From well-defined poly( N -acryloylmorpholine)-stabilized nanospheres to uniform mannuronan- and guluronan-decorated nanoparticles by RAFT polymerization-induced self-assembly

Degradable Block Copolymer Nanoparticles Synthesized by Polymerization-Induced Self-Assembly

Polymerization-induced self-assembly (PISA) combines polymerization and in situ self-assembly of block copolymers in one system and has become a widely used method to prepare block copolymer nanoparticles at high concentrations. The persistence of polymers in the environment poses a huge threat to the ecosystem and represents a significant waste of resources. There is an urgent need to develop novel chemical approaches to synthesize degradable polymers. To meet with this demand, it is crucial to install degradability into PISA nanoparticles. Most recently, degradable PISA nanoparticles have been synthesized by introducing degradation mechanisms into either shell-forming or core-forming blocks. This Minireview summarizes the development in degradable block copolymer nanoparticles synthesized by PISA, including shell-degradable, core-degradable, and all-degradable nanoparticles. Future development will benefit from expansion of polymerization techniques with new degradation mechanisms and adaptation of high-throughput approaches for both PISA syntheses and degradation studies.

Low-Viscosity Route to High-Molecular-Weight Water-Soluble Polymers: Exploiting the Salt Sensitivity of Poly(N-acryloylmorpholine)

We report a new one-pot low-viscosity synthetic route to high molecular weight non-ionic water-soluble polymers based on polymerization-induced self-assembly (PISA). The RAFT aqueous dispersion polymerization of N-acryloylmorpholine (NAM) is conducted at 30 °C using a suitable redox initiator and a poly(2-hydroxyethyl acrylamide) (PHEAC) precursor in the presence of 0.60 M ammonium sulfate. This relatively low level of added electrolyte is sufficient to salt out the PNAM block, while steric stabilization is conferred by the relatively short salt-tolerant PHEAC block. A mean degree of polymerization (DP) of up to 6000 was targeted for the PNAM block, and high NAM conversions (>96%) were obtained in all cases. On dilution with deionized water, the as-synthesized sterically stabilized particles undergo dissociation to afford molecularly dissolved chains, as judged by dynamic light scattering and 1H NMR spectroscopy studies. DMF GPC analysis confirmed a high chain extension efficiency for the PHEAC precursor, but relatively broad molecular weight distributions were observed for the PHEAC-PNAM diblock copolymer chains (Mw/Mn > 1.9). This has been observed for many other PISA formulations when targeting high core-forming block DPs and is tentatively attributed to chain transfer to polymer, which is well known for polyacrylamide-based polymers. In fact, relatively high dispersities are actually desirable if such copolymers are to be used as viscosity modifiers because solution viscosity correlates closely with Mw. Static light scattering studies were also conducted, with a Zimm plot indicating an absolute Mw of approximately 2.5 × 106 g mol-1 when targeting a PNAM DP of 6000. Finally, it is emphasized that targeting such high DPs leads to a sulfur content for this latter formulation of just 23 ppm, which minimizes the cost, color, and malodor associated with the organosulfur RAFT agent.

Probing the Effect of Rigidity on the Cellular Uptake of Core-Shell Nanoparticles: Stiffness Effects are Size Dependent

Nanoparticles are well established vectors for the delivery of a wide range of biomedically relevant cargoes. Numerous studies have investigated the impact of size, shape, charge, and surface functionality of nanoparticles on mammalian cellular uptake. Rigidity has been studied to a far lesser extent, and its effects are still unclear. Here, the importance of this property, and its interplay with particle size, is systematically explored using a library of core-shell spherical PEGylated nanoparticles synthesized by RAFT emulsion polymerization. Rigidity of these particles is controlled by altering the intrinsic glass transition temperature of their constituting polymers. Three polymeric core rigidities are tested: hard, medium, and soft using two particle sizes, 50 and 100 nm diameters. Cellular uptake studies indicate that softer particles are taken up faster and threefold more than harder nanoparticles with the larger 100 nm particles. In addition, the study indicates major differences in the cellular uptake pathway, with harder particles being internalized through clathrin- and caveolae-mediated endocytosis as well as macropinocytosis, while softer particles are taken up bycaveolae- and non-receptormediated endocytosis. However, 50 nm derivatives do not show any appreciable differences in uptake efficiency, suggesting that rigidity as a parameter in the biological regime may be size dependent.

