Bioinspired colloidal systems via layer-by-layer assembly

Tackling breast cancer with gold nanoparticles: twinning synthesis and particle engineering with efficacy

The World Health Organization identifies breast cancer as the most prevalent cancer despite predominantly affecting women. Surgery, hormonal therapy, chemotherapy, and radiation therapy are the current treatment modalities. Site-directed nanotherapeutics, engineered with multidimensional functionality are now the frontrunners in breast cancer diagnosis and treatment. Gold nanoparticles with their unique colloidal, optical, quantum, magnetic, mechanical, and electrical properties have become the most valuable weapon in this arsenal. Their advantages include facile modulation of shape and size, a high degree of reproducibility and stability, biocompatibility, and ease of particle engineering to induce multifunctionality. Additionally, the surface plasmon oscillation and high atomic number of gold provide distinct advantages for tailor-made diagnosis, therapy or theranostic applications in breast cancer such as photothermal therapy, radiotherapy, molecular labeling, imaging, and sensing. Although pre-clinical and clinical data are promising for nano-dimensional gold, their clinical translation is hampered by toxicity signs in major organs like the liver, kidneys and spleen. This has instigated global scientific brainstorming to explore feasible particle synthesis and engineering techniques to simultaneously improve the efficacy and versatility and widen the safety window of gold nanoparticles. The present work marks the first study on gold nanoparticle design and maneuvering techniques, elucidating their impact on the pharmacodynamics character and providing a clear-cut scientific roadmap for their fast-track entry into clinical practice.

A Facile Method to Coat Nanoparticles with Lipid Bilayer Membrane: Hybrid Silica Nanoparticles Disguised as Biomembrane Vesicles by Particle Penetration of Concentrated Lipid Layers

Natural membrane vesicles, including extracellular vesicles and enveloped viruses, participate in various events in vivo. To study and manipulate these events, biomembrane-coated nanoparticles inspired by natural membrane vesicles are developed. Herein, an efficient method is presented to prepare organic-inorganic hybrid materials in high yields that can accommodate various lipid compositions and particle sizes. To demonstrate this method, silica nanoparticles are passed through concentrated lipid layers prepared using density gradient centrifugation, followed by purification, to obtain lipid membrane-coated nanoparticles. Various lipids, including neutral, anionic, and cationic lipids, are used to prepare concentrated lipid layers. Single-particle analysis by imaging flow cytometry determines that silica nanoparticles are uniformly coated with a single lipid bilayer. Moreover, cellular uptake of silica nanoparticles is enhanced when covered with a lipid membrane containing cationic lipids. Finally, cell-free protein expression is applied to embed a membrane protein, namely the Spike protein of severe acute respiratory syndrome coronavirus 2, into the coating of the nanoparticles, with the correct orientation. Therefore, this method can be used to develop organic-inorganic hybrid nanomaterials with an inorganic core and a virus-like coating, serving as carriers for targeted delivery of cargos such as proteins, DNA, and drugs.

Surface Modification with Particles Coated or Made of Polymer Multilayers

The coating of particles or decomposable cores with polyelectrolytes via Layer-by-Layer (LbL) assembly creates free-standing LbL-coated functional particles. Due to the numerous functions that their polymers can bestow, the particles are preferentially selected for a plethora of applications, including, but not limited to coatings, cargo-carriers, drug delivery vehicles and fabric enhancements. The number of publications discussing the fabrication and usage of LbL-assembled particles has consistently increased over the last vicennial. However, past literature fails to either mention or expand upon how these LbL-assembled particles immobilize on to a solid surface. This review evaluates examples of LbL-assembled particles that have been immobilized on to solid surfaces. To aid in the formulation of a mechanism for immobilization, this review examines which forces and factors influence immobilization, and how the latter can be confirmed. The predominant forces in the immobilization of the particles studied here are the Coulombic, capillary, and adhesive forces; hydrogen bonding as well as van der Waal's and hydrophobic interactions are also considered. These are heavily dependent on the factors that influenced immobilization, such as the particle morphology and surface charge. The shape of the LbL particle is related to the particle core, whereas the charge was dependant on the outermost polyelectrolyte in the multilayer coating. The polyelectrolytes also determine the type of bonding that a particle can form with a solid surface. These can be via either physical (non-covalent) or chemical (covalent) bonds; the latter enforcing a stronger immobilization. This review proposes a fundamental theory for immobilization pathways and can be used to support future research in the field of surface patterning and for the general modification of solid surfaces with polymer-based nano- and micro-sized polymer structures.

