Biomimetic stimulus-responsive star diblock gelators

Novel biomimetic gelators with star diblock copolymer architectures have been synthesized by atom-transfer radical polymerization (ATRP). Two types of trifunctional ATRP initiator were used to polymerize 2-(methacryloyloxy)ethyl phosphorylcholine [MPC] at 20 degrees C, followed by sequential monomer addition of various tertiary amine methacrylates or mixtures thereof. Poor living character was achieved using an amide-based trifunctional initiator, but the analogous triester initiator gave reasonably well-defined thermo-responsive and pH-responsive star diblock copolymers. The most effective thermo-responsive gelators were obtained by the statistical terpolymerization of 2-(dimethylamino)ethyl methacrylate [DMA], 2-(diethylamino)ethyl methacrylate [DEA], and a monomethoxy-capped poly(propylene oxide) methacrylate [PPOMA], whereas pH-responsive gelators were prepared using 2-(diisopropylamino)ethyl methacrylate [DPA] as the second monomer. Star diblock copolymer gelators that were both thermo-responsive and pH-responsive were obtained by the statistical copolymerization of DMA with DPA. Copolymer compositions were assessed by 1H NMR spectroscopy, and the molecular weight distributions of the three-arm star MPC homopolymer precursors were assessed by aqueous gel permeation chromatography. Static light scattering was used to obtain weight-average molecular weights of selected star diblock copolymers and rheological measurements and variable-temperature 1H NMR were used to probe the onset of gelation.     

in vitro biological evaluation of folate-functionalized block copolymer micelles for selective anti-cancer drug delivery

The main objective of this study was to evaluate the ability of folic acid-functionalized diblock copolymer micelles to improve the delivery and uptake of two poorly water-soluble anti-tumor drugs, tamoxifen and paclitaxel, to cancer cells through folate receptor targeting. The diblock copolymer used in this study comprised a hydrophilic poly[2-(methacryloyloxy)ethyl phosphorylcholine] (MPC) block, carrying at the chain end the folate targeting moiety, and a pH-sensitive hydrophobic poly[2-(diisopropylamino)ethyl methacrylate] (DPA) block (FA-MPC-DPA). The drug-loading capacities of tamoxifen- and paclitaxel-loaded micelles were determined by high performance liquid chromatography and the micelle dimensions were determined by dynamic light scattering and transmission electron microscopy. Cell viability studies were carried out on human chronic myelogenous leukaemia (K-562) and colon carcinoma cell lines (Caco-2) in order to demonstrate that drug-loaded FA-MPC-DPA micelles exhibited higher cytotoxicities toward cancer cells than unfunctionalized MPC-DPA micelles. Uptake studies confirmed that folate-conjugated micelles led to increased drug uptake within cancer cells, demonstrating the expected selectivity toward these tumor cells.     

Facile synthesis of highly biocompatible poly(2-(methacryloyloxy)ethyl phosphorylcholine)-coated gold nanoparticles in aqueous solution

Diblock copolymers comprising a highly biocompatible poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC) block and a poly(2-(dimethylamino)ethyl methacrylate) (PDMA) block were evaluated for the synthesis of sterically stabilized gold nanoparticles in aqueous solution. The PDMA block becomes partially protonated on addition of HAuCl4, and the remaining nonprotonated tertiary amine groups reduce the AuCl4- counterion to zerovalent gold in situ. This approach results in the adsorption of the PDMA block onto the gold nanoparticle surface while the PMPC chains serve as a stabilizing block, producing highly biocompatible gold sols in aqueous solution at ambient temperature without any external reducing agent. The size and shape of gold nanoparticles could be readily controlled by tuning synthesis parameters such as the block composition and the relative and absolute concentrations of the PMPC-PDMA diblock copolymer and HAuCl4. These highly biocompatible gold sols have potential biomedical applications.     

