Core Cross-Linking of Dynamic Diblock Copolymer Micelles: Quantitative Study of Photopolymerization Efficiency and Micelle Structure

Threonine-Based Stimuli-Responsive Nanoparticles with Aggregation-Induced Emission-Type Fixed Cores for Detection of Amines in Aqueous Solutions

Stimuli-responsive polymeric nanoparticles (NPs) exhibit reversible changes in the dispersion or aggregation state in response to external stimuli. In this context, we designed and synthesized core-shell NPs with threonine-containing weak polyelectrolyte shells and fluorescent cross-linked cores, which are applicable for the detection of pH changes and amine compounds in aqueous solution. Stable and uniform NP(dTh) and NP(Fl), consisting of fluorescent symmetric diphenyl dithiophene (dTh) and diphenyl fluorene (Fl) cross-linked cores, were prepared by site-selective Suzuki coupling reactions in self-assembled block copolymer. NP(Fl) with the Fl unit in the core showed a high fluorescence intensity in different solvents, which is regarded as an aggregation-induced emission-type NP showing strong emission in aggregated states in the cross-linked core. Unimodal NPs were observed in water at different pH values, and the diameter of NP(Fl) changed from 122 (pH = 2) to 220 nm (pH = 11). Furthermore, pH-dependent changes of the fluorescence peak positions and intensities were detected, which may be due to the core aggregation derived from the deprotonation of the threonine-based shell fragment. Specific interactions between the threonine-based shell of NP(Fl) and amine compounds (triethylamine and p-phenylenediamine) resulted in fluorescence quenching, suggesting the feasibility of fluorescent amine detection.

Toward Physicochemical and Rheological Characterization of Different Injectable Hyaluronic Acid Dermal Fillers Cross-Linked with Polyethylene Glycol Diglycidyl Ether

(1) Background: Injectable hyaluronic acid (HA) dermal fillers are used to restore volume, hydration and skin tone in aesthetic medicine. HA fillers differ from each other due to their cross-linking technologies, with the aim to increase mechanical and biological activities. One of the most recent and promising cross-linkers is polyethylene glycol diglycidyl ether (PEGDE), used by the company Matex Lab S.p.A., (Brindisi, Italy) to create the HA dermal filler PEGDE family. Over the last few years, several studies have been performed to investigate the biocompatibility and biodegradability of these formulations, but little information is available regarding their matrix structure, rheological and physicochemical properties related to their cross-linking technologies, the HA content or the degree of cross-linking. (2) Methods: Seven different injectable HA hydrogels were subjected to optical microscopic examination, cohesivity evaluation and rheological characterization in order to investigate their behavior. (3) Results: The analyzed cross-linked dermal fillers showed a fibrous "spiderweb-like" matrix structure, with each medical device presenting different and peculiar rheological features. Except for HA non cross-linked hydrogel 18 mg/mL, all showed an elastic and cohesive profile. (4) Conclusions: The comparative analysis with other literature works makes a preliminary characterization of these injectable medical devices possible.

Directing Amphiphilic Self-Assembly: From Microstructure Control to Interfacial Engineering

The self-assembly of small molecules into complex nanoscale structures is driven by the interplay of various noncovalent interactions. It has now become evident that by maneuvering this intermolecular interaction the geometry and interfacial properties of several nanoscale objects can be tamed. In particular, diverse structures such as spheres, rods, worms, ribbons, and vesicles can be produced by tuning the packing of molecules in the aggregate. Stimuli-sensitive assemblies that can reversibly associate or dissociate in response to environmental changes have been fabricated as model systems for the self-regulated drug delivery vehicle. Surface passivation of inorganic materials can be achieved by the selective organization of molecules at the interface. Such surface functionalization of inorganic materials by organic counterparts provides kinetic stability in biological media and permits the selective binding of active ingredients. Advances made in the area of molecular self-assembly and factors governing such association processes have made it possible to control the interfacial properties and microstructure of nanoscale materials.

