Thermally responsive core-shell nanoparticles self-assembled from cholesteryl end-capped and grafted polyacrylamides:

Constrained thermoresponsive polymers - new insights into fundamentals and applications

In the last decades, numerous stimuli-responsive polymers have been developed and investigated regarding their switching properties. In particular, thermoresponsive polymers, which form a miscibility gap with the ambient solvent with a lower or upper critical demixing point depending on the temperature, have been intensively studied in solution. For the application of such polymers in novel sensors, drug delivery systems or as multifunctional coatings, they typically have to be transferred into specific arrangements, such as micelles, polymer films or grafted nanoparticles. However, it turns out that the thermodynamic concept for the phase transition of free polymer chains fails, when thermoresponsive polymers are assembled into such sterically confined architectures. Whereas many published studies focus on synthetic aspects as well as individual applications of thermoresponsive polymers, the underlying structure-property relationships governing the thermoresponse of sterically constrained assemblies, are still poorly understood. Furthermore, the clear majority of publications deals with polymers that exhibit a lower critical solution temperature (LCST) behavior, with PNIPAAM as their main representative. In contrast, for polymer arrangements with an upper critical solution temperature (UCST), there is only limited knowledge about preparation, application and precise physical understanding of the phase transition. This review article provides an overview about the current knowledge of thermoresponsive polymers with limited mobility focusing on UCST behavior and the possibilities for influencing their thermoresponsive switching characteristics. It comprises star polymers, micelles as well as polymer chains grafted to flat substrates and particulate inorganic surfaces. The elaboration of the physicochemical interplay between the architecture of the polymer assembly and the resulting thermoresponsive switching behavior will be in the foreground of this consideration.

Synthesis of Biocompatible Cholesteryl-Carboxymethyl Xylan Micelles for Tumor-Targeting Intracellular DOX Delivery

Patients with cancer suffer from severe side effects and reduced life quality, as chemotherapeutic drugs are cytotoxic toward normal cells as well as toward cancer cells. In recent years, nanoparticles have been explored as targeted drug delivery systems; however, problems such as toxicity and instability prevent their practical application. Here, we report the synthesis of cholesteryl-carboxymethyl xylan (CCMX) via an esterification reaction between the carboxyl group of carboxymethyl xylan and the hydroxyl group of cholesterol to form biocompatible micelles as a vehicle for targeted drugs. With its critical micelle concentration (CMC) depending on the degree of substitution (DS) of cholesteryl and ranging from 0.0024 to 0.017 mg/mL, CCMX could self-assemble and form nanoscale micelles in aqueous media. Taking doxorubicin (DOX) as a model drug, the drug encapsulation efficiency (EE%) of CCMX-3 (DS of 0.35 for cholesteryl) reached 91.3%, and this system exhibited excellent internalization ability, as verified by tumor cellular uptake tests. The results of in vitro cytotoxicity and in vivo antitumor activity tests of nude mice demonstrated that CCMX-3/DOX micelles effectively suppressed the growth of tumor cells by maintaining the cytotoxicity of commercial DOX injection while reducing the toxicity against normal cells and increasing the survival time.

Fluorescent Polyvinylphosphonate Bioconjugates for Selective Cellular Delivery

To date, many poly(ethylene glycol) (PEG) and poly(N-isopropylacrylamide) (PNIPAAm) biomolecule conjugates have been described, but they often show long response times, are not bio-inert, or lose function in biological fluids. Herein, we present a modular synthetic approach to generate polyvinylphosphonate biomolecule conjugates. These conjugates exhibit a sharp phase transition temperature even under physiological conditions where few other examples with this property have been described to date. Furthermore, it was feasible to add biological functions to the polymers via the conjugation step. The polyvinylphosphonate cholesterol constructs are attached to the cellular membrane and the folic acid anchored polymers are shuttled into the cells. This is an exceptional finding through a straightforward synthetic approach.

