Polymer Multilayers that Promote the Rapid Release and Contact Transfer of DNA

We report a layer-by-layer approach to the fabrication of thin polymer-based multilayers that release DNA rapidly in physiologically relevant environments. This approach exploits the properties of a weak anionic polyelectrolyte [poly(acrylic acid); PAA] to disrupt ionic interactions and promote disassembly in coatings that otherwise erode slowly. We investigated this approach using multilayers fabricated from plasmid DNA and linear poly(ethylenimine) (LPEI), a model synthetic cationic polymer used widely for DNA delivery. LPEI/DNA multilayers erode and release DNA slowly over ∼4 days when incubated in PBS buffer. In contrast, substitution of every other layer of DNA with PAA lead to thin films that released DNA rapidly, with >60% being released in the first 5 min. These quick-release coatings release bioactive DNA and can be used to fabricate uniform coatings on a variety of objects, including the tips of inflatable balloon catheters. We demonstrate that these coatings can promote high levels of cell transfection in vitro and the robust contact transfer and expression of DNA in vascular tissue in vivo using a rat model of vascular injury. These materials provide useful alternatives to multilayers and other coatings that promote the prolonged release of DNA. More broadly, approaches that depart from the use of degradable polymers to promote film erosion create opportunities to design new gene delivery coatings using a broader range of polymer-based building blocks designed for other gene delivery applications. With further development, this approach could thus provide a new and useful platform for the rapid contact transfer of DNA to cells and tissues of interest in a range of fundamental and applied contexts.

Nanoporous Superhydrophobic Coatings that Promote the Extended Release of Water-Labile Quorum Sensing Inhibitors and Enable Long-Term Modulation of Quorum Sensing in Staphylococcus aureus

Materials and coatings that inhibit bacterial colonization are of interest in a broad range of biomedical, environmental, and industrial applications. In view of the rapid increase in bacterial resistance to conventional antibiotics, the development of new strategies that target nonessential pathways in bacterial pathogens—and that thereby limit growth and reduce virulence through nonbiocidal means—has attracted considerable attention. Bacterial quorum sensing (QS) represents one such target, and is intimately connected to virulence in many human pathogens. Here, we demonstrate that the properties of nanoporous, polymer-based superhydrophobic coatings can be exploited to host and subsequently sustain the extended release of potent and water-labile peptide-based inhibitors of QS (QSIs) in Staphylococcus aureus. Our results demonstrate that these peptidic QSIs can be released into surrounding media for periods of at least 8 months, and that they strongly inhibit agr-based QS in S. aureus for at least 40 days. These results also suggest that these extremely nonwetting coatings can confer protection against the rapid hydrolysis of these water-labile peptides, thereby extending their useful lifetimes. Finally, we demonstrate that these peptide-loaded superhydrophobic coatings can strongly modulate the QS-controlled formation of biofilm in wild-type S. aureus. These nanoporous superhydrophobic films provide a new, useful, and nonbiocidal approach to the design of coatings that attenuate bacterial virulence. This approach has the potential to be general, and could prove suitable for the encapsulation, protection, and release of other classes of water-sensitive agents. We anticipate that the materials, strategies, and concepts reported here will enable new approaches to the long-term attenuation of QS and associated bacterial phenotypes in a range of basic research and applied contexts.

Antifungal Activity of 14-Helical β-Peptides against Planktonic Cells and Biofilms of Candida Species

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.

Fabrication of liquid-infused surfaces using reactive polymer multilayers: principles for manipulating the behaviors and mobilities of aqueous fluids on slippery liquid interfaces

The design of slippery liquid-infused porous surfaces (SLIPS) using nanoporous and chemically reactive polymer multilayers is reported. This approach permits fabrication of slippery anti-fouling coatings on complex surfaces and provides new means to manipulate the mobilities of contacting aqueous fluids. The results expand the range of tools that can be used to manipulate the behaviors of SLIPS and open the door to new applications of this emerging class of soft materials.

Surfactant-induced ordering and wetting transitions of droplets of thermotropic liquid crystals "caged" inside partially filled polymeric capsules

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.