Magnetically responsive polycaprolactone nanocarriers for application in the biomedical field: magnetic hyperthermia, magnetic resonance imaging, and magnetic drug delivery

There are huge demands on multifunctional nanocarriers to be used in nanomedicine. Herein, we present a simple and efficient method for the preparation of multifunctional magnetically responsive polymeric-based nanocarriers optimized for biomedical applications. The hybrid delivery system is composed of drug-loaded polymer nanoparticles (poly(caprolactone), PCL) coated with a multilayer shell of polyglutamic acid (PGA) and superparamagnetic iron oxide nanoparticles (SPIONs), which are known as bio-acceptable components. The PCL nanocarriers with a model anticancer drug (Paclitaxel, PTX) were formed by the spontaneous emulsification solvent evaporation (SESE) method, while the magnetically responsive multilayer shell was formed via the layer-by-layer (LbL) method. As a result, we obtained magnetically responsive polycaprolactone nanocarriers (MN-PCL NCs) with an average size of about 120 nm. Using the 9.4 T preclinical magnetic resonance imaging (MRI) scanner we confirmed, that obtained MN-PCL NCs can be successfully used as a MRI-detectable drug delivery system. The magnetic hyperthermia effect of the MN-PCL NCs was demonstrated by applying a 25 mT radio-frequency (f = 429 kHz) alternating magnetic field. We found a Specific Absorption Rate (SAR) of 55 W g-1. The conducted research fulfills the first step of investigation for biomedical application, which is mandatory for the planning of any in vitro and in vivo studies.

Biomedical Applications of Multifunctional Polymeric Nanocarriers: A Review of Current Literature

Polymeric nanomaterials have become a prominent area of research in the field of drug delivery. Their application in nanomedicine can improve bioavailability, pharmacokinetics, and, therefore, the effectiveness of various therapeutics or contrast agents. There are many studies for developing new polymeric nanocarriers; however, their clinical application is somewhat limited. In this review, we present new complex and multifunctional polymeric nanocarriers as promising and innovative diagnostic or therapeutic systems. Their multifunctionality, resulting from the unique chemical and biological properties of the polymers used, ensures better delivery, and a controlled, sequential release of many different therapeutics to the diseased tissue. We present a brief introduction of the classical formulation techniques and describe examples of multifunctional nanocarriers, whose biological assessment has been carried out at least in vitro. Most of them, however, also underwent evaluation in vivo on animal models. Selected polymeric nanocarriers were grouped depending on their medical application: anti-cancer drug nanocarriers, nanomaterials delivering compounds for cancer immunotherapy or regenerative medicine, components of vaccines nanomaterials used for topical application, and lifestyle diseases, ie, diabetes.

Electrostatic Assembly Technique for Novel Composites Fabrication

Electrostatic assembly is one of the bottom–up approaches used for multiscale composite fabrication. Since its discovery, this method has been actively used in molecular bioscience as well as materials design and fabrication for various applications. Despite the recent advances and controlled assembly reported using electrostatic interaction, the method still possesses vast potentials for various materials design and fabrication. This review article is a timely revisit of the electrostatic assembly method with a brief introduction of the method followed by surveys of recent advances and applications of the composites fabricated. Emphasis is also given to the significant potential of this method for advanced materials and composite fabrication in line with sustainable development goals. Prospective outlook and future developments for micro-/nanocomposite materials fabrication for emerging applications such as energy-related fields and additive manufacturing are also mentioned.

Polymeric Core-Shell Nanoparticles Prepared by Spontaneous Emulsification Solvent Evaporation and Functionalized by the Layer-by-Layer Method

The aim of our study was to develop a novel method for the preparation of polymeric core-shell nanoparticles loaded with various actives for biomedical applications. Poly(caprolactone) (PCL), poly(lactic acid) (PLA) and poly(lactide-co-glycolide) (PLGA) nanoparticles were prepared using the spontaneous emulsification solvent evaporation (SESE) method. The model active substance, Coumarin-6, was encapsulated into formed polymeric nanoparticles, then they were modified/functionalized by multilayer shells' formation. Three types of multilayered shells were formed: two types of polyelectrolyte shell composed of biocompatible and biodegradable polyelectrolytes poly-L-lysine hydrobromide (PLL), fluorescently-labeled poly-L-lysine (PLL-ROD), poly-L-glutamic acid sodium salt (PGA) and pegylated-PGA (PGA-g-PEG), and hybrid shell composed of PLL, PGA, and SPIONs (superparamagnetic iron oxide nanoparticles) were used. Multilayer shells were constructed by the saturation technique of the layer-by-layer (LbL) method. Properties of our polymeric core-shell nanoparticle were optimized for bioimaging, passive and magnetic targeting.