Structure and Surface Properties of High-density Polyelectrolyte Brushes at the Interface of Aqueous Solution

Zwitterionic and cationic polyelectrolyte brushes were prepared by surface-initiated atom transfer radical polymerization of 2-methacryloyloxy- ethyl phosphorylcholine (MPC) and 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA), respectively. The poly(DMAEMA) brush was treated with methyl iodide to form poly[2-(methacryloyloxy) ethyltrimethylammonium iodide] [poly(METAI)]. The effects of ionic strength on brush structure and surface properties of densely grafted polyelectrolyte brushes were analyzed by contact angle measurements, neutron reflectivity (NR) and macroscopic friction tests. Both polyelectrolyte brushes exhibited hydrophilic properties. The contact angle of the poly(MPC) brush surface against water was ca. 0° in air and the contact angle of the air bubble in water was ca. 170°. The air bubble in water hardly attached to the poly(MPC) brush surface, indicating super hydrophilic characteristics. NR measurements of poly(MPC) and poly(METAI) brushes showed that the grafted polymer chains were extended from the substrate surface in a good solvent such as water. Interestingly, NR study did not reveal the shrinkage of the brush chain in salt solution. The polyelectrolyte brushes immersed in both water and NaCl solution at various concentrations showed a low friction coefficient and low adhesion force.     

Synthesis of graft copolymers having phospholipid polar group by macromonomer method and their properties in water

Water-soluble graft copolymers with phospholipid polar group were synthesized by the macromonomer method and their properties in water were investigated by surface tension and fluorescence spectroscopic measurements. At first, 2-methacryloyloxyethyl phosphorylcholine (MPC) was polymerized in the presence of 3-mercapt propionic acid as a chain transfer agent and carboxyl group-terminated oligo (MPC) was obtained. The oligo (MPC) reacted with glycidyl methacrylate to convert the carboxyl group to a polymerizable methacryloyl group. The MPC macromonomer obtained was copolymerized with hydrophobic n-butyl methacrylate (BMA) and a graft copolymer was obtained. The graft copolymer, poly(MPC-graft-BMA), was water-soluble when the MPC unit mole fraction was above 0.40. The surface tension of the aqueous solution of poly(MPC-graft-BMA) did not depend on the polymer concentration below 0.1 wt %. This tendency was the same as that which appeared in aqueous poly(MPC) solution. The fluorescence intensity of hydrophobic probes observed in an aqueous solution of the poly (MPC-graft-BMA) was also the same level as that observed in the case of poly(MPC). These results clearly indicated that the poly(MPC-graft-BMA) took a domain structure like micelle in water, i.e., the hydrophobic poly(BMA) backbone was in the core part and the hydrophilic poly(MPC) chain formed the shell part of the micelle. © 1994 John Wiley & Sons, Inc.     

Quantitative evaluation of mechanosensing of cells on dynamically tunable hydrogels

Thin hydrogel films based on an ABA triblock copolymer gelator [where A is pH-sensitive poly(2-(diisopropylamino)ethyl methacrylate) (PDPA) and B is biocompatible poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC)] were used as a stimulus-responsive substrate that allows fine adjustment of the mechanical environment experienced by mouse myoblast cells. The hydrogel film elasticity could be reversibly modulated by a factor of 40 via careful pH adjustment without adversely affecting cell viability. Myoblast cells exhibited pronounced stress fiber formation and flattening on increasing the hydrogel elasticity. As a new tool to evaluate the strength of cell adhesion, we combined a picosecond laser with an inverted microscope and utilized the strong shock wave created by the laser pulse to determine the critical pressure required for cell detachment. Furthermore, we demonstrate that an abrupt jump in the hydrogel elasticity can be utilized to monitor how cells adapt their morphology to changes in their mechanical environment.     

Adsorption of protein on the surface of thermosensitive poly(methyl methacrylate) microspheres modified with the N-(2-hydroxypropyl)methacrylamide and 2-(methacryloyloxy)ethyl phosphorylcholine moieties

