter tubes. This strategy has the potential to be general; we anticipate that the materials, strategies, and concepts reported here will enable new approaches to the design of slippery surfaces with improved anti-fouling properties and open the door to new applications of slippery liquid-infused materials that host or promote the release of a variety of other active agents.

No abstract

Candida albicans is one of the most prevalent fungal pathogens, causing both mucosal candidiasis and invasive candidemia. Antimicrobial peptides (AMPs), part of the human innate immune system, have been shown to exhibit antifungal activity but have not been effective as pharmaceuticals because of low activity and selectivity in physiologically relevant environments. Nevertheless, studies on α-peptide AMPs have revealed key features that can be designed into more stable structures, such as the 14-helix of β-peptide-based oligomers. Here, we report on the ways in which two of those features, hydrophobicity and helicity, govern the activity and selectivity of 14-helical β-peptides against C. albicans and human red blood cells. Our results reveal both antifungal activity and hemolysis to correlate to hydrophobicity, with intermediate levels of hydrophobicity leading to high antifungal activity and high selectivity toward C. albicans. Helical structure-forming propensity further influenced this window of selective antifungal activity, with more stable helical structures eliciting specificity for C. albicans over a broader range of hydrophobicity. Our findings also reveal cooperativity between hydrophobicity and helicity in regulating antifungal activity and specificity. The results of this study provide critical insight into the ways in which hydrophobicity and helicity govern the activity and specificity of AMPs and identify criteria that may be useful for the design of potent and selective antifungal agents.

Candida albicans is the most common fungal pathogen responsible for hospital-acquired infections. Most C albicans infections are associated with the implantation of medical devices that act as points of entry for the pathogen and as substrates for the growth of fungal biofilms that are notoriously difficult to eliminate by systemic administration of conventional antifungal agents. In this study, we report a fill-and-purge approach to the layer-by-layer fabrication of biocompatible, nanoscale ‘polyelectrolyte multilayers’ (PEMs) on the luminal surfaces of flexible catheters, and an investigation of this platform for the localized, intraluminal release of a cationic β-peptide-based antifungal agent. We demonstrate that polyethylene catheter tubes with luminal surfaces coated with multilayers ~700 nm thick fabricated from poly-L-glutamic acid (PGA) and poly-L-lysine (PLL) can be loaded, post-fabrication, by infusion with β-peptide, and that this approach promotes extended intraluminal release of this agent (over ~4 months) when incubated in physiological media. The β-peptide remained potent against intraluminal inoculation of the catheters with C albicans and substantially reduced the formation of C albicans biofilms on the inner surfaces of film-coated catheters. Finally, we report that these β-peptide-loaded coatings exhibit antifungal activity under conditions that simulate intermittent catheter use and microbial challenge for at least three weeks. We conclude that β-peptide-loaded PEMs offer a novel and promising approach to kill C albicans and prevent fungal biofilm formation on surfaces, with the potential to substantially reduce the incidence of device-associated infections in indwelling catheters. β-Peptides comprise a promising new class of antifungal agents that could help address problems associated with the use of conventional antifungal agents. The versatility of the layer-by-layer approach used here thus suggests additional opportunities to exploit these new agents in other biomedical and personal care applications in which fungal infections are endemic.

Candida albicans is the most prevalent cause of fungal infections and treatment is further complicated by the formation of drug resistant biofilms, often on the surfaces of implanted medical devices. In recent years, the incidence of fungal infections by other pathogenic Candida species such as C. glabrata, C. parapsilosis and C. tropicalis has increased. Amphiphilic, helical β-peptide structural mimetics of natural antimicrobial α-peptides have been shown to exhibit specific planktonic antifungal and anti-biofilm formation activity against C. albicans in vitro. Here, we demonstrate that β-peptides are also active against clinically isolated and drug resistant strains of C. albicans and against other opportunistic Candida spp. Different Candida species were susceptible to β-peptides to varying degrees, with C. tropicalis being the most and C. glabrata being the least susceptible. β-peptide hydrophobicity directly correlated with antifungal activity against all the Candida clinical strains and species tested. While β-peptides were largely ineffective at disrupting existing Candida biofilms, hydrophobic β-peptides were able to prevent the formation of C. albicans, C. glabrata, C. parapsilosis and C. tropicalis biofilms. The broad-spectrum antifungal activity of β-peptides against planktonic cells and in preventing biofilm formation suggests the promise of this class of molecules as therapeutics.