Micro- and Nano-assembly of Composite Particles by Electrostatic Adsorption

This work reports on a novel controlled nanocomposite fabrication technique which is applicable for material design via a micro- and nano-assembly method. The principle is based on the use of electrostatic adsorption of the surface charge-modified particles via layer-by-layer assembly. The polarity and the zeta potential of the surface charge was controlled using polycation and polyanion, while the zeta potential strength was controlled via the number of alternating coating layers which was determined using zeta potential measurement. A systematic study was conducted to demonstrate the feasibility of composite material assembly via electrostatic adsorption using alumina (Al2O3) and silica (SiO2) composite as a study model, which was carried out as a function of surface zeta potential, surface coverage percentage, and processing time. The considerable potential of this technique for composite material design is also further demonstrated with controlled assembly involving different materials in various structural forms such as fiber, whisker, nanosheets, and even irregular-shaped foam-like structured urethane. The composite materials designed using this EA method possess good potentials to be utilized for various applications such as mechanical property control, composite ceramic films formation, selective laser sintering, and rechargeable metal-air battery.

Microcapsule-Based Signal Amplification Method for Biomolecules

The direct signal amplification of target molecules could be an effective means of increasing the sensitivity and reducing the size of biosensors. The purpose of this study was to propose a novel signal amplification method suitable for the detection of biomolecules using microcapsules that can quickly respond to concentration variation. This microcapsule-based amplification method consists of two elements-microcapsules and a well-array. The microcapsules consist of (i) an inner shell fabricated through layer-by-layer assembly, (ii) a lipid bilayer, and (iii) loaded target molecules. In this method, the inner surface of the well-array was modified using TiO2 as a photocatalyst. The diameter and thickness of the fabricated micro-capsules for biomarker loading were shown to be 2.7 μm and 78 nm, respectively. An ultraviolet (UV) irradiation time of 5 min was needed when the change in optical density reached 90% saturation of the optical density change. Dye molecules were incorporated into the microcapsules and were subsequently released, and the concentration of the released solution changed in proportion with the encapsulated dye concentration. This demonstrates the proof of concept for this novel signal amplification method based on microcapsules.

Encapsulation of Multiple Microalgal Cells via a Combination of Biomimetic Mineralization and LbL Coating

The encapsulation of living cells is appealing for its various applications to cell-based sensors, bioreactors, biocatalysts, and bioenergy. In this work, we introduce the encapsulation of multiple microalgal cells in hollow polymer shells of rhombohedral shape by the following sequential processes: embedding of microalgae in CaCO₃ crystals; layer-by-layer (LbL) coating of polyelectrolytes; and removal of sacrificial crystals. The microcapsule size was controlled by the alteration of CaCO₃ crystal size, which is dependent on CaCl₂/Na₂CO₃ concentration. The microalgal cells could be embedded in CaCO₃ crystals by a two-step process: heterogeneous nucleation of crystal on the cell surface followed by cell embedment by the subsequent growth of crystal. The surfaces of the microalgal cells were highly favorable for the crystal growth of calcite; thus, micrometer-sized microalgae could be perfectly occluded in the calcite crystal without changing its rhombohedral shape. The surfaces of the microcapsules, moreover, could be decorated with gold nanoparticles, Fe₃O₄ magnetic nanoparticles, and carbon nanotubes (CNTs), by which we would expect the functionalities of a light-triggered release, magnetic separation, and enhanced mechanical and electrical strength, respectively. This approach, entailing the encapsulation of microalgae in semi-permeable and hollow polymer microcapsules, has the potential for application to microbial-cell immobilization for high-biomass-concentration cultivation as well as various other bioapplications.

