Oppositely Charged, Stimuli-Responsive Anisotropic Nanoparticles for Colloidal Self-Assembly

Stimuli-responsive plasmonic core-satellite hybrid nanostructures with tunable nanogaps

Incorporating stimuli-responsive block copolymers to hierarchical metallic nanoparticles (MNPs) is of particular interest due to their tunable plasmonic properties responding to environmental stimuli. We herein report thermo-responsive plasmonic core-satellite hybrid nanostructures with tunable nanogaps as surface-enhanced Raman scattering (SERS) nanotags. Two different diblock copolymers with opposite charges, poly(acrylic acid-b-N-isopropylacrylamide) (p(AAc-b-NIPAM)) and poly(N,N-dimethylaminoethyl methacrylate-b-N-isopropylacrylamide) (p(DMAEMA-b-NIPAM)), were synthesized. The negatively charged p(AAc-b-NIPAM)s were bound to gold nanospheres (GNSs), while the positively charged p(DMAEMA-b-NIPAM)s were conjugated to gold nanorods (GNRs) via gold-sulfur bonds. When p(AAc-b-NIPAM)-GNSs and p(DMAEMA-b-NIPAM)-GNRs were electrostatically complexed, plasmonic hybrid nanostructures consisting of both GNS satellites and a GNR core were formed. Dynamic tuning of electromagnetic coupling of their nanogaps was achieved via a temperature-triggered conformational change of p(NIPAM) blocks. Furthermore, a sandwich-type immunoassay for the detection of immunoglobulin G was performed to demonstrate these core-satellites as potential SERS nanotags. Our results showed that these plasmonic core-satellites with stimuli-responsiveness are promising for SERS-based biosensing applications.

Improved Magneto-Microfluidic Separation of Nanoparticles through Formation of the β-Cyclodextrin-Curcumin Inclusion Complex

Molecular adsorption to the nanoparticle surface may switch the colloidal interactions from repulsive to attractive and promote nanoparticle agglomeration. If the nanoparticles are magnetic, then their agglomerates exhibit a much stronger response to external magnetic fields than individual nanoparticles. Coupling between adsorption, agglomeration, and magnetism allows a synergy between the high specific area of nanoparticles (∼100 m²/g) and their easy guidance or separation by magnetic fields. This yet poorly explored concept is believed to overcome severe restrictions for several biomedical applications of magnetic nanoparticles related to their poor magnetic remote control. In this paper, we test this concept using curcumin (CUR) binding (adsorption) to β-cyclodextrin (βCD)-coated iron oxide nanoparticles (IONP). CUR adsorption is governed by host-guest hydrophobic interactions with βCD through the formation of 1:1 and, possibly, 2:1 βCD:CUR inclusion complexes on the IONP surface. A 2:1 stoichiometry is supposed to promote IONP primary agglomeration, facilitating the formation of the secondary needle-like agglomerates under external magnetic fields and their magneto-microfluidic separation. The efficiency of these field-induced processes increases with CUR concentration and βCD surface density, while their relatively short timescale (<5 min) is compatible with magnetic drug delivery application.

Facile Fabrication of Anisotropic Multicompartmental Microfibers Using Charge Reversal Electrohydrodynamic Co-Jetting

Anisotropic microstructures are utilized in various fields owing to their unique properties, such as reversible shape transitions or on-demand and sequential release of drug combinations. In this study, anisotropic multicompartmental microfibers composed of different polymers are prepared via charge reversal electrohydrodynamic (EHD) co-jetting. The combination of various polymers, such as thermoplastic polyurethane, poly(D,L-lactide-co-glycolide), poly(vinyl cinnamate), and poly(methyl methacrylate), results in microfibers with distinct compositional boundaries. Charge reversal during EHD co-jetting enables facile fabrication of multicompartmental microfibers with the desired composition and tunable inner architecture, broadening their spectrum of potential applications, such as functional microfibers and cell scaffolds with multiple physical and chemical properties.

Protein-like particles through nanoprecipitation of mixtures of polymers of opposite charge

HYPOTHESIS

Polymer nanoparticles (NPs) have a very high potential for applications notably in the biomedical field. However, synthetic polymer NPs cannot yet concurrence the functionalities of proteins, their natural counterparts, notably in terms of size, control over internal structure and interactions with biological environments. We hypothesize that kinetic trapping of polymers bearing oppositely charged groups in NPs could bring a new level of control and allow mimicking the surfaces of proteins.

