Multilayered films fabricated from an oligoarginine-conjugated protein promote efficient surface-mediated protein transduction

Histatin 5 variant reduces Candida albicans biofilm viability and inhibits biofilm formation

Candida albicans is a commensal organism and opportunistic pathogen that can form biofilms that colonize surfaces of medical devices, such as implants, catheters, and dentures. Compared to planktonic C. albicans cells, cells in biofilms exhibit increased resistance to treatment. Histatin 5 (Hst-5) is an antimicrobial peptide that is natively secreted by human salivary glands and has strong antifungal activity against C. albicans. However, C. albicans produces secreted aspartic proteases (Saps) that can cleave and inactivate Hst-5, limiting its antifungal properties. We previously showed that residue substitutions K11R and K17R within Hst-5 improve its antifungal activity and prevent proteolytic degradation by Saps when treating planktonic C. albicans. Here, we investigated the use of the K11R-K17R peptide as an alternative therapeutic against C. albicans biofilms by assessing its ability to reduce viability of pre-formed biofilms and to inhibit the formation of biofilms and showed that K11R-K17R had improved activity compared to Hst-5. Based on these results, we incorporated K11R-K17R and Hst-5 into polyelectrolyte multilayer (PEM) surface coatings and demonstrated that films functionalized with K11R-K17R reduced the formation of C. albicans biofilms. Our results demonstrate the therapeutic potential of the K11R-K17R Hst-5 variant in preventing and treating biofilms.

Engineering Cell Surfaces with Polyelectrolyte Materials for Translational Applications

Engineering cell surfaces with natural or synthetic materials is a unique and powerful strategy for biomedical applications. Cells exhibit more sophisticated migration, control, and functional capabilities compared to nanoparticles, scaffolds, viruses, and other engineered materials or agents commonly used in the biomedical field. Over the past decade, modification of cell surfaces with natural or synthetic materials has been studied to exploit this complexity for both fundamental and translational goals. In this review we present the existing biomedical technologies for engineering cell surfaces with one important class of materials, polyelectrolytes. We begin by introducing the challenges facing the cell surface engineering field. We then discuss the features of polyelectrolytes and how these properties can be harnessed to solve challenges in cell therapy, tissue engineering, cell-based drug delivery, sensing and tracking, and immune modulation. Throughout the review, we highlight opportunities to drive the field forward by bridging new knowledge of polyelectrolytes with existing translational challenges.

Assembly and Immunological Processing of Polyelectrolyte Multilayers Composed of Antigens and Adjuvants

While biomaterials provide a platform to control the delivery of vaccines, the recently discovered intrinsic inflammatory characteristics of many polymeric carriers can also complicate rational design because the carrier itself can alter the response to other vaccine components. To address this challenge, we recently developed immune-polyelectrolyte multilayer (iPEMs) capsules electrostatically assembled entirely from peptide antigen and molecular adjuvants. Here, we use iPEMs built from SIINFEKL model antigen and polyIC, a stimulatory toll-like receptor agonist, to investigate the impact of pH on iPEM assembly, the processing and interactions of each iPEM component with primary immune cells, and the role of these interactions during antigen-specific T cell responses in coculture and mice. We discovered that iPEM assembly is pH dependent with respect to both the antigen and adjuvant component. Controlling the pH also allows tuning of the relative loading of SIINFEKL and polyIC in iPEM capsules. During in vitro studies with primary dendritic cells (DCs), iPEM capsules ensure that greater than 95% of cells containing at least one signal (i.e., antigen, adjuvant) also contained the other signal. This codelivery leads to DC maturation and SIINFEKL presentation via the MHC-I antigen presentation pathway, resulting in antigen-specific T cell proliferation and pro-inflammatory cytokine secretion. In mice, iPEM capsules potently expand antigen-specific T cells compared with equivalent admixed formulations. Of note, these enhancements become more pronounced with successive booster injections, suggesting that iPEMs functionally improve memory recall response. Together our results reveal some of the features that can be tuned to modulate the properties of iPEM capsules, and how these modular vaccine structures can be used to enhance interactions with immune cells in vitro and in mice.

