Preparation and characterization of microgels sensitive toward copper II ions

Bio-Responsive Carriers for Controlled Delivery of Doxorubicin to Cancer Cells

The cellular internalization of drug carriers occurs via different endocytic pathways that ultimately involve the endosomes and the lysosomes, organelles where the pH value drops to 6.0 and 5.0, respectively. We aimed to design and characterize pH/temperature-responsive carriers for the effective delivery of the anti-tumoral drug doxorubicin. To this purpose, poly(N-isopropylacrylamide-co-vinylimidazole) was synthesized as an attractive pH/temperature-sensitive copolymer. Microspheres made of this copolymer, loaded with doxorubicin (MS-DXR), disintegrate in monodisperse nanospheres (NS-DXR) under conditions similar to that found in the bloodstream (pH = 7.4, temperature of 36 °C) releasing a small amount of payload. However, in environments that simulate the endosomal and lysosomal conditions, nanospheres solubilize, releasing the entire amount of drug. We followed the NS-DXR internalization using two cancer cell lines, hepatic carcinoma HepG2 cells and lung adenocarcinoma A549 cells. The data showed that NS-DXR are internalized to a greater extent by HepG2 cells than A549 cells, and this correlated with increased cytotoxicity induced by NS-DXR in HepG2 cells compared with A549 cells. Moreover, NS-DXR particles do not cause hemolysis and erythrocytes aggregation. Administered in vivo, NS-DXR localized in the liver and kidneys of mice, and the loading of DXR into NS resulted in the reduced renal clearance of DXR. In conclusion, the newly developed poly(N-isopropylacrylamide-co-vinyl imidazole) particles are biocompatible and may be introduced as carriers for doxorubicin to hepatic tumors.

Fabrication of a novel core-shell-shell temperature-sensitive magnetic composite with excellent performance for papain adsorption

Herein, a novel temperature-sensitive magnetic composite (Fe3O4@SiO2@P(NIPAM-co-VI)/Cu2+) with a uniform core-shell-shell structure was successfully prepared via a layer-by-layer method. The resulting magnetic composite revealed good magnetic properties and remarkable affinity to papain with a maximum adsorption capacity of 199.17 mg g-1. The adsorption equilibrium data fitted the pseudo-second-order kinetic and Freundlich models well, and the major thermodynamics parameters indicated that adsorption was an endothermic and spontaneous process. Fe3O4@SiO2@P(NIPAM-co-VI)/Cu2+ could thermally protect papain, which is attributed to the reversible hydrophilic-hydrophobic transition of the composite at temperatures below and above the lower critical solution temperature. More importantly, the magnetic composite could be recycled at least six times without a remarkable loss in its adsorption capacity, and the process of adsorption and elution had no significant effect on the activity and structure of papain. This work could provide a novel separation method for papain without loss of its activity.

Decoupled pH- and Thermo-Responsive Injectable Chitosan/PNIPAM Hydrogel via Thiol-Ene Click Chemistry for Potential Applications in Tissue Engineering

Stimuli-responsive chitosan (CS) hydrogels exhibit great potential for drug delivery and tissue engineering; however, the structure of these stimuli-responsive CS hydrogels, such as dual pH- and thermo-responsive hydrogels, is difficult to control or needs additional crosslinking agents. Here, a new dual pH- and thermo-responsive hydrogel system is developed by combining pH-responsive C₆ -OH allyl-modified CS (OAL-CS) with thermo-responsive poly(N-isopropylacrylamide) (PNIPAM). The thiol groups in PNIPAM and the allyl groups in OAL-CS can rapidly form crosslinking hydrogel network by "thiol-ene" click chemistry under UV irradiation. As expected, the swelling ratio of the OAL-CS/PNIPAM hydrogel can be controlled by changing pH and temperature. Moreover, the hydrogel displays non-cytotoxic nature toward human bone marrow mesenchymal stem cells, and the histological analyses reveal the subcutaneous tissue with no signs of inflammation after 5 days of injection in vivo. The results indicate that the new OAL-CS/PNIPAM hydrogel has potential to serve as a smart injectable platform for application in drug delivery and tissue engineering.

Sugar-responsive Pickering emulsions mediated by switching hydrophobicity in microgels

HYPOTHESIS

Pickering emulsions stabilized by soft and responsive microgels can demulsify on demand upon microgel collapse. The concept has been explored with simple model microgels such as poly(N-isopropylacrylamide) (pNIPAM) and their derivatives, but the role of functionalization is largely unexplored.

EXPERIMENTS

Saccharide-responsive phenylboronic-modified microgels are used as Pickering emulsion stabilizers. Emulsion stability and microgel organization at drop surface are studied as a function of saccharide concentration. Better insight into their behavior at interfaces is gained through adsorption kinetics and Langmuir film studies at air-water interface.