Synthesis of sharply thermo and PH responsive PMA-b-PNIPAM-b-PEG-b-PNIPAM-b-PMA by RAFT radical polymerization and its schizophrenic micellization in aqueous solutions

Sharply thermo- and pH-responsive pentablock terpolymer with a core-shell-corona structure was prepared by RAFT polymerization of N-isopropylacrylamide and methacrylic acid monomers using PEG-based benzoate-type of RAFT agent. The PEG-based RAFT agent could be easily synthesized by dihydroxyl-capped PEG with 4-cyano-4-(thiobenzoyl) sulfanylpentanoic acids, using esterification reaction. This pentablock terpolymer was characterized by 1H NMR, FT-IR, and GPC. The PDI was obtained by GPC, indicating that the molecular weight distribution was narrow and the polymerization was well controlled. The thermo- and pH-responsive micellization of the pentablock terpolymer in aqueous solution was investigated using fluorescence spectroscopy technique, UV-vis transmittance, and TEM. The LCST of pentablock terpolymer increased (over 50 °C) compared to the NIPAM homopolymer (~32 °C), due to the incorporation of the hydrophilic PEG and PMA blocks in pentablock terpolymer (PNIPAM block as the core, PEG the block and the hydrophilic PMA block as the shell and the corona). Also, pH-dependent phase transition behavior shows at a pH value of about ~5.8, according to pKa of MAA. Thus, in acidic solution at room temperature, the pentablock terpolymer self-assembled to form core-shell-corona micelles, with the hydrophobic PMA block as the core, the PNIPAM block and the hydrophilic PEG block as the shell and the corona, respectively.

Amphiphilic Polymers Containing Cholesterol for Drug Delivery Systems

The interaction of binary copolymers poly(maleic anhydride-co-poly(ethylene glycol) methyl ether methacrylate) with cholesterol results in formation of cholesterol containing polymers, which contain from 4.6 to 46.0 mol % monocholesteryl maleic links. Their structure was confirmed using functional analysis and IR spectroscopy. Acidic and anhydride links of these copolymers form polymeric salts if react with alkali. These salts are surfactants which in aqueous medium form a hierarchy micelles and micellar aggregates depending on the copolymer concentration. Using conductometry it was found that preferably monomolecular micelles are formed in dilute solutions, and micellar aggregates begin to form at higher concentrations. In aqueous media polymeric salts are able to solubilize such lipophilic substances as Sudan III dye and anticancer drug curcumin. Efficiency of solubilization towards Sudan III grows if the content of monocholesteryl maleic fragment in surfactant increases.

A Review of Thermo- and Ultrasound-Responsive Polymeric Systems for Delivery of Chemotherapeutic Agents

There has been an exponential increase in research into the development of thermal- and ultrasound-activated delivery systems for cancer therapy. The majority of researchers employ polymer technology that responds to environmental stimuli some of which are physiologically induced such as temperature, pH, as well as electrical impulses, which are considered as internal stimuli. External stimuli include ultrasound, light, laser, and magnetic induction. Biodegradable polymers may possess thermoresponsive and/or ultrasound-responsive properties that can complement cancer therapy through sonoporation and hyperthermia by means of High Intensity Focused Ultrasound (HIFU). Thermoresponsive and other stimuli-responsive polymers employed in drug delivery systems can be activated via ultrasound stimulation. Polyethylene oxide/polypropylene oxide co-block or triblock polymers and polymethacrylates are thermal- and pH-responsive polymer groups, respectively but both have proven to have successful activity and contribution in chemotherapy when exposed to ultrasound stimulation. This review focused on collating thermal- and ultrasound-responsive delivery systems, and combined thermo-ultrasonic responsive systems; and elaborating on the advantages, as well as shortcomings, of these systems in cancer chemotherapy. The mechanisms of these systems are explicated through their physical alteration when exposed to the corresponding stimuli. The properties they possess and the modifications that enhance the mechanism of chemotherapeutic drug delivery from systems are discussed, and the concept of pseudo-ultrasound responsive systems is introduced.

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.