Post-Fabrication Placement of Arbitrary Chemical Functionality on Microphase-Separated Thin Films of Amine-Reactive Block Copolymers

We report an approach to the post-fabrication placement of chemical functionality on microphase-separated thin films of a reactive block copolymer. Our approach makes use of an azlactone-containing block copolymer that microphase separates into domains of perpendicularly-oriented lamellae. These thin films present nanoscale patterns of amine-reactive groups (reactive stripes) that serve as handles for the immobilization of primary amine-containing functionality. We demonstrate that arbitrary chemical functionality can be installed by treatment with aqueous solutions under mild conditions that do not perturb underlying microphase-separated patterns dictated by the structure of the reactive block copolymer. This post-fabrication approach provides a basis for the development of modular approaches to the design of microphase-separated block copolymer thin films and access to coatings with patterned chemical domains and surface properties that would be difficult to prepare by the self-assembly and processing of functionally complex block copolymers.

Hydrophobicity and helicity regulate the antifungal activity of 14-helical β-peptides

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.

Polymer multilayers loaded with antifungal β-peptides kill planktonic Candida albicans and reduce formation of fungal biofilms on the surfaces of flexible catheter tubes

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 ~700nm 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 ~4months) 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.

Influence of the Phase State of Self-Assembling Redox Mediators on their Electrochemical Activity

Self-assembling redox mediators have the potential to be broadly useful in a range of interfacial electrochemical contexts because the oxidation state and state of assembly of the mediator are closely coupled. In this paper, we report an investigation of the self-assembly of single- and double-tailed ferrocenyl amphiphiles (FTMA and BFDMA, respectively) at the surfaces of Pt electrodes and the impact of the dynamic assembled state of the amphiphiles on their rate of oxidation. We conclude that frozen aggregates of BFDMA adsorb to the surfaces of the Pt electrodes, and that slow dynamics of reorganization BFDMA within these aggregates limits the rate of electrooxidation of BFDMA. In contrast, FTMA, while forming assemblies on the surfaces of Pt electrodes, is characterized by fast reorganization dynamics and a corresponding rate of oxidation that is an order of magnitude greater than BFDMA.

Surface coatings that promote rapid release of peptide-based AgrC inhibitors for attenuation of quorum sensing in Staphylococcus aureus

Staphylococcus aureus is a major human pathogen responsible for a variety of life-threatening infections. The pathogenicity of this organism is attributed to its ability to produce a range of virulence factors and toxins, including the superantigen toxic shock syndrome toxin-1 (TSST-1). While many S. aureus infections can be treated using conventional antibiotics, strains resistant to these bactericidal agents have emerged. Approaches that suppress pathogenicity through mechanisms that are nonbactericidal (i.e., antivirulence approaches) could provide new options for treating infections, including those caused by resistant strains. Here, we report a nonbactericidal approach to suppressing pathogenicity based on the release of macrocyclic peptides (1 and 2) that inhibit the agr quorum sensing (QS) circuit in group-III S. aureus. It is demonstrated that these peptides can be immobilized on planar and complex objects (on glass slides, nonwoven meshes, or within absorbent tampons) using the rapidly dissolving polymer carboxymethylcellulose (CMC). Peptide-loaded CMC films released peptide rapidly (<5 min) and promoted strong (>95%) inhibition of the agr QS circuit without inducing cell death when incubated in the presence of a group-III S. aureus gfp-reporter strain. Peptide 1 is among the most potent inhibitors of QS in S. aureus reported to date, and the group-III QS circuit regulates production of TSST-1, the primary cause of toxic shock syndrome (TSS). These results thus suggest approaches to treat the outer covers of tampons, wound dressings, or other objects to suppress toxin production and reduce the severity of TSS in clinical and personal care contexts. Because peptide 1 also inhibits QS in S. aureus groups-I, -II, and -IV, this approach could also provide a pathway for attenuation of QS and associated virulence phenotypes in a broader range of contexts.

Superhydrophobic polymer multilayers that promote the extended, long-term release of embedded water-soluble agents

Polymer multilayers that exhibit surface and bulk superhydrophobicity are demonstrated to promote long-term release of water-soluble agents (for ca.1 year) when submerged in water. The extremely nonwetting nature of these materials prevents rapid influx of water, addressing a key limitation inherent to polyelectrolytebased multilayers that release imbedded agents quickly. Our results provide new and potentially general principles for the design of surface coatings in the context of controlled release.

Multivalent alteration of quorum sensing in Staphylococcus aureus

Virulence in Staphylococcus aureus is strongly and positively correlated with local cell density. Here we present an effective approach to modulate this group behaviour using multivalent peptide-polymer conjugates. Our results show that by attaching multiple AIP-4' units to macromolecular scaffolds, the agr QS response in S. aureus was affected strongly, while displaying a clear multivalency effect.

