The exploration of endocytic mechanisms of PLA-PEG nanoparticles prepared by coaxialtri-capillary electrospray-template removal method.

The nano-sized poly(lactic acid)-poly(ethylene glycol) (PLA-PEG) particles with core-shell structure were efficiently prepared by using coaxial tri-capillary electrospray-template removal method. The cellular uptake mechanism, intracellular distribution and exocytosis in A549 cell model of electrosprayed PLA-PEG nanoparticles were systemically studied. The drug release behavior of electrosprayed PLA-PEG nanoparticles were also investigated. Our results showed that PLA-PEG nanoparticles can be endocytosed quickly by A549 cells. The cellular uptake of PLA-PEG nanoparticles was an energy dependent endocytosis process. Caveolae-mediated endocytosis was only one of endocytosis pathways in A549 cells for PLA-PEG nanoparticles, while clathrin mediated endocytosis was not involved in the endocytosis process. The endocytosed PLA-PEG nanoparticles enriched in the head of A549 cells and only a small amount of them was transported into lysosome after 24h incubation. These findings provided insights into the application of electrosprayed PLA-PEG nanoparticles in nano drug delivery field.

A new strategy based on electrospray technique to prepare dual-responsive poly(ether urethane) nanogels.

In this work, we proposed a new strategy based on electrospray technique to prepare nanogels. Compared with other methods of preparing nanogels, electrospray technique is more simple and efficient. A biodegradable and multi-responsive poly(ether urethane) (PEU) was synthesized via a facile one-pot method and used as the electrospray material. By using electrospray technique, pH- and redox-responsive poly(ether urethane) nanogels were prepared. The morphologies of the electrospray nanoparticles before and after swelling were demonstrated to be spherical and uniform, as characterized by scanning electron microscope (SEM) and transmission electron microscopy (TEM). Dynamic light scattering (DLS) results showed that the mean hydrodynamic diameter of nanogels was about 500 nm. The pH- and redox-sensitive behaviors of nanogels were studied with DLS and TEM. In acidic media the nanogels dissociated, while in the presence of GSH the nanogels degraded. The nanogels suspension was stored at 4 °C and was stable without aggregation for at least 30 days. Doxorubicin (DOX) can be further loaded into the poly(ether urethane) nanogels. The electrospray nanogels can change the release rate of loaded drug in response to pH and GSH stimuli.

Synthesis of Hemoglobin Conjugated Polymeric Micelle: A ZnPc Carrier with Oxygen Self-Compensating Ability for Photodynamic Therapy.

Photodynamic therapy (PDT) is a promising singlet oxygen ((1)O2) mediated clinical treatment for many tumors. As the source of (1)O2, oxygen plays an important role in the curative effect of PDT. However, the facts of photochemical depletion of oxygen and the intrinsic hypoxic microenvironment of tumors remain the major challenges. In this work, a novel photosensitizer carrier with oxygen self-compensating ability was designed for PDT. It was synthesized via chemical conjugation of hemoglobin (Hb) to polymeric micelles formed by triblock copolymers of poly(ethylene glycol)-block-poly(acrylic acid)-block-polystyrene (PEG-b-PAA-b-PS). The PEG-b-PAA-b-PS and resultant micelles in aqueous solution were comprehensively characterized by means of FTIR, (1)H NMR, GPC, DLS, TEM, and fluorescence spectroscopy. The oxygen-binding capacity and antioxidative activity of the Hb conjugated micelles were evaluated via UV-vis spectroscopy. In addition, compared with the control micelles without Hb, the Hb conjugated photosensitizer carrier was able to generate more (1)O2 and exert greater photocytotoxicity on Hela cells in vitro.

Facile preparation of cancer-specific polyelectrolyte nanogels from natural and synthetic sugar polymers.

