Brush-type Copolymers Research Articles

Rod-Shaped Micelles Based on PHF-g-(PCL-PEG) with pH-Triggered Doxorubicin Release and Enhanced Cellular Uptake

A biodegradable brush-type copolymer PHF- g-(PCL-PEG) based on a cleavable polyacetal backbone and biodegradable side chain modified with polyethylene glycol (PEG) was synthesized in this paper. This particular structure was directional to facilitate the formation of spherical or rod-shaped micelles. Flow cytometry showed that rod-shaped micelles displayed enhanced cellular uptake compared to spherical micelles. Rod-shaped micelles were selected to investigate their drug delivery abilities in detail. In vitro experiments verified the pH-triggered drug release of DOX-loaded micelles, and the release rate of doxorubicin (DOX) was 77% at pH 5.0 and 26% at pH 7.4. In drug-release kinetic analysis, a double-exponential model achieved the best fit. The copolymer appeared to be almost nontoxic, while the DOX-loaded micelles showed equivalent cytotoxicity compared to DOX at high concentration. The endocytosis of DOX-loaded micelles was two times that of DOX. Our findings suggest that the pH-sensitive brush type copolymer could be a possible carrier in drug delivery.

Preparation of well-defined brush-like block copolymers for gene delivery applications under biorelevant reaction conditions.

Well-defined oligo(ethylene glycol) methyl ether methacrylate (OEOMA) based block copolymers with cationic segments composed by N,N-(dimethylamino) ethyl methacrylate (DMAEMA) and/or 2-(diisopropylamino) ethyl methacrylate (DPA) were developed under biorelevant reaction conditions. These brush-type copolymers were synthesized through supplemental activator and reducing agent (SARA) atom transfer radical polymerization (ATRP) using sodium dithionite as SARA agent. The synthesis was carried out using an eco-friendly solvent mixture, very low copper catalyst concentration, and mild reaction conditions. The structure of the block copolymers was characterized by size exclusion chromatography (SEC) analysis and 1H nuclear magnetic resonance (NMR) spectroscopy. The pH-dependent protonation of these copolymers enables the efficient complexation with plasmid DNA (pDNA), yielding polyplexes with sizes ranging from 200 up to 700 nm, depending on the molecular weight of the copolymers, composition and concentration used. Agarose gel electrophoresis confirmed the successful pDNA encapsulation. No cytotoxicity effect was observed, even for N/P ratios higher than 50, for human fibroblasts and cervical cancer cell lines cells. The in vitro cellular uptake experiments demonstrated that the pDNA-loaded block copolymers were efficiently delivered into nucleus of cervical cancer cells. The polymerization approach, the unique structure of the block copolymers and the efficient DNA encapsulation presented can open new avenues for development of efficient tailor made gene delivery systems under biorelevant conditions.

Increasing the anticancer performance of bufalin (BUF) by introducing an endosome-escaping polymer and tumor-targeting peptide in the design of a polymeric prodrug.

