Shaoliang Lin

Drug releasing behavior of hybrid micelles containing polypeptide triblock copolymer

We report a new type of hybrid polymeric micelles for drug delivery applications. These micelles consist of PLGA (PLGA: poly(l-glutamic acid)) and PEG (PEG: polyethylene glycol) mixed corona chains. In acidic condition, PLGA undergoes a transformation from water-soluble random coils to water-insoluble alpha-helix, leading to microphase separation in micelle coronas and formation of PEG channels. These channels connect the inner core and the outer milieu, accelerating the diffusion of drugs from micelles. The micelles were prepared through a co-micellization of PLGA-b-PPO-b-PLGA (PPO: poly(propylene oxide)) and PEG-b-PPO in water. During the self-assembly, the PPO blocks of both block copolymers aggregated into cores that were surrounded by mixed corona chains of PLGA and PEG blocks. We confirmed this structure by using a number of characterization techniques including nuclear magnetic resonance spectroscopy, zeta potential, circular dichroism, and dynamic light scattering. We also performed molecular dynamics (MD) simulations to verify the models of the hybrid micelle structure. One advantage of the hybrid micelles as drug carriers is their tunable release rate without sacrificing colloidal stability. The rate can be tuned by either micelle structures such as the composition of the mixture or external parameters such as pH.

Structural Evolution of Multicompartment Micelles Self-Assembled from Linear ABC Triblock Copolymer in Selective Solvents

Using dissipative particle dynamics simulation, structural evolution from concentric multicompartment micelles to raspberry-like multicompartment micelles self-assembled from linear ABC triblock copolymers in selective solvents was investigated. The structural transformation from concentric micelles to raspberry-like micelles can be controlled by changing either the length of B blocks or the solubility of B block. It was found that the structures with B bumps on C surface (B-bump-C) are formed at shorter B block length and the structures with C bumps on B surface (C-bump-B) are formed at relative lower solubility of B blocks. The formation of B-bump-C is entropy-driven, while the formation of C-bump-B is enthalpy-dominated. Furthermore, when the length of C blocks is much lower than that of B blocks, an inner-penetrating vesicle was discovered. The results gained through the simulations provide an insight into the mechanism behind the formation of raspberry-like micelles.

Simulation‐Assisted Self‐Assembly of Multicomponent Polymers into Hierarchical Assemblies with Varied Morphologies

As you like it: The synthesis of supramolecular hierarchical nanostructures with designed morphologies has been realized through computer-simulation-guided multicomponent assembly of polypeptide-based block copolymers and homopolymers. By adjusting the attraction between hydrophobic polypeptide rods, as well as other parameters such as the molar ratio of copolymers and the rigidity of polymers, a variety of morphologies were obtained.

Water-soluble dendritic-linear triblock copolymer-modified magnetic nanoparticles: preparation, characterization and drug release properties

One route has been employed to prepare dendritic-linear block copolymer modified superparamagnetic iron oxide nanoparticles (SPIONs), which consist of a Fe3O4 magnetic nanoparticle core and a dendritic-linear block copolymer, the focal point polyamidoamine-type dendron-b-poly(2-dimethylaminoethyl methacrylate)-b-poly(N-isopropylacrylamide) (PAMAM-b-PDMAEMA-b-PNIPAM) shell by two-step atom transfer radical polymerization (ATRP). Firstly, Fe3O4 nanoparticles were prepared by a high-temperature solution phase reaction in the presence of iron(III) acetylacetonate [Fe(acac)3], oleic acid and oleylamine. Then propargyl focal point PAMAM-type dendron (generation 2.0, denoted as propargyl-D2.0) with four carboxyl acid end groups as a cap displaced the oleic acid and oleylamine on the surfaces. Subsequently, an initiator for ATRP was introduced onto the propargyl-D2.0-modified Fe3O4 nanoparticle surfaces via click chemistry with 2′-azidoethyl-2-bromoisobutylate (AEBIB). PDMAEMA and PNIPAM were grown gradually from nanoparticle surfaces using two-step copper-mediated ATRP. Finally, a crosslinking reaction between PDMAEMA block with 1,2-bis(2-iodoethoxy)ethane (BIEE) was used to stabilize the nanoparticles and reverse aggregation. The modified nanoparticles were subjected to detailed characterization using FT-IR, DLS, XRD and TGA. Magnetization measurements confirmed the characteristic superparamagnetic behavior of all magnetic nanoparticles under room temperature. In addition, doxorubicin (DOX) as an anticancer drug model was loaded into the dendritic-linear block copolymer shell of the modified nanoparticles, and subsequently the drug release was performed in phosphoric acid buffer solution (pH 7.4) at 25 °C or 37 °C. The results verify that dendritic-linear block copolymer-modified nanoparticles as a drug carrier possess thermosensitive drug release behaviors. Furthermore, a methyl tetrazolium (MTT) assay of DOX-loaded dendritic-linear block copolymer-modified nanoparticles against Hela cells was evaluated. The results show that the modified nanoparticles can be used for drug delivery.