Restoration of superhydrophobicity in crushed polymer films by treatment with water: self-healing and recovery of damaged topographic features aided by an unlikely source

The crushing of superhydrophobic polymer multilayers destroys micro/nanoscale topographic features critical for the maintenance of superhydrophobicity. We demonstrate that these surface features can be recovered, and that superhydrophobicity can be fully restored, by treatment of damaged films with liquid water. These polymer-based films can also sustain other forms of severe abuse without loss of superhydrophobicity. This combination of features addresses several important practical issues associated with the durability of artificial superhydrophobic surfaces.

Spatial control of cell transfection using soluble or solid-phase redox agents and a redox-active ferrocenyl lipid

We report principles for active, user-defined control over the locations and timing with which DNA is expressed in cells. Our approach exploits unique properties of a ferrocenyl cationic lipid that is inactive when oxidized, but active when chemically reduced. We show that methods that exert spatial control over the administration of reducing agents can lead to local activation of lipoplexes and spatial control over gene expression. The versatility of this approach is demonstrated using both soluble and solid-phase reducing agents. These methods provide control over cell transfection, including methods for remote activation and the patterning of expression using solid-phase redox agents, that are difficult to achieve using conventional lipoplexes.

Patterning and impregnation of superhydrophobic surfaces using aqueous solutions

We report a solvent-assisted approach to the patterning and impregnation of porous superhydrophobic coatings that permits the use of entirely aqueous solutions. This approach permits immobilization of proteins and enzymes, creating opportunities to decorate superhydrophobic surfaces with hydrophilic domains and channels that can capture aliquots of aqueous media, guide and mix aqueous solutions, and chemically process streams of organic molecules. Because this approach does not require destruction of non-wetting features, it can also be used to transfer highly water-soluble polymers and small molecules without compromising superhydrophobicity, providing methods for post-fabrication loading of water-soluble agents into protective non-wetting coatings that are difficult to achieve using other approaches.

Surface-mediated release of a small-molecule modulator of bacterial biofilm formation: a non-bactericidal approach to inhibiting biofilm formation in Pseudomonas aeruginosa

We report an approach to preventing bacterial biofilm formation that is based on the surface-mediated release of 5,6-dimethyl-2-aminobenzimidazole (DMABI), a potent and non-bactericidal small-molecule inhibitor of bacterial biofilm growth. Our results demonstrate that DMABI can be encapsulated in thin films of a model biocompatible polymer [poly(lactide-co-glycolide), PLG] and be released in quantities that inhibit the formation of Pseudomonas aeruginosa biofilms by up to 75-90% on surfaces that otherwise support robust biofilm growth. This approach enables the release of this new anti-biofilm agent for over one month, and it can be used to inhibit biofilm growth on both film-coated surfaces and other adjacent surfaces (e.g., on other uncoated surfaces and at air/water interfaces). Our results demonstrate a non-bactericidal approach to the prevention of biofilm growth and provide proof of concept using a clinically relevant human pathogen. In contrast to coatings designed to kill bacteria on contact, this approach should also permit the design of strategically placed depots that disseminate DMABI more broadly and exert inhibitory effects over larger areas. In a broader context, the non-bactericidal nature of DMABI could also provide opportunities to address concerns related to evolved resistance that currently face approaches based on the release of traditional microbicidal agents (e.g., antibiotics). Finally, the results of initial in vitro mammalian cell culture studies indicate that DMABI is not toxic to cells at concentrations required for strong anti-biofilm activity, suggesting that this new agent is well suited for further investigation in biomedical and personal care contexts.

"Shrink-to-fit" superhydrophobicity: thermally-induced microscale wrinkling of thin hydrophobic multilayers fabricated on flexible shrink-wrap substrates

An approach to the design of flexible superhydrophobic surfaces based on thermally induced wrinkling of thin, hydrophobic polymer multilayers on heat-shrinkable polymer films is reported. This approach exploits shrinking processes common to "heat-shrink" plastics, and can thus be used to create "shrink-to-fit" superhydrophobic coatings on complex surfaces, manipulate the dimensions and densities of patterned features, and promote heat-activated repair of full-thickness defects.