Stimulus-responsive polymeric nanogels as smart drug delivery systems

Nanogels are three-dimensional nanoscale networks formed by physically or chemically cross-linking polymers. Nanogels have been explored as drug delivery systems due to their advantageous properties, such as biocompatibility, high stability, tunable particle size, drug loading capacity, and possible modification of the surface for active targeting by attaching ligands that recognize cognate receptors on the target cells or tissues. Nanogels can be designed to be stimulus responsive, and react to internal or external stimuli such as pH, temperature, light and redox, thus resulting in the controlled release of loaded drugs. This "smart" targeting ability prevents drug accumulation in non-target tissues and minimizes the side effects of the drug. This review aims to provide an introduction to nanogels, their preparation methods, and to discuss the design of various stimulus-responsive nanogels that are able to provide controlled drug release in response to particular stimuli. STATEMENT OF SIGNIFICANCE: Smart and stimulus-responsive drug delivery is a rapidly growing area of biomaterial research. The explosive rise in nanotechnology and nanomedicine, has provided a host of nanoparticles and nanovehicles which may bewilder the uninitiated reader. This review will lay out the evidence that polymeric nanogels have an important role to play in the design of innovative drug delivery vehicles that respond to internal and external stimuli such as temperature, pH, redox, and light.

Basic concepts and recent advances in nanogels as carriers for medical applications

Nanogels in biomedical field are promising and innovative materials as dispersions of hydrogel nanoparticles based on crosslinked polymeric networks that have been called as next generation drug delivery systems due to their relatively high drug encapsulation capacity, uniformity, tunable size, ease of preparation, minimal toxicity, stability in the presence of serum, and stimuli responsiveness. Nanogels show a great potential in chemotherapy, diagnosis, organ targeting and delivery of bioactive substances. The main subjects reviewed in this article concentrates on: (i) Nanogel assimilation in the nanomedicine domain; (ii) Features and advantages of nanogels, the main characteristics, such as: swelling capacity, stimuli sensitivity, the great surface area, functionalization, bioconjugation and encapsulation of bioactive substances, which are taken into account in designing the structures according to the application; some data on the advantages and limitations of the preparation techniques; (iii) Recent progress in nanogels as a carrier of genetic material, protein and vaccine. The majority of the scientific literature presents the multivalency potential of bioconjugated nanogels in various conditions. Today's research focuses over the overcoming of the restrictions imposed by cost, some medical requirements and technological issues, for nanogels' commercial scale production and their integration as a new platform in biomedicine.

Tunable Permeability of Cross-Linked Microcapsules from pH-Responsive Amphiphilic Diblock Copolymers: A Dissipative Particle Dynamics Study

Using dissipative particle dynamics simulation, we probe the tunable permeability of cross-linked microcapsules made from pH-sensitive diblock copolymers poly(ethylene oxide)-b-poly(N,N-diethylamino-2-ethyl methacrylate) (PEO-b-PDEAEMA). We first examine the self-assembly of non-cross-linked microcapsules and their pH-responsive collapse and then explore the effects of cross-linking and block interaction on the swelling or deswelling of cross-linked microcapsules. Our results reveal a preferential loading of hydrophobic dicyclopentadiene (DCPD) molecules in PEO-b-PDEAEMA copolymers. Upon reduction of pH, non-cross-linked microcapsules fully decompose into small wormlike clusters as a result of large self-repulsions of protonated copolymers. With increasing degree of cross-linking, the morphology of the microcapsule becomes more stable to pH change. The highly cross-linked microcapsule shell undergoes significant local polymer rearrangement in acidic solution, which eliminates the amphiphilicility and therefore enlarges the permeability of the shell. The responsive cross-linked shell experiences a disperse-to-buckle configurational transition upon reduction of pH, which is effective for the steady or pulsatile regulation of shell permeability. The swelling rate of the cross-linked shell is dependent on both electrostatic and nonelectrostatic interactions between the pH-sensitive groups as well as the other groups. Our study highlights the combination of cross-linking structure and block interactions in stabilizing microcapsules and tuning their selective permeability.