Complement activation by gold nanoparticles passivated with polyelectrolyte ligands

Gold nanoparticles passivated by polyelectrolyte ligands are widely used to confer stability and biofunctionality. While nanoparticles and polyelectrolytes have been reported as activators, their ability to activate the complement system as hybrid polyelectrolyte-coated nanoparticles is poorly characterized. Here, we found that gold nanoparticles passivated by common polyelectrolytes activated the system differently. The surface area of AuNPs appeared to be a major determinant of complement activation level as it determined the amount of adsorbed polyelectrolytes. Although a moderate negative correlation between AuNP surface hydrophilicity and their activation level was observed, the surface charge and functional group of polyelectrolyte ligands also influenced the final complement activation level.

We reported that the surface area and hydrophilicity of polyelectrolyte-coated gold nanoparticles influence their complement activation, a biological response not well understood to date.

Equilibrium, Kinetic and Thermodynamic Study of Removal of Eosin Yellow from Aqueous Solution Using Teak Leaf Litter Powder

Low-cost teak leaf litter powder (TLLP) was prepared as possible substitute for activated carbon. The feasibility of using the adsorbent to remove eosin yellow (EY) dye from aqueous solution was investigated through equilibrium adsorption, kinetic and thermodynamic studies. The removal of dye from aqueous solution was feasible but influenced by temperature, pH, adsorbent dosage and contact time. Variation in the initial concentration of dye did not influence the equilibrium contact time. Optimum adsorption of dye occurred at low adsorbent dosages, alkaline pH and high temperatures. Langmuir isotherm model best fit the equilibrium adsorption data and the maximum monolayer capacity of the adsorbent was 31.64 mg g-1 at 303 K. The adsorption process was best described by pseudo-second order kinetic model at 303 K. Boundary layer diffusion played a key role in the adsorption process. The mechanism of uptake of EY by TLLP was controlled by both liquid film diffusion and intraparticle diffusion. The values of mean adsorption free energy, E (7.91 kJ mol-1), and standard enthalpy, ΔH° (+13.34 kJ mol-1), suggest physical adsorption. The adsorption process was endothermic and spontaneous. Teak leaf litter powder is a promising low-cost adsorbent for treating wastewaters containing eosin yellow.

Reversible Assembly of Graphitic Carbon Nitride 3D Network for Highly Selective Dyes Absorption and Regeneration

Responsive assembly of 2D materials is of great interest for a range of applications. In this work, interfacial functionalized carbon nitride (CN) nanofibers were synthesized by hydrolyzing bulk CN in sodium hydroxide solution. The reversible assemble and disassemble behavior of the as-prepared CN nanofibers was investigated by using CO2 as a trigger to form a hydrogel network at first. Compared to the most widespread absorbent materials such as active carbon, graphene and previously reported supramolecular gel, the proposed CN hydrogel not only exhibited a competitive absorbing capacity (maximum absorbing capacity of methylene blue up to 402 mg/g) but also overcame the typical deficiencies such as poor selectivity and high energy-consuming regeneration. This work would provide a strategy to construct a 3D CN network and open an avenue for developing smart assembly for potential applications ranging from environment to selective extraction.

Encapsulation of clozapine in polymeric nanocapsules and its biological effects

Clozapine is an effective atypical antipsychotic drug that unfortunately exhibits poor oral bioavailability. Moreover, the clinical use of the compound is limited because of its numerous unfavorable and unsafe side effects. Therefore, the aim of the present study was the development of a new nanocarrier for a more effective clozapine delivery. Here, clozapine was encapsulated into polymeric nanocapsules (NCs). Polyelectrolyte multilayer shells were constructed by the technique of sequential adsorption of polyelectrolytes (LbL) using biocompatible polyanion PGA (Poly-L-glutamic acid, sodium salt) and polycation PLL (poly-L-lysine) on clozapine-loaded nanoemulsion cores. Pegylated external layers were prepared using PGA-g-PEG (PGA grafted by PEG (polyethylene glycol)). Clozapine was successfully loaded into the PLL-PGA nanocarriers (CLO-NCs) with an average size of 100 nm. In vitro analysis of the interactions of the CLO-NCs with the cells of the mononuclear phagocytic system (MPS) was conducted. Cell biocompatibility, phagocytosis potential, and cellular uptake were studied. Additionally, the biodistribution and behavioral effects of the encapsulated clozapine were also studied. The results indicate that surface modified (by PEG grafting) polymeric PLL-PGA CLO-NCs are very promising nanovehicles for improving clozapine delivery.

