David M. Lynn

Multilayered polyelectrolyte assemblies as platforms for the delivery of DNA and other nucleic acid-based therapeutics.

Materials that provide spatial and temporal control over the delivery of DNA and other nucleic acid-based agents from surfaces play important roles in the development of localized gene-based therapies. This review focuses on a relatively new approach to the immobilization and release of DNA from surfaces: methods based on the layer-by-layer assembly of thin multilayered films (or polyelectrolyte multilayers, PEMs). Layer-by-layer methods provide convenient, nanometer-scale control over the incorporation of DNA, RNA, and oligonucleotide constructs into thin polyelectrolyte films. Provided that these assemblies can be designed in ways that permit controlled film disassembly under physiological conditions, this approach can contribute new methods for spatial and/or temporal control over the delivery of nucleic acid-based therapeutics in vitro and in vivo. We describe applications of layer-by-layer assembly to the fabrication of DNA-containing films that can be used to provide control over the release of plasmid DNA from the surfaces of macroscopic objects and promote surface-mediated cell transfection. We also highlight the application of these methods to the coating of colloidal substrates and the fabrication of hollow micrometer-scale capsules that can be used to encapsulate and control the release or delivery of DNA and oligonucleotides. Current challenges, gaps in knowledge, and new opportunities for the development of these methods in the general area of gene delivery are discussed.

Moving smaller in drug discovery and delivery.

Advances in new micro- and nanotechnologies are accelerating the identification and evaluation of drug candidates, and the development of new delivery technologies that are required to transform biological potential into medical reality. This article will highlight the emerging micro- and nanotechnology tools, techniques and devices that are being applied to advance the fields of drug discovery and drug delivery. Many of the promising applications of micro- and nanotechnology are likely to occur at the interfaces between microtechnology, nanotechnology and biochemistry.

Controlling interlayer diffusion to achieve sustained, multiagent delivery from layer-by-layer thin films.

We present the fabrication of conformal, hydrolytically degradable thin films capable of administering sustained, multiagent release profiles. Films are constructed one molecular layer at a time by using the layer-by-layer, directed-deposition technique; the subsequent hydrolytic surface erosion of these systems results in the release of incorporated materials in a sequence that reflects their relative positions in the film. The position of each species is determined by its ability to diffuse throughout the film architecture, and, as such, the major focus of this work is to define strategies that physically block interlayer diffusion during assembly to create multicomponent, stratified films. By using a series of radiolabeled polyelectrolytes as experimental probes, we show that covalently crosslinked barriers can effectively block interlayer diffusion, leading to compartmentalized structures, although even very large numbers of ionically crosslinked (degradable or nondegradable) barrier layers cannot block interlayer diffusion. By using these principles, we designed degradable films capable of extended release as well as both parallel and serial multiagent release. The ability to fabricate multicomponent thin films with nanoscale resolution may lead to a host of new materials and applications.

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.

Layers of opportunity: nanostructured polymer assemblies for the delivery of macromolecular therapeutics

Layer-by-layer approaches to the fabrication of nanostructured polymer assemblies have contributed to the design of thin films and composites of interest in a variety of areas. Here, we highlight recent contributions from our laboratory toward the design of multilayered assemblies that erode controllably and predictably in physiological environments and permit spatial and temporal control over the administration of macromolecular therapeutics, such as DNA. Our approach makes use of assemblies fabricated from hydrolytically degradable polyamines. We place this work in the context of recent progress from other laboratories and discuss new opportunities and connections that illustrate the potential of these layered assemblies as platforms for the controlled release of one or several therapeutic agents.

Chemical Modification of Reactive Multilayered Films Fabricated from Poly(2-alkenyl azlactone)s: Design of Surfaces that Prevent or Promote Mammalian Cell Adhesion and Bacterial Biofilm Growth

We report an approach to the design of reactive polymer films that can be functionalized post-fabrication to either prevent or promote the attachment and growth of cells. Our approach is based on the reactive layer-by-layer assembly of covalently crosslinked thin films using a synthetic polyamine and a polymer containing reactive azlactone functionality. Our results demonstrate (i) that the residual azlactone functionality in these films can be exploited to immobilize amine-functionalized chemical motifs similar to those that promote or prevent cell and protein adhesion when assembled as self-assembled monolayers on gold-coated surfaces and (ii) that the immobilization of these motifs changes significantly the behaviors and interactions of cells with the surfaces of these polymer films. We demonstrate that films treated with the hydrophobic molecule decylamine support the attachment and growth of mammalian cells in vitro. In contrast, films treated with the hydrophilic carbohydrate d-glucamine prevent cell adhesion and growth almost completely. The results of additional experiments suggest that these large differences in cell behavior can be understood, at least in part, in terms of differences in the abilities of these two different chemical motifs to promote or prevent the adsorption of protein onto film-coated surfaces. We demonstrate further that this approach can be used to pattern regions of these reactive films that resist the initial attachment and subsequent invasion of mammalian cells for periods of at least one month in the presence of serum-containing cell culture media. Finally, we report that films that prevent the adhesion and growth of mammalian cells also prevent the initial formation of bacterial biofilms when incubated in the presence of the clinically relevant pathogen Pseudomonas aeruginosa . The results of these studies, collectively, suggest the basis of general approaches to the fabrication and functionalization of thin films that prevent, promote, or pattern cell growth or the formation of biofilms on surfaces of interest in the contexts of both fundamental biological studies and a broad range of other practical applications.