Polyelectrolyte Multilayers Assembled Entirely from Immune Signals on Gold Nanoparticle Templates Promote Antigen-Specific T Cell Response

Materials that allow modular, defined assembly of immune signals could support a new generation of rationally designed vaccines that promote tunable immune responses. Toward this goal, we have developed the first polyelectrolyte multilayer (PEM) coatings built entirely from immune signals. These immune-PEMs (iPEMs) are self-assembled on gold nanoparticle templates through stepwise electrostatic interactions between peptide antigen and polyanionic toll-like receptor (TLR) agonists that serve as molecular adjuvants. iPEMs do not require solvents or mixing, offer direct control over the composition and loading of vaccine components, and can be coated on substrates at any scale. These films also do not require other structural components, eliminating the potentially confounding effects caused by the inherent immune-stimulatory characteristics of many synthetic polymers. iPEM loading on gold nanoparticle substrates is tunable, and cryoTEM reveals iPEM shells coated on gold cores. These nanoparticles are efficiently internalized by primary dendritic cells (DCs), resulting in activation, selective triggering of TLR signaling, and presentation of the antigens used to assemble iPEMs. In coculture, iPEMs drive antigen-specific T cell proliferation and effector cytokines but not cytokines associated with more generalized inflammation. Compared to mice treated with soluble antigen and adjuvant, iPEM immunization promotes high levels of antigen-specific CD8(+) T cells in peripheral blood after 1 week. These enhancements result from increased DC activation and antigen presentation in draining lymph nodes. iPEM-immunized mice also exhibit a potent recall response after boosting, supporting the potential of iPEMs for designing well-defined vaccine coatings that provide high cargo density and eliminate synthetic film components.

Bioaffinity sensor based on nanoarchitectonic films: control of the specific adsorption of proteins through the dual role of an ethylene oxide spacer

The identification and quantification of biomarkers or proteins is a real challenge in allowing the early detection of diseases. The functionalization of the biosensor surface has to be properly designed to prevent nonspecific interactions and to detect the biomolecule of interest specifically. A multilayered nanoarchitecture, based on polyelectrolyte multilayers (PEM) and the sequential immobilization of streptavidin and a biotinylated antibody, was elaborated as a promising platform for the label-free sensing of targeted proteins. We choose ovalbumin as an example. Thanks to the versatility of PEM films, the platform was built on two types of sensor surface and was evaluated using both optical- and viscoelastic-based techniques, namely, optical waveguide lightmode spectroscopy and the quartz crystal microbalance, respectively. A library of biotinylated poly(acrylic acids) (PAAs) was synthesized by grafting biotin moieties at different grafting ratios (GR). The biotin moieties were linked to the PAA chains through ethylene oxide (EO) spacers of different lengths. The adsorption of the PAA-EOn-biotin (GR) layer on a PEM precursor film allows tuning the surface density in biotin and thus the streptavidin adsorption mainly through the grafting ratio. The nonspecific adsorption of serum was reduced and even suppressed depending on the length of the EO arms. We showed that to obtain an antifouling polyelectrolyte the grafting of EO9 or EO19 chains at 25% in GR is sufficient. Thus, the spacer has a dual role: ensuring the antifouling property and allowing the accessibility of biotin moieties. Finally, an optimized platform based on the PAA-EO9-biotin (25%)/streptavidin/biotinylated-antibody architecture was built and demonstrated promising performance as interface architecture for bioaffinity sensing of a targeted protein, in our case, ovalbumin.

Therapeutic strategies to combat neointimal hyperplasia in vascular grafts

Neointimal hyperplasia (NIH) in bypass conduits such as veins and prosthetic grafts is an important clinical entity that limits the long-term success of vascular interventions. Although the development of NIH in the conduits shares many of the same features of NIH that develops in native arteries after injury, vascular grafts are exposed to unique circumstances that predispose them to NIH, including surgical trauma related to vein handling, hemodynamic changes creating areas of low flow, and differences in biocompatibility between the conduit and the host environment. Multiple different approaches, including novel surgical techniques and targeted gene therapies, have been developed to target and prevent the causes of NIH. Recently, the PREVENT trials, the first molecular biology trials in vascular surgery aimed at preventing NIH, have failed to produce improved clinical outcomes, highlighting the incomplete knowledge of the pathways leading to NIH in vascular grafts. In this review, we aim to summarize the pathophysiologic pathways that underlie the formation of NIH in both vein and synthetic grafts and discuss current and potential mechanical and molecular approaches under investigation that may limit NIH in vascular grafts.