(Bio)degradable and Biocompatible Nano-Objects from Polymerization-Induced and Crystallization-Driven Self-Assembly

Polymerization-induced self-assembly (PISA) and crystallization-driven self-assembly (CDSA) techniques have emerged as powerful approaches to produce a broad range of advanced synthetic nano-objects with high potential in biomedical applications. PISA produces nano-objects of different morphologies (e.g., spheres, vesicles and worms), with high solids content (∼10-50 wt %) and without additional surfactant. CDSA can finely control the self-assembly of block copolymers and readily forms nonspherical crystalline nano-objects and more complex, hierarchical assemblies, with spatial and dimensional control over particle length or surface area, which is typically difficult to achieve by PISA. Considering the importance of these two assembly techniques in the current scientific landscape of block copolymer self-assembly and the craze for their use in the biomedical field, this review will focus on the advances in PISA and CDSA to produce nano-objects suitable for biomedical applications in terms of (bio)degradability and biocompatibility. This review will therefore discuss these two aspects in order to guide the future design of block copolymer nanoparticles for future translation toward clinical applications.

Simultaneous Synthesis and Self-Assembly of Bottlebrush Block Copolymers at Room Temperature via Photoinitiated RAFT Dispersion Polymerization

Bottlebrush polymers exhibiting unique properties have attracted considerable attention for applications in many research areas. Herein, we report the first simultaneous synthesis and self-assembly of bottlebrush block copolymers at room temperature via photoinitiated polymerization-induced self-assembly (photo-PISA) using multifunctional macromolecular chain transfer agents (macro-CTAs). Compare with linear block copolymers, the bottlebrush block copolymers could promote the formation of higher-order morphologies (e.g. vesicles) when targeting similar degrees of polymerization (DPs). Moreover, a higher polymerization rate was observed in the case of bottlebrush block copolymers. Gel permeation chromatography (GPC) analysis showed that good polymerization control was maintained when synthesizing bottlebrush block copolymers by photo-PISA. Finally, the obtained bottlebrush block copolymer vesicles were used as seeds for further chain extension and multicomponent nanoparticles with a sponge internal structure were formed. We expect this study will not only expand polymer architectures employed in PISA, but also provides a new strategy to synthesize polymer nanoparticles with unique structures. This article is protected by copyright. All rights reserved.

Dextran-Coated Latex Nanoparticles via Photo-RAFT Mediated Polymerization Induced Self-Assembly

Polysaccharide coated nanoparticles represent a promising class of environmentally friendly latex to replace those stabilized by small toxic molecular surfactants. We report here an in situ formulation of free-surfactant core/shell nanoparticles latex consisting of dextran-based diblock amphiphilic copolymers. The synthesis of copolymers and the immediate latex formulation were performed directly in water using a photo-initiated reversible addition fragmentation chain transfer-mediated polymerization induced self-assembly strategy. A hydrophilic macromolecular chain transfer-bearing photosensitive thiocarbonylthio group (eDexCTA) was first prepared by a modification of the reducing chain end of dextran in two steps: (i) reductive amination by ethylenediamine in the presence of sodium cyanoborohydride, (ii) then introduction of CTA by amidation reaction. Latex nanoparticles were then formulated in situ by chain-extending eDexCTA using 2-hydroxypropyl methacrylate (HPMA) under 365 nm irradiation, leading to amphiphilic dextran-b-poly(2-hydroxypropyl methacrylate) diblock copolymers (DHX). Solid concentration (SC) and the average degree of polymerization - Xn-- of PHPMA block (X) were varied to investigate their impact on the size and the morphology of latex nanoparticles termed here SCDHX. Light scattering and transmission electron microscopy analysis revealed that SCDHX form exclusively spherical nano-objects. However, the size of nano-objects, ranging from 20 nm to 240 nm, increases according to PHPMA block length.

