Recent advances in the self-assembly of sparsely grafted amphiphilic copolymers in aqueous solution

This review describes the self-assembly of sparsely grafted amphiphilic copolymers and highlights the effects of structural factors and solvents on their self-assembly behaviour.

Microstructure and Biological Properties of Electrospun In Situ Polymerization of Polycaprolactone-Graft-Polyacrylic Acid Nanofibers and Its Composite Nanofiber Dressings

In this study, polycaprolactone (PCL)- and poly(acrylic acid) (PAA)-based electrospun nanofibers were prepared for the carriers of antimicrobials and designed composite nanofiber mats for chronic wound care. The PCL- and PAA-based electrospun nanofibers were prepared through in situ polymerization starting from PCL and acrylic acid (AA). Different amounts of AA were introduced to improve the hydrophilicity of the PCL electrospun nanofibers. A compatibilizer and a photoinitiator were then added to the electrospinning solution to form a grafted structure composed of PCL and PAA (PCL-g-PAA). The grafted PAA was mainly located on the surface of a PCL nanofiber. The optimization of the composition of PCL, AA, compatibilizer, and photoinitiator was studied, and the PCL-g-PAA electrospun nanofibers were characterized through scanning electron microscopy and 1H-NMR spectroscopy. Results showed that the addition of AA to PCL improved the hydrophilicity of the electrospun PCL nanofibers, and a PCL/AA ratio of 80/20 presented the best composition and had smooth nanofiber morphology. Moreover, poly[2 -(tert-butylaminoethyl) methacrylate]-grafted graphene oxide nanosheets (GO-g-PTA) functioned as an antimicrobial agent and was used as filler for PCL-g-PAA nanofibers in the preparation of composite nanofiber mats, which exerted synergistic effects promoted by the antibacterial properties of GO-g-PTA and the hydrophilicity of PCL-g-PAA electrospun nanofibers. Thus, the composite nanofiber mats had antibacterial properties and absorbed body fluids in the wound healing process, thereby promoting cell proliferation. The biodegradation of the PCL-g-PAA electrospun nanofibers also demonstrated an encouraging result of three-fold weight reduction compared to the neat PCL nanofiber. Our findings may serve as guidelines for the fabrication of electrospun nanofiber composites that can be used mats for chronic wound care.

Polymer Brushes: Efficient Synthesis and Applications

Polymer brushes are special macromolecular structures with polymer chains densely tethered to another polymer chain (one-dimensional, 1D) or the surface of a planar (two-dimensional, 2D), spherical or cylindrical (three-dimensional, 3D) solid via a stable covalent or noncovalent bond linkage. In comparison with the corresponding linear counterpart with similar molecular composition, one-dimension polymer brushes have some fascinating properties including wormlike conformation, compact molecular dimension, and notable chain end effects due to their compact and confined densely grafted structure. The introduction of polymer chains onto the surface of planar and spherical or cylindrical matrix will not only significantly change the surface-related properties of the matrix but also endows the obtained hybrid polymer brushes with new functionalities. Thus, polymer brushes are of great interest in the fields of polymer and material science due to their broad applications, such as catalysis, nanolithography, biomineralization, drug delivery, medical diagnosis, optoelectronics, and so on. Although a variety of 1D, 2D, and 3D polymer brushes have been prepared with the advent of living/controlled polymerization, the development of more efficient and facile synthetic protocols that permit access to polymer brushes with precisely controlled composition, structure, and functionality still represents a key contemporary challenge. In this Account, we summarize our recent efforts on the development of efficient methods to prepare 1D, 2D, and 3D polymer brushes and exploration of their potential applications in drug delivery, antifouling coating, catalysis, and lithium-ion batteries and also highlight related achievements by other groups. First, we briefly introduce the precedent examples of efficient synthesis of polymer brushes with different structures and functionalities by the combination of monomer design with living/controlled polymerization. Given the excellent tolerance and use of the same catalytic system without any mutual interference of ATRP and Cu-catalyzed alkyne-azide cyclization (CuAAC) click reaction, a versatile and efficient platform for precise synthesis of complex asymmetric (Janus-type) 1D polymer brushes was developed on the basis of the "trifunctional monomer" strategy without polymeric functionality transformation. Subsequently, a noncovalent strategy based on crystallization-driven self assembly to prepare well-defined polymer brushes with precise control over their composition and dimensions is described. Notably, the crystallization-driven self assembly can be treated as a living/controlled polymerization of "polymeric monomer" with a special building segment for crystallization, which allows for preparing linear polymer brushes with length as high as tens of micrometers. Moreover, the properties and related applications of polymer brushes as interesting building blocks for constructing hierarchical nanostructures, efficient drug deliver carriers, antifouling films, and lithium-ion batteries are addressed by some typical examples. These advancements in this field will provide a new avenue for obtaining fascinating polymer-brush-based functional materials.

