Temperature-responsive telechelic dipalmitoylglyceryl poly(N-isopropylacrylamide) vesicles: real-time morphology observation in aqueous suspension and in the presence of giant liposomes

Telechelic α,ω-di(twin-tailed poly(N-isopropylacrylamides)) form polymersomes in water that increase in size by fusion when the water temperature exceeds the polymers cloud point temperature. Hybrid vesicles form in mixed suspensions of giant phospholipid liposomes and polymersomes by adsorption/fusion, and undergo further transformations, such as fission.

Tethered poly(2-isopropyl-2-oxazoline) chains: temperature effects on layer structure and interactions probed by AFM experiments and modeling

Thermoresponsive polymer layers on silica surfaces have been obtained by utilizing electrostatically driven adsorption of a cationic-nonionic diblock copolymer. The cationic block provides strong anchoring to the surface for the nonionic block of poly(2-isopropyl-2-oxazoline), referred to as PIPOZ. The PIPOZ chain interacts favorably with water at low temperatures, but above 46 °C aqueous solutions of PIPOZ phase separate as water becomes a poor solvent for the polymer. We explore how a change in solvent condition affects interactions between such adsorbed layers and report temperature effects on both normal forces and friction forces. To gain further insight, we utilize self-consistent lattice mean-field theory to follow how changes in temperature affect the polymer segment density distributions and to calculate surface force curves. We find that with worsening of the solvent condition an attraction develops between the adsorbed PIPOZ layers, and this observation is in good agreement with predictions of the mean-field theory. The modeling also demonstrates that the segment density profile and the degree of chain interpenetration under a given load between two PIPOZ-coated surfaces rise significantly with increasing temperature.

Phosphorylcholine-modified chitosan films as effective promoters of cell aggregation: correlation between the films properties and cellular response

This study describes chitosan-phosphorylcholine (CH-PC) films able to support the formation of cell aggregates (spheroids), which are important for tissue engineering and pharmacological studies. The surface topography, charge, thickness, and rheology of CH-PC thin films were characterized by AFM, zeta-potential measurements, SPR spectroscopy, and QCM-D measurements. The CH-PC films are highly hydrated gels, independently of the level of PC incorporation (15-40 mol-% PC/glucosamine units). QCM-D studies established that the amount of fibrinogen adsorbed on CH-PC films decreased with increasing PC content. CH-PC surfaces underwent a transition from moderately cell-adhesive (CH-PC15) to non-adhesive (CH-PC40). Optical micrographs of HUVEC and MCF-7 cell lines cultured on CH-PC surfaces showed that they form spheroids on CH-PC25 and CH-PC40 films.

Prevention of thermally induced aggregation of IgG antibodies by noncovalent interaction with poly(acrylate) derivatives

Prevention of thermal aggregation of antibodies in aqueous solutions was achieved by noncovalent association with hydrophobically modified poly(acrylate) copolymers. Using a polyclonal immunoglobin G (IgG) as a model system for antibodies, we have studied the mechanisms by which this multidomain protein interacts with polyanions when incubated at physiological pH and at temperatures below and above the protein unfolding/denaturation temperature, in salt-free solutions and in 0.1 M NaCl solutions. The polyanions selected were sodium poly(acrylates), random copolymers of sodium acrylate and N-n-octadecylacrylamide (3 mol %), and a random copolymer of sodium acrylate, N-n-octylacrylamide (25 mol %), and N-isopropylacrylamide (40 mol %). They were derived from two poly(acrylic acid) parent chains of Mw 5000 and 150000 g·mol(-1). The IgG/polyanion interactions were monitored by static and dynamic light scattering, fluorescence correlation spectroscopy, capillary zone electrophoresis, and high sensitivity differential scanning calorimetry. In salt-free solutions, the hydrophilic PAA chains form complexes with IgG upon thermal unfolding of the protein (1:1 w/w IgG/PAA), but they do not interact with native IgG. The complexes exhibit a remarkable protective effect against IgG aggregation and maintain low aggregation numbers (average degree of oligomerization <12 at a temperature up to 85 °C). These interactions are screened in 0.1 M NaCl and, consequently, PAAs lose their protective effect. Amphiphilic PAA derivatives (1:1 w/w IgG/polymer) are able to prevent thermal aggregation (preserving IgG monomers) or retard aggregation of IgG (formation of oligomers and slow growth), revealing the importance of both hydrophobic interactions and modulation of the Coulomb interactions with or without NaCl present. This study leads the way toward the design of new formulations of therapeutic proteins using noncovalent 1:1 polymer/protein association that are transient and require a markedly lower additive concentration compared to conventional osmolyte protecting agents. They do not modify IgG permanently, which is an asset for applications in therapeutic protein formulations since the in vivo efficacy of the protein should not be affected.