Core crosslinked H-type poly(methacrylic acid)-block-hydroxyl terminated polybutadiene-block-poly(methacrylic acid) four-armed star block copolymer micelles for intercellular drug release

H-type four-armed star block copolymers with hydroxyl-terminated polybutadiene as hydrophobic sections and poly(methacrylic acid) as hydrophilic fragments were synthesized through atom transform radical polymerization and the follow-up acidolysis, named PMAA2- b-HTPB- b-PMAA2. The core crosslinking reaction was conducted by ultraviolet light irradiation. 1H nuclear magnetic resonance, Fourier transform infrared, size exclusion chromatography, and thermal gravimetric analysis were adopted to confirm the chemical structure of the resulting copolymers. The effect of the ultraviolet light crosslinking on the physicochemical properties of the block copolymer micelles was investigated by fluorescent spectrometry, ultraviolet transmittance, dynamic light scattering, and transmission electron microscope measurements. The results showed that the crosslinking resulted in formation of the stable copolymer micelles and change in the physicochemical parameters, for example, lower critical micelle concentration and smaller micellar size than the uncrosslinked one. Drug loading and in vitro drug release disclosed that the crosslinked copolymer micelles had enhanced drug loading capacity and encapsulation efficiency, less drug leakage, and thus smaller harm to the normal cells but better therapy effect than the uncrosslinked counterpart by the aid of the pH-induced paclitaxel release. The copolymer micelles exhibited pH-dependent cytotoxicity, and therefore, they might be a promising drug target release carrier in biomedical applications.

Aqueous copper(0) mediated reversible deactivation radical polymerization of 2-hydroxyethyl acrylate

Lowering the concentration of adsorbed radicals on the Cu(0) surface, achieved by reducing catalyst and adding NaBr, is the key to the synthesis of well-defined P(HEA) without a high molecular weight shoulder in aqueous solution using two-step Cu(0) in situ mediation.

Nanogel Carrier Design for Targeted Drug Delivery

Polymer-based nanogel formulations offer features attractive for drug delivery, including ease of synthesis, controllable swelling and viscoelasticity as well as drug loading and release characteristics, passive and active targeting, and the ability to formulate nanogel carriers that can respond to biological stimuli. These unique features and low toxicity make the nanogels a favorable option for vascular drug targeting. In this review, we address key chemical and biological aspects of nanogel drug carrier design. In particular, we highlight published studies of nanogel design, descriptions of nanogel functional characteristics and their behavior in biological models. These studies form a compendium of information that supports the scientific and clinical rationale for development of this carrier for targeted therapeutic interventions.

Bioreducible cross-linked Pluronic micelles: pH-triggered release of doxorubicin and folate-mediated cellular uptake

Bioreducible are described here, cross-linked Pluronic micelles carrying doxorubicin (DOX) for folate-mediated cancer targeting. The amine-terminated Pluronic® F-127 was functionalized by grafting acrylic acid (AA) to the hydrophobic block (AA-Pluronic-NH2). Folic acid (FA), hydrazine (H), and cystamine (C) were sequentially conjugated to AA-Pluronic-NH2, followed by DOX conjugation via an acid-labile hydrazone bond (FA-Pluronic-C/H-DOX). The DOX content was approximately 143 µg/mg of polymer. We prepared bioreducible cross-linked micelles using FA-Pluronic-C/H-DOX, which had a diameter of 156.1 nm. After incubation for 24 h with 10 mM of dithiothreitol, the micelle size decreased dramatically to 87.6 nm with a broad distribution, indicating that disulfide bonds in the micelle core were reductively cleaved. In vitro release data showed that the conjugated DOX was released slowly from the FA-Pluronic C/H-DOX micelles at pH 7.4, whereas there was a rapid DOX release at pH 5.2. Confocal images of HeLa cells showed enhanced cellular uptake of FA-Pluronic-C/H-DOX micelles as compared to nontargeted Pluronic-C/H-DOX micelles. The FA-Pluronic-C/H-DOX micelles killed more cells than the nontargeted micelles, but the cytotoxic effect was not as significant as free DOX. Additionally, micelles without DOX were not cytotoxic. On the basis of these results, pH- and redox potential–responsive FA-Pluronic-C/H-DOX micelles could potentially function as cancer-targeted and controlled DOX delivery systems.