Cellular uptake of multilayered capsules produced with natural and genetically engineered biomimetic macromolecules

Multilayered microcapsules of chitosan and biomimetic elastin-like recombinamers (ELRs) were prepared envisaging the intracellular delivery of active agents. Two ELRs containing either a bioactive RGD sequence or a scrambled non-functional RDG were used to construct two types of functionalized polymeric microcapsules, both of spherical shape ∼4μm in diameter. Cell viability studies with human mesenchymal stem cells (hMSCs) were performed using microcapsule/cell ratios between 5:1 and 100:1. After 3 and 72h of co-incubation, no signs of cytotoxicity were found, but cells incubated with RGD-functionalized microcapsules exhibited higher viability values than RDG cells. The internalization efficacy and bioavailability of encapsulated DQ-ovalbumin were assessed by monitoring the fluorescence changes in the cargo. The data show that surface functionalization did not significantly influence internalization by hMSCs, but the bioavailability of DQ-ovalbumin degraded faster when encapsulated within RGD-functionalized microcapsules. The microcapsules developed show promise for intracellular drug delivery with increased drug efficacy.

kT-Scale interactions between supported lipid bilayers

We use total internal reflection microscopy (TIRM) and confocal laser scanning microscopy (CSLM) to study supported lipid bilayer (SLB)-modified silica colloids with various SLB compositions (e.g., PEGylated vs. non-PEGylated) that control colloidal and bilayer stability. Measured and predicted potentials accurately capture stable configurations. For unstable conditions when SLBs adhere, fuse, or spread between surfaces, SLB structures are connected to effective potentials as well as time-dependent behavior. In all cases, directly measured and inferred interactions are well described by steric interactions between PEG brushes and van der Waals weakened by substrate roughness. Our findings quantify non-specific kT-scale interactions between SLB-modified colloids and surfaces, which enables the design of such systems for use in biomedical applications and studies of biomolecular interactions.

Characterization of PAH/DPPG layer-by-layer films by VUV spectroscopy

The spectroscopic characterization of layer-by-layer (LbL) films containing liposomes is essential not only for determining the precise film architecture but also to guide the design of drug delivery systems. In this study we provide the first report of vacuum ultraviolet spectroscopy (VUV) characterization of LbL films made with liposomes from 1.2-dipalmitoyl-sn-Glycero-3-[Phospho-rac-(1-glycerol)] (Sodium Salt) (DPPG) alternated with poly(allylamine hydrochloride) (PAH). Measurements in the 6.0-9.5eV range allowed us to identify the electronic transitions responsible for the spectra, which were assigned to carboxyl, hydroxyl and phosphate groups in DPPG while the PAH spectra were governed by electronic transitions in the amino groups. The surface mass density of the LbL films could be determined, from which the formation of a DPPG bilayer was inferred. This rupture of the liposomes into bilayers was confirmed with atomic force microscopy measurements. In subsidiary experiments we ensured that the UV irradiation in vacuum had negligible damage in the DPPG liposomes during the course of the VUV measurements. In addition to demonstrating the usefulness of VUV spectroscopy, the results presented here may be exploited in biological applications of liposome-containing films.

In situ-ATR-FTIR analysis on the uptake and release of streptomycin from polyelectrolyte complex layers

In-situ ATR-FTIR spectroscopy and line shape analysis of the diagnostic spectral region was used to quantify the bound amount and release of the antibiotic streptomycin (STRP) at polyelectrolyte (PEL) multilayers (PEM) of poly(ethyleneimine) (PEI) and poly(acrylic acid) (PAA) or PEI and sodium alginate (ALG). Unlike common concepts based on the drug enrichment of the release medium, this analytical concept allowed to measure quantitatively the drug depletion in the delivery matrix. The measured kinetic in situ ATR-FTIR data were analysed by a modified Korsmeyer-Peppas equation based on two characteristic release parameters k and n. As main experimental parameters the number of PEL layers (adsorption steps) z and the STRP/PEL ratio were varied. For z=8 the STRP/PEL ratio showed the most significant influence on release kinetics, whereby for STRP/PEL=1:25 slowest (n=0.77) and lowest (k=21.4%) and for STRP/PEL=1:5 most rapid (n=0.30) and highest (k=58.6%) drug releases were found. PEM-PEI/ALG-8 (STRP/PEL=1:5) revealed slower release rates (n=0.58) and lower released STRP amounts (k=17.1%) compared to PEI/PAA. UV-VIS data on time dependent STRP enrichment of the release medium showed a similar trend compared to respective ATR-FTIR data on STRP depletion in PEM. Released amounts of around 1-2mg from the herein introduced PEM films could be determined. The introduced analytical concept will be used as screening tool for other drugs, drug eluting films and bone substituting materials.