EXPERIMENTS

Here, the assembly of mixed-charge polymer NPs through nanoprecipitation of mixtures of oppositely charged polymers is studied. Two series of copolymers made of ethyl methacrylate and 1 to 25 mol% of either methacrylic acid or a trimethylammonium bearing methacrylate are synthesized. These carboxylic acid or trimethylammonium bearing polymers are then mixed in different ratios and nanoprecipitated. The influence of the charge fraction, mixing ratio of the polymers, and precipitation conditions on NP size and surface charge is studied.

FINDINGS

Using this approach, NPs of less than 25 nm with tunable surface charge from +40 mV to -40 mV are assembled. The resulting NPs are sensitive to pH and certain NP formulations have an isoelectric point allowing repeated charge reversal. Encapsulation of fluorescent dyes yields very bright fluorescent NPs, whose interactions with cells are studied through fluorescence microscopy. The obtained results show the potential of nanoprecipitation of oppositely charged polymers for the design of NPs with precisely tuned surface properties.

Adsorption of Organic Dyes on Magnetic Iron Oxide Nanoparticles. Part II: Field-Induced Nanoparticle Agglomeration and Magnetic Separation

This paper (part II) is devoted to the effect of molecular adsorption on the surface of magnetic iron oxide nanoparticles (IONP) on the enhancement of their (secondary) field-induced agglomeration and magnetic separation. Experimentally, we use Methylene Blue (MB) cationic dye adsorption on citrate-coated maghemite nanoparticles to provoke primary agglomeration of IONP in the absence of the field. The secondary agglomeration is manifested through the appearance of needlelike micron-sized agglomerates in the presence of an applied magnetic field. With the increasing amount of adsorbed MB molecules, the size of the field-induced agglomerates increases and the magnetic separation on a magnetized micropillar becomes more efficient. These effects are mainly governed by the ratio of magnetic-to-thermal energy α, suspension supersaturation Δ₀, and Brownian diffusivity D_eff of primary agglomerates. The three parameters (α, Δ₀, and D_eff) are implicitly related to the surface coverage θ of IONP by MB molecules through the hydrodynamic size of primary agglomerates exponentially increasing with θ. Experiments and developed theoretical models allow quantitative evaluation of the θ effect on the efficiency of the secondary agglomeration and magnetic separation.

Utilizing Stimuli Responsive Linkages to Engineer and Enhance Polymer Nanoparticle-Based Drug Delivery Platforms

The devastating nature of cancer continues to be one of the leading causes of death in the world. Chemotherapy is among the most common forms of cancer treatment but comes with a host of adverse effects caused by the therapeutic agents damaging healthy tissue and organs. To limit these side effects, scientists have been designing stimuli responsive drug delivery vessels for targeted release. This Review focuses on the incorporation of stimuli responsive linkages in targeted drug delivery systems to enhance therapeutic efficiency. These platforms are primarily employed to control the distribution of anticancer agents in the body to reduce the adverse side effects caused by their toxicities. We will outline how drug delivery vessels are constructed so that exposure to select environmental and external stimuli releases the enclosed drug only at the target site. Stimuli responsive components are integrated within drug delivery vessels in the form of cross-linkers, polymers, and surface modifications. The changes, these moieties undergo upon stimuli exposure, cascade into larger scale alterations to the platforms, resulting in complete disassembly, reversible morphological variations, and enhanced cellular uptake. The ability for these modes of delivery to be initiated exclusively under stimuli exposure allows for release of toxic therapeutic agents to be confined only to the affected area.

Study of the aggregation behavior of Janus particles by coupling experiments and Brownian dynamics simulations

HYPOTHESIS

New colloids such as inverse patchy particles or Janus particles are considered as smart building blocks in the development of innovative and performant materials. For example, the control of the self-assembly of oxide-based charged Janus particles is interesting for ceramic shaping. Thus, the synthesis of silica based Janus particles as well as a detailed study of their behavior in suspension are presented in this paper.

EXPERIMENTS

Fluorescent silica particles are partially modified in surface by grafting amine groups using a Pickering emulsion route. Zeta potential measurements, sedimentation tests and confocal microscopy observations are carried out to analyze the aggregation of the obtained particles in aqueous suspension as a function of the patch size and of the pH. Brownian dynamics simulations are also performed to better understand the aggregate structures.