Dynamic arm exchange facilitates crystallization and jamming of starlike polymers by spontaneous fine-tuning of the number of arms

The effect of dynamic arm exchange on the crystallization and the jamming of multiarm starlike polymers was studied using small angle x-ray scattering and rheology. Poly(ethylene oxide) end capped with a small hydrophobic chain formed spherical micelles in water. Dynamic arm exchange allowed rapid crystallization and caused a discontinuous liquid-solid transition in dense suspensions after cooling. It is shown here that this is caused by spontaneous fine-tuning of the number of arms per micelle (f). Elimination of arm exchange by in situ photo-cross-linking of the core did not influence the behavior when f was at the optimum value. However, suboptimal values of f inhibited crystallization and the liquid-solid transition.

Synthesis, self-assembly, and pH-responsive behavior of (photo-crosslinked) star amphiphilic triblock copolymer

Conventional polymeric micelles employed as drug carriers suffer from the drawback of disaggregation when diluted into body fluids, giving rise to premature release of drugs. In this work, cinnamate was chosen as a crosslinker to overcome this issue and regulate pH response. A series of photo-crosslinkable star amphiphilic triblock copolymers, star poly(ε-caprolactone)-b-poly(2-cinnamoyloxyethyl methacrylate)-b-poly(2-(dimethylamino)ethyl methacrylate) (SPCL-b-PCEMA-b-PDMAEMA), were prepared by combination of stepwise reversible addition-fragment chain transfer (RAFT) polymerization and carbodiimide-mediated coupling reaction. These star amphiphilic copolymers could self-assemble into core-shell-corona micelles. Facile photo crosslinking of the micelles was carried out via UV irradiation. The crosslinked micelles showed an improved stability determined by critical micelle concentration (CMC). The degree of photo crosslinking was easily regulated by tuning UV irradiation time, and the hydrodynamic diameters (D(h)) decreased with increasing degree of photo crosslinking. The pH responses of micelles were investigated by dynamic light scattering (DLS), indicating pH-induced swelling-shrinking behavior. For photo-crosslinked micelle, its capability of swelling-shrinking weakened with increasing crosslinking degree, suggesting that pH response was controlled by crosslinking density. This novel photo-crosslinked micelle system with adjustable pH response was expected to have potential as drug carriers for controlled release.

Cyclopolymerization To Synthesize Conjugated Polymers Containing Meldrum's Acid as a Precursor for Ketene Functionality

Recently, the importance of Meldrum's acid has been reinvestigated because it serves as a great precursor for ketene generation by thermolysis. In this study, we synthesized conjugated polymers containing Meldrum's acid via controlled cyclopolymerization using a third-generation Grubbs catalyst. To avoid the solubility issue, copolymerization with soluble monomers was successfully used to provide various random and block copolymers containing Meldrum's acid in the conjugated backbone. Interestingly, when a polyacetylene derivative containing Meldrum's acid was incorporated into the second block of the diblock copolymers, highly stable core-shell supramolecules spontaneously formed during the polymerization via in situ nanoparticlization of conjugated polymer. This direct fabrication of nanostructures without requiring any post-treatments was due to the strong π-π interactions and the insolubility of the polyacetylene segment leading to the formation of core in situ. Moreover, thermolysis of Meldrum's acid to generate ketene in the conjugated polymer core was monitored by IR, and its consecutive cycloaddition to afford the cross-linked core improved the stability of the supramolecules.

Polymer nanogels: a versatile nanoscopic drug delivery platform

In this review we put the spotlight on crosslinked polymer nanogels, a promising platform that has the characteristics of an "ideal" drug delivery vehicle. Some of the key aspects of drug delivery vehicle design like stability, response to biologically relevant stimuli, passive targeting, active targeting, toxicity and ease of synthesis are discussed. We discuss several delivery systems in this light and highlight some examples of systems, which satisfy some or all of these design requirements. In particular, we point to the advantages that crosslinked polymeric systems bring to drug delivery. We review some of the synthetic methods of nanogel synthesis and conclude with the diverse applications in drug delivery where nanogels have been fruitfully employed.