Gradient copolymer micelles: an introduction to structures as well as structural transitions

Exhibiting variation of the composition along a chain, gradient copolymers bring new blood to the old story of polymeric micelles. The gradient chain structure results in some special features in micellar structures and leads to unique structural transitions, potentially leading to new properties and applications. Henceforth, gradient copolymer micellar structures and their transitions from the viewpoint of soft matter physics will be reviewed. Concepts such as a diffuse interface, shrinkage-stretching of micelles, and intrinsic temperature responsiveness are summarized from current research, which highlight new characteristic structures, relaxation modes and novel properties of micelles, respectively.

Folate-Conjugated Polyphosphoester with Reversible Cross-Linkage and Reduction Sensitivity for Drug Delivery

To improve the therapeutic efficacy and circulation stability in vivo, we synthesized a new kind of drug delivery carrier based on folic acid conjugated polyphosphoester via the combined reactions of Michael addition polymerization and esterification. The produced amphiphilic polymer, abbreviated as P(EAEP-AP)-LA-FA, could self-assemble into nanoparticles (NPs) with core-shell structure in water and reversible core cross-linked by lipoyl groups. Using the core cross-linked FA-conjugated nanoparticles (CCL-FA NPs) to encapsulate hydrophobic anticancer drug doxorubicin (DOX), we studied the stability of NPs, in vitro drug release, cellular uptake, and targeting intracellular release compared with both un-cross-linked FA-conjugated nanoparticles (UCL-FA NPs) and core cross-linked nanoparticles without FA conjugation (CCL NPs). The results showed that under the condition of pH 7.4, the DOX-loaded CCL-FA NPs could maintain stable over 72 h, and only a little DOX release (∼15%) was observed. However, under the reductive condition (pH 7.4 containing 10 mM GSH), the disulfide-cross-linked core would be broken up and resulted in 90% of DOX release at the same incubation period. The study of methyl thiazolyl tetrazolium (MTT) assay indicated that the DOX-loaded CCL-FA NPs exhibited higher cytotoxicity (IC₅₀: 0.33 mg L^-1) against HeLa cells than the DOX-loaded CCL NPs without FA. These results indicate that the core cross-linked FA-conjugated nanoparticles have unique stability and targetability.

Characterization of complexes made of polylysine-polyleucine-polylysine and pDNA

Polylysine shows unique physical and biological abilities in its application. In this study, different kinds of tri-block co-polypeptides are used as gene delivery vectors with hydrophobic polyleucine (L) in the middle and polylysine (K) on both sides. We explored their physical properties in aqueous solution as well as their biological effects toward gene transfection efficiency. After reaching critical micelle concentration, it is found that these tri-block polypeptides could form vesicles, and the size of each sample is independent of concentration. The self-assembly of each kind of tri-block co-polypeptide could obtain higher molecular weight vectors for gene delivery. After measuring the transfection efficiency and cell viability, these samples showed a high gene transfer ability, together with similar or lower cytotoxicity. Additionally, pDNA binding strength tests and zeta-potential assays reveal that the addition of an L part would reduce the charge density of the vector chains and thus lower the binding strength, leading to the easier release of pDNA from the complexes and an increase in transfection efficiency.

Polymeric prodrugs conjugated with reduction-sensitive dextran–camptothecin and pH-responsive dextran–doxorubicin: an effective combinatorial drug delivery platform for cancer therapy

Two types of stimuli-sensitive polymeric prodrugs for combinatorial cancer therapy have been prepared and found to exhibit favorable anticancer activity in vitro and in vivo.

Precise modular synthesis and a structure–property study of acid-cleavable star-block copolymers for pH-triggered drug delivery

A series of well-defined three-armed star-block copolymers (mPEG-a-PCL-a-)₃ linked with acid-cleavable acetal groups have been prepared and used for the pH-triggered delivery of doxorubicin.

A polyphosphoester-conjugated camptothecin prodrug with disulfide linkage for potent reduction-triggered drug delivery

A reduction-cleavable polyphosphoester-camptothecin (CPT) prodrug tailored for enhancing drug loading content and triggering drug release has been prepared and applied in tumor chemotherapy.

Core cross-linked polyphosphoester micelles with folate-targeted and acid-cleavable features for pH-triggered drug delivery

Novel folate-conjugated acid-cleavable core cross-linked polyphosphoester micelles have been prepared and used for pH and enzyme-triggered delivery of doxorubicin.

Galactosylated reduction and pH dual-responsive triblock terpolymer Gal-PEEP-a-PCL-ss-PDMAEMA: a multifunctional carrier for the targeted and simultaneous delivery of doxorubicin and DNA

A multifunctional bioreducible system based on galactosamine-modified PEEP-a-PCL-ss-PDMAEMA has been prepared and used for the targeted co-delivery of doxorubicin and DNA.

Hollow block copolymer nanoparticles through a spontaneous one-step structural reorganization

The spontaneous one-step synthesis of hollow nanocages and nanotubes from spherical and cylindrical micelles based on poly(acrylic acid)-b-polylactide (P(AA)-b-P(LA)) block copolymers (BCPs) has been achieved. This structural reorganization, which occurs simply upon drying of the samples, was elucidated by transmission electron microscopy (TEM) and atomic force microscopy (AFM). We show that it was necessary to use stain-free imaging to examine these nanoscale assemblies, as the hollow nature of the particles was obscured by application of a heavy metal stain. Additionally, the internal topology of the P(AA)-b-P(LA) particles could be tuned by manipulating the drying conditions to give solid or compartmentalized structures. Upon resuspension, these reorganized nanoparticles retain their hollow structure and display significantly enhanced loading of a hydrophobic dye compared to the original solid cylinders.

Mechanism of co-nanoprecipitation of organic actives and block copolymers in a microfluidic environment

Microreactors have been shown to be a powerful tool for the production of nanoparticles (NPs); however, there is still a lack of understanding of the role that the microfluidic environment plays in directing the nanoprecipitation process. Here we investigate the mechanism of nanoprecipitation of block copolymer stabilized organic NPs using a microfluidic-based reactor in combination with computational fluid dynamics (CFD) modelling of the microfluidic implementation. The latter also accounts for the complex interplay between molecular and hydrodynamic phenomena during the nanoprecipitation process, in order to understand the hydrodynamics and its influence on the NP formation process. It is demonstrated that the competitive reactions result in the formation of two types of NPs, i.e., either with or without loading organic actives. The obtained results are interpreted by taking into consideration a new parameter representing the mismatching between the aggregations of the polymers and actives, which plays a decisive role in determining the size and polydispersity of the prepared hybrid NPs. These results expand the current understanding of the co-nanoprecipitation mechanism of active and block copolymer stabilizer, and on the role exerted by the microfluidic environment, giving information that could be translated to the emerging fields of microfluidic formation of NPs and nanomedicine.