Polyelectrolyte multilayers fabricated from antifungal β-peptides: design of surfaces that exhibit antifungal activity against Candida albicans.

The fungal pathogen Candida albicans can form biofilms on the surfaces of medical devices that are resistant to drug treatment and provide a reservoir for recurrent infections. The use of fungicidal or fungistatic materials to fabricate or coat the surfaces of medical devices has the potential to reduce or eliminate the incidence of biofilm-associated infections. Here we report on (i) the fabrication of multilayered polyelectrolyte thin films (PEMs) that promote the surface-mediated release of an antifungal β-peptide and (ii) the ability of these films to inhibit the growth of C. albicans on film-coated surfaces. We incorporated a fluorescently labeled antifungal β-peptide into the structures of PEMs fabricated from poly-l-glutamic acid (PGA) and poly-l-lysine (PLL) using a layer-by-layer fabrication procedure. These films remained stable when incubated in culture media at 37 °C and released β-peptide gradually into solution for up to 400 h. Surfaces coated with β-peptide-containing films inhibited the growth of C. albicans , resulting in a 20% reduction of cell viability after 2 h and a 74% decrease in metabolic activity after 7 h when compared to cells incubated on PGA/PLL-coated surfaces without β-peptide. In addition, β-peptide-containing films inhibited hyphal elongation by 55%. These results, when combined, demonstrate that it is possible to fabricate β-peptide-containing thin films that inhibit the growth and proliferation of C. albicans and provide the basis of an approach that could be used to inhibit the formation of C. albicans biofilms on film-coated surfaces. The layer-by-layer approach reported here could ultimately be used to coat the surfaces of catheters, surgical instruments, and other devices to inhibit drug-resistant C. albicans biofilm formation in clinical settings.

Immobilization of Polymer-Decorated Liquid Crystal Droplets on Chemically Tailored Surfaces

We demonstrate that the assembly of an amphiphilic polyamine on the interfaces of micrometer-sized droplets of a thermotropic liquid crystal (LC) dispersed in aqueous solutions can be used to facilitate the immobilization of LC droplets on chemically functionalized surfaces. Polymer 1 was designed to contain both hydrophobic (alkyl-functionalized) and hydrophilic (primary and tertiary amine-functionalized) side chain functionality. The assembly of this polymer at the interfaces of aqueous dispersions of LC droplets was achieved by the spontaneous adsorption of polymer from aqueous solution. Polymer adsorption triggered transitions in the orientational ordering of the LCs, as observed by polarized light and bright-field microscopy. We demonstrate that the presence of polymer 1 on the interfaces of these droplets can be exploited to immobilize LC droplets on planar solid surfaces through covalent bond formation (e.g., for surfaces coated with polymer multilayers containing reactive azlactone functionality) or through electrostatic interactions (e.g., for surfaces coated with multilayers containing hydrolyzed azlactone functionality). The characterization of immobilized LC droplets by polarized, fluorescence, and laser scanning confocal microscopy revealed the general spherical shape of the polymer-coated LC droplets to be maintained after immobilization, and that immobilization led to additional ordering transitions within the droplets that were dependent on the nature of the surfaces with which they were in contact. Polymer 1-functionalized LC droplets were not immobilized on polymer multilayers treated with poly(ethylene imine) (PEI). We demonstrate that the ability to design surfaces that promote or prevent the immobilization of polymer-functionalized LC droplets can be exploited to pattern the immobilization of LC droplets on surfaces. The results of this investigation provide the basis of an approach that could be used to tailor the properties of dispersed LC emulsions and to immobilize these droplets on functional surfaces of interest in a broad range of fundamental and applied contexts.

Synthetic Surfaces with Robust and Tunable Underwater Superoleophobicity

The present invention provides multilayer polymer films, materials and coatings which exhibit robust underwater superoleophobicity and have remarkable structural functional tolerance to a broad range of physical, chemical, and environmental challenges encountered by surfaces deployed in aqueous or aquatic environments. These materials can be fabricated on surfaces of arbitrary shape, size, and composition and provide straightforward means to manipulate surface chemistry and fine-tune other useful features of the interfacial behavior (e.g., underwater oil-adhesiveness). These materials address key obstacles to the application of non-wetting surfaces and anti-fouling ‘super-phobic’ materials in practical, real-world scenarios.

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.