A series of microspheres composed of methyl methacrylate (MMA) and N-(2-hydroxypropyl)methacrylamide (HPMA), and/or 2-(methacryloyloxy)ethyl phosphorylcholine (MPC), i.e., binary copolymer microspheres [poly(HPMA-co-MMA)_KPS and poly(HPMA-co-MMA)_ABIP] and ternary ones [poly(HPMA/MPC-co-MMA)_KPS and poly(HPMA/MPC-co-MMA)_ABIP], were prepared by emulsifier-free emulsion copolymerization using potassium peroxodisulfate (KPS) or 2,2′-azobis[2-(imidazolin-2-yl)propane] dihydrochloride (ABIP) as initiators. The decrease in ζ-potential of the polymer microspheres is caused by the addition of the HPMA and/or MPC moieties. Equilibrium water content of poly(HPMA-co-MMA)_ABIP showed a remarkable swelling change with a change in response to temperature: the hydrated conformation at 28°C and the dehydrated one at above 40°C. The adsorption of protein on the polymer microspheres also changed in response to change in temperature. The ternary polymer microspheres effectively suppressed the adsorption both of Alb and Glo, less than binary ones. A series of polymer microspheres are expected to apply as a novel drug carrier with both thermosensitive and nonthrombogenic functions. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 3349–3357, 1997     

Novel biomimetic surfactant: synthesis and micellar characteristics

Novel biomimetic surfactants based on cholesterol as the hydrophobic segment and poly[2-(methacryloyloxy)ethyl phosphorylcholine] (pMPC) as the hydrophilic segment were synthesized in the present study by atom transfer radical polymerization (ATRP) of 2-(methacryloyloxy)ethyl phosphorylcholine (MPC) using a cholesterol-based macroinitiator. The association behavior of cholesterol-block-poly[2-(methacryloyloxy)ethyl phosphorylcholine] (Chol-pMPCs) in aqueous solution was studied by (1)H NMR spectroscopy, fluorescence probe technique, and atomic force microscopy (AFM). The (1)H NMR spectrum of the polymer in CD(3)OD showed both the cholesterol group and the phosphorylcholine group while the cholesterol group did not appeared in the (1)H NMR spectrum of the polymer in D(2)O, which implied the formation of a micelle structure. Fluorescence excitation spectra of a pyrene probe solubilized in the aggregates of Chol-pMPCs suggested the presence of a critical micelle concentration (cmc) in water. The critical micelle concentrations of the polymers CMPC10, CMPC20 and CMPC40 were determined to be 7.27 x 10(-3), 13.47 x 10(-3), and 20.77 x 10(-3) mg . mL(-1), respectively. AFM images of the aggregates on mica suggested that the pMPC block formed the biocompatible micelle coronas and the cholesterol block formed the hydrophobic micelle cores. These new biomimetic diblock copolymers were evaluated as "stealthy" nanocapsules for the delivery of hydrophobic drugs. The anti-cancer drug adriamycin (ADR) was chosen as a hydrophobic drug to be incorporated into the inner core of the micelles and the morphology of the drug-loaded micelles were observed by AFM.     

Synthesis and biocompatibility of phosphoryl polymer and relationship between biocompatibility and water structure

A series of copolymers, poly(methylmethacrylate-co-2-methacryloyloxyethyl phosphorylcholine), with various compositions of methyl methacrylate (MMA) and 2-methacryloyloxyethyl phosphorylcholine (MPC) were synthesized by radical copolymerization in a mixed solvent of ethanol and chloroform. The structures of the copolymers were confirmed by proton nuclear magnetic resonance and elemental analysis. The properties and morphologies of the copolymers were characterized by differential scanning calorimeter, scanning electron microscopy, and optical microscope. The adsorption of bovine serum albumin (BSA) and the adhesion of platelet on the surfaces of the copolymer membrane significantly decreased with increasing the MPC composition. The copolymers containing MPC above 18% showed excellent biocompatibility. Moreover, the relationship between the water structure and the biocompatibility was illustrated by changing quantity of the MPC in copolymers. The result showed that the amount of free water affected the platelet compatibility of the copolymer.     

