PDEGMA‐b‐PDIPAEMA copolymers via RAFT polymerization and their pH and thermoresponsive schizophrenic self‐assembly in aqueous media

Block and Statistical Copolymers of Methacrylate Monomers with Dimethylamino and Diisopropylamino Groups on the Side Chains: Synthesis, Chemical Modification and Self-Assembly in Aqueous Media

The synthesis of amphiphilic diblock and statistical (random) copolymers of poly(dimethylamino ethyl methacrylate) and poly((2-(diisopropylamino) ethyl methacrylate) using the reversible addition-fragmentation chain transfer polymerization technique (RAFT polymerization) is reported. The precursor copolymers were chemically modified to create derivative copolymers of polyelectrolyte and polyampholyte nature with novel solution properties. Moreover, their molecular and physicochemical characteristics, as well as their self-assembly in aqueous media as a function of molecular architecture and composition, are investigated by using size exclusion chromatography, spectroscopic characterization techniques and light scattering techniques. Furthermore, the behavior and properties of the obtained micelles and aggregates were studied, depending on the pH, temperature and ionic strength of the aqueous solutions. The response of the systems to changes in these parameters shows interesting behavior and new properties that are useful for their utilization as nanocarriers of pharmaceutical compounds.

Closely Packed Core-Shell Micelle Structures of Double Hydrophilic Miktoarm Star Copolymers at the Air-Water Interface

The aggregation behavior of amphiphilic block copolymers at the air-water interface has been extensively studied, but less attention was given to that of star copolymers. In this work, we studied the interfacial aggregation behavior of two double hydrophilic pH- and temperature-responsive miktoarm star copolymers of poly[di(ethylene glycol) methyl ether methacrylate]-poly[2-(dimethylamino)ethyl methacrylate] (PDEGMA3-PDMAEMA3 and PDEGMA4-PDMAEMA7, the subscripts denote arm numbers) with different molecular weights. The effects of subphase pH and temperature on the monolayer isotherms and hysteresis curves of the two star copolymers and the morphologies of their Langmuir-Blodgett (LB) films were studied by the Langmuir film balance technique and atomic force microscopy, respectively. At the air-water interface, the two star copolymers tend to form closely packed micelles. These micelles exhibit a core-shell structure, where the small hydrophobic core consists of cross-linker of ethylene glycol dimethacrylate (EGDMA) and the carbon backbones of PDEGMA and PDMAEMA arms and the short hydrophilic shell is composed of di(ethylene glycol) and tertiary amine side groups. With increasing subphase pH, the surface pressure versus molecular area isotherms shift toward larger mean molecular areas as a result of the enhanced interface adsorption of nonprotonated tertiary amine groups. The isotherm shift of PDEGMA3-PDMAEMA3 monolayers is primarily attributed to high density of tertiary amine groups in the shells, while that of PDEGMA4-PDMAEMA7 is mainly attributed to high density of di(ethylene glycol) groups in the shells. The hysteresis degrees in the monolayers of the two copolymers under alkaline and neutral conditions are greater than those under acidic conditions due to the decreased protonation degree of the tertiary amine groups. At 10 °C, the mobility of the shells is poor and the isotherms are located on the right. Above the lower critical solution temperature, di(ethylene glycol) groups contract, which causes a slight shift of the isotherms toward smaller mean molecular areas.

H-bond-type thermo-responsive schizophrenic copolymers: The phase transition correlation with their parent polymers and the improved protein co-assembly ability

Schizophrenic copolymers are one type of the popular smart polymers that show invertible colloidal structures in response to temperature stimulus. However, the lack of principles to predict the phase transition temperature of a schizophrenic copolymer from its corresponding parent thermo-responsive polymers limits their development. Additionally, studies on their applications remain scarce. Herein, a series of schizophrenic copolymers were synthesized by polymerization of a RAFT-made polymer precursor poly(acrylamide-co-N-acryloxysuccinimide-co-acrylic acid) (P(AAm-co-NAS-co-AAc)) with the mixture of N-isopropylmethacrylamide (NIPAm) and acrylamide (AAm) in varying molar ratios. In aqueous solution, the block P(AAm-co-NAS-co-AAc) and the block poly(NIPAm-co-AAm) exhibited upper and lower critical solution temperature (UCST and LCST) behavior, respectively. The schizophrenic copolymers featured either UCST-LCST, LCST-UCST, or only LCST thermo-responsive transition. A preliminary correlation of phase transition between the schizophrenic copolymers and their parent polymers was summarized. Furthermore, the co-assembly of the schizophrenic copolymers and proteins were conducted and the kinetics of protein loading and protein activity were investigated, which showed that the schizophrenic copolymers were efficient platforms for protein co-assembly with ultra-high protein loading while preserving the protein bioactivities. Additionally, all the materials were non-toxic towards NIH 3T3 and MCF-7 cells. This work offers the prospects of the schizophrenic polymers in soft colloidal and assembly systems, particularly in guiding the design of new materials and their use in biomedical applications.