Elucidating preparation-structure relationships for the morphology evolution during the RAFT dispersion polymerization of N-acryloyl thiomorpholine

Depending on the conditions, nearly monodisperse spherical micelles or complex morphologies are formed during a polymerization induced self-assembly (PISA) process based on the water-soluble monomer N-acryloylthiomorpholine.

Polymerization-induced self-assembly via RAFT in emulsion: effect of Z-group on the nucleation step

It is demonstrated that the nature of the Z-group of trithiocarbonate RAFT agents can have a major effect on the nucleation step of aqueous RAFT PISA performed as emulsion polymerization.

Preparation of Doxorubicin-Loaded Amphiphilic Poly(D,L-Lactide-Co-Glycolide)-b-Poly(N-Acryloylmorpholine) AB2 Miktoarm Star Block Copolymers for Anticancer Drug Delivery

Owing to their unique topology and physical properties, micelles based on miktoarm amphiphilic star block copolymers play an important role in the biomedical field for drug delivery. Herein, we developed a series of AB2-type poly(D,L-lactide-co-glycolide)-b-poly(N-acryloyl morpholine) (PLGA-b-PNAM2) miktoarm star block copolymers by reversible addition-fragmentation chain-transfer polymerization and ring-opening copolymerization. The resulting miktoarm star polymers were investigated by 1H NMR spectroscopy and gel permeation chromatography. The critical micellar concentration value of the micelles increases with an increase in PNAM block length. As revealed by transmission electron microscopy and dynamic light scattering, the amphiphilic miktoarm star block copolymers can self-assemble to form spherical micellar aggregates in water. The anticancer drug doxorubicin (DOX) was encapsulated by polymeric micelles; the drug-loading efficiency and drug-loading content of the DOX-loaded micelles were 81.7% and 9.1%, respectively. Acidic environments triggered the dissociation of the polymeric micelles, which led to the more release of DOX in pH 6.4 than pH 7.4. The amphiphilic PLGA-b-PNAM2 miktoarm star block copolymers may have broad application as nanocarriers for controlled drug delivery.

Synthesis of nano-capsules via aqueous emulsion RCMP-PISA and encapsulation

Synthesis of nano-capsules using aqueous RCMP-PISA and encapsulation of rhodamine-B (Rh-B).

Poly(ethylene glycol)-b-poly(vinyl acetate) block copolymer particles with various morphologies via RAFT/MADIX aqueous emulsion PISA

The polymerization-induced self-assembly (PISA) of amphiphilic diblock copolymers of poly(ethylene glycol)-b-poly(vinyl acetate) in water was achieved through macromolecular design via interchange of xanthate (MADIX) polymerization in emulsion.

Synthesis of lipase–polymer conjugates by Cu(0)-mediated reversible deactivation radical polymerization: polymerization vs. degradation

Cu(0)-RDRP was first used for the polymerization-induced self-assembly of lipase–polymer conjugates, inducing the formation of nanospheres with preserved activity and degradability.

Polymerization induced self-assembly: an opportunity toward the self-assembly of polysaccharide-containing copolymers into high-order morphologies

Self-assembly of polysaccharide-containing amphiphilic copolymers: polymerization induced self-assembly versus traditional techniques.