Near-monodisperse poly(2-(methacryloyloxy)ethyl phosphorylcholine)-based macromonomers prepared by atom transfer radical polymerization and thiol-ene click chemistry: novel reactive steric stabilizers for aqueous emulsion polymerization

Poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC) macromonomers have been prepared by the atom transfer radical polymerization (ATRP) of 2-(methacryloyloxy)ethyl phosphorylcholine (MPC) using a bifunctional disulfide-based initiator. To attach a terminal polymerizable methacrylate group, the central disulfide bond was cleaved and the resulting thiols were conjugated to 3-(acryloyloxy)-2-hydroxypropyl methacrylate using tris(2-carboxyethyl)phosphine (TCEP) in water. Here TCEP serves as both the disulfide cleavage agent and also the catalyst for the subsequent Michael addition, which is highly selective for the acrylate group. The resulting methacrylate-terminated macromonomers were used as a reactive steric stabilizer for the aqueous emulsion polymerization of styrene, yielding near-monodisperse PMPC-stabilized polystyrene (PS) latexes of around 100-200 nm in diameter. As a comparison, the disulfide-containing PMPC homopolymer precursor and the intermediate thiol-functional PMPC homopolymer (PMPC-SH) were also evaluated as potential steric stabilizers. Interestingly, near-monodisperse latexes were also obtained in each case. These three sterically-stabilized latexes, prepared using either PMPC macromonomer, disulfide-based PMPC homopolymer, or PMPC-SH homopolymer as a reactive steric stabilizer, remained colloidally stable after both freeze-thaw experiments and the addition of an electrolyte, indicating that a coronal layer of PMPC chains prevented flocculation in each case. In contrast, both a charge-stabilized PS latex prepared in the absence of any steric stabilizer and a PS latex prepared in the presence of a nonfunctional PMPC homopolymer exhibited very poor colloidal stability when subjected to a freeze-thaw cycle or the addition of an electrolyte, as expected.     

pH-sensitive vesicles based on a biocompatible zwitterionic diblock copolymer

Highly biocompatible pH-sensitive diblock copolymer vesicles were prepared from the self-assembly of a biocompatible zwitterionic copolymer, poly[2-(methacryloyloxy)ethyl phosphorylcholine-block-2-(diisopropylamino)ethyl methacrylate], PMPC-b-PDPA. Vesicle formation occurred spontaneously by adjusting the solution pH from pH 2 to above 6, with the hydrophobic PDPA chains forming the vesicle walls. Transmission electron microscopy (TEM), dynamic laser light scattering (DLS), and UV-visible absorption spectrophotometry were used to characterize these vesicles. Gold nanoparticle-decorated vesicles were also obtained by treating the vesicles with HAuCl4, followed by NaBH4.     

pH-responsive Polymersome Based on PMCP-b-PDPA as a Drug Delivery System to Enhance Cellular Internalization and Intracellular Drug Release

Choline phosphate(CP) as a novel zwitterion possesses specific and excellent properties compared with phosphorylcholine(PC), as well as its polymer, such as poly(2-(methacryloyloxy)ethyl choline phosphate)(PMCP), has been studied extensively due to its unique characteristics of rapid cellular internalization via the special quadrupole interactions with the cell membrane. Recently, we reported a novel PMCP-based drug delivery system to enhance the cellular internalization where the drug was conjugated to the polymer via reversible acylhydrazone bond. Herein, to make full use of this feature of PMCP, we synthesized the diblock copolymer poly(2-(methacryloyloxy)ethyl choline phosphate)-b-poly(2-(diisopropylamino)ethyl methacrylate)(PMCP-b-PDPA), which could self-assemble into polymersomes with hydrophilic PMCP corona and hydrophobic membrane wall in mild conditions when the p H value is ≥ 6.4. It has been found that these polymersomes can be successfully used to load anticancer drug Dox with the loading content of about 11.30 wt%. After the polymersome is rapidly internalized by the cell with the aid of PMCP, the loaded drug can be burst-released in endosomes since PDPA segment is protonated at low p H environment, which renders PDPA to transfer from hydrophobic to hydrophilic,and the subsequent polymersomes collapse thoroughly. Ultimately, the "proton sponge" effect of PDPA chain can further accelerate the Dox to escape from endosome to cytoplasm to exert cytostatic effects. Meanwhile, the cell viability assays showed that the Dox-loaded polymersomes exhibited significant inhibitory effect on tumor cells, indicating its great potential as a targeted intracellular delivery system with high efficiency.     