Bioluminescent microcapsules: applications in activating a photosensitizer

Bioluminescent microcapsules uploading D-luciferin have been fabricated by using the covalent assembly of firefly luciferase and alginate dialdehyde through a layer-by-layer technique. Such assembled microcapsules can produce visible light in the region of 520-680 nm, which can activate the photosensitizers rose bengal (RB) and hypocrellin B (HB) after adding ATP. The microcapsules uploading photosensitizers (RB or HB) have an obvious property to prevent the proliferation of tumor cells in the dark. The assembled bioluminescent microcapsules can be potentially used as photon donors for bioimaging, ATP detection, and photodynamic therapy.

Surface functionalization of nanoparticles to control cell interactions and drug release

Nanoparticles made from poly(dl-lactide-co-glycolide) (PLGA) are used to deliver a wide range of bioactive molecules, due to their biocompatibility and biodegradability. This study investigates the surface modification of PLGA nanoparticles via the layer-by-layer (LbL) deposition of polyelectrolytes, and the effects of these coatings on the release behavior, cytotoxicity, hemolytic activity, and cellular uptake efficiency. PLGA nanoparticles are modified via LbL adsorption of two polyelectrolyte pairs: 1) poly(allylamine hydrochloride) (PAH) and poly(styrene sulfonate) (PSS) and 2) poly(L-lysine hydrobromide) (PLL) and dextran sulfate (DES). It is demonstrated that both PAH/PSS and PLL/DES coatings suppress the burst release usually observed for unmodified PLGA nanoparticles and that the release behavior can be adjusted by changing the layer numbers, layer materials, or by crosslinking the layer constituents. Neither bare nor polyelectrolyte-modified PLGA nanoparticles show any signs of cytotoxicity. However, nanoparticles with a positively charged polyelectrolyte as the outermost layer induce hemolysis, whereas uncoated particles or particles with a negatively charged polyelectrolyte as the outermost layer show no hemolytic activity. Furthermore, particles with either PAH or PLL as the outermost layer also demonstrate a higher uptake efficiency by L929 fibroblast cells, due to a higher cell-particle affinity. This study suggests that LbL coating of PLGA nanoparticles can control the release behavior of bioactive molecules as well as the surface activity, therefore providing a promising strategy to enhance the efficiency of nanoparticulate drug-delivery systems.

Rapid release of plasmid DNA from surfaces coated with polyelectrolyte multilayers promoted by the application of electrochemical potentials

We report an approach to the rapid release of DNA based on the application of electrochemical potentials to surfaces coated with polyelectrolyte-based thin films. We fabricated multilayered polyelectrolyte films (or "polyelectrolyte multilayers", PEMs) using plasmid DNA and a model hydrolytically degradable cationic poly(β-amino ester) (polymer 1) on stainless steel substrates using a layer-by-layer approach. The application of continuous reduction potentials in the range of -1.1 to -0.7 V (vs a Ag/AgCl electrode) to film-coated electrodes in PBS at 37 °C resulted in the complete release of DNA over a period of 1-2 min. Film-coated electrodes incubated under identical conditions in the absence of applied potentials required 1-2 days for complete release. Control over the magnitude of the applied potential provided control over the rate at which DNA was released. The results of these and additional physical characterization experiments are consistent with a mechanism of film disruption that is promoted by local increases in pH at the film/electrode interface (resulting from electrochemical reduction of water or dissolved oxygen) that disrupt ionic interactions in these materials. The results of cell-based experiments demonstrated that DNA was released in a form that remains intact and able to promote transgene expression in mammalian cells. Finally, we demonstrate that short-term (i.e., non-continuous) electrochemical treatments can also be used to promote faster film erosion (e.g., over 1-2 h) once the potential is removed. Past studies demonstrate that PEMs fabricated using polymer 1 can promote surface-mediated transfection of cells and tissues in vitro and in vivo. With further development, the electrochemical approaches reported here could thus provide new methods for the rapid, triggered, or spatially patterned transfer of DNA (or other agents) from surfaces of interest in a variety of fundamental and applied contexts.