A well-defined multifunctional brush-type polymeric prodrug covalently linked with an anticancer drug (bufalin, BUF), a tumor-targeting peptide (RGD), and an endosome-escaping polymer, poly(N,N-diethylaminoethyl methacrylate-co-butyl methacrylate (P(DEA-co-BMA)), was developed. Its anticancer performance against colon cancer was investigated in vitro and in vivo. Reversible addition-fragmentation transfer (RAFT) polymerization of oligo(ethylene glycol) monomethyl ether methacrylate (OEGMA), 2-((3-(tert-butoxy)-3-oxopropyl)thio)ethyl methacrylate (BSTMA), and 2-(2-bromoisobutyryloxy)ethylmethacrylate (BIEM) afforded the multifunctional random copolymer, P(OEGMA-co-BSTMA-co-BIEM), in which hydrophilic POEGMA can stabilize nanoparticles in water, PBSTMA can be converted into carboxyl groups, and PBIEM can be employed as a macromolecular atom radical transfer polymerization (ATRP) initiator. The ATRP of DEA and BMA using P(OEGMA-co-BSTMA-co-BIEM) as a macromolecular ATRP initiator led to the formation of the pH-responsive brush-type copolymer, P(OEGMA-co-BSTMA)-g-P(DEA-co- BMA). After hydrolysis by trifluoroacetic acid and post-functionalization the final polymeric prodrug, P(OEGMA-co-BUF-co-RGD)-g-P(DEA-co-BMA), was obtained with a drug content of ∼7.8 wt%. P(OEGMA-co-BUF-co-RGD)-g-P(DEA-co-BMA) can be assembled into nanoparticles (BUF- NP-RGD) in aqueous solution with a diameter of 148.4 ± 0.7 nm and a zeta potential of -7.6 ± 0.4 mV. BUF-NP-RGD exhibited controlled drug release in the presence of esterase. Additionally, P(OEGMA-co- BSMA)-g-P(DEA-co-BMA) showed a significant hemolysis effect at a pH comparable to that of endosomes/lysosomes. Cell viability and a tumor-bearing nude mouse model were employed to evaluate the anticancer efficacy of BUF-NP-RGD. It was revealed that BUF-NP-RGD showed improved anticancer performance compared with that of free BUF both in vitro and in vivo. Histological and immunochemical analysis further demonstrated that BUF-NP-RGD exhibited improved cell apoptosis, angiogenesis inhibition, and an anti-proliferation effect.

Biodegradable brush-type copolymer modified with targeting peptide as a nanoscopic platform for targeting drug delivery to treat castration-resistant prostate cancer

Well-defined amphiphilic tumor-targeting brush-type copolymers, poly(oligo(ethylene glycol) monomethyl ether methacrylate-co-G3-C12)-g-poly(ε-caprolactone) (P(OEGMA-co-G3-C12)-g- PCL), were synthesized by the combination of ring-opening polymerization (ROP), reversible addition-fragmentation transfer (RAFT) polymerization and polymer post-functionalization, in which G3-C12 was castration-resistant prostate cancer (CRPC) targeting peptide. The obtained polymers were then employed for the targeted treatment of CRPC by delivering a hydrophobic anticancer drug (bufalin, BUF). Polymerizable monomer, 3-((2-(methacryloyloxy)ethyl)thio)propanoic acid (BSMA) and PCL-based macromolecular monomer (PCLMA) were synthesized at first. RAFT polymerization of OEGMA, BSMA, and PCLMA afforded amphiphilic brush-type copolymers, P(OEGMA-co-BSMA)-g-PCL. Post-functionalization of the obtained polymers with G3-C12 led to the formation of the final amphiphilic targeting brush-type copolymers, P(OEGMA-co-G3-C12)-g- PCL. In aqueous media, P(OEGMA-co-G3-C12)-g-PCL self-assembles into micelles with a hydrodynamic diameter (Dh) of ∼66.1±0.44nm. It was demonstrated that the obtained micellar nanoparticles exhibited good biocompatibility and biodegradability. Besides, BUF-loaded micellar nanoparticles assembled from P(OEGMA-co-G3-C12)-g-PCL, BUF-NP-(G3-C12), showed a controlled drug release in vitro and improved anticancer efficacy both in vitro and in vivo.

Synthesis of pH- and thermo-responsive poly (ε-caprolactone-b-4-vinyl benzyl-g-dimethyl amino ethyl methacrylate) brush type graft copolymers via RAFT polymerization

