Defoliation and Plasmid Delivery with Layer-by-Layer Coated Colloids

Layer-by-Layer Nanoparticle Assembly for Biomedicine: Mechanisms, Technologies, and Advancement via Acoustofluidics

The deposition of thin films plays a crucial role in surface engineering, tailoring structural modifications, and functionalization across diverse applications. Layer-by-layer self-assembly, a prominent thin-film deposition method, has witnessed substantial growth since its mid-20th-century inception, driven by the discovery of eligible materials and innovative assembly technologies. Of these materials, micro- and nanoscopic substrates have received far less interest than their macroscopic counterparts; however, this is changing. The catalogue of eligible materials, including nanoparticles, quantum dots, polymers, proteins, cells and liposomes, along with some well-established layer-by-layer technologies, have combined to unlock impactful applications in biomedicine, as well as other areas like food fortification, and water remediation. To access these fields, several well-established technologies have been used, including tangential flow filtration, fluidized bed, atomization, electrophoretic assembly, and dielectrophoresis. Despite the invention of these technologies, the field of particle layer-by-layer still requires further technological development to achieve a high-yield, automatable, and industrially ready process, a requirement for the diverse, reactionary field of biomedicine and high-throughput pharmaceutical industry. This review provides a background on layer-by-layer, focusing on how its constituent building blocks and bonding mechanisms enable unmatched versatility. The discussion then extends to established and recent technologies employed for coating micro- and nanoscopic matter, evaluating their drawbacks and advantages, and highlighting promising areas in microfluidic approaches, where one distinctly auspicious technology emerges, acoustofluidics. The review also explores the potential and demonstrated application of acoustofluidics in layer-by-layer technology, as well as analyzing existing acoustofluidic technologies beyond LbL coating in areas such as cell trapping, cell sorting, and multidimensional particle manipulation. Finally, the review concludes with future perspectives on layer-by-layer nanoparticle coating and the potential impact of integrating acoustofluidic methods.

Recent advances in microfluidic-based electroporation techniques for cell membranes

Electroporation is a fundamental technique for applications in biotechnology. To date, the ongoing research on cell membrane electroporation has explored its mechanism, principles and potential applications. Therefore, in this review, we first discuss the primary electroporation mechanism to help establish a clear framework. Within the context of its principles, several critical terms are highlighted to present a better understanding of the theory of aqueous pores. Different degrees of electroporation can be used in different applications. Thus, we discuss the electric factors (shock strength, shock duration, and shock frequency) responsible for the degree of electroporation. In addition, finding an effective electroporation detection method is of great significance to optimize electroporation experiments. Accordingly, we summarize several primary electroporation detection methods in the following sections. Finally, given the development of micro- and nano-technology has greatly promoted the innovation of microfluidic-based electroporation devices, we also present the recent advances in microfluidic-based electroporation devices. Also, the challenges and outlook of the electroporation technique for cell membrane electroporation are presented.

Polyelectrolyte Multilayered Capsules as Biomedical Tools

Polyelectrolyte multilayered capsules (PEMUCs) obtained using the Layer-by-Layer (LbL) method have become powerful tools for different biomedical applications, which include drug delivery, theranosis or biosensing. However, the exploitation of PEMUCs in the biomedical field requires a deep understanding of the most fundamental bases underlying their assembly processes, and the control of their properties to fabricate novel materials with optimized ability for specific targeting and therapeutic capacity. This review presents an updated perspective on the multiple avenues opened for the application of PEMUCs to the biomedical field, aiming to highlight some of the most important advantages offered by the LbL method for the fabrication of platforms for their use in the detection and treatment of different diseases.

The Metabolic Response of Various Cell Lines to Microtubule-Driven Uptake of Lipid- and Polymer-Coated Layer-by-Layer Microcarriers

Lipid structures, such as liposomes or micelles, are of high interest as an approach to support the transport and delivery of active agents as a drug delivery system. However, there are many open questions regarding their uptake and impact on cellular metabolism. In this study, lipid structures were assembled as a supported lipid bilayer on top of biopolymer-coated microcarriers based on the Layer-by-Layer assembly strategy. The functionalized microcarriers were then applied to various human and animal cell lines in addition to primary human macrophages (MΦ). Here, their influence on cellular metabolism and their intracellular localization were detected by extracellular flux analysis and immunofluorescence analysis, respectively. The impact of microcarriers on metabolic parameters was in most cell types rather low. However, lipid bilayer-supported microcarriers induced a decrease in oxygen consumption rate (OCR, indicative for mitochondrial respiration) and extracellular acidification rate (ECAR, indicative for glycolysis) in Vero cells. Additionally, in Vero cells lipid bilayer microcarriers showed a more pronounced association with microtubule filaments than polymer-coated microcarrier. Furthermore, they localized to a perinuclear region and induced nuclei with some deformations at a higher rate than unfunctionalized carriers. This association was reduced through the application of the microtubule polymerization inhibitor nocodazole. Thus, the effect of respective lipid structures as a drug delivery system on cells has to be considered in the context of the respective target cell, but in general can be regarded as rather low.