Surface modification on microfluidic devices with 2-methacryloyloxyethyl phosphorylcholine polymers for reducing unfavorable protein adsorption

Surface modification of polymer materials for preparing microfluidic devices including poly(dimethyl siloxane) (PDMS) was investigated with phospholipids polymers such as poly(2-methacryloyloxylethyl phosphorylcholine(MPC)-co-n-butyl methacrylate) (PMB) and poly(MPC-co-2-ethylhexyl methacrylate-co-2-(N,N-dimethylamino)ethyl methacrylate) (PMED). The hydrophilicity of every surface on the polymer materials modified with these MPC polymers increased and the value of zeta-potential became close to zero. The protein adsorption on the polymer materials with and without the surface modification was evaluated using a protein mixture of human plasma fibrinogen and serum albumin. Amount of proteins adsorbed on these polymeric materials showed significant reduction by the surface modification with the MPC polymers compared to the uncoated surfaces ranging from 56 to 90%. Furthermore, we successfully prepared PDMS-based microchannel which was modified by simple coating with the PMB and PMED. The modified microchannel also revealed a significant reduction of adsorption of serum albumin. We conclude that the MPC polymers are useful for reducing unfavorable protein adsorption on microfluidic devices.     

Kinetics of pH-Induced formation and dissociation of polymeric vesicles assembled from a water-soluble zwitterionic diblock copolymer

The kinetics of pH-induced formation and dissociation of vesicles self-assembled from a biocompatible zwitterionic diblock copolymer, poly(2-(methacryloyloxy)ethyl phosphorylcholine)-b-poly(2-(diisopropylamino)ethyl methacrylate) (PMPC- b-PDPA), was investigated in detail via a combination of stopped-flow light scattering and laser light scattering (LLS). Upon jumping from pH 2 to 10, stopped-flow light scattering reveals three distinct relaxation processes for the early stages of vesicle self-assembly (0-40 s). Kinetic sequences associated with the obtained three characteristic relaxation times have been tentatively proposed. Moreover, the kinetics of vesicle formation in the later stage (from 3 min onward) was investigated by dynamic LLS. It was found that both the intensity-averaged hydrodynamic radius, R h, and the polydispersity, mu2/Gamma (2), decrease exponentially, yielding a characteristic relaxation time of approximately 350 s. To our knowledge, this is the first report on the kinetics of the unimer-to-vesicle transition of a stimulus-responsive diblock copolymer. The kinetics of vesicle dissociation for a pH jump from 12 to 2 was also investigated. The breakdown of polymeric vesicles is extremely fast and is independent of polymer concentration; it is complete within approximately 5 ms and is in marked contrast to the much slower rate of vesicle formation.     

Synthesis and characterization of PEGylated comb-like cationic polymer by polycondensation and ATRP

PEGylated poly(2-(dimethylamino)ethyl methacrylate) with comb-like architecture was synthesized by two-step polymerization. First,poly(oligo(ethylene glycol) malicate)(POEGMA) bearing pendant hydroxyl groups was prepared by direct polycondensation of oligo(ethylene glycol) and malic acid in the presence of scandium triflate as chemoselective catalyst.Then the poly(2- (dimethylamino)ethyl methacrylate) side chains were grafted from the POEGMA backbone by atom transfer radical polymerization (ATRP) after the hydroxyl groups were modified into bromo-ester form,resulting in a PEGylated cationic copolymer with branched architecture.     

Graft copolymerization of 2‐methacryloyloxyethyl phosphorylcholine to cellulose in homogeneous media using atom transfer radical polymerization for providing new hemocompatible coating materials

To develop new hemopurification systems based on cellulose membrane, we synthesized a graft copolymer of cellulose with poly(2‐methacryloyloxyethyl phosphorylcholine) (MPC) by a metal‐catalyzed atom transfer radical polymerization process in homogeneous media. First, cellulose was dissolved in a DMAc/LiCl solution system, and it reacted with 2‐bromoisobutyloyl bromide to produce macroinitiator (cell‐BiB). Then, MPC was polymerized to the cellulose backbone in a homogeneous DMSO/methanol mixture solution in the presence of cell‐BiB. Characterization with FT‐IR, NMR, and GPC measurements showed that there obtained a graft copolymer of cellulose backbone and poly(MPC) side chains (cell‐PMPC) with well‐defined structure, indicating a controlled/“living” radical polymerization. The proteins adsorption studies showed that cellulose membranes modified by the as‐prepared cell‐PMPC owns good protein adsorption resistance. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3306–3313, 2008     