Candida albicans is the most prevalent cause of hospital-acquired fungal infections and forms biofilms on indwelling medical devices that are notoriously difficult to treat or remove. We recently demonstrated that the colonization of C. albicans on the surfaces of catheter tube segments can be reduced in vitro by coating them with polyelectrolyte multilayers (PEMs) that release a potent antifungal β-peptide. Here, we report on the impact of polymer structure and film composition on both the inherent and β-peptide-mediated ability of PEM-coated catheters to prevent or reduce the formation of C. albicans biofilms in vitro and in vivo using a rat model of central venous catheter infection. Coatings fabricated using polysaccharide-based components [hyaluronic acid (HA) and chitosan (CH)] and coatings fabricated using polypeptide-based components [poly-l-lysine (PLL) and poly-l-glutamic acid (PGA)] both served as reservoirs for the loading and sustained release of β-peptide, but differed substantially in loading and release profiles and in their inherent antifungal properties (e.g., the ability to prevent colonization and biofilm growth in the absence of β-peptide). In particular, CH/HA films exhibited inherent antifungal and antibiofilm behaviors in vitro and in vivo, a result we attribute to the incorporation of CH, a weak polycation demonstrated to exhibit antimicrobial properties in other contexts. The antifungal properties of both types of films were improved substantially when β-peptide was incorporated. Catheter segments coated with β-peptide-loaded CH/HA and PLL/PGA films were both strongly antifungal against planktonic C. albicans and the formation of surface-associated biofilms in vitro and in vivo. Our results demonstrate that PEM coatings provide a useful platform for the design of new antifungal materials, and suggest opportunities to design multifunctional or dual-action platforms to prevent or reduce the severity of fungal infections in applied biomedical contexts or other areas in which fungal biofilms are endemic.

Antimicrobial peptides (AMPs) are attractive antifungal drug candidates because they kill microbes via membrane disruption and are thus less likely to provoke development of resistance. Low selectivity for fungal vs. human cells and instability in physiological environments have limited the development of AMPs as therapeutics, but peptidomimetic AMPs can overcome these obstacles and also provide useful insight into AMP structure-function relationships. Here, we describe antifungal peptidomimetic α/β-peptides templated on the natural α-peptidic AMP aurein 1.2. These α/β-aurein analogues fold into i → i+4 H-bonded helices that present arrays of side chain functionality in a manner virtually identical to that of aurein 1.2. By varying charge, hydrophobicity, conformational stability, and α/β-amino acid organization we designed active and selective α/β-peptide aurein analogues that exhibit minimum inhibitory concentrations (MIC) against the opportunistic pathogen Candida albicans that are 4-fold lower than that of aurein 1.2 and elicit less than 5% hemolysis at the MIC. These α/β-aurein analogues are promising candidates for development as antifungal therapeutics and as tools to elucidate mechanisms of AMP activity and specificity.

Catheter-associated urinary tract infections (CAUTI) are the most common type of hospital-acquired infection, with more than 30 million catheters placed annually in the US and a 10–30% incidence of infection. Candida albicans forms fungal biofilms on the surfaces of urinary catheters and is the leading cause of fungal urinary tract infections. As a step toward new strategies that could prevent or reduce the occurrence of C. albicans-based CAUTI, we investigated the ability of antifungal β-peptide-based mimetics of antimicrobial peptides (AMPs) to kill C. albicans and prevent biofilm formation in synthetic urine. Many α-peptide-based AMPs exhibit antifungal activities, but are unstable in high ionic strength media and are easily degraded by proteases—features that limit their use in urinary catheter applications. Here, we demonstrate that β-peptides designed to mimic the amphiphilic helical structures of AMPs retain 100% of their structural stability and exhibit antifungal and anti-biofilm activity against C. albicans in a synthetic medium that mimics the composition of urine. We demonstrate further that these agents can be loaded into and released from polymer-based multilayer coatings applied to polyurethane, polyethylene, and silicone tubing commonly used as urinary catheters. Our results reveal catheters coated with β-peptide-loaded multilayers to kill planktonic fungal cells for up to 21 days of intermittent challenges with C. albicans and prevent biofilm formation on catheter walls for at least 48 hours. These new materials and approaches could lead to advances that reduce the occurrence of fungal CAUTI.