Redox-based control of the transformation and activation of siRNA complexes in extracellular environments using ferrocenyl lipids

We report physical characterization and biological evaluation of complexes of small interfering RNA (siRNA) formed using a cationic lipid [bis(11-ferrocenylundecyl)dimethylammonium bromide (BFDMA)] containing redox-active ferrocenyl groups at the end of each hydrophobic tail. We demonstrate that control over the redox state of BFDMA can be used to influence key physical properties and control the activities of lipoplexes formed using siRNA-based constructs. Specifically, lipoplexes of siRNA and reduced BFDMA lead to high levels of sequence-specific gene silencing in cells, but lipoplexes formed using oxidized BFDMA do not. Lipoplexes of oxidized BFDMA can be activated in situ to induce high levels of silencing by addition of a chemical reducing agent, demonstrating a basis for external control over the activation/delivery of siRNA in cellular environments. Differences in activity arise from the inability of oxidized BFDMA to promote efficient internalization of siRNA; these differences also correlated to significant differences in the nanostructures of these lipoplexes (determined by cryo-TEM) and their ζ potentials as a function of oxidation state. These results are considered in view of recent studies characterizing the nanostructures, properties, and behaviors of lipoplexes formed using BFDMA and macromolecular plasmid DNA. We find that several key structural features and aspects of redox control observed for lipoplexes of plasmid DNA are maintained in complexes formed using smaller and more rigid siRNA. The ability to transform BFDMA in complex media presents opportunities to exert control over the nanostructures and behaviors of siRNA lipoplexes in ways not possible using conventional lipids. The approaches reported here could thus prove useful in both fundamental and applied contexts.

Polyelectrolyte multilayers promote stent-mediated delivery of DNA to vascular tissue

We report an approach to deliver DNA to vascular tissue in vivo using intravascular stents coated with degradable, DNA-containing polyelectrolyte multilayers (PEMs). Ionically cross-linked multilayers ∼120 nm thick were fabricated layer-by-layer on the surfaces of balloon-mounted stainless steel stents using plasmid DNA and a hydrolytically degradable poly(β-amino ester) (polymer 1). Characterization of stents coated using a fluorescently end-labeled analog of polymer 1 revealed film erosion to be uniform across the surfaces of the stents; differential stresses experienced upon balloon expansion did not lead to faster film erosion or dose dumping of DNA in areas near stent joints when stents were incubated in physiologically relevant media. The ability of film-coated stents to transfer DNA and transfect arterial tissue in vivo was then investigated in pigs and rabbits. Stents coated with films fabricated using fluorescently labeled DNA resulted in uniform transfer of DNA to sub-endothelial tissue in the arteries of pigs in patterns corresponding to the locations and geometries of stent struts. Stents coated with films fabricated using polymer 1 and plasmid DNA encoding EGFP resulted in expression of EGFP in the medial layers of stented tissue in both pigs and rabbits two days after implantation. The results of this study, combined with the modular and versatile nature of layer-by-layer assembly, provide a polymer-based platform that is well suited for fundamental studies of stent-mediated gene transfer. With further development, this approach could also prove useful for the design of nonviral, gene-based approaches for prevention of complications that arise from the implantation of stents and other implantable interventional devices.

Fabrication of oligonucleotide and protein arrays on rigid and flexible substrates coated with reactive polymer multilayers

We report a top-down approach to the fabrication of oligonucleotide and protein arrays on surfaces coated with ultrathin, amine-reactive polymer multilayers fabricated by the covalent "layer-by-layer" (LbL) assembly of polyethyleneimine (PEI) and the amine-reactive, azlactone-functionalized polymer poly(2-vinyl-4,4-dimethylazlactone) (PVDMA). Manual spotting of amine-terminated oligonucleotide probe sequences on planar glass slides coated with PEI/PVDMA multilayers (~35 nm thick) yielded arrays of immobilized probes that hybridized fluorescently labeled complementary sequences with high signal intensities, high signal-to-noise ratios, and high sequence specificity. Treatment of residual azlactone functionality with the nonfouling small-molecule amine d-glucamine resulted in regions between the features of these arrays that resisted adsorption of protein and permitted hybridization in complex media containing up to 10 mg/mL protein. The residual azlactone groups in these films were also exploited to immobilize proteins on film-coated surfaces and fabricate functional arrays of proteins and enzymes. The ability to deposit PEI/PVDMA multilayers on substrates of arbitrary size, shape, and composition permitted the fabrication of arrays of oligonucleotides on the surfaces of multilayer-coated sheets of poly(ethylene terephthalate) and heat-shrinkable polymer film. Arrays fabricated on these flexible plastic substrates can be bent, cut, resized, and manipulated physically in ways that are difficult using more conventional rigid substrates. This approach could thus contribute to the development of new assay formats and new applications of biomolecule arrays. The methods described here are straightforward to implement, do not require access to specialized equipment, and should also be compatible with automated liquid-handling methods used to fabricate higher-density arrays of oligonucleotides and proteins on more traditional surfaces.