Synthesis of biocompatible poly[2-(methacryloyloxy)ethyl phosphorylcholine]-coated magnetite nanoparticles

A well-defined, double-hydrophilic diblock copolymer comprising poly[2-(methacryloyloxy)ethyl phosphorylcholine]-block-(glycerol monomethacrylate) (PMPC30-PGMA30, where the numbers represent the average degrees of polymerization for each block) was evaluated for the synthesis of colloidally stable ultrafine magnetite sols. Sterically stabilized paramagnetic sols were prepared in aqueous solution by chemical coprecipitation of ferric and ferrous salts in the presence of this block copolymer. The PMPC30-PGMA30-stabilized magnetite sol had a mean transmission electron microscopy (TEM) diameter of 9.4 +/- 1.7 nm and a mean hydrodynamic diameter of 34 nm. This sol exhibited improved colloidal stability with respect to long-term storage and pH variation compared with magnetite sols prepared in the presence of alternative water-soluble homopolymers and diblock copolymers. Fourier transform infrared (FT-IR) spectroscopy, thermogravimetry, electron spectroscopy imaging (ESI), and zeta potential studies indicate that the PMPC30-PGMA30 diblock copolymer was adsorbed onto the surface of the sol via the PGMA30 block, with the PMPC30 chains acting as the stabilizing block. Such sterically stabilized sols are expected to be improved contrast agents for magnetic resonance imaging (MRI) applications.     

SYNTHESIS OF POLY(METHYL METHACRYLATE)-graft-POLYSTYRENE BY ATOM TRANSFER RADICAL POLYMERIZATION

The radical copolymerization of methyl methacrylate and 2-hydroxyethyl methacrylate was carried out via atomtransfer radical polymerization (ATRP) initiated by ethyl 2-bromoisobutyrate and catalyzed by CuBr/2,2'-bipyridinecomplex. This polymerization proceeds in a living fashion with controlled molecular weight and low polydispersity. Theobtained copolymer was esterified with 2-bromoisobutylryl bromide yielding a macroinitiator, poly(methyl methacrylate-co-2-hydroxyethyl methacrylate-co-2-(2-bromoisobutyryloxy)ethyl methacrylate), and its structure was characterized by ~1H-NMR. This macroinitiator was used for ATRP of styrene to synthesize poly(methyl methacrylate)-graft-polystyrene. Themolecular weight of graft copolymer increased with the monomer conversion, and the polydispersity remained relatively low.The individual grafted polystyrene chains were cleaved from the macroinitiator backbone by hydrolysis and the hydrolyzed product was characterized by ~1H-NMR and GPC.     

Thermoresponsive PPEGMEA‐g‐PPEGEEMA well‐defined double hydrophilic graft copolymer synthesized by successive SET‐LRP and ATRP

A series of well‐defined double hydrophilic graft copolymers containing poly[poly(ethylene glycol) methyl ether acrylate] (PPEGMEA) backbone and poly[poly(ethylene glycol) ethyl ether methacrylate] (PPEGEEMA) side chains were synthesized by the combination of single electron transfer‐living radical polymerization (SET‐LRP) and atom transfer radical polymerization (ATRP). The backbone was first prepared by SET‐LRP of poly(ethylene glycol) methyl ether acrylate macromonomer using CuBr/tris(2‐(dimethylamino)ethyl)amine as catalytic system. The obtained comb copolymer was treated with lithium diisopropylamide and 2‐bromoisobutyryl bromide to give PPEGMEA‐Br macroinitiator. Finally, PPEGMEA‐g‐PPEGEEMA graft copolymers were synthesized by ATRP of poly(ethylene glycol) ethyl ether methacrylate macromonomer using PPEGMEA‐Br macroinitiator via the grafting