Polymer Nanospheres with Hydrophobic Surface Groups as Supramolecular Building Blocks Produced by Aqueous PISA

A robust and straightforward synthesis of waterborne polymer nanospheres bearing the supramolecular association unit dialkoxynapthalene at their surface is presented using polymerization-induced self-assembly (PISA). A RAFT agent bearing this unit is first employed to produce poly(acrylic acid) chains, which are then chain-extended with styrene (S) to spontaneously form the nano-objects via RAFT aqueous emulsion polymerization. The particular challenge posed by the dialkoxynapthalene hydrophobicity can be overcome by the use of PISA and the deprotonation of the poly(acrylic acid). At pH = 7, very homogeneous latexes are obtained. The particle diameters can be tuned from 36 to 105 nm (with a narrow particle size distribution) by varying the molar mass of the PS block. The surface accessibility of the dialkoxynapthalene moieties is demonstrated by complexation with the complementary host cyclobis(paraquat-p-phenylene) (CBPQT⁴⁺ · Cl^- ), highlighting the potential of the nanospheres to act as building blocks for responsive supramolecular structures.

Controlling Nanomaterial Size and Shape for Biomedical Applications via Polymerization-Induced Self-Assembly

Rapid developments in the polymerization-induced self-assembly (PISA) technique have paved the way for the environmentally friendly production of nanoparticles with tunable size and shape for a diverse range of applications. In this feature article, the biomedical applications of PISA nanoparticles and the substantial progress made in controlling their size and shape are highlighted. In addition to early investigations into drug delivery, applications such as medical imaging, tissue culture, and blood cryopreservation are also described. Various parameters for controlling the morphology of PISA nanoparticles are discussed, including the degree of polymerization of the macro-CTA and core-forming polymers, the concentration of macro-CTA and core-forming monomers, the solid content of the final products, the solution pH, the thermoresponsitivity of the macro-CTA, the macro-CTA end group, and the initiator concentration. Finally, several limitations and challenges for the PISA technique that have been recently addressed, along with those that will require further efforts into the future, will be highlighted.

Synthesis of High Molecular Weight Poly(glycerol monomethacrylate) via RAFT Emulsion Polymerization of Isopropylideneglycerol Methacrylate

High molecular weight water-soluble polymers are widely used as flocculants or thickeners. However, synthesis of such polymers via solution polymerization invariably results in highly viscous fluids, which makes subsequent processing somewhat problematic. Alternatively, such polymers can be prepared as colloidal dispersions; in principle, this is advantageous because the particulate nature of the polymer chains ensures a much lower fluid viscosity. Herein we exemplify the latter approach by reporting the convenient one-pot synthesis of high molecular weight poly(glycerol monomethacrylate) (PGMA) via the reversible addition-fragmentation chain transfer (RAFT) aqueous emulsion polymerization of a water-immiscible protected monomer precursor, isopropylideneglycerol methacrylate (IPGMA) at 70 °C, using a water-soluble poly(glycerol monomethacrylate) (PGMA) chain transfer agent as a steric stabilizer. This formulation produces a low-viscosity aqueous dispersion of PGMA-PIPGMA diblock copolymer nanoparticles at 20% solids. Subsequent acid deprotection of the hydrophobic core-forming PIPGMA block leads to particle dissolution and affords a viscous aqueous solution comprising high molecular weight PGMA homopolymer chains with a relatively narrow molecular weight distribution. Moreover, it is shown that this latex precursor route offers an important advantage compared to the RAFT aqueous solution polymerization of glycerol monomethacrylate since it provides a significantly faster rate of polymerization (and hence higher monomer conversion) under comparable conditions.

Recent advances in RAFT-mediated surfactant-free emulsion polymerization

We summarized the RAFT-mediated surfactant-free emulsion polymerization using various RAFT agents and the polymerization types for the preparation of organic/inorganic hybrid materials.

Oxidation-responsive micelles by a one-pot polymerization-induced self-assembly approach

Combining a sequential, one-pot RAFT polymerization with the polymerization-induced self-assembly process results in a versatile oxidation-responsive carrier system.

Synthesis of well-defined epoxy-functional spherical nanoparticles by RAFT aqueous emulsion polymerization

The environmentally-friendly synthesis of epoxy-functional spherical nanoparticles is achieved via RAFT aqueous emulsion polymerization of glycidyl methacrylate under mild conditions; derivatization of such nanoparticles with sodium azide or diamines is demonstrated.