Layer-by-layer assembly of DNA- and protein-containing films on microneedles for drug delivery to the skin

Microneedle patches contain micrometer-scale needles coated with bioactive agents for minimally invasive drug delivery to the skin. In this study, we introduce layer-by-layer approaches to the fabrication of ultrathin DNA- and protein-containing polyelectrolyte films (or "polyelectrolyte multilayers", PEMs) on the surfaces of stainless steel microneedles. DNA-containing PEMs were fabricated on microneedles by the alternating deposition of plasmid DNA and a hydrolytically degradable poly(β-amino ester). Protein-containing PEMs were fabricated using sodium poly(styrene sulfonate) (SPS) and bovine pancreatic ribonuclease A (RNase A) conjugated to a synthetic protein transduction domain. Layer-by-layer assembly resulted in ultrathin, uniform, and defect-free coatings on the surfaces of the microneedles, as characterized by fluorescence microscopy. These films eroded and thereby released DNA or protein when incubated in saline or when inserted into porcine cadaver skin and deposited DNA or protein along the edges of microneedle tracks to depths of ∼500 to 600 μm. We conclude that PEM-coated microneedles offer a novel and useful approach to the transdermal delivery of DNA- and protein-based therapeutics and could also prove useful in other applications.

Drug releasing polymer thin films: new era of surface-mediated drug delivery

Polymer films and coatings are among the popular and most successful tools to modulate surface properties of biomaterials, specifically tissue responses and fouling behavior. Over the past decade, a novel opportunity has been widely investigated, namely utility of surface coatings in surface-mediated drug delivery. In these applications, deposited polymer films act as both a coating to modulate surface properties and a reservoir for active therapeutic cargo. The field has recently accelerated beyond the proof-of-concept reports toward delivering practical solutions and established technologies for biomedical applications. This review briefly summarizes the recent successes of polymer thin films, specifically those constructed by sequential polymer deposition technique, in surface-mediated drug delivery.

Tuning the formation and degradation of layer-by-layer assembled polymer hydrogel microcapsules

Engineered polymer capsules are finding widespread importance in the delivery of encapsulated toxic or fragile drugs. The effectiveness of polymer capsules as therapeutic delivery vehicles is often dependent on the degradation behavior of the capsules because it is often necessary to release the encapsulated drugs at specific times and in certain locations. Herein we investigate the parameters that govern the formation and degradation of a recently introduced new class of polymer hydrogel capsules based on disulfide cross-linked poly(methacrylic acid). We report a new and efficient method for the synthesis of thiol-functionalized poly(methacrylic acid) (PMA(SH)), the main component of the capsules. Polymeric capsules were synthesized by the layer-by-layer deposition of PMA(SH) and poly(vinylpyrrolidone) (PVPON) on silica particle templates, followed by cross-linking the PMA(SH) layers and removing PVPON and the template particles. The disulfide cross-links provided a redox-active trigger for degradation that was initiated by a cellular concentration of glutathione. We demonstrate that increasing the degree of PMA(SH) thiol modification affords direct control over the thickness of the polymer film and the degradation rate of the polymer capsules. Furthermore, the degradation rate of the PMA(SH) capsules was independent of film thickness, suggesting a bulk erosion process.