PAA-g-PLA amphiphilic graft copolymer: synthesis, self-assembly, and drug loading ability

This article reports the synthesis of a PAA-g-PLA amphiphilic polymer by the combination of RAFT polymerization and organocatalytic ROP, which could self-assemble into spheres in aqueous media for sustained release of doxorubicin.

Synthesis of an amphiphilic graft copolymer bearing a hydrophilic poly(acrylate acid) backbone for drug delivery of methotrexate

This article reports the synthesis of a PAA-g-PLA amphiphilic graft polymer, which could self-assemble into large compound micelles in aqueous media for sustained release of MTX.

Preparation of thermo-responsive graft copolymer by using a novel macro-RAFT agent and its application for drug delivery

A methodology to prepare thermo-responsive graft copolymer by using a novel macro-RAFT agent was proposed. The macro-RAFT agent with pendant dithioester (ZC(S)SR) was facilely prepared via the combination of RAFT polymerization and esterification reaction. By means of ZC(S)SR-initiated RAFT polymerization, the thermo-responsive graft copolymer consisting of poly(methyl methacrylate-co-hydroxylethyl methacrylate) (P(MMA-co-HEMA)) backbone and hydrophilic poly(N-isopropylacrylamide) (PNIPAAm) side chains was constructed through the "grafting from" approach. The chemical compositions and molecular weight distributions of the synthesized polymers were respectively characterized by (1)H nuclear magnetic resonance ((1)H NMR) and gel permeation chromatography (GPC). Self-assembly behavior of the amphiphilic graft copolymers (P(MMA-co-HEMA)-g-PNIPAAm) was studied by transmission electron microscopy (TEM), dynamic light scattering (DLS) and spectrofluorimeter. The critical micelle concentration (CMC) value was 0.052 mg mL(-1). These micelles have thermo-responsibility and a low critical solution temperature (LCST) of 33.5°C. Further investigation indicated that the guest molecule release property of these micelles, which can be well described by a first-order kinetic model, was significantly affected by temperature. Besides, the micelles exhibited excellent biocompatibility and cellular uptake property. Hence, these micelles are considered to have potential application in controlled drug delivery.

The synthesis and comparison of poly(methacrylic acid)–poly(ε-caprolactone) block copolymers with and without symmetrical disulfide linkages in the center for enhanced cellular uptake

A self-assembled poly(methacrylic acid)–poly(ε-caprolactone) block copolymer with a disulfide linkage, PMAA-b-PCL-SS-PCL-b-PMAA, was synthesized for enhanced cellular uptake due to a reduction response to GSH and pH-sensitive characteristics.

Construction of PEG-based amphiphilic brush polymers bearing hydrophobic poly(lactic acid) side chains via successive RAFT polymerization and ROP

This article reports the synthesis of PEG-b-(PAA-g-PLA) amphiphilic brush polymers by the combination of RAFT polymerization and organocatalytic ROP, which could self-assemble into spheres for sustained release of doxorubicin.

A novel methacrylate with a bisphosphonate group: RAFT polymerization and flame retardant property of the resultant polymers

In this work, a novel methacrylate monomer with a bisphosphonate group was synthesized and then polymerized by RAFT polymerization to obtain well-defined polymers with better thermal and flame-retardant properties.

Multi-responsive graft copolymer micelles comprising acetal and disulfide linkages for stimuli-triggered drug delivery

Dual-cleavable polymeric aggregates were efficiently used for thermo-, pH and reduction triggered controlled release of doxorubicin due to the stimuli-dependent topological transformation and reaggregation of copolymer aggregates.

Preparation of polysaccharide derivates chitosan-graft-poly(ɛ-caprolactone) amphiphilic copolymer micelles for 5-fluorouracil drug delivery

Biodegradable graft copolymer, chitosan-graft-poly(ɛ-caprolactone) (CS-g-PCL) was synthesized via ring opening polymerization and characterized by (1)H NMR and FTIR spectroscopy. Then graft copolymers were self-assembled into micelles as drug delivery system. To evaluate drug-polymer compatibility, the Flory-Huggins interaction parameter between 5-fluorouraci (5-Fu) and hydrophobic segment was calculated. The result was in agreement with experimental data from drug loading content and drug loading efficiency. Meanwhile, DLS and TEM were utilized to evaluate the trend of particle size and morphology in aqueous solution with different repeating units of ɛ-CL. The in vitro drug release data was fitted with three kinetic models, usually applied in the drug delivery system. Results indicated that the release of 5-Fu was controllable and the release half-time could reach as long as 54.46 h, much slower than that of free 5-Fu. Cytotoxicity evaluation and cellular apoptosis study suggested good biocompatibility of CS-g-PCL micelles. Moreover, 5-Fu loaded micelles could delay the release of drug and exert comparable cytotoxicity against A549 cells.

Synthesis of an amphiphilic PEG-PCL-PSt-PLLA-PAA star quintopolymer and its self-assembly for pH-sensitive drug delivery

A novel amphiphilic ABCDE-type star quintopolymer was achieved via modular synthesis and self-assembled into polymersomes for stimuli-triggered drug release.