Degradation of Drug Delivery Nanocarriers and Payload Release: A Review of Physical Methods for Tracing Nanocarrier Biological Fate

Nanoformulations offer multiple advantages over conventional drug delivery, enhancing solubility, biocompatibility, and bioavailability of drugs. Nanocarriers can be engineered with targeting ligands for reaching specific tissue or cells, thus reducing the side effects of payloads. Following systemic delivery, nanocarriers must deliver encapsulated drugs, usually through nanocarrier degradation. A premature degradation, or the loss of the nanocarrier coating, may prevent the drug's delivery to the targeted tissue. Despite their importance, stability and degradation of nanocarriers in biological environments are largely not studied in the literature. Here we review techniques for tracing the fate of nanocarriers, focusing on nanocarrier degradation and drug release both intracellularly and in vivo. Intracellularly, we will discuss different fluorescence techniques: confocal laser scanning microscopy, fluorescence correlation spectroscopy, lifetime imaging, flow cytometry, etc. We also consider confocal Raman microscopy as a label-free technique to trace colocalization of nanocarriers and drugs. In vivo we will consider fluorescence and nuclear imaging for tracing nanocarriers. Positron emission tomography and single-photon emission computed tomography are used for a quantitative assessment of nanocarrier and payload biodistribution. Strategies for dual radiolabelling of the nanocarriers and the payload for tracing carrier degradation, as well as the efficacy of the payload delivery in vivo, are also discussed.

Nanotechnology-based approaches for emerging and re-emerging viruses: Special emphasis on COVID-19

In recent decades, the major concern of emerging and re-emerging viral diseases has become an increasingly important area of public health concern, and it is of significance to anticipate future pandemic that would inevitably threaten human lives. The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a newly emerged virus that causes mild to severe pneumonia. Coronavirus disease (COVID-19) became a very much concerned issue worldwide after its super-spread across the globe and emerging viral diseases have not got specific and reliable diagnostic and treatments. As the COVID-19 pandemic brings about a massive life-loss across the globe, there is an unmet need to discover a promising and typically effective diagnosis and treatment to prevent super-spreading and mortality from being decreased or even eliminated. This study was carried out to overview nanotechnology-based diagnostic and treatment approaches for emerging and re-emerging viruses with the current treatment of the disease and shed light on nanotechnology's remarkable potential to provide more effective treatment and prevention to a special focus on recently emerged coronavirus.

Dual Transport of Active Substances with a Layer-by-Layer-Based Drug Delivery System to Terminate Inflammatory Processes

Conventional therapies for chronic inflammation with high dose application of active agents are often accompanied with severe side effects so that other therapeutical strategies shall be developed to be less physically demanding but still highly efficient. Locally applied Layer-by-Layer (LbL) microcarriers transporting a low, but efficient dosage of active agents directly into the inflamed tissue offer a gentle therapy option. Here, the inhibition of highly degradative enzyme human neutrophile elastase (HNE) is adressed, which is produced and secreted by neutrophile granulocytes (PMNs) in the progress of inflammation. The protected transport and release of its natural inhibitor α1-antitrypsin (AT) as a constituent of the microcarrier's biopolymer multilayer allows for an efficient inhibition of extra- and intracellular elastase. The HOCl scavenger molecule cefoperazone, which preserves AT activity, as an additional multilayer constituent induces a much higher efficacy of the inhibitor. The successful assembly of both agents in different layers of the multilayer and the subsequent HNE inhibition in PMNs is investigated. The parallel application of cefoperazone leads to an enhanced inhibitory effect even with reduced AT amount and reduced carrier:cell ratio. It is demonstrated that the modular assembly strategy of LbL carriers allows for efficient synergistic effect of active agents in inflammatory process.