A novel pH- and thermo-responsive poly (e-caprolactone-b-4-vinyl benzyl-g-2-(dimethyl amino ethyl) methacrylate), poly (CL-b-VB-g-DMAEMA), brush type copolymer has been described. In this study, a reversible addition–fragmentation chain transfer (RAFT) agent, 1,2-propanediol-3-ethyl xanthogenate, was obtained through the reaction of 3-chloro-1,2-propanediol with potassium salt of ethyl xanthogenate. Poly (CL-b-VB) block copolymer was synthesized in one-pot polymerization of e-caprolactone (CL) and 4-vinyl benzyl chloride (VB) using a new dual macro-RAFT agent. In the second step of the work, chloride side groups of poly-VB in poly (CL-b-VB) block copolymer were reacted with potassium salt of ethyl xanthogenate to obtain another novel macro-RAFT agent, poly (CL-b-VB)-g-xanthate (PCL-PVB-Xa). Controlled free radical living polymerization of 2-(dimethylaminoethyl) methacrylate (DMAEMA) was initiated with this PCL-VB-Xa macro-RAFT agent to obtain new poly (CL-b-VB-g-DMAEMA) comb type pH- and thermo-responsive heterograft copolymer. The homopolymer was soluble in water at pH = 10–11 and not soluble at pH = 12.5. A pH-sensitive feature of the brush type graft copolymer was observed between pH 9.4 and 11.5 in view of their swelling/solution properties depending on the acrylic polymer inclusion. The LCST values of the multiblock brush type copolymers were found to be as low as 42.8 °C, while that of PDMAEMA homopolymer was 46.6 °C. The characterization of the products was achieved using gel-permeation chromatography (GPC), thermal, and spectrometric analysis techniques. pH- and thermo-responsiveness of the copolymers were verified by surface tension and zeta potential measurements.

Synthesis of PEGylated brush-type copolymers for a plurality of plug-and-play functions

A well-defined brush-type copolymer P(PEGMA-N3-co-PEGMEMA)-b-PMAA via ATRP is successfully synthesized and demonstrated with a plurality of plug-and-play functions.

Synthesis and Characterization of PEGylated Brush-type Polycation Modified with Galactosamine

Gene therapy has been generally regarded as a promising treatment for numerous hard curable diseases, such as cancer, genetic and infectious diseases. Seeking a safe and efficient vector plays the most challenging role in gene therapy. In the past decades, non-viral polycation has attracted much more attentions as a promising gene vector due to their good biocompatibility, high condensation ability, as well as easily-adjustable and controlled structures. In the present work, a series of galactosamine (Gal)-conjugated brush-type cationic copolymer P(PEGMEMA-co-PEGMA-Gal)-b-PDMAEMA were prepared via a combination of two-step atom transfer radical polymerization (ATRP) technique and polymer reaction. Firstly, random copolymerization of poly(ethylene glycol)methyl ether methacrylate (PEGMEMA) and poly(ethylene glycol) methacrylate (PEGMA) was carried out to yield the copolymer P(PEGMEMA-co-PEGMA), which was further used as a macroinitiator to polymerize 2-(N ,N-dimethylamino)ethyl methacrylate (DMAEMA), producing the cationic copolymer P(PEGMEMA-co-PEGMA)-b-PDMAEMA. Finally, the brush-type copolymer P(PEGMEMA-co-PEGMA-Gal)-bPDMAEMA was obtained by the modification of pendent hydroxyl groups with galactosamine using N,N'-carbonyldiimidazole (CDI) as the coupling agent. PDMAEMA is a well-known pH-sensitive polycation and has been widely applied for non-viral gene delivery, while the brush-type hydrophilic chains provide the carrier with favorable biocompatibility, prolonged blood circulation time, and reduced non-specific adsorption of proteins. PDMAEMA block would be partially protonated to afford some hydrophobic domains and positive charges at neutral condition, which can bind with DNA via electrostatic interaction to form polycation/DNA polyplex. The Gal moiety on the surface made the polyplex easily recognized by asialoglycoprotein receptors (ASGPRs) over-expressing hepatoma cells and internalized via a receptor-mediated endocytosis process. The chemical structures, molecular weights and molecular weight distributions of P(PEGMEMA-co-PEGMA-Gal)-b-PDMAEMA copolymer were characterized by H NMR, FT-IR, and GPC measurements. The DNA binding capacity of this copolymer was investigated by agarose gel electrophoresis and zeta potential measurements, which indicated that DNA migration could be completely retarded when the N/P ratio was higher than 1.5. The DLS DOI: 10.6023/A14030185

Directed self-assembly of block copolymers in the extreme: guiding microdomains from the small to the large

The self-assembly of block copolymers (BCPs) is emerging as a promising route for numerous applications to generate templates and scaffolds for the fabrication of nanostructured materials. Here, we present an overview of recent progress in the directed self-assembly of BCPs with a focus on guiding the assemblies of extreme (small and large) features over large areas. We introduce inorganic-containing hybrid BCPs that enable access to ultra-small feature sizes. To achieve the desired orientation and lateral ordering of the BCP microdomains, we discuss routes that combine top-down (lithographic) processes with the bottom-up self-assembly of BCPs. On the extreme large size scale, high-molecular-weight BCPs and brush-type copolymers are discussed, covering the other extreme of this promising strategy.