Drug-loaded polyelectrolyte microcapsules for sustained targeting of cancer cells

In this review we will overview novel nanotechnological nanocarrier systems for cancer therapy focusing on recent development in polyelectrolyte capsules for targeted delivery of antineoplastic drugs against cancer cells. Biodegradable polyelectrolyte microcapsules (PMCs) are supramolecular assemblies of particular interest for therapeutic purposes, as they can be enzymatically degraded into viable cells, under physiological conditions. Incorporation of small bioactive molecules into nano-to-microscale delivery systems may increase drug's bioavailability and therapeutic efficacy at single cell level giving desirable targeted therapy. Layer-by-layer (LbL) self-assembled PMCs are efficient microcarriers that maximize drug's exposure enhancing antitumor activity of neoplastic drug in cancer cells. They can be envisaged as novel multifunctional carriers for resistant or relapsed patients or for reducing dose escalation in clinical settings.

Stimuli-responsive LbL capsules and nanoshells for drug delivery

Review of basic principles and recent developments in the area of stimuli responsive polymeric capsules and nanoshells formed via layer-by-layer (LbL) is presented. The most essential attributes of the LbL approach are multifunctionality and responsiveness to a multitude of stimuli. The stimuli can be logically divided into three categories: physical (light, electric, magnetic, ultrasound, mechanical, and temperature), chemical (pH, ionic strength, solvent, and electrochemical) and biological (enzymes and receptors). Using these stimuli, numerous functionalities of nanoshells have been demonstrated: encapsulation, release including that inside living cells or in tissue, sensors, enzymatic reactions, enhancement of mechanical properties, and fusion. This review describes mechanisms and basic principles of stimuli effects, describes progress in the area, and gives an outlook on emerging trends such as theranostics and nanomedicine.

Layer-by-layer nanoparticles with a pH-sheddable layer for in vivo targeting of tumor hypoxia

Inspired by the simplicity and versatility of layer-by-layer (LbL) assembly, we applied multilayered polyelectrolyte assemblies on nanoparticles to create viable systemic delivery systems. Focusing on tumor-specific delivery, LbL nanoparticles that exhibit a pH-sensitive outer stealth layer are demonstrated to target and be retained in hypoxic tumor regions. The neutral layers shed in response to acidity to reveal a charged nanoparticle surface that is readily taken up by tumor cells. The first in vivo demonstration of this mechanism of targeting is presented, as well as an initial examination of the mechanism of uptake of the nanoparticles. We further demonstrate that this concept for tumor targeting is potentially valid for a broad range of cancers, with applicability for therapies that target hypoxic tumor tissue.

Interfacing multicellular organisms with polyelectrolyte shells and nanoparticles: a Caenorhabtidis elegans study

We report the surface modification of microscopic live multicellular nematodes Caenorhabtidis elegans with polyelectrolyte multilayers (pure and doped with 20 nm gold nanoparticles) and the direct magnetic functionalization of nematodes with biocompatible magnetic nanoparticles. Magnetically functionalized "ironoxideclad" nematodes can be effectively separated and moved using an external magnetic field. The surface-functionalized nematodes preserve their viability and reproduction.

Nanotubes protruding from poly(allylamine hydrochloride)-graft-pyrene microcapsules

Protrusion of one-dimensional nanotubes or nanorods from the poly(allylamine hydrochloride)-graft-pyrene (PAH-Py) microcapsules was discovered when the microcapsules were incubated in pH 0 and pH 2 solutions, respectively. Micelles assembled from deliberately synthesized PAH-Py polymers were also able to transform into one-dimensional structures, demonstrating the chemistry driven nature of the phenomenon. The one-dimensional nanotubes consisted of only 1-pyrenecarboxaldehyde with ordered π-π stacking, and showed a helical structure and anisotropic property. The hydrolysis of Schiff base and its rate at different pH values (10 times slower at pH 0 than at pH 2) played a key role in determining the final nanostructures, and the linear PAH directed the regular building up process especially for the nanotubes. Hollow capsules budded with nanotubes or nanorods mimicking the cellular protrusion of filopodia were successfully prepared by tuning the incubation pH and time. These results and the proposed mechanism open new opportunities for design of novel micronanostructures and materials for nanoscience, and biological and other advanced technologies.