In Vitro Bioeffects of Polyelectrolyte Multilayer Microcapsules Post-Loaded with Water-Soluble Cationic Photosensitizer

Microencapsulation and targeted delivery of cytotoxic and antibacterial agents of photodynamic therapy (PDT) improve the treatment outcomes for infectious diseases and cancer. In many cases, the loss of activity, poor encapsulation efficiency, and inadequate drug dosing hamper the success of this strategy. Therefore, the development of novel and reliable microencapsulated drug formulations granting high efficacy is of paramount importance. Here we report the in vitro delivery of a water-soluble cationic PDT drug, zinc phthalocyanine choline derivative (Cholosens), by biodegradable microcapsules assembled from dextran sulfate (DS) and poly-l-arginine (PArg). A photosensitizer was loaded in pre-formed [DS/PArg]4 hollow microcapsules with or without exposure to heat. Loading efficacy and drug release were quantitatively studied depending on the capsule concentration to emphasize the interactions between the DS/PArg multilayer network and Cholosens. The loading data were used to determine the dosage for heated and intact capsules to measure their PDT activity in vitro. The capsules were tested using human cervical adenocarcinoma (HeLa) and normal human dermal fibroblast (NHDF) cell lines, and two bacterial strains, Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli. Our results provide compelling evidence that encapsulated forms of Cholosens are efficient as PDT drugs for both eukaryotic cells and bacteria at specified capsule-to-cell ratios.

Enhanced Uptake and Endosomal Release of LbL Microcarriers Functionalized with Reversible Fusion Proteins

The efficient application of smart drug-delivery systems requires further improvement of their cellular uptake and in particular their release from endolysosomal compartments into the cytoplasm of target cells. The usage of virus proteins allows for such developments, as viruses have evolved efficient entry mechanisms into the cell, mediated by their fusion proteins. In our investigations, the transferability of the glycoprotein G which is a fusion protein of the vesicular stomatitis virus (VSV-G) onto the surface of a layer-by-layer (LbL) designed microcarrier was investigated. The assembly of VSV-G as a reversible viral fusion protein onto LbL microcarriers indeed induced an enhanced uptake rate on Vero cells as well as a fast and efficient release of the intact carriers from endolysosomes into the cytoplasm. Additionally, neither virus-associated effects on cellular viability nor activation of an interferon response were detected. Our study emphasizes the suitability of VSV-G as an efficient surface functionalization of drug-delivery systems.

Destruction of Polyelectrolyte Microcapsules Formed on CaCO3 Microparticles and the Release of a Protein Included by the Adsorption Method

The degradation of polyelectrolyte microcapsules formed on protein-free CaCO₃ particles consisting of polyallylamine (PAH) and polystyrene sulfonate (PSS) and the resulting yield of protein in the presence of various salts of different concentrations, as well as at two pH values, was studied by fluorescence spectroscopy; the protein was incorporated into prepared microcapsules by adsorption. It was found that a high concentration of sodium chloride (2 M) leads to considerable dissociation of PAH, which is apparently due to the loosening of polyelectrolytes under the action of ionic strength. At the same time, 0.2 M sodium chloride and ammonium sulfate of the same ionic strength (0.1 M) exert less influence on the amount of dissociated polymer. In the case of ammonium sulfate (0.1 M), the effect is due to the competitive binding of sulfate anions to the amino groups of the polyelectrolyte. However, unlike microcapsules formed on CaCO₃ particles containing protein, the dissociation of polyelectrolyte from microcapsules formed on protein-free particles increased with increasing temperature. Apparently, a similar effect is associated with the absence of a distinct shell, which was observed on microcapsules formed on protein-containing CaCO₃ particles. The high level of the presence of Fluorescein isothiocyanate (FITC)-labeled Bovine Serum Albumin (BSA) in the supernatant is explained by the large amount of electrostatically bound protein and the absence of a shell that prevents the release of the protein from the microcapsules. In 2M NaCl, during the observation period, the amount of the released protein did not exceed 70% of the total protein content in the capsules, in control samples, this value does not exceed 8%, which indicates the predominantly electrostatic nature of protein retention in capsules formed on protein-free CaCO₃ particles. The increase in protein yield and peeling of PAH with increasing pH is explained by the proximity of pH 7 to the point of charge exchange of the amino group of polyelectrolyte, as a result of the dissociation of the microcapsule.

