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.

Micrometer-scale droplets of thermotropic liquid crystals (LCs) suspended in aqueous media can act as exquisitely sensitive reporters of environmental analytes. [1][2][3][4][5][6][7][8] Aqueous emulsions of the nematic LC 4-cyano-4'-pentylbiphenyl (5CB), for example, can quantify exposure to bacterial endotoxin (a key component of the outer membranes of Gram-negative bacteria and a major cause of disease and contamination) at pg mL À1 concentrations. [4] The interaction of amphiphilic species with LC droplets promotes changes in orientational order that can be detected as changes in optical appearance [2,8] that reflect both the concentration and structure of the analyte. [2,4] The speed and sensitivity with which these changes occur, combined with the ease with which they can be detected using optical methods (e.g., polarized light microscopy), provide new principles for the design of dispersed, droplet-based sensors that can report on the presence of chemical and biological agents in aqueous solutions. [1][2][3][4][5][6][7][8] Here, we report the design of droplet-based LC sensors that can be immobilized directly on the surfaces of cells. We demonstrate that cells decorated with encapsulated LC droplets can report-in real-time and at the level of single droplets and individual cells-on the presence of toxic agents in surrounding media. This approach provides principles for the design of droplet-based LC sensors and methods for the local (mm scale) detection of agents in cellular environments in ways that are difficult to achieve in situ using free-floating LC droplets or other analytical methods. Our approach is based on the confinement of small droplets of nematic LC within covalently crosslinked, cell-adhesive polymer microcapsules.Our design incorporates several features important for the manipulation and immobilization of LC droplets in cellular environments: 1) encapsulation of LCs in polymeric microcapsules provides means to control LC droplet size, 2) sequestration of LC in a protective membrane prevents LC droplets from coalescing or wetting other surfaces (e.g., culture dishes) and can insulate cells from direct contact with the LC, 3) polymer capsules can be decorated with functionality that can interact with cell membranes to anchor droplets in specific locations, and 4) the use of capsules with semipermeable walls can protect the LC from contact with macromolecular components of culture media, while allowing smaller analytes to pass through unhindered. The work reported here demonstrates proof of concept and underscores the utility of these design features in the context of cell-based sensing using several different well-defined model systems.We selected the thermotropic LC known as E7 (Figure 1 A) here because it exhibits a nematic/isotropic transition temperature (ca. 60 8C) well above that used for mammalian Figure 1. A) Structures of E7 and HTAB. B, C) Schematic showing a SiO 2 particle coated with PEI/PVDMA multilayers (B) and reaction of azlactones to yield amine-functionalized coatings (C). E...

We report the fabrication of reactive and degradable cross-linked polymer multilayers by the reactive/covalent layer-by-layer assembly of a non-degradable azlactone-functionalized polymer [poly(2-vinyl-4,4-dimethylazlactone), PVDMA] with hydrolytically or enzymatically degradable polyamine building blocks. Fabrication of multilayers using PVDMA and a hydrolytically degradable poly(β-amino ester) (PBAE) containing primary amine side chains yielded multilayers (∼100 nm thick) that degraded over ∼12 days in physiologically relevant media. Physicochemical characterization and studies on stable films fabricated using PVDMA and an analogous non-degradable poly(amidoamine) suggested that erosion occurred by chemical hydrolysis of backbone esters in the PBAE components of these assemblies. These degradable assemblies also contained residual amine-reactive azlactone functionality that could be used to impart new functionality to the coatings post-fabrication. Cross-linked multilayers fabricated using PVDMA and the enzymatically degradable polymer poly(l-lysine) were structurally stable for prolonged periods in physiological media, but degraded over ∼24 h when the enzyme trypsin was added. Past studies demonstrate that multilayers fabricated using PVDMA and non-degradable polyamines [e.g., poly(ethylenimine)] enable the design and patterning of useful nano/biointerfaces and other materials that are structurally stable in physiological media. The introduction of degradable functionality into PVDMA-based multilayers creates opportunities to exploit the reactivity of azlactone groups for the design of reactive materials and functional coatings that degrade or erode in environments that are relevant in biomedical, biotechnological, and environmental contexts. This "degradable building block" strategy should be general; we anticipate that this approach can also be extended to the design of amine-reactive multilayers that degrade upon exposure to specific chemical triggers, selective enzymes, or contact with cells by judicious design of the degradable polyamine building blocks used to fabricate the coatings.