Glyco-nanogels are glycopolymer-decorated nanoparticles of three-dimensional cross-linked networks, which have attracted ever-increasing interest of the biomedical-related community. However, most of the current reported glycosylated nanogels are prepared by copolymerization of glycopolymers with co-monomers and cross-linkers. Physically self-assembled glyco-nanogels remain a big challenge and are rarely explored. Herein, we report a new synthesis of glycosylated polyelectrolyte nanogels (glyco/CS nanogels), which are self-assembled from glycopolymers (PMAG-b-PMAA) synthesized through reversible addition-fragmentation chain transfer polymerization (RAFT) and quaternary ammonium chitosan (QACS) via electrostatic interactions under physiological conditions (pH 7.4, NaCl 0.15 M). The resultant glyco-nanogels have been demonstrated to be very stable in 10 mM HEPES buffer solution at least for 7 days and possess a specific binding capability to Con A. Their structure composed of an ionically cross-linked core and a glucose corona was confirmed by TEM. Compared with normal cells, glyco/CS nanogels exhibited a much higher affinity and cytotoxicity towards K562 cancer cells. In addition, the cellular uptake of these nanogels by K562 was further imaged via fluorescent microscopy in which nanogels with yellow-green signals were found to eventually co-locate within the cell nuclei of K562. The incorporation of natural and synthetic sugar polymers into polyelectrolytes has provided an insight to easily prepare glyco-nanogels with excellent colloidal stability, specific bioactivities and imaging ability, suggesting their great potential for biomedical applications.

Novel chitosan-based pH-sensitive and disintegrable polyelectrolyte nanogels.

A novel approach to design pH-sensitive and disintegrable polyelectrolyte nanogels composed of citraconic-based N-(carboxyacyl) chitosan (polyanion) and quaternary chitosan (polycation) was reported. Firstly, the hydrolysis of citraconic-modified chitosan was monitored using fluorescamine assay and it could selectively dissociate in acidic media (e.g., pH ∼5.0) due to the isomerization during the addition of citraconic anhydride to chitosan. Secondly, the self-assembly behaviors of different polyelectrolyte pairs between citraconic-based chitosan and quaternary chitosan were investigated via colloidal titration assay. It was indicated that the difference in molecular weight (MW) of opposite charged polyelectrolytes played an important role on the formation of polyelectrolyte nanogels. Results showed that polyelectrolyte nanogels (ca. 300nm in size) only formed when polyanion and polycation had a very large difference in MW. The pH-sensitive behavior of polyelectrolyte nanogels was comprehensively investigated by dynamic light scattering (DLS) and transmission electron microscope (TEM). The incorporation of charge-conversional citraconic-based chitosan into polyelectrolyte complexes has provided an effective approach to prepare polyelectrolyte nanogels which were very stable at neutral pH but disintegrated quickly in acidic media.

Generation of nano-sized core-shell particles using a coaxial tri-capillary electrospray-template removal method.

This study proposed a new strategy based on a coaxial tri-capillary electrospray-template removal process for producing nanosized polylactide-b-polyethylene glycol (PLA-PEG) particles with a core-shell structure. Microparticles with core-shell-corona structures were first fabricated by coaxial tri-capillary electrospray, and core-shell nanoparticles less than 200 nm in size were subsequently obtained by removing the PEG template from the core-shell-corona microparticles. The nanoparticle size could be modulated by adjusting the flow rate of corona fluid, and nanoparticles with an average diameter of 106±5 nm were obtained. The nanoparticles displayed excellent dispersion stability in aqueous media and very low cytotoxicity. Paclitaxel was used as a model drug to be incorporated into the core section of the nanoparticles. A drug loading content in the nanoparticles as high as 50.7±1.5 wt% with an encapsulation efficiency of greater than 70% could be achieved by simply increasing the feed rate of the drug solution. Paclitaxel exhibited sustained release from the nanoparticles for more than 40 days. The location of the paclitaxel in the nanoparticles, i.e., in the core or shell layer, did not have a significant effect on its release.

Novel complex hydrogels based on N-carboxyethyl chitosan and quaternized chitosan and their controlled in vitro protein release property.