Enhanced cytoplasmic release of drug delivery systems: chloroquine as a multilayer and template constituent of layer-by-layer microcarriers

Nano- and microcarriers as vehicles for active agents are applied to support them to reach their target in a defined, specific, and protected way. This implies not only a safe transport of agents towards the desired cell type or tissue but also the intracellular processing of the carrier: in particular, release of the incorporated carriers into the cytoplasm is a prerequisite for the successful subsequent delivery of most active agents and is often impeded by endolysosomal degenerative enzymes. We address this issue by using the layer-by-layer strategy of carrier assembly offering the opportunity to independently integrate and carry active agents but also specific agents preventing endolysosomal acidification. The weak base chloroquine (CQ) was investigated as a multilayer, template and capsule constituent regarding its ability to delay endolysosomal acidification and prolong the tolerable time frame in endolysosomes, which allows the carrier to finally escape into the cytoplasm. As a model and reporter active agent, plasmid encoding enhanced green fluorescent protein was used as a multilayer-assembly component to illustrate the cytoplasmic release of the intact carrier by final expression of the green fluorescent protein. Integrating CQ into the carrier, GFP expression could be strongly increased and a transfection efficiency of up to 20% could be obtained. This represents a very high transfection rate for a drug delivery system reached by only one additional reagent that has no further influence on the activity of the transported drug and cell viability, offering a significantly enhanced delivery efficiency.

Reversible Fusion Proteins as a Tool to Enhance Uptake of Virus-Functionalized LbL Microcarriers

For the efficient treatment of an increasing number of diseases the development of new therapeutics as well as novel drug delivery systems is essential. Such drug delivery systems (DDS) must not only consider biodegradability and protective packaging but must also target and control the release of active substances, which is one of the most important points in DDS application. We highlight the improvement of these key aspects, the increased interaction rate of Layer-by-Layer (LbL) designed microcarriers as a promising DDS after functionalization with vesicular stomatitis virus (VSV). We make use of the unique conformational reversibility of the fusion protein of VSV as a surface functionalization of LbL microcarriers. This reversibility allows for VSV to be used both as a tool for assembly onto the DDS and as an initiator for an efficient cellular uptake. We could show that the evolutionary optimized viral fusion machinery can be successfully combined with a biophysical DDS for optimization of its cellular interaction.

Cellular interaction of a layer-by-layer based drug delivery system depending on material properties and cell types

Background

Drug delivery systems (DDS) and their interaction with cells are a controversial topic in the development of therapeutic concepts and approaches. On one hand, DDS are very useful for protected and targeted transport of defined dosages of active agents. On the other hand, their physicochemical properties such as material, size, shape, charge, or stiffness have a huge impact on cellular uptake and intracellular processing. Additionally, even identical DDS can undergo a completely diverse interaction with different cell types. However, quite often in in vitro DDS/cell interaction experiments, those aspects are not considered and DDS and cells are randomly chosen.

Methods and results

Hence, our investigations provide an insight into layer-by-layer designed microcarriers with modifications of only some of the most important parameters (surface charge, stiffness, and applied microcarrier/cell ratio) and their influence on cellular uptake and viability. We also considered the interaction of these differently equipped DDS with several cell types and investigated professional phagocytes (neutrophil granulocytes; macrophages) as well as non-professional phagocytes (epithelial cells) under comparable conditions. We found that even small modifications such as layer-by-layer (LbL)-microcarriers with positive or negative surface charge, or LbL-microcarriers with solid core or as hollow capsules but equipped with the same surface properties, show significant differences in interaction and viability, and several cell types react very differently to the offered DDS.

Conclusion

As a consequence, the properties of the DDS have to be carefully chosen with respect to the addressed cell type with the aim to efficiently transport a desired agent.

Effects of Polyelectrolyte Microcapsules with Different Surface Charge on Erythrocyte Sedimentation Rate

Relationship between changes in the erythrocyte sedimentation rate in rats and concentration and charge of polyelectrolyte microcapsules was studied by the Panchenkov method. Positively charged microcapsules reduced erythrocyte sedimentation rate in a concentrationdependent manner. This effect was related to a decrease in the content of high-molecularweight proteins in the plasma due to their adsorption in positively charged microcapsules with polyacrylamide surface layer.