Postdiffusion of oligo-peptide within exponential growth multilayer films for localized peptide delivery

The multilayers of poly(L-lysine) (PLL) and hyaluronic acid (HA) were constructed by alternating deposition of PLL at high pH and HA at low pH. The exponential growth of the multilayer was proved to be amplified by increasing the pH difference between the two deposition solutions. The exponential growth multilayers of PLL/HA assembled at different pH were utilized as reservoirs for loading a trans-activating transcriptional factor (TAT) peptide. The confocal laser scanning microscopy (CLSM) results indicated that the FITC-labeled TAT could diffuse throughout the exponentially growing PLL/HA film. The amount of peptide embedded within multilayer could be adjusted by both multilayer assembly pH and the TAT loading pH. Compared with (PLL/HA 6.5/6.5)5 multilayer (PLL/HA a/b means that the multilayer film was constructed by using PLL at pH a and HA at pH b), the (PLL/HA 9.5/2.9)5 film can be loaded with more TAT peptide at the same loading pH 6.5. The excess of positively charged TAT peptide within (PLL/HA 9.5/2.9)5 film could not only be ascribed to its extraordinary thickness but also be attributed to its uncompensated negative charge density enhanced by the pH difference between film buildup and peptide loading process. Increasing of the TAT loading pH from 6.5 to 9.5, which increases the pH difference between multilayer assembly and peptide loading process, enhances the uncompensated charge density within (PLL/HA 9.5/2.9)5 film and elevates the peptide density from 13.8 to 25.0 microg/cm2. Compared with direct layer-by-layer assembly of TAT and HA, the postdiffusion of TAT into (PLL/HA 9.5/2.9)5 film was loaded much more peptide. The postdiffusion of peptide into a rapid growth multilayer can be more favorable to load and sustainedly release functional oligo-peptide. The cell culture results indicated that the TAT embedded within the film maintained the ability to traverse across the Hep G2 cell membrane. The functionalized (PLL/HA 9.5/2.9)5 TAT 9.5 film was more efficient than the equivalent amount of free TAT peptide in the TAT uptake test. The postdiffusion of oligo-peptide within an exponential growth multilayer can serve as an effective approach for localized and sustained peptide delivery.

Assembly of erodible, DNA-containing thin films on the surfaces of polymer microparticles: toward a layer-by-layer approach to the delivery of DNA to antigen-presenting cells

We report a layer-by-layer approach to the assembly of ultrathin and erodible DNA-containing films on the surfaces of polymer microparticles. DNA-containing multilayered films were fabricated layer-by-layer on the surfaces of polystyrene microspheres (approximately 6 microm) by iterative and alternating cycles of particle suspension, centrifugation and resuspension in solutions of plasmid DNA and a hydrolytically degradable polyamine. Film growth occurred in a stepwise manner, as demonstrated by characterization of the zeta potentials and fluorescence intensities of film-coated particles during film assembly. Characterization of film-coated particles by confocal fluorescence microscopy and scanning electron microscopy revealed the multilayered particle coatings to be smooth, uniform and free of large-scale physical defects. Film-coated microparticles sustained the release of transcriptionally active DNA into solution for approximately three days when incubated in physiologically relevant media. Previous studies have demonstrated that the adsorption of DNA onto the surfaces of cationic microparticles can be used to target the delivery of DNA to antigen-presenting cells. As a first step toward the application of this layer-by-layer approach to the development of methods for the delivery of DNA to antigen-presenting cells, we demonstrated that film-coated microparticles could be used to transport DNA into macrophage cells in vitro using a model mouse macrophage cell line. Our results suggest the basis of a general approach that could, with further development, prove useful for the delivery of DNA-encoded antigens to macrophages, or other antigen-presenting cells, and provide new materials-based methods for the formulation and delivery of DNA vaccines.

Swelling and contraction of ferrocyanide-containing polyelectrolyte multilayers upon application of an electric potential

We developed a new platform at the interface of polyelectrolyte multilayers (PEMs) and electroactive polymers (EAPs) by combining the easy buildup of PEM thin films and the deformation characteristics of the EAPs. The PEM films were made of poly(L-glutamic acid) (PGA) and poly(allylamine hydrochloride) (PAH). After [Fe(CN)6]4- ions (FCIV) were added, cyclic voltammetry (CV) was performed, resulting in a reversible expansion and contraction of the film. The shape change as well as the film buildup prior to the cycling were monitored in situ using the electrochemical quartz crystal microbalance with dissipation monitoring (EC-QCM-D). Electrochemical atomic force microscopy (EC-AFM) images confirmed the rapid shape deformation. The process takes place in an aqueous environment under mild conditions (maximum potential of 600 mV and no pH change), which makes it a promising tool for biomedical applications. In addition, the electrochemically active films are produced using the layer-by-layer (LbL) method that is already established in biotechnology and biomaterials science; therefore, the presented approach can be readily adapted in these areas, bringing about a new possibility for the nanoscale dynamic control of coating thickness in various applications.