A novel pH-responsive hydrogel (CHC) composed of N-carboxyethyl chitosan (CEC) and N-[(2-hydroxy-3-trimethylammonium) propyl] chitosan chloride (HTCC) was synthesized by the redox polymerization technique. Turbidimetric titrations were used to determine the stoichiometric ratio of these two chitosan derivatives. The hydrogel was characterized by FT-IR, thermal gravimetric analysis (TGA), X-ray diffractometry (XRD), and scanning electron microscopy (SEM). The dynamic transport of water showed that the hydrogel reached equilibrium within 48h. The swelling ratio of CHC hydrogel depended significantly on the pH of the buffer solution. The performance of the CHC as a matrix for the controlled release of BSA was investigated. It was found that the release behavior was determined by pH value of the medium as well as the intermolecular interaction between BSA and the hydrogels.

Mild immobilization of diverse macromolecular bioactive agents onto multifunctional fibrous membranes prepared by coaxial electrospinning.

Coaxial electrospinning was proved to be a facile method to produce multifunctional fibrous matrices which could essentially emulate certain features of native extracellular matrix. In order to further confer capability of immobilizing diverse macromolecular bioactive agents to the fibers, composite membranes composed of cationized gelatin-coated polycaprolactone (PCL) fibers were prepared by coaxial electrospinning. Gelatin was cationized by derivation with N,N-dimethylethylenediamine. The cationized gelatin (CG) was used as a shell material for constructing a core-shell fibrous membrane. PCL formed the core section of the core-shell fibers thereby improving the mechanical properties of nanofibrous CG hydrogel. The outer CG layer was crosslinked by exposing the membranes in glutaraldehyde vapor. The adsorption behaviors of FITC-labeled bovine serum albumin (FITC-BSA) or FITC-heparin onto the fibers were investigated. The core-shell fibers could effectively immobilize the two types of agents under mild conditions. The adsorption amount could reach about 12 microg of BSA per mg of membrane and 23 microg mg(-1) for heparin. Furthermore, vascular endothelial growth factor (VEGF) could be conveniently impregnated into the fibers through specific interactions with the adsorbed heparin in the outer CG layer. Sustained release of bioactive VEGF could be achieved for more than 15 days.

A facile route for regioselective conjugation of organo-soluble polymers onto chitosan.

A facile route is described for the regioselective conjugation of organo-soluble polymers onto chitosan under very mild conditions, using SCC as intermediates. SCC could be prepared simply by mixing chitosan acidic aqueous solution with SDS. PEG or PCL were then grafted to SCC using the NHS/DCC coupling method. In addition, the polymers were found to be linked to chitosan through the hydroxyl groups of chitosan when stoichiometric SCC was used as a precursor. SDS could be removed simply by either precipitating the solution of SCC-graft-polymer in DMSO into Tris aqueous solution or dialyzing against Tris solution.

Micellization phenomena of amphiphilic block copolymers based on methoxy poly(ethylene glycol) and either crystalline or amorphous poly(caprolactone-b-lactide).

This study focuses on the aggregation behavior of the biodegradable amphiphilic block copolymers based on methoxy poly(ethylene glycol) (mPEG) as a hydrophilic block and either crystalline poly(caprolactone-b-l-lactide) (P(CL-LLA)) or amorphous poly(caprolactone-b-D,L-lactide) (P(CL-DLLA)) as a hydrophobic block. These block copolymers have a strong tendency to form micelles in aqueous medium, with very low critical micelle concentrations (CMCs). The CMC of P(CL-LLA)-b-mPEG is higher than that of P(CL-DLLA)-b-mPEG when the mPEG block has the same molecular weight. Furthermore, the partition equilibrium coefficient (K(v)) of pyrene in the micellar solution of P(CL-LLA)-b-mPEG copolymer was lower than that of P(CL-DLLA)-b-mPEG copolymer when the mPEG block was the same length. These differences were believed to be related to the physical state of the core-forming blocks, i.e., the crystalline P(CL-LLA) block and the amorphous P(CL-DLLA) block. The TEM images showed that micelles formed by P(CL-LLA)-b-mPEG assembled in a cylindrical morphology, whereas those formed by P(CL-DLLA)-b-mPEG took a classical spherical shape. In addition, with differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) analyses, it is believed that the crystallization tendency of the core-forming blocks is the main factor governing the morphology of micelles in water. A possible mechanism for the cylindrical assembly morphology was discussed.