FINDINGS

The functionalization of water-swollen microgels by phenylboronic functions imparts some hydrophobicity to the structure, at the origin of additional internal cross-links analogous which rigidify the structure compared to non-functionalized microgels, as proved by their slow adsorption kinetics and poor interfacial compressibility. Upon boronate ester formation with diol groups of the saccharide, the hydrophobic character of the phenylboronic acid decreases, increasing the adsorption kinetics and their interfacial compressibility. Emulsions are stable in the presence of saccharide, given the high deformability of the yet-hydrophilic microgels, and mechanically unstable with less deformable particles in low saccharide concentration. The hydrophobic-hydrophilic switch acts as a trigger to tune the microgel stabilizing properties.

Dual-stimuli responsive injectable microgel/solid drug nanoparticle nanocomposites for release of poorly soluble drugs

An in situ forming implant (ISFI) for drug delivery combines the potential to improve therapeutic adherence for patients with simple administration by injection. Herein, we describe the preparation of an injectable nanocomposite ISFI composed of thermoresponsive poly(N-isopropylacrylamide) based microgels and solid drug nanoparticles. Monodisperse poly(N-isopropylacrylamide) or poly(N-isopropylacrylamide-co-allylamine) microgels were prepared by precipitation polymerisation with mean diameters of approximately 550 nm at 25 °C. Concentrated dispersions of these microgels displayed dual-stimuli responsive behaviour, forming shape persistent bulk aggregates in the presence of both salt (at physiological ionic strength) and at body temperature (above the lower critical solution temperature of the polymer). These dual-stimuli responsive microgels could be injected into an agarose gel tissue mimic leading to rapid aggregation of the particles to form a drug depot. Additionally, the microgel particles aggregated in the presence of other payload nanoparticles (such as dye-containing polystyrene nanoparticles or lopinavir solid drug nanoparticles) to form nanocomposites with high entrapment efficiency of the payload. The resulting microgel and solid drug nanoparticle nanocomposites displayed sustained drug release for at least 120 days, with the rate of release tuned by blending microgels of poly(N-isopropylacrylamide) with poly(N-isopropylacrylamide-co-allylamine) microgels. Cytotoxicity studies revealed that the microgels were not toxic to MDCK-II cells even at high concentrations. Collectively, these results demonstrate a novel, easily injectable, nanocomposite ISFI that provides long-term sustained release for poorly water-soluble drugs without a burst release.

Triple Hit with Drug Carriers: pH- and Temperature-Responsive Theranostics for Multimodal Chemo- and Photothermal Therapy and Diagnostic Applications

Currently there is a strong need for new drug delivery systems, which enable targeted and controlled function in delivering drugs while satisfying highly sensitive imaging modality for early detection of the disease symptoms and damaged sites. To meet these criteria we develop a system that integrates therapeutic and diagnostic capabilities (theranostics). Importantly, therapeutic efficacy of the system is enhanced by exploiting synergies between nanoparticles, drug, and hyperthermia. At the core of our innovation is near-infrared (NIR) responsive gold nanorods (Au) coated with drug reservoirs--mesoporous silica shell (mSi)--that is capped with thermoresponsive polymer. Such design of theranostics allows the detection of the system using computed tomography (CT), while finely controlled release of the drug is achieved by external trigger, NIR light irradiation--ON/OFF switch. Doxorubicin (DOX) was loaded into mSi formed on the gold core (Au@mSi-DOX). Pores were then capped with the temperature-sensitive poly(N-isopropylacrylamide)-based N-butyl imidazolium copolymer (poly(NIPAAm-co-BVIm)) resulting in a hybrid system-Au@mSi-DOX@P. A 5 min exposure to NIR induces polymer transition, which triggers the drug release (pores opening), increases local temperature above 43 °C (hyperthermia), and upregulates particle uptake (polymer becomes hydrophilic). The DOX release is also triggered by drop in pH enabling localized drug release when particles are taken up by cancer cells. Importantly, the synergies between chemo- and photothermal therapy for DOX-loaded theranostics were confirmed. Furthermore, higher X-ray attenuation value of the theranostics was confirmed via X-ray CT test indicating that the nanoparticles act as contrast agent and can be detected by CT.

Synthesis of poly(N-isopropylacrylamide) particles for metal affinity binding of peptides

Temperature-sensitive poly(N-isopropylacrylamide) (PNIPAM) microgel particles with metal affinity ligands were prepared for selective binding of peptides containing the His6-tag (six consecutive histidine residues). The PNIPAM particles were copolymerized with the functional ligand vinylbenzyl iminodiacetic acid (VBIDA) through a two-stage dispersion polymerization using poly(N-vinyl pyrrolidone) (PVP) as a steric stabilizer. The resulting particles were monodisperse in size and colloidally stable over a wide range of temperature and ionic strength due to chemically grafted PVP chains. The particle size was also found to be sensitive to ionic strength and pH of the aqueous environment, likely due to the electrostatic repulsion between ionized VBIDA groups. Divalent nickel ions were chelated to the VBIDA groups, allowing selective metal affinity attachment of a His6-Cys peptide. The peptide was released upon the addition of the competitive ligand imidazole, demonstrating that the peptide attachment to the particles is reversible and selective.