Length fractionation of boron nitride nanotubes using creamed oil-in-water emulsions

The fractionation by length of multiwalled boron nitride nanotubes (BNNTs) was achieved by emulsification and creaming of an oil/water/surfactant mixture. The length separation is based on the fact that nanoparticle-coated oil droplets polydisperse in size move toward the upper surface or the bottom of an emulsified mixture depending on the density of the droplets, such that droplets of different sizes are located at different heights. By sampling heightwise an unstable hexane/water/Tween 20/BNNT (1-20 μm long) emulsion, we observed that the lengths of the BNNTs adsorbed on the droplets display a strong correlation with the droplets sizes, thus leading to selective separation of the BNNT lengths, as confirmed by dark-field optical imaging and dynamic light scattering. This method may potentially be extended to other high aspect ratio nanomaterials exhibiting emulsification properties similar to those of BNNTs.

Synthesis of a poly(N-isopropylacrylamide) charm bracelet decorated with a photomobile α-cyclodextrin charm

Cyclic poly(N-isopropylacrylamide) (PNIPAM) with an interlocked α-cyclodextrin was prepared using supramolecular interactions with an azobenzene group inserted in the PNIPAM ring.

Caspase-1 activity in microglia stimulated by pro-inflammagen nanocrystals

Although caspase-1 is a key participant in inflammation, there is no sensitive assay to measure its enzymatic activity in real time in cells or animals. Here we describe a nanosensor for caspase-1 ratiometric measurements, consisting of a rhodamine-labeled, caspase-1 cleavable peptide linked to quantum dots (QDs). Microglia cells were stimulated by lipopolysaccharide (LPS) and by hybrid nanoparticles LPS-QDs. These stimuli activated caspase-1 in microglia monolayers and in the mouse brain, while a selected caspase inhibitor markedly reduced it. LPS-QDs entered into the lysosomal compartment and led to an enlargement of these cellular organelles in the exposed microglia. Both lysosomal swelling and mitochondrial impairment contributed to caspase-1 activation and to the consequent interleukin-1β release. The results from these studies highlight how the unique properties of QDs can be used to create versatile biotools in the study of inflammation in real time in vivo.

Linear polyethylenimine produced by partial acid hydrolysis of poly(2-ethyl-2-oxazoline) for DNA and siRNA delivery in vitro

Polyethylenimines (PEIs) are the most efficient synthetic vectors for gene delivery available to date. With its high charge density and strong proton-buffering effect, PEI has an ability to condense DNA and small interfering RNA at physiologic pH. However, the polymer suffers from the disadvantage of high cellular toxicity. To reduce its cellular toxicity, we synthesized linear PEIs by partial hydrolysis of poly(2-ethyl-2-oxazoline). Three linear PEIs with different hydrolysis percentages (30%, 70%, and 96%, respectively) were produced as PEI30, PEI70, and PEI96. PEI30 and PEI96 cannot be considered as suitable transfection agents because of low transfection efficiency (PEI30) or high cellular toxicity (PEI96). PEI70 displayed very weak cell toxicity. The charge density of this polymer (PEI70) was strong enough to condense DNA and small interfering RNA at a physiologic pH of 7.4. Our results also show that PEI70 was highly efficient in DNA delivery and small interfering RNA-mediated knockdown of target genes. Thus, polymers such as PEI70 appear to be very promising vectors for gene delivery.