Novel Multi-Responsive Hyperbranched Polyelectrolyte Polyplexes as Potential Gene Delivery Vectors

In this work, we investigate the complexation behavior of poly(oligo(ethylene glycol)methyl methacrylate)-co-poly(2-(diisopropylamino)ethyl methacrylate), P(OEGMA-co-DIPAEMA), hyperbranched polyelectrolyte copolymers, synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization, with short-linear DNA molecules. The synthesized hyperbranched copolymers (HBC), having a different chemical composition, are prepared in order to study their ability to bind with a linear nucleic acid at various N/P ratios (amine over phosphate groups). Specifically, the three pH and thermo-responsive P(OEGMA-co-DIPAEMA) hyperbranched copolymers were able to form polyplexes with DNA, with dimensions in the nanoscale. Using several physicochemical methods, such as dynamic and electrophoretic light scattering (DLS, ELS), as well as fluorescence spectroscopy (FS), the complexation process and the properties of formed polyplexes were explored in response to physical and chemical stimuli such as temperature, pH, and ionic strength. The mass and the size of polyplexes are shown to be affected by the hydrophobicity of the copolymer utilized each time, as well as the N/P ratio. Additionally, the stability of polyplexes in the presence of serum proteins is found to be excellent. Finally, the multi-responsive hyperbranched copolymers were evaluated regarding their cytotoxicity via in vitro experiments on HEK 293 non-cancerous cell lines and found to be sufficiently non-toxic. Based on our results, these polyplexes could be useful candidates for gene delivery and related biomedical applications.

Triple Hydrophilic Statistical Terpolymers via RAFT Polymerization: Synthesis and Properties in Aqueous Solutions

In this work, we report the synthesis of novel triple hydrophilic statistical terpolymers consisting of three different methacrylate monomers with varying degrees of responsivity to solution conditions. Terpolymers of the type poly(di(ethylene glycol) methyl ether methacrylate-co-2-(dimethylamino)ethylmethacrylate-co-oligoethylene glycol methyl ether methacrylate), P(DEGMA-co-DMAEMA-co-OEGMA), and of different compositions, were prepared by using the RAFT methodology. Their molecular characterization was carried out using size exclusion chromatography (SEC) and spectroscopic techniques, including ¹H-NMR and ATR-FTIR. Studies in dilute aqueous media by dynamic and electrophoretic light scattering (DLS and ELS) show their potential responsiveness regarding changes in temperature, pH, and kosmotropic salt concentration. Finally, the change in hydrophilic/hydrophobic balance of the formed terpolymer nanoparticles during heating and cooling was studied using fluorescence spectroscopy (FS) in conjunction with pyrene giving additional information on the responsiveness and internal structure of the self-assembled nanoaggregates.

Surfactant and Block Copolymer Nanostructures: From Design and Development to Nanomedicine Preclinical Studies

The medical application of nanotechnology in the field of drug delivery has so far exhibited many efforts in treating simple to extremely complicated and life-threatening human conditions, with multiple products already existing in the market. A plethora of innovative drug delivery carriers, using polymers, surfactants and the combination of the above, have been developed and tested pre-clinically, offering great advantages in terms of targeted drug delivery, low toxicity and immune system activation, cellular biomimicry and enhanced pharmacokinetic properties. Furthermore, such artificial systems can be tailor-made with respect to each therapeutic protocol and disease type falling under the scope of personalized medicine. The simultaneous delivery of multiple therapeutic entities of different nature, such as genes and drugs, can be achieved, while novel technologies can offer systems with multiple modalities often combining therapy with diagnosis. In this review, we present prominent, innovative and state-of-the-art scientific efforts on the applications of surfactant-based, polymer-based, and mixed surfactant-polymer nanoparticle drug formulations intended for use in the medical field and in drug delivery. The materials used, formulation steps, nature, properties, physicochemical characteristics, characterization techniques and pharmacokinetic behavior of those systems, are presented extensively in the length of this work. The material presented is focused on research projects that are currently in the developmental, pre-clinical stage.