Reduction of intimal hyperplasia in injured rat arteries promoted by catheter balloons coated with polyelectrolyte multilayers that contain plasmid DNA encoding PKCδ

New therapeutic approaches that eliminate or reduce the occurrence of intimal hyperplasia following balloon angioplasty could improve the efficacy of vascular interventions and improve the quality of life of patients suffering from vascular diseases. Here, we report that treatment of arteries using catheter balloons coated with thin polyelectrolyte-based films ('polyelectrolyte multilayers', PEMs) can substantially reduce intimal hyperplasia in an in vivo rat model of vascular injury. We used a layer-by-layer (LbL) process to coat the surfaces of inflatable catheter balloons with PEMs composed of nanolayers of a cationic poly(β-amino ester) (polymer 1) and plasmid DNA (pPKCδ) encoding the δ isoform of protein kinase C (PKCδ), a regulator of apoptosis and other cell processes that has been demonstrated to reduce intimal hyperplasia in injured arterial tissue when administered via perfusion using viral vectors. Insertion of balloons coated with polymer 1/pPKCδ multilayers into injured arteries for 20 min resulted in local transfer of DNA and elevated levels of PKCδ expression in the media of treated tissue three days after delivery. IFC and IHC analysis revealed these levels of expression to promote downstream cellular processes associated with up-regulation of apoptosis. Analysis of arterial tissue 14 days after treatment revealed polymer 1/pPKCδ-coated balloons to reduce the occurrence of intimal hyperplasia by ~60% compared to balloons coated with films containing empty plasmid vectors. Our results demonstrate the potential therapeutic value of this nanotechnology-based approach to local gene delivery in the clinically important context of balloon-mediated vascular interventions. These PEM-based methods could also prove useful for other in vivo applications that require short-term, surface-mediated transfer of plasmid DNA.

Chemical patterning and physical refinement of reactive superhydrophobic surfaces

An approach to the modification and post-fabrication chemical patterning of amine-reactive superhydrophobic surfaces is reported. The approach is based on the layer-by-layer fabrication of azlactone-containing polymer multilayers, and permits the direct covalent attachment and subsequent patterning of chemical and biological "inks" using a variety of practical and low-cost pattern-transfer methods.

Chemical oxidation of a redox-active, ferrocene-containing cationic lipid: influence on interactions with DNA and characterization in the context of cell transfection

We report an approach to the chemical oxidation of a ferrocene-containing cationic lipid [bis(11-ferrocenylundecyl)dimethylammonium bromide, BFDMA] that provides redox-based control over the delivery of DNA to cells. We demonstrate that BFDMA can be oxidized rapidly and quantitatively by treatment with Fe(III)sulfate. This chemical approach, while offering practical advantages compared to electrochemical methods used in past studies, was found to yield BFDMA/DNA lipoplexes that behave differently in the context of cell transfection from lipoplexes formed using electrochemically oxidized BFDMA. Specifically, while lipoplexes of the latter do not transfect cells efficiently, lipoplexes of chemically oxidized BFDMA promoted high levels of transgene expression (similar to levels promoted by reduced BFDMA). Characterization by SANS and cryo-TEM revealed lipoplexes of chemically and electrochemically oxidized BFDMA to both have amorphous nanostructures, but these lipoplexes differed significantly in size and zeta potential. Our results suggest that differences in zeta potential arise from the presence of residual Fe(2+) and Fe(3+) ions in samples of chemically oxidized BFDMA. Addition of the iron chelating agent EDTA to solutions of chemically oxidized BFDMA produced samples functionally similar to electrochemically oxidized BFDMA. These EDTA-treated samples could also be chemically reduced by treatment with ascorbic acid to produce samples of reduced BFDMA that do promote transfection. Our results demonstrate that entirely chemical approaches to oxidation and reduction can be used to achieve redox-based 'on/off' control of cell transfection similar to that achieved using electrochemical methods.