Engineering nanolayered particles for modular drug delivery

Layer-by-layer (LbL) based self-assembly of nanoparticles is an emerging and powerful method to develop multifunctional and tissue responsive nanomedicines for a broad range of diseases. This unique assembly technique is able to confer a high degree of modularity, versatility, and compositional heterogeneity to nanoparticles via the sequential deposition of alternately charged polyelectrolytes onto a colloidal template. LbL assembly can provide added functionality by directly incorporating a range of functional materials within the multilayers including nucleic acids, synthetic polymers, polypeptides, polysaccharides, and functional proteins. These materials can be used to generate hierarchically complex, heterogeneous thin films on an extensive range of both traditional and novel nanoscale colloidal templates, providing the opportunity to engineer highly precise systems capable of performing the numerous tasks required for systemic drug delivery. In this review, we will discuss the recent advancements towards the development of LbL nanoparticles for drug delivery and diagnostic applications, with a special emphasis on the incorporation of biostability, active targeting, desirable drug release kinetics, and combination therapies into LbL nanomaterials. In addition to these topics, we will touch upon the next steps for the translation of these systems towards the clinic.

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.

Specifically targeted delivery of protein to phagocytic macrophages

Macrophages play important roles in the pathogenesis of various diseases, and are important potential therapeutic targets. Furthermore, macrophages are key antigen-presenting cells and important in vaccine design. In this study, we report on the novel formulation (bovine serum albumin [BSA]-loaded glucan particles [GMP-BSA]) based on β-glucan particles from cell walls of baker’s yeast for the targeted delivery of protein to macrophages. Using this formulation, chitosan, tripolyphosphate, and alginate were used to fabricate colloidal particles with the model protein BSA via electrostatic interactions, which were caged and incorporated BSA very tightly within the β-glucan particle shells. The prepared GMP-BSA exhibited good protein-release behavior and avoided protein leakage. The particles were also highly specific to phagocytic macrophages, such as Raw 264.7 cells, primary bone marrow-derived macrophages, and peritoneal exudate macrophages, whereas the particles were not taken up by nonphagocytic cells, including NIH3T3, AD293, HeLa, and Caco-2. We hypothesize that these tightly encapsulated protein-loaded glucan particles deliver various types of proteins to macrophages with notably high selectivity, and may have broad applications in targeted drug delivery or vaccine design against macrophages.

Gold nanodome-patterned microchips for intracellular surface-enhanced Raman spectroscopy

Top-down patterned gold nanodome microchips are taken up by living cells and serve as a uniform and reproducible sensor for intracellular surface-enhanced Raman scattering.

Layered polymeric capsules inhibiting the activity of RNases for intracellular delivery of messenger RNA

Delivery of luciferase messenger RNA to HEK293T cells is successfully performed by polymer multilayer microcapsules co-encapsulating RNase inhibitors.

Layer-by-layer nanoparticles as an efficient siRNA delivery vehicle for SPARC silencing

Efficient and safe delivery systems for siRNA therapeutics remain a challenge. Elevated secreted protein, acidic, and rich in cysteine (SPARC) protein expression is associated with tissue scarring and fibrosis. Here we investigate the feasibility of encapsulating SPARC-siRNA in the bilayers of layer-by-layer (LbL) nanoparticles (NPs) with poly(L-arginine) (ARG) and dextran (DXS) as polyelectrolytes. Cellular binding and uptake of LbL NPs as well as siRNA delivery were studied in FibroGRO cells. siGLO-siRNA and SPARC-siRNA were efficiently coated onto hydroxyapatite nanoparticles. The multilayered NPs were characterized with regard to particle size, zeta potential and surface morphology using dynamic light scattering and transmission electron microscopy. The SPARC-gene silencing and mRNA levels were analyzed using ChemiDOC western blot technique and RT-PCR. The multilayer SPARC-siRNA incorporated nanoparticles are about 200 nm in diameter and are efficiently internalized into FibroGRO cells. Their intracellular fate was also followed by tagging with suitable reporter siRNA as well as with lysotracker dye; confocal microscopy clearly indicates endosomal escape of the particles. Significant (60%) SPARC-gene knock down was achieved by using 0.4 pmole siRNA/μg of LbL NPs in FibroGRO cells and the relative expression of SPARC mRNA reduced significantly (60%) against untreated cells. The cytotoxicity as evaluated by xCelligence real-time cell proliferation and MTT cell assay, indicated that the SPARC-siRNA-loaded LbL NPs are non-toxic. In conclusion, the LbL NP system described provides a promising, safe and efficient delivery platform as a non-viral vector for siRNA delivery that uses biopolymers to enhance the gene knock down efficiency for the development of siRNA therapeutics.