Thermo-triggered drug delivery from polymeric micelles of poly(N-isopropylacrylamide-co-acrylamide)-b-poly(n-butyl methacrylate) for tumor targeting

Novel temperature-sensitive micelles, possessing a core-shell structure, were successfully fabricated and evaluated as possible systems for targeting anticancer drugs to solid tumors. The amphiphilic block copolymer poly( N-isopropylacrylamide- co-acrylamide)-b-poly( n-butyl methacrylate) was used to achieve a stimuli-responsive on/off release and spatial specificity. The anticancer drug methotrexate, which is poorly water soluble, was used as the model. Fourier transform–infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, gel-permeation chromatography, and critical micelle concentration were used to evaluate the successful synthesis of block copolymers with a lower critical solution temperature ~40°C. Based on transmission electron microscope images, the micelles are spherical particles with narrow size distribution. The thermally triggered release of methotrexate was observed in vitro. Quartz crystal microbalance with dissipation was used to investigate the interactions of the polymeric micelles with bovine serum albumin, to illustrate protein adsorption and cell attachment. Cytotoxicity studies were conducted on Lewis lung carcinoma cells, and the anticancer activity of methotrexate-loaded micelles was significantly enhanced in combination with hyperthermia. The thermo-sensitive characteristics of the micelles make them applicable as smart drug delivery systems, when combined with localized hyperthermia.

Simulating the co-encapsulation of drugs in a "smart" core-shell-shell polymer nanoparticle

A coarse-grained lattice Monte Carlo method is used to simulate co-encapsulation and delivery of both a hydrophilic and hydrophobic drug from polymer nanoparticles. In particular, core-shell-shell polymer nanoparticles with acid-labile bonds are simulated, and the preferential release of the encapsulated drugs near more acidic tumors is captured. While these simple models lack the molecular details of a real system, they can reveal interesting insights concerning the effects of entropy and enthalpy in these systems.

Cholesterol--a biological compound as a building block in bionanotechnology

Cholesterol is a molecule with many tasks in nature but also a long history in science. This feature article highlights the contribution of this small compound to bionanotechnology. We discuss relevant chemical aspects in this context followed by an overview of its self-assembly capabilities both as a free molecule and when conjugated to a polymer. Further, cholesterol in the context of liposomes is reviewed and its impact ranging from biosensing to drug delivery is outlined. Cholesterol is and will be an indispensable player in bionanotechnology, contributing to the progress of this potent field of research.

Thermoresponsive aggregation behavior of triterpene-poly(ethylene oxide) conjugates in water

Bioconjugate amphiphiles comprising triterpene and poly(ethylene oxide) (PEO) were studied according to their thermoresponsive aggregation behavior (LCST) in water. Cholesteryl-PEO (CE) and betulinyl-PEO (BE) comprising <70 wt% PEO precipitated from water upon heating. CE, but not BE, solutions contained nanoscopic aggregates at room temperature causing different thermoprecipitation behaviors. Solutions containing 5 wt% solutions of BE with short PEO chains demonstrated dual thermoresponsive behavior, precipitating at high temperature and forming hydrogel at low temperature. A BE multiblock copolymer was found to form large aggregates, presumably vesicles, in water. Results suggest that the solution properties of triterpene-PEO amphiphiles can be controlled by the chemical composition and structure.

Nanobiomaterials: a review of the existing science and technology, and new approaches

Nanotechnology has made great strides forward in the creation of new surfaces, new materials and new forms which also find application in the biomedical field. Traditional biomedical applications started benefiting from the use nanotechnology in an array of areas, such as biosensors, tissue engineering, controlled release systems, intelligent systems and nanocomposites used in implant design. In this manuscript a review of developments in these areas will be provided along with some applications from our laboratories.

Self-assembled micelles of novel graft amphiphilic copolymers for drug controlled release

In this study, with the aim of designing an ideal anticancer drug carrier, we synthesized novel amphiphilic graft copolymers, P(Glu-alt-PEG)-graft-PCLA, based on poly(ethylene glycol) (PEG) segments and glutamic acid (Glu) units as the hydrophilic main chain, and poly(ɛ-caprolactone-co-lactide) (PCLA) as hydrophobic branches. The chemical structure of the copolymers was characterized by (1)H MNR and FT-IR. The self-assembly of the copolymers to form micelles was studied by TEM, DLS and fluorescence spectroscopy. In vitro doxorubicin controlled release studies demonstrated that these graft copolymer micelles had high drug loading capacity and good controlled released properties, demonstrating their potential as a novel anticancer drug carrier. The drug loaded graft copolymer micelles exhibited efficient inhibition of HeLa cells in in vitro studies.

In vivo evaluation of novel nanoparticles containing dexamethasone for ocular drug delivery on rabbit eye

PURPOSE

The purpose of this study was to investigate the in vivo effects of a new smart polymer loaded with dexamethasone on inflamed rabbit eye.