Controlling in vivo stability and biodistribution in electrostatically assembled nanoparticles for systemic delivery

This paper demonstrates the generation of systemically deliverable layer-by-layer (LbL) nanoparticles for cancer applications. LbL-based nanoparticles designed to navigate the body and deliver therapeutics in a programmable fashion are promising new and alternative systems for drug delivery, but there have been very few demonstrations of their systemic delivery in vivo due to a lack of knowledge in building LbL nanofilms that mimic traditional nanoparticle design to optimize delivery. The key to the successful application of these nanocarriers in vivo requires a systematic analysis of the influence of film architecture and adsorbed polyelectrolyte outer layer on their pharmacokinetics, which has thus far not been examined for this new approach to nanoparticle delivery. Herein, we have taken the first steps in stabilizing and controlling the systemic distribution of multilayer nanoparticles. Our findings highlight the unique character of LbL systems; the electrostatically assembled nanoparticles gain increased stability in vivo with larger numbers of deposited layers, and the final layer adsorbed generates a critical surface cascade, which dictates the surface chemistry and biological properties of the nanoparticle. This outer polyelectrolyte layer dramatically affects not only the degree of nonspecific particle uptake, but also the nanoparticle biodistribution. For hyaluronic acid (HA) outer layers, a long blood elimination half-life (∼9 h) and low accumulation (∼10-15% recovered fluorescence/g) in the liver were observed, illustrating that these systems can be designed to be highly appropriate for clinical translation.

Fabrication of Covalently Crosslinked and Amine-Reactive Microcapsules by Reactive Layer-by-Layer Assembly of Azlactone-Containing Polymer Multilayers on Sacrificial Microparticle Templates

We report on the fabrication of covalently crosslinked and amine-reactive hollow microcapsules using 'reactive' layer-by-layer assembly to deposit thin polymer films on sacrificial microparticle templates. Our approach is based on the alternating deposition of layers of a synthetic polyamine and a polymer containing reactive azlactone functionality. Multilayered films composed of branched poly(ethylene imine) (BPEI) and poly(2-vinyl-4,4-dimethylazlactone) (PVDMA) were fabricated layer-by-layer on the surfaces of calcium carbonate and glass microparticle templates. After fabrication, these films contained residual azlactone functionality that was accessible for reaction with amine-containing molecules. Dissolution of the calcium carbonate or glass cores using aqueous ethylenediamine tetraacetic acid (EDTA) or hydrofluoric acid (HF), respectively, led to the formation of hollow polymer microcapsules. These microcapsules were robust enough to encapsulate and retain a model macromolecule (FITC-dextran) and were stable for at least 22 hours in high ionic strength environments, in low and high pH solutions, and in several common organic solvents. Significant differences in the behaviors of capsules fabricated on CaCO(3) and glass cores were observed and characterized using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Whereas capsules fabricated on CaCO(3) templates collapsed upon drying, capsules fabricated on glass templates remained rigid and spherical. Characterization using EDS suggested that this latter behavior results, at least in part, from the presence of insoluble metal fluoride salts that are trapped or precipitate within the walls of capsules after etching of the glass cores using HF. Our results demonstrate that the assembly of BPEI/PVDMA films on sacrificial templates can be used to fabricate reactive microcapsules of potential use in a wide range of fields, including catalysis, drug and gene delivery, imaging, and biomedical research.

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.

pH-Sensitive breathing of clay within the polyelectrolyte matrix

Stimuli-responsive organic-inorganic hybrid spheres were synthesized by coating the colloidal polystyrene spheres with polyelectrolyte-protected aminoclay, Mg phyllo(organo)silicate layers in a layer-by-layer method. The clay layers are sandwiched between the polyelectrolyte layers. The aminoclay swells in water due to protonation of amino groups, and the degree of swelling depends on the pH of the medium. As a result, the hybrid spheres undergo a size change up to 60% as the pH is changed from 9 to 4. The stimuli-responsive property of the hybrid spheres was used for the release of ibuprofen and eosin at different pH.