Innovation in nanomedicine through materials nanoarchitectonics

Materials nanoarchitectonics has led to important innovations in the design and construction of systems in nanoelectronics, nanomachinery, and energy conversion. Recent publications point to the fact that the same approach may be applied successfully to other fields. In this Perspective, we define the key features of materials nanoarchitectonics and examine how they can be used to address current challenges in nanomedicine, placing emphasis on colloidal agents for therapeutic and diagnostic applications.

Quantum dot cytotoxicity and ways to reduce it

The dramatic increase in the use of nanoparticles (NP) in industry and research has raised questions about the potential toxicity of such materials. Unfortunately, not enough is known about how the novel, technologically-attractive properties of NPs correlate with the interactions that may take place at the nano/bio interface. The academic, industrial, and regulatory communities are actively seeking answers to the growing concerns on the impact of nanotechnology on humans. In this Account we adopt quantum dots (QDs) as an illustrative example of the difficulties associated with the development of a rational science-based approach to nanotoxicology. The optical properties of QDs are far superior to those of organic dyes in terms of emission and absorption bandwidths, quantum yield, and resistance to photobleaching. Moreover, QDs may be decorated with targeting moieties or drugs and, therefore, are candidates for site-specific medical imaging and for drug delivery, for example in cancer treatment. Earlier this year researchers demonstrated that QD-based imaging using monkeys caused no adverse effects although QDs accumulated in lymph nodes, bone marrow, liver, and spleen for up to 3 months after injection. Such persistence of QDs in live animals does, however, raise concerns about the safety of using QDs both in the laboratory and in the clinic. Researchers anticipate that QDs will be increasingly used not only in clinical applications but also in various manufactured products. For example, QD-solar cells have emerged as viable contenders to complement or replace dye-sensitized solar cells; CdTe/CdS thin film cells have already captured approximately 10 percent of the global market, and in addition, QDs can serve as components of sensors and as emitting materials in LEDs. Given the clear indications that QDs will inevitably become components of a wide range of manufactured and consumer products, researchers and policy makers need to understand the possible health risks associated with exposure to QDs. In this Account, we initially review the known mechanisms by which QDs can damage cells, including oxidative stress elicited by reactive oxygen species (ROS). We discuss lesser-known impairments induced in cells by nanomolar to picomolar concentrations of QDs, which imply that cadmium-containing QDs can exert genotoxic, epigenetic, and metalloestrogenic effects. These observations strongly suggest that minute concentrations of QDs could be sufficient to cause long lasting, even transgenerational, effects. We also consider various modes by which humans could be exposed to QDs in their work or through the environment. Although considerable advances have been made in enhancing the stability and overall quality of QDs, over time they can partially degrade in the environment or in biological systems, and eventually cause small, but cumulative undesirable effects. A combination of toxicological, genetic, epigenetic and imaging approaches is required to create comprehensive guidelines for evaluating the nanotoxicity of nanomaterials, including QDs. Prior to biological investigations with these materials, an indispensible step must be the full characterization of NPs by complementary techniques. Specifically, the concentration, size, charge, and ligand stability of NPs in biological media must be known if we are to understand fully how the properties of nanoparticles and of their biological environment contribute to cytotoxicity.

Separation science: Principles and applications for the analysis of bionanoparticles by asymmetrical flow field-flow fractionation (AF4)

Field-flow fractionation is an analytical technique that allows the separation of particles over a size range, from a few nanometers to several microns in diameter. The separation takes place under mild conditions and is suited for the analysis of neutral or charged particles. A single measurement yields the size and concentration of each component of a mixture. However, developing a suitable fractionation method can be tedious and time-consuming. In this chapter, we present asymmetrical flow field-flow fractionation (AF4) conditions that have proven their reliability for the analysis of quantum dots and other nanoparticles in the 5-50 nm size range. Common pitfalls are emphasized together with strategies to overcome them.