FINDINGS

The aggregation of the synthesized silica-based Janus particles can be tuned by modifying the experimental parameters, and elongated or on the contrary more compact structures could be observed. This control of aggregation makes such particles promising to build new ceramic materials.

Controllable and Diversiform Topological Morphologies of Self-Assembling Supra-Amphiphiles with Aggregation-Induced Emission Characteristics for Mimicking Light-Harvesting Antenna

Controllable construction of diversiform topological morphologies through supramolecular self-assembly on the basis of single building block is of vital importance, but still remains a big challenge. Herein, a bola-type supra-amphiphile, namely DAdDMA@2β-CD, is rationally designed and successfully prepared by typical host-guest binding β-cyclodextrin units with an aggregation-induced emission (AIE)-active scaffold DAdDMA. Self-assembling investigation reveals that several morphologies of self-assembled DAdDMA@2β-CD including leaf-like lamellar structure, nanoribbons, vesicles, nanofibers, helical nanofibers, and toroids, can be straightforwardly fabricated by simply manipulating the self-assembling solvent proportioning and/or temperature. To the best of knowledge, this presented protocol probably holds the most types of self-assembling morphology alterations using a single entity. Moreover, the developed leaf-like lamellar structure performs well in mimicking the light-harvesting antenna system by incorporating with a Förster resonance energy transfer acceptor, providing up to 94.2% of energy transfer efficiency.

Temperature and pH Responsive Janus Silica Nanoplates Prepared by the Sol-Gel Process and Postmodification

During the process of emulsifying and hydrolyzing, reactive poly(3-(triethoxysilyl)propyl methacrylate)-b-polystyrene (PTEPM-b-PS) diblock copolymers can self-assemble and become cross-linked to form hollow spheres in situ with polystyrene on their inner surfaces. The addition of tetraethoxysilane (TEOS), which was hydrolyzed and condensed together with PTEPM block, can make those spheres as soft foldable capsules or hard hollow spheres depending on the amount of added TESO. Then postmodification, the surface-initiated Atom Transfer Radical Polymerization (ATRP) was applied to afford stimuli-responsive spheres, and the corresponding responsive Janus nanoplates (RJPs) were finally obtained by crushing those responsive hollow spheres (HSs) showing smart tunable emulsifiability and great potential in oily water purification. This facile method to fabricate HSs and RJPs could be used for preparing different Janus polymer-inorganic capsules and nanoplates with varied functions by changing the chemical composition of copolymer surfactants as well as the postmodification process.

Tunable Decoupling of Dual Drug Release of Oppositely Charged, Stimuli-Responsive Anisotropic Nanoparticles

Multicompartmentalized nanostructures are of interest because they can provide unique physicochemical properties and multifunctionalities in each compartment. Furthermore, stimuli-responsive anisotropic nanostructures (ANPs) with distinct opposite charges would be useful for drug delivery systems because different drug release kinetics could be achieved from each compartment in response to both charge and stimuli. In this study, stimuli-responsive ANPs were formed via electrohydrodynamic cojetting of poly(N-isopropylacrylamide)-based copolymers with opposite charges. The positively charged compartment consisted of poly(N-isopropylacylamide-co-stearyl acrylate-co-allylamine) (poly(NIPAM-co-SA-co-AAm)) (i.e., PNSAAm) and poly(N-isopropylacylamide-co-stearyl acrylate-co-acrylic acid) (poly(NIPAM-co-SA-co-AAc)) (i.e., PNSAAc). The two distinct compartments of ANPs were physically cross-linked through hydrophobic interactions within the copolymers. Oppositely charged, small-molecule model drugs (fluorescein sodium salt and rhodamine 6G) were separately encapsulated within each compartment and released based on changes in noncovalent interactions and temperature. Furthermore, two different biomacromolecule drugs with opposite charges, bovine serum albumin and lysozyme (which were complexed with polysaccharides by hydrophobic ion pairing), were loaded within the ANPs. Electrostatic interactions between the encapsulated drugs and each ANP compartment controlled the rate of drug release from the ANPs. In addition, these ANPs showed a thermally induced actuation, leading to drug release at different rates due to the collapse of poly(NIPAM)-based copolymers under aqueous conditions. This work may be useful for decoupled drug release kinetics.