Embedded silver ions-containing liposomes in polyelectrolyte multilayers: cargos films for antibacterial agents

A new antibacterial coating made of poly(L-lysine)/hyaluronic acid (PLL/HA) multilayer films and liposome aggregates loaded with silver ions was designed. Liposomes filled with an AgNO 3 solution were first aggregated by the addition of PLL in solution. The obtained micrometer-sized aggregates were then deposited on a PLL/HA multilayer film, playing the role of a spacer with the support. Finally, HA/PLL/HA capping layers were deposited on top of the architecture to form a composite AgNO 3 coating. Release of encapsulated AgNO 3 from this composite coating was followed and triggered upon temperature increase over the transition temperature of vesicles, found to be equal to 34 degrees C. After determination of the minimal inhibitory concentration (MIC) of AgNO 3 in solution, the antibacterial activity of the AgNO 3 coating was investigated against Escherichia coli. A 4-log reduction in the number of viable E. coli cells was observed after contact for 120 min with a 120 ng/cm (2) AgNO 3 coating. In comparison, no bactericidal activity was found for PLL/HA films previously dipped in an AgNO 3 solution and for PLL/HA films with liposome aggregates containing no AgNO 3 solution. The strong bactericidal effect could be linked to the diffusion of silver ions out of the AgNO 3 coating, leading to an important bactericidal concentration close to the membrane of the bacteria. A simple method to prepare antibacterial coatings loaded with a high and controlled amount of AgNO 3 is therefore proposed. This procedure is far superior to that soaking AgNO 3 or Ag nanoparticles into a coating. In principle, other small bactericidal chemicals like antibiotics could be encapsulated by this method. This study opens a new route to modify surfaces with small solutes that are not permeating phospholipid membranes below the phase transition temperature.

Micro-stratified architectures based on successive stacking of alginate gel layers and poly(l-lysine)-hyaluronic acid multilayer films aimed at tissue engineering

A micro-stratified 3D scaffold was designed by successive stacking of alginate gel layers (AGLs) and poly(l-lysine)-hyaluronic acid (PLL-HA) multilayer films. AGLs are obtained by complexation of alginate by Ca2+ ions. Alginate solutions are first sprayed onto a solid substrate inclined such that the excess of solution be removed by natural drainage. A CaCl2 solution is then either sprayed onto the substrate or the alginate covered substrate is dipped into a CaCl2 solution. The spraying of the CaCl2 solution leads to micro-porous AGLs, whereas the dipping in a CaCl2 aqueous solution leads to a more homogeneous gel layer without porosity. The second process also allows the formation of AGLs with a controlled thickness. With the goal of stacking different AGLs and PLL-HA films, the influence of a PLL-HA precursor film on the formation of AGLs is firstly investigated. It is found that when an alginate solution is sprayed on a PLL-HA multilayer built in the presence of CaCl2, the multilayer plays the role of reservoir of Ca2+ ions and of PLL chains, which both diffuse out of the multilayer film and complex alginate chains. This leads to the formation of a "pre-alginate gel". When this film is further dipped in the CaCl2 solution, an additional AGL forms, which is, however, free of PLL chains. Finally after the build-up of a PLL-HA film on the top of AGL, we succeeded in designing micro-stratified 3D scaffolds constituted by alternating strata of AGLs and PLL-HA films. This micro-stratified gel provides a new scaffold design with a perfectly controlled build-up: AGL aims to be a 3D scaffold for cell culture, and the PLL-HA multilayers should act as reservoirs for biologically active molecules.