We report a study of the wetting and ordering of thermotropic liquid crystal (LC) droplets that are trapped (or “caged”) within micrometer-sized cationic polymeric microcapsules dispersed in aqueous solutions of surfactants. When they were initially dispersed in water, we observed caged, nearly spherical droplets of E7, a nematic LC mixture, to occupy ∼40% of the interior volume of the polymeric capsules [diameter of 6.7 ± 0.3 μm, formed via covalent layer-by-layer assembly of branched polyethylenimine and poly(2-vinyl-4,4-dimethylazlactone)] and to contact the interior surface of the capsule wall at an angle of ∼157 ± 11°. The internal ordering of LC within the droplets corresponded to the so-called bipolar configuration (distorted by contact with the capsule walls). While the effects of dodecyltrimethylammonium bromide (DTAB) and sodium dodecyl sulfate (SDS) on the internal ordering of “free” LC droplets are similar, we observed the two surfactants to trigger strikingly different wetting and configurational transitions when LC droplets were caged within polymeric capsules. Specifically, upon addition of SDS to the aqueous phase, we observed the contact angles (θ) of caged LC on the interior surface of the capsule to decrease, resulting in a progression of complex droplet shapes, including lenses (θ ≈ 130 ± 10°), hemispheres (θ ≈ 89 ± 5°), and concave hemispheres (θ < 85°). The wetting transitions induced by SDS also resulted in changes in the internal ordering of the LC to yield states topologically equivalent to axial and radial configurations. Although topologically equivalent to free droplets, the contributions that surface anchoring, LC elasticity, and topological defects make to the free energy of caged LC droplets differ from those of free droplets. Overall, these results and others reported herein lead us to conclude that caged LC droplets offer a platform for new designs of LC-droplet-based responsive soft matter that cannot be realized in dispersions of free droplets.

We report the reactive layer-by-layer assembly of amine-reactive polymer multilayers using an azlactone-functionalized polymer and small-molecule diamine linkers. This approach yields crosslinked polymer/linker-type films that can be further functionalized, after fabrication, by treatment with functional primary amines, and provides opportunities to incorporate other useful functionality that can be difficult to introduce using other polyamine building blocks. Films fabricated using poly(2-vinyl-4,4-dimethylazlactone) (PVDMA) and three model non-degradable aliphatic diamine linkers yielded reactive thin films that were stable upon incubation in physiologically relevant media. In contrast, films fabricated using PVDMA and varying amounts of the model disulfide-containing diamine linker cystamine were stable in normal physiological media, but were unstable and eroded rapidly upon exposure to chemical reducing agents. We demonstrate that this approach can be used to fabricate functionalized polymer microcapsules that degrade in reducing environments, and that rates of erosion, extents of capsule swelling, and capsule degradation can be tuned by control over the relative concentration of cystamine linker used during fabrication. The polymer/linker approach used here expands the range of properties and functions that can be designed into reactive PVDMA-based coatings, including functionality that can degrade, erode, and undergo triggered destruction in aqueous environments. We therefore anticipate that these approaches will be useful for the functionalization, patterning, and customization of coatings, membranes, capsules, and interfaces of potential utility in biotechnical or biomedical contexts and other areas where degradation and transience are desired. The proof of concept strategies reported here are likely to be general, and should prove useful for the design of amine-reactive coatings containing other functional structures by judicious control of the structures of the linkers used during assembly.