MATERIALS AND METHODS

Polymeric micelles were prepared using N-isopropylacrylamide (NIPAAM), vinyl pyrrolidone (VP), and methacrylate (MAA) as monomers in the presence of N,N-methylene bis-acrylamide (MBA) and triethyleneglycol dimethacrylate (TEGDMA) as cross-linking agents. These micelles were characterized on their physicochemical properties using a particle size analyzer, FT-IR, and (1)H NMR. Dexamethasone-containing nanosuspensions consisting of these temperature- and pH-sensitive micellar nanoparticles were prepared. To evaluate the efficacy of the novel ocular drug delivery using these novel micellar nanoparticles, uveitis was induced by intravitreal injection of the endotoxin within the rabbit eyes. Clinical distinctions for the inflammation within eyes were performed using Hogan's classification method and statistically analyzed using independent student t-tests and Mann-Whitney U-tests.

RESULTS

Cross-linked copolymer of NIPAAM-VP-MAA was prepared by free radical copolymerization of the monomers in the presence of NIPAAM and TEGDMA as cross-linking agents and ammonium per sulfate (APS) as the initiator in high yields. The PSA data represented that the particles have mean sizes between 300-450 nm. Topical administration of prepared nanosuspensions clearly reduced uveitis symptoms, which were qualified with Hogan scoring. Statistical analysis represented that both of the nano formulations significantly reduced inflammation (p < 0.05) during 48 hr after LPS injection.

CONCLUSION

Nanosuspension prepared with MBA showed rapid treatment in comparison with other nano formulations. The formulation also showed higher anti-inflammatory activity for a longer duration compared to aqueous suspension of the drug, which is due to small particle size and mucoadhesiveness of polymeric micelles.

Cationic fluorine-containing amphiphilic graft copolymers as DNA carriers

A series of cationic fluorine-containing amphiphilic graft copolymers P(HFMA-St-MOTAC)-g-PEG comprising poly(hexafluorobutyl methacrylate) (PHFMA) poly(methacryl oxyethyl trimethylammonium chloride) (PMOTAC) polystyrene (PSt) backbones and poly(ethylene glycol) (PEG) side chains are synthesized as a type of non-viral gene vector. The copolymers self-assemble into spherical micelles in the aqueous media and turbidity and cytotoxicity measurements show that those micelles have excellent dispersive stability and low cytotoxicity. The interactions between the copolymers and calf-thymus DNA are studied by fluorescence spectroscopy and viscosity. The former discloses electrostatic interaction, hydrophobic interaction, and hydrogen bonding in the copolymer/DNA system, whereas the latter indicates that these graft copolymers can bind DNA via the electrostatic and classical intercalation modes. The DNA-binding capacity determined by the gel retardation assay and UV-visible spectrophotometry shows that the copolymers have good binding capacity to DNA and a high charge density or HFMA content in the copolymers bode well for DNA-binding. Transmission electron microscopy, photon correlation spectroscopy, and zeta potential data reveal that stable colloidal complexes (particles) can form easily between the copolymer micelles and DNA. Our results suggest that the copolymers are a promising non-viral vector in a gene delivery system.

Synthesis and anaerobic biodegradation of indomethacin-conjugated cellulose ethers used for colon-specific drug delivery

Water soluble cellulose ethers, including methylcellulose and two hydroxyethylcelluloses with different molecular weights, were conjugate with indomethacin at room temperature. The chemical structures of the conjugates were characterized by FTIR, (1)H NMR and UV-vis spectroscopy. The results confirmed that different amounts of IND residues were covalently bonded to cellulose ether backbones through ester linkages. Their anaerobic biodegradation in colonic fermentation was investigated by gel permeation chromatography, gas chromatography and UV-vis spectroscopy. These conjugates were found to have different biodegradabilities, depending on the cellulose ether used and the amount of conjugated indomethacin residues. In vitro release experiments showed that hydroxyethylcellulose-based conjugates with low IND residues content could exhibit a sustained drug release behavior in colonic fermentation and were stable in the simulated media of the stomach and small intestine. Therefore, they are promising candidates for future applications in colon-specific drug delivery.