Self-assembly and photo-responsive behavior of novel ABC2-type block copolymers containing azobenzene moieties

The self-assembly behavior and photo-responsive properties of novel azobenzene based copolymers poly(ethylene oxide) monomethyl ether-block-polystyrene-block-{poly[6-(4-methoxy-azobenzene-4′-oxy) hexylmethacrylate]}2 [MPEO-b-PS-b-(PMMAZO)2] with various block lengths of PMMAZO segments in aqueous media were studied by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM), laser light scattering (LLS) and UV-Vis spectrophotometry. It was found that the critical water content for the aggregate formation increases with the PMMAZO weight fraction. By tailoring the molecular structure and copolymer concentration, various self-assembled aggregates were obtained. At a lower concentration, all the copolymers self-assembled into simple vesicles. With increasing the polymer concentration, large compound vesicles were formed. The photo-sensitive properties of the formed aggregates were also studied. Upon irradiation with a polarized light, the aggregates were elongated. Large compound vesicles were found to deform into compact spindles with a very large axial ratio.

Directional photomanipulation of breath figure arrays

Porous polymeric films are of paramount importance in many areas of modern science and technology. However, processing methods typically based on direct writing, imprint, and lithography techniques have low throughput and are often limited to specific fabricated shapes. Herein, we demonstrate the directional photomanipulation of breath figure arrays (BFAs) formed by an azobenzene-containing block copolymer to address the aforementioned problems. Under the irradiation of linearly polarized light, the round pores in the BFAs were converted to rectangular, rhombic, and parallelogram-shaped pores in 30 min, due to the anisotropic mass migration based on the photo-reconfiguration of the azobenzene units. Through a secondary irradiation after rotating the sample by 90°, the transformed pores were apparently recovered. Therefore, this non-contacted, directional photomanipulation technique in conjunction with breath figure processing opens a new route to nano/microporous films with finely tuned features.

Preparation of thermostable PBO/graphene nanocomposites with high dielectric constant

In this study, poly(p-phenylene benzobisoxazole) (PBO)/graphene composites were prepared using PBO and poly(4,6-dihydroxymetaphenylenediamine terephthalamide) (PHA)-modified graphene oxide (GO-PHA). PHA is the precursor of PBO. GO-PHA was obtained via chemical coupling reaction of amino-terminated PHA and acyl-chloride-functionalized GO. Partially reduced graphene nanosheets and benzoxazole rings were formed after heating. GO-PHA could be stably dispersed in methane sulfonic acid (MSA), which facilitated its uniform distribution in the PBO matrix. The PBO/graphene nanocomposites were obtained by the dissolution of GO-PHA and PBO in MSA. The thermogravimetric analysis results showed that the PBO/graphene composites had good thermal stability below 400 ° C. The dielectric constant of the composites increased as the amount of GO-PHA increased, and the percolation threshold was f(c) = 0.037. The nanocomposite had a dielectric constant of 15.8, which was approximately five times larger than that of pure PBO polymer.

Hierarchical nanostructures self-assembled from a mixture system containing rod-coil block copolymers and rigid homopolymers.

Self-assembly behavior of a mixture system containing rod-coil block copolymers and rigid homopolymers was investigated by using Brownian dynamics simulations. The morphologies of formed hierarchical self-assemblies were found to be dependent on the Lennard-Jones (LJ) interaction εRR between rod blocks, lengths of rod and coil blocks in copolymer, and mixture ratio of block copolymers to homopolymers. As the εRR value decreases, the self-assembled structures of mixtures are transformed from an abacus-like structure to a helical structure, to a plain fiber, and finally are broken into unimers. The order parameter of rod blocks was calculated to confirm the structure transition. Through varying the length of rod and coil blocks, the regions of thermodynamic stability of abacus, helix, plain fiber, and unimers were mapped. Moreover, it was discovered that two levels of rod block ordering exist in the helices. The block copolymers are helically wrapped on the homopolymer bundles to form helical string, while the rod blocks are twistingly packed inside the string. In addition, the simulation results are in good agreement with experimental observations. The present work reveals the mechanism behind the formation of helical (experimentally super-helical) structures and may provide useful information for design and preparation of the complex structures.

Effect of electric field on phase separation of polymer dispersed liquid crystal

Abstract The kinetics of the polymerization induced phase separation of liquid crystal (LC)/monomer mixture has been investigated by means of depolarized light intensity technique and polarized light microscope (PLM). To examine the effect of the electric field, a DC electric field was applied across the mixtures during the phase separation process. The kinetic study indicates that the phase separation process is accelerated when the electric field is applied. The morphologies of the formed polymer dispersed liquid crystal (PDLC) films were observed by PLM. The electric field applied during the phase separation process yields the PDLC with small LC domains and fine morphologies. The clearing temperature ( T NI ) of the formed PDLC films was measured by the PLM and it is found that the T NI increases with the applied electric field intensity.

Effect of Molecular Architecture on Phase Behavior of Graft Copolymers

Influence of molecular architecture on phase behavior of graft copolymer melts was studied by using a reciprocal-space self-consistent filed theory (SCFT). The phase diagrams were examined as functions of the architectural parameters describing the graft copolymers (i.e., the number of grafts and the position of first junction). In comparison with the well-known phase diagram of diblock copolymers, the phase diagrams of the graft copolymers are asymmetric. When the number of grafts or the position of first junction varies, the boundaries of order-order transitions have shifts due to the variation in the chain stretching energy. The change in molecular architecture also significantly alters the domain spacing of ordered structures but has weak impact on the density distributions of graft copolymers. For comparison of the theoretical predictions with the existing experimental results, the phase diagrams of graft copolymers were also calculated at strong segregation. The SCFT calculations can accurately capture the characteristics of the phase behavior of graft copolymer melts.