Polymer coatings that display specific biological signals while preventing nonspecific interactions

Control over cell-material surface interactions is the key to many new and improved biomedical devices. It can only be achieved if interactions that are mediated by nonspecifically adsorbed serum proteins are minimized and if cells instead respond to specific ligand molecules presented on the surface. Here, we present a simple yet effective surface modification method that allows for the covalent coupling and presentation of specific biological signals on coatings which have significantly reduced nonspecific biointerfacial interactions. To achieve this we synthesized bottle brush type copolymers consisting of poly(ethylene glycol) methyl ether methacrylate and (meth)acrylates providing activated NHS ester groups as well as different spacer lengths between the NHS groups and the polymer backbone. Copolymers containing different molar ratios of these monomers were grafted to amine functionalized polystyrene cell culture substrates, followed by the covalent immobilization of the cyclic peptides cRGDfK and cRADfK using residual NHS groups. Polymers were characterized by GPC and NMR and surface modification steps were analyzed using XPS. The cellular response was evaluated using HeLa cell attachment experiments. The results showed strong correlations between the effectiveness of the control over biointerfacial interactions and the polymer architecture. They also demonstrate that optimized fully synthetic copolymer coatings, which can be applied to a wide range of substrate materials, provide excellent control over biointerfacial interactions.

Effect of chain topology on the self-organization and the mechanical properties of poly(n-butyl acrylate)-b-polystyrene block copolymers

A series of well defined ABA, 3-arm star and bottle brush type copolymers, containing soft poly(n-butyl acrylate) (PBA) blocks and hard blocks of polystyrene (PS) were synthesized by atom transfer radical polymerization (ATRP). Small angle X-ray scattering was used to study the phase separation in these systems and dynamic mechanical analysis and tensile tests were performed to characterize their thermo-mechanical properties. The specific molecular architecture has a major effect on the copolymers self-organization and material properties. The linear ABA type copolymers showed micro phase separation and thermoplastic elastomer (TPE) behavior only at very high PS content. The change of molecular architecture from linear to 3-arm star type resulted in an improved phase separation at lower PS content and better thermoplastic elastomer properties. In contrast the specific brush type molecular architecture seems to prevent the micro phase separation of the PBA and PS components, resulting in amorphous bulk material with single glass transition temperature.

Preparation of Hairy Particles and Antifouling Films Using Brush-Type Amphiphilic Block Copolymer Surfactants in Emulsion Polymerization

Two series of well-defined brush-type amphiphilic block copolymers of polystyrene-b-poly[poly(ethylene glycol) methyl ether methacrylate] (PS-b-P(PEGMA300) and PS-b-P(PEGMA1100)) were synthesized via atom transfer radical polymerization (ATRP) and used as surfactants in emulsion polymerization. The self-assembly behavior of these block copolymers in aqueous solution was studied by dynamic light scattering and cryogenic transmission electron microscopy. The critical micelle concentration of the synthesized polymers was found to depend on the length of the PEG side chains, but neither on the molar mass of the P(PEGMA) blocks nor the temperature. All of the block copolymers form micelles in the nanometer range. Emulsion polymerizations of styrene were carried out using the obtained brush-type amphiphilic block copolymers, and the influence of the block copolymer structure, surfactant concentration, and temperature was studied. The PS-b-P(PEGMA1100) copolymers seem to be the most efficient surfactants at low polymerization temperature, providing good colloidal stability. Monodisperse hairy particles with core−shell structures (observed by cryo-TEM) were obtained using the block copolymers with the long PEG side chain and the highest molar mass. Polystyrene films prepared from the latexes, containing the brush-type copolymers, display a lower contact angle than that obtained in films with conventional low molecular weight surfactants. In addition, the incorporation of PEGMA brushes on the polystyrene particles, and hence on the films, decreases the adsorption of proteins and, in this particular case, of bovine serum albumin.

Temperature-Induced Control of Conformation and Conjugation Length in Water-Soluble Fluorescent Polythiophenes

Application of fluorescent polythiophenes and related conjugated polymers as a platform for highly sensitive chemo- and biodetection can benefit from the possibility to effectively control their conformation and conjugation length by applying external stimuli. Temperature can be used as such a stimulus if a substantial effect can be achieved in a relatively narrow temperature range. To investigate the temperature-induced conformational switching, a series of polythiophenes with different degree of regioregularity were prepared and functionalized by grafting temperature-responsive poly(N-isopropylacrylamide) (PNIPAm) side chains to their conjugated backbones. These highly water-soluble fluorescent brush-type copolymers featured almost complete lack of intermolecular electronic interactions even in aggregated state owing to remarkably insulating properties of the PNIPAm grafts. Therefore, these grafted copolymers provided an opportunity to study the effects originating from the conformational switching with...

Brush Type Copolymers of Poly(3‐hydroxybutyrate) and Poly(3‐hydroxyoctanoate) with Same Vinyl Monomers via “Grafting From” Technique by Using Atom Transfer Radical Polymerization Method

AbstractBrush type graft copolymers of poly(3‐hydroxybutyrate) (PHB) and poly(3‐hydroxyoctanoate) (PHO) with methylmethacrylate, (MMA), styrene, (S), and n‐butylmethacrylate, (n‐BuMA) were obtained by using Atom Transfer Radical Polymerization Method, (ATRP), via “grafting from” technique. Firstly PHB and PHO were chlorinated by passing chlorine gas through their solution in CHCl3/CCl4 (75/25 v/v) mixture and CCl4, respectively, in order to prepare chlorinated PHB, PHB‐Cl, and chlorinated PHO, PHO‐Cl, with different chlorine contents. The determination of the chlorine content in chlorinated poly(3‐hydroxyalkanoate) (PHA‐Cl) was performed by the Volhard Method. Then ATRP of vinyl monomers was initiated by using PHA‐Cl as macroinitiators in the presence of cuprous chloride (CuCl)/2,2′‐bipyridine complex as catalyst, at 90 °C in order to obtain brushes containing PHAs. The polymer brushes were fractionated by fractional precipitation methods and the γ values calculated from the ratio of the volume of nonsolvent (methanol) and the volume of solvent (chloroform) of brushes varied between 0.82 and 6.50 depending on the composition of brushes. The polymer products were characterized by gel permeation chromatography (GPC), 1H NMR, FTIR, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) techniques.

Synthesis and Properties of a Novel Brush-type Copolymers Bearing Thiophene Backbone and 3-(N-carbazolyl)propyl Acrylate Side Chains for Light-emitting Applications

A new light-emitting and hole transporting copolymer 2,5-Poly(3-[1-ethyl-2-(2-[poly(3-(N-carbazolyl)propyl acrylate)]propionate)]thiophene) (PT-g-PCPA) was prepared via atom transfer radical polymerization (ATRP) of a 3-(N-carbazolyl)propyl acrylate (CPA) monomer, initiated by a macroinitiator with ATRP initiating sites distributed along polythiophene (PT) backbone. The resulting polymers were characterized by gel permeation chromatography (GPC), nuclear magnetic resonance (1H and 13C NMR) spectroscopy and differential scanning calorimetry (DSC). The optical properties of polymers were investigated by UV-vis and fluorescence analyses. The electrochemical properties of polymers were investigated by cyclic voltammetric (CV) measurements. The results confirmed that the introduction of the PCPA side chains trapped the polythiophene backbone in a “solution-like” conformation, which inhibited the aggregation of polythiophene backbone effectively. Additionally, the energy transfer process from PCPA side chains to the PT backbone in both solution and film states were also evidenced. Electroluminescence devices fabricated from the copolymer demonstrated that copolymer could act as both light emissive and hole-transporting materials.

Novel Brush-Type Copolymers Bearing Thiophene Backbone and Side Chain Quinoline Blocks. Synthesis and Their Use as a Compatibilizer in Thiophene−Quinoline Polymer Blends

New copolymers bearing different degree of grafted polyquinoline segments onto a polythiophene backbone were obtained via atom transfer radical polymerization of a vinyl quinoline monomer using a properly modified polythiophene backbone as macroinitiator. The initiator preparation was based on the bromination to a certain extent of a commercially available poly(3-hexylthiophene-2,5-diyl) (P3HT) and subsequent conversion of the bromine groups to proper propionyl bromide units through a three-step process. Polymerization of the vinyl quinoline monomer, using typical ATRP conditions, resulted in the desired copolymers, which were effectively characterized using 1H NMR, UV−vis, and luminescence spectroscopy, as well as cyclic voltammetry. These copolymers were used in order to study their compatibilization efficiency in an immiscible P3HT/polyquinoline blend, which has been tested previously with respect to its photovoltaic efficiency. A detailed morphology study using atomic force microscopy (AFM) has shown that nanophase separated systems were obtained and the domain size was dependent on the blend composition, as well as the copolymer grafting density.

Brush-type amphiphilic polystyrene- g-poly(2-(dimethylamino)ethyl methacrylate)) copolymers from ATRP and their self-assembly in selective solvents

A series of well-defined brush-type amphiphilic polystyrene- g-poly(2-(dimethylamino) ethyl methacrylate)) (PS- g-PDMAEMA) copolymers were successfully synthesized via atom transfer radical polymerization (ATRP), using chloromethylated polystyrene (CMPS) as the macroinitiator. The self-assembly behavior of the resulting brush-type copolymers in deionized water and deionized water/acetone (v/v=2/3) mixture was studied by high performance particle sizer (HPPS). The results showed that the Z-average size of the micelles in deionized water increased with the increase of molecular weight of PDMAEMA, and the corresponding size was larger than that in mixed solvent of deionized water and acetone (v/v=2/3). The morphologies of the micelles self-assembled from PS- g-PDMAEMA in selective solvents were studied by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). When the micelles were prepared in water/acetone (v/v=2/3) mixture and cast them on a glass slide at different temperatures (from 50 up to 200 °C), the transformation of the morphologies of aggregates, from needle-like solid to microcubic particles, was observed using SEM.

Influence of polymer architecture on the structure of complexes formed by PEG–tertiary amine methacrylate copolymers and phosphorothioate oligonucleotide

The influence of polymer structure on the characteristics of complexes of a phosphorothioate antisense oligonucleotide (ISIS 5132) was studied, using well-defined cationic copolymers based on 2-(dimethylamino) ethyl methacrylate (DMAEMA) and poly(ethylene glycol) (PEG). The three related copolymer structures were: DMAEMA–PEG (a diblock copolymer) DMAEMA–OEGMA 7 (a brush-type copolymer), DMAEMA–stat-PEGMA (a comb-type copolymer); each of these were examined together with DMAEMA homopolymer, which served as a control. The results revealed that all the polymers exhibited good binding ability with the oligonucleotide (ON). Interestingly, the comb-type polymer DMAEMA–stat-PEGMA demonstrated the highest binding ability and DMAEMA homopolymer the lowest, as judged by a dye displacement assay. DMAEMA homopolymer produced large agglomerates of smaller individual complexes as observed by optical density, photon correlation spectroscopy and transmission electron microscopy studies. In contrast, two PEG-block copolymers, DMAEMA–PEG and DMAEMA–OEGMA 7, formed compact complexes of 80–150 nm which had good long-term colloidal stability. This is attributed to the steric stabilisation effect of the PEG chains on the ON–copolymer complexes. These two copolymers are believed to form complexes with ON that have a micellar structure. Comb-type DMAEMA–stat-PEGMA copolymer formed highly soluble complexes with the ON that did not phase separate from the buffer solution. This study clearly demonstrates that varying the copolymer architecture allows access to a range of ON complexes. In vitro cytotoxicity experiments on HepG2 cells showed that all of the tertiary amine methacrylate copolymers displayed lower cytotoxicity than the control poly( l-lysine).