Maintenance of α(1)-antitrypsin activity by means of co-application of hypochlorous acid-scavengers in vitro and in the supernatant of polymorphonuclear leukocytes: as a basis for a new drug delivery approach

Tissue destruction, pain and loss of function in chronically inflamed tissues can result from noxious agents released from myeloperoxidase (MPO) and its highly reactive product hypochlorous acid (HOCl) or proteases such as neutrophil elastase (NE). Currently there exists a high demand for medications that provide gentle treatments, free from side effects inherent in those prescribed today. One method to circumvent side effects is through the use of locally applied drug delivery. In contrast to systemic therapy, the main advantages of transport systems are the low dosages of drug with a time-controlled delivery. The aim of this study was to ascertain interactions of NE and its inhibitor α(1)-antitrypsin (AT), the influence of hypochlorous acid (HOCl), as well as its scavengers, in order to define an effective mixture of drugs acting in a synergistic way which can be applied by means of drug delivery systems. These investigations determine the effective amounts of AT/HOCl-scavengers that drug mixtures need for delivery under inflammatory conditions in order to prevent tissue damage. AT was shown to inhibit NE in a dose-dependent manner, whereas a physiological concentration of 1.14 µM AT caused a significant NE inhibition (78%, pH 7.5). The concomitant existence of MPO/HOCl inactivated AT in a dose-dependent manner as well. To regain AT efficacy, HOCl-scavengers, such as L-methionine, α-aminosalicylic acid and cefoperazone were additionally applied. Finally, AT was assembled as surface layer onto layer-by-layer biopolymer-coated microcarriers and carrier phagocytosis by polymorphonuclear leukocytes could be shown.

Multiple internalization pathways of polyelectrolyte multilayer capsules into mammalian cells

Polyelectrolyte multilayer (PEM) capsules are carrier vehicles with great potential for biomedical applications. With the future aim of designing biocompatible, effective therapeutic delivery systems (e.g., for cancer), the pathway of internalization (uptake and fate) of PEM capsules was investigated. In particular the following experiments were performed: (i) the study of capsule co-localization with established endocytic markers, (ii) switching-off endocytotic pathways with pharmaceutical/chemical inhibitors, and (iii) characterization and quantification of capsule uptake with confocal and electron microscopy. As result, capsules co-localized with lipid rafts and with phagolysosomes, but not with other endocytic vesicles. Chemical interference of endocytosis with chemical blockers indicated that PEM capsules enter the investigated cell lines through a mechanism slightly sensitive to electrostatic interactions, independent of clathrin and caveolae, and strongly dependent on cholesterol-rich domains and organelle acidification. Microscopic characterization of cells during capsule uptake showed the formation of phagocytic cups (vesicles) to engulf the capsules, an increased number of mitochondria, and a final localization in the perinuclear cytoplasma. Combining all these indicators we conclude that PEM capsule internalization in general occurs as a combination of different sequential mechanisms. Initially, an adsorptive mechanism due to strong electrostatic interactions governs the stabilization of the capsules at the cell surface. Membrane ruffling and filopodia extensions are responsible for capsule engulfing through the formation of a phagocytic cup. Co-localization with lipid raft domains activates the cell to initiate a lipid-raft-mediated macropinocytosis. Internalization vesicles are very acidic and co-localize only with phagolysosome markers, excluding caveolin-mediated pathways and indicating that upon phagocytosis the capsules are sorted to heterophagolysosomes.

The architecture and biological performance of drug-loaded LbL nanoparticles

Layer-by-Layer (LbL) nanoparticles are an emerging class of therapeutic carriers that afford precise control over key design parameters that facilitate improved drug and carrier pharmacokinetics, and enhanced molecular-targeting capabilities. This paper advances the development of these systems by establishing them as drug carriers, with the means to control drug release in a systemic environment and retard particle clearance from circulation, promoting improved biodistribution of the drug-containing system. Using dual-fluorescent tracking in vivo, this work establishes a robust means of screening libraries of LbL systems generated, affording simultaneous resolution over persistence and biodistribution of both the drug and carrier following systemic administration of a single particle formulation. Employing a PLGA drug-containing core as a substrate for LbL deposition, a range of coated systems were fabricated to investigate the abilities of these films to stabilize drug for delivery as well as to improve the pharmacokinetics of both the drug and carrier. Significant reductions in liver accumulation were observed for different formulations of the layered architectures within the first 30 min of systemic circulation. LbL architectures diminished liver localization of the surrogate drug, cardiogreen, by 10-25% ID/g relative to native PLGA nanoparticles and modulated carrier accumulation in the liver >50% ID/g. Further, enhanced persistence of the drug was observed with the coated systems, significantly increasing the drug half-life from 2 to 3 min for free drug and 1.87 h for the uncoated core to 4.17 h and 4.54 h for the coated systems. These systems provide an exciting, modular platform that improves the pharmacokinetic properties of the therapeutic, reduces bolus release of drug from nanoparticles, and enhances the safety and circulation half-life of the drug in vivo, proving them to be highly clinically-relevant and a promising approach for future development of molecularly-targeted and combination therapeutics.

A simple method to evaluate the biochemical compatibility of oil/surfactant mixtures for experiments in microdroplets

The enormous reduction of assay volume afforded by compartmentalization into picolitre water-in-oil droplets is an exciting prospect for high-throughput biology. Maintaining the activity of encapsulated proteins is critical for experimental success, for example in in vitro directed evolution, where protein variants are expressed in droplets to identify mutants with improved properties. Here, we present a simple and rapid method to quantitatively compare concentrations of fluorescent molecules in microdroplets. This approach allows an assessment of different emulsification procedures and several oil/surfactant mixtures for biochemical compatibility, in particular in vitro protein expression. Based on determining droplet fluorescence vs. droplet diameter, the method uses the gradient of such curves as a 'concentration correlation coefficient' (CCC) that is directly proportional to fluorophore concentration. Our findings suggest that generation of droplets using a microfluidic flow-focusing device gave no more protein expression than droplet production by the bulk methods of vortexing and homogenizing. The choice of oil/surfactant, however, was found to be critical for protein expression and even encapsulation of purified protein, highlighting the importance of careful selection of these components when carrying out biochemical experiments in droplets. This methodology will serve as a quantitative test for the rapid optimization of droplet-based experiments such as in vitro protein expression or enzymatic assays.

Inhibition of human neutrophil elastase by α1-antitrypsin functionalized colloidal microcarriers

Layer-by-layer (LbL)-coated microcarriers offer a good opportunity as transport systems for active agents into specific cells and tissues. The assembling of oppositely charged polyelectrolytes enables a modular construction of the carriers and therefore an optimized integration and application of drug molecules. Here, we report the multilayer incorporation and transport of α(1)-antitrypsin (AT) by colloidal microcarriers. AT is an anti-inflammatory agent and shows inhibitory effects toward its pro-inflammatory antagonist, human neutrophil elastase (HNE). The highly proteolytic enzyme HNE is released by polymorphonuclear leukocytes (PMNs) during inflammatory processes and can cause host tissue destruction and pain. The high potential of this study is based on a simultaneous intra- and extracellular application of AT-functionalized LbL carriers. Carrier application in PMNs results in significant HNE inhibition within 21 h. Microcarriers phagocytosed by PMNs were time dependently decomposed inside phagolysosomes, which enables the step-by-step release of AT. Here, AT inactivates HNE before being released, which avoids a further HNE concentration increase in the extracellular space and, subsequently, reduces the risk of further tissue destruction. Additionally, AT surface-functionalized microcarriers allow the inhibition of already released HNE in the extracellular space. Finally, this study demonstrates the successful application of LbL carriers for a concurrent extra- and intracellular HNE inhibition aiming the rebalancing of protease and antiprotease concentrations and the subsequent termination of chronic inflammations.

Tailoring layer-by-layer capsules for biomedical applications

Polymeric capsules have attracted great interest as versatile carrier systems in the area of medicine and pharmaceutics. These capsules are made by stepwise layer-by-layer adsorption of polymers onto a template core, which can be removed to produce hollow capsules. The cavity of these capsules can host various cargo molecules while the capsules’ wall can be functionalized towards desired properties by embedding specific moieties into the multilayers. Tuning of the capsules’ properties influences their interaction with cells and tissues and paves the way towards the development of stimuli-responsive capsules releasing their payload at a target site. In this review, we describe the generation of tailored layer-by-layer capsules and focus hereby on numerous potential applications of this multifunctional delivery platform in biomedical settings. We review the current status in the field and discuss the opportunities, as well as the hurdles, to be overcome to successfully transfer this technology to therapeutic and diagnostic applications.

Characterization of degradable polyelectrolyte multilayers fabricated using DNA and a fluorescently-labeled poly(β-amino ester): shedding light on the role of the cationic polymer in promoting surface-mediated gene delivery

Polyelectrolyte multilayers (PEMs) fabricated from cationic polymers and DNA have been investigated broadly as materials for surface-mediated DNA delivery. One attractive aspect of this "multilayered" approach is the potential to exploit the presence of cationic polymer "layers" in these films to deliver DNA to cells more effectively. Past studies demonstrate that these films can promote transgene expression in vitro and in vivo, but significant questions remain regarding roles that the cationic polymers could play in promoting the internalization and processing of DNA. Here, we report physicochemical and in vitro cell-based characterization of DNA-containing PEMs fabricated using fluorescently end-labeled derivatives of a degradable polycation (polymer 1) used in past studies of surface-mediated transfection. This approach permitted simultaneous characterization of polymer and DNA in solution and in cells using fluorescence-based techniques, and provided information about the locations and behaviors of polymer 1 that could not be obtained using other methods. LSCM and flow cytometry experiments revealed that polymer 1 and DNA released from film-coated objects were both internalized extensively by cells and that they were colocalized to a significant extent inside cells (e.g., ~58% of DNA was colocalized with polymer). Fluorescence anisotropy measurements of solutions containing partially eroded films were also consistent with the presence of aggregates of polymer 1 and DNA in solution (e.g., after release from surfaces, but prior to internalization by cells). Our results support the view that polymer 1, which is incorporated into these materials as "layers" rather than as part of optimized, preformed "polyplexes", can act to promote or enhance surface-mediated DNA delivery. More broadly, our results suggest opportunities to improve the delivery properties of DNA-containing PEMs by incorporation of additional "layers" of other conventional cationic polymers designed to address specific intracellular barriers to transfection, such as endosomal escape, more effectively.

Interaction, uptake, and processing of LbL-coated microcarriers by PMNs

Functionalized microcarriers or hollow capsules transporting active agents offer the opportunity for drug delivery inside cells. A promising application of these drug delivery systems is the direct transport as well as the release of immobilized antiinflammatory substances (AIS) into polymorphonuclear leukocytes (PMNs), which play a key role in the course of inflammatory processes. The intended delivery of AIS into the inflamed tissue could alleviate tissue destruction taking place during chronic inflammation, as well as facilitate the termination of these processes. In this study, the capability of functionalized CaCO(3) microcarriers as AIS transporter system targeted at PMNs is investigated. The time-dependent interaction of protamine sulfate and dextran sulfate multilayer-coated 5 μm ± 1 μm CaCO(3) carriers with PMNs, in comparison with the usage of SiO(2) carriers as monodisperse model system of defined sizes (1, 3, and 5 μm), reveals a sufficient carrier/cell interaction and uptake for coincubation periods between 2 and 24 h. Furthermore, the microcarriers are exposed to an environment simulating primary granule/phagosomal conditions after phagocytosis by means of PMN stimulation. The incubation of CaCO(3) microcarriers with cell supernatant demonstrates a partial multilayer decomposition (three to five layers) within 24 h, allowing the gradual release of AIS within the short PMN life span. This observation suggests a potential application for this drug delivery system inside immunologically active cells and may open the way to new alternatives in the treatment of chronic processes.

Polymeric multilayer capsules delivering biotherapeutics

Polymeric multilayer capsules have emerged as a novel drug delivery platform. These capsules are fabricated through layer-by-layer sequential deposition of polymers onto a sacrificial core template followed by the decomposition of this core yielding hollow capsules. The resulting nanometer thin membrane is permselective, allowing diffusion of water and ions but excluding larger molecules. Moreover, the sequential fabrication procedure allows a precise fine-tuning of the capsules' physicochemical and biological properties. These properties have put polymeric multilayer capsules under major attention in the field of drug delivery. In this review we focus on polymeric multilayer capsule mediated delivery of biotechnological macromolecular drugs such as peptides, proteins and nucleic acids.

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.

Spontaneous confocal Raman microscopy--a tool to study the uptake of nanoparticles and carbon nanotubes into cells

Confocal Raman microscopy as a label-free technique was applied to study the uptake and internalization of poly(lactide-co-glycolide) (PLGA) nanoparticles (NPs) and carbon nanotubes (CNTs) into hepatocarcinoma human HepG2 cells. Spontaneous confocal Raman spectra was recorded from the cells exposed to oxidized CNTs and to PLGA NPs. The Raman spectra showed bands arising from the cellular environment: lipids, proteins, nucleic acids, as well as bands characteristic for either PLGA NPs or CNTs. The simultaneous generation of Raman bands from the cell and nanomaterials from the same spot proves internalization, and also indicates the cellular region, where the nanomaterial is located. For PLGA NPs, it was found that they preferentially co-localized with lipid bodies, while the oxidized CNTs are located in the cytoplasm.