Temperature- and pH-Responsive Polymeric Photocatalysts for Enhanced Control and Recovery

The emergence of heterogeneous photocatalysis has facilitated redox reactions with high efficiency, without compromising the recyclability of the photocatalyst. Recently, stimuli-responsive heterogeneous photocatalytic materials have emerged as a powerful synthetic tool, with simple and rapid recovery, as well as an enhanced dynamic control over reactions. Stimuli-responsive polymers are often inexpensive and easy to produce. They can be switched from an active "on" state to an inert "off" state in response to external stimuli, allowing the production of photocatalyst with adaptability, recyclability, and orthogonal control on different chemical reactions. Despite this versatility, the application of artificial smart material in the field of heterogeneous photocatalysis has not yet been maximized. In this Minireview, we will examine the recent developments of this emerging class of stimuli-responsive heterogeneous photocatalytic systems. We will discuss the synthesis route of appending photoactive components into different triggerable systems and, in particular, the controlled activation and recovery of the materials.

Dual-Responsive Amphiphilic P(DMAEMA-co-LMA-co-OEGMA) Terpolymer Nano-Assemblies in Aqueous Media

This work reports on the synthesis and self-assembly of a novel series of dual-responsive poly[2-(dimethylamino)ethylmethacrylate-co-laurylmethacrylate-co-(oligoethyleneglycol)methacrylate], P(DMAEMA-co-LMA-co-OEGMA)statistical terpolymers in aqueous solutions. Five P(DMAEMA-co-LMA-co-OEGMA) amphiphilic terpolymers, having different content of the three monomers, were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. The success of the synthesis was confirmed by the molecular characterization of the terpolymers via size exclusion chromatography (SEC) for the determination of molecular weights and the molecular weight distributions. By using nuclear magnetic resonance (¹H-NMR) and Fourier-transform infrared (FTIR) spectroscopy, it was possible to determine the exact composition of the terpolymers. Dynamic light scattering (DLS) and fluorescence spectroscopy (FS) indicated the formation of P(DMAEMA-co-LMA-co-OEGMA) unimolecular or multichain aggregates in aqueous solutions, as a response to pH, temperature and ionic strength changes, with their dimensions being largely affected. The amphiphilic terpolymers were able to encapsulate the hydrophobic drug curcumin (CUR) and demonstrate stability to fetal bovine serum (FBS) solutions. These terpolymer aggregates were studied by DLS, FS and UV-Vis, and it was found that they may have been used as potential nanocarriers for drug delivery and bio-imaging applications.

Salt-Dependent Phase Transition Behavior of Doubly Thermoresponsive Poly(sulfobetaine)-Based Diblock Copolymer Thin Films

The water vapor-induced swelling, as well as subsequent phase-transition kinetics, of thin films of a diblock copolymer (DBC) loaded with different amounts of the salt NaBr, is investigated in situ. In dilute aqueous solution, the DBC features an orthogonally thermoresponsive behavior. It consists of a zwitterionic poly(sulfobetaine) block, namely, poly(4-(N-(3'-methacrylamidopropyl)-N,N-dimethylammonio) butane-1-sulfonate) (PSBP), showing an upper critical solution temperature, and a nonionic block, namely, poly(N-isopropylmethacrylamide) (PNIPMAM), exhibiting a lower critical solution temperature. The swelling kinetics in D₂O vapor at 15 °C and the phase transition kinetics upon heating the swollen film to 60 °C and cooling back to 15 °C are followed with simultaneous time-of-flight neutron reflectometry and spectral reflectance measurements. These are complemented by Fourier transform infrared spectroscopy. The collapse temperature of PNIPMAM and the swelling temperature of PSBP are found at lower temperatures than in aqueous solution, which is attributed to the high polymer concentration in the thin-film geometry. Upon inclusion of sub-stoichiometric amounts (relative to the monomer units) of NaBr in the films, the water incorporation is significantly increased. This increase is mainly attributed to a salting-in effect on the zwitterionic PSBP block. Whereas the addition of NaBr notably shifts the swelling temperature of PSBP to lower temperatures, the collapse temperature of PNIPMAM remains unaffected by the presence of salt in the films.

Multi-responsive poly(oligo(ethylene glycol)methyl methacrylate)-co-poly(2-(diisopropylamino)ethyl methacrylate) hyperbranched copolymers via reversible addition fragmentation chain transfer polymerization

Multi-responsive P(OEGMA-co-DIPAEMA) hyperbranched copolymers are synthesized via RAFT polymerization. The copolymers form different aggregates in aqueous media depending on solution pH, temperature and copolymer composition.