Tuning the properties and functions of 17β-estradiol-polysaccharide conjugates in thin films: impact of sample history

In addition to its role in the regulation of sex-related processes, 17β-estradiol (E2) participates in the prevention and treatment of cardiovascular diseases via nongenomic pathways mediated by estrogen receptors (ER-α) located in the cell membrane. To achieve specific nongenomic activity of E2, we linked E2 (4.4 mol %) to chitosan-phosphorylcholine (CH-PC) (20 mol % PC). Injections of ER-α solutions (5 to 100 nmol L(-1)) over rehydrated CH-PC-E2 thin films led to permanent adsorption of ER-α to the film surface, as detected by quartz crystal microbalance with dissipation (QCM-D). However, ER-α did not bind onto CH-PC-E2 films formed in situ and never dried. X-ray photoelectron spectroscopy (XPS) analysis of spin-cast CH-PC-E2 films revealed significant E2 enrichment of the topmost section of the film, attributed to the preferential migration of E2 toward the film/air interface upon drying. Mechanical analysis of CH-PC-E2 films in the frequency domain probed by QCM-D indicated that rehydrated films behave as an entangled network with junction points formed by self-assembly of hydrophobic E2 moieties and by ion pairing among PC groups, whereas films formed in situ are entangled polymer solutions with temporary junctions. The structural analysis presented offers useful guidelines for the study of amphiphilic biomacromolecules designed for therapeutic use as thin films.

Amphipol mediated surface immobilization of FhuA: a platform for label-free detection of the bacteriophage protein pb5

Biotinylated amphipol was used to entrap FhuA (an E. coli outer membrane protein) and immobilize the FhuA-amphipol complex on streptavidin surfaces. Using this assembly, we have successfully devised surface-based assays for studying the recognition of FhuA by pb5 (a bacteriophage T5 protein) and determination of the affinity constant.

Efficient Nonviral Gene Therapy Using Folate-Targeted Chitosan-DNA Nanoparticles In Vitro

Nonviral cationic polymers like chitosan can be combined with DNA to protect it from degradation. The chitosan is a biocompatible, biodegradable, nontoxic, and cheap polycationic polymer with low immunogenicity. The objective of this study was to synthesize and then assess different chitosan-DNA nanoparticles and to select the best ones for selective in vitro transfection in human epidermoid carcinoma (KB) cell lines. It revealed that different combinations of molecular weight, the presence or absence of folic acid ligand, and different plasmid DNA sizes can lead to nanoparticles with various diameters and diverse transfection efficiencies. The intracellular trafficking, nuclear uptake, and localization are also studied by confocal microscopy, which confirmed that DNA was delivered to cell nuclei to be expressed.

Strategies in biomimetic surface engineering of nanoparticles for biomedical applications

Engineered nanoparticles (NPs) play an increasingly important role in biomedical sciences and in nanomedicine. Yet, in spite of significant advances, it remains difficult to construct drug-loaded NPs with precisely defined therapeutic effects, in terms of release time and spatial targeting. The body is a highly complex system that imposes multiple physiological and cellular barriers to foreign objects. Upon injection in the blood stream or following oral administation, NPs have to bypass numerous barriers prior to reaching their intended target. A particularly successful design strategy consists in masking the NP to the biological environment by covering it with an outer surface mimicking the composition and functionality of the cell's external membrane. This review describes this biomimetic approach. First, we outline key features of the composition and function of the cell membrane. Then, we present recent developments in the fabrication of molecules that mimic biomolecules present on the cell membrane, such as proteins, peptides, and carbohydrates. We present effective strategies to link such bioactive molecules to the NPs surface and we highlight the power of this approach by presenting some exciting examples of biomimetically engineered NPs useful for multimodal diagnostics and for target-specific drug/gene delivery applications. Finally, critical directions for future research and applications of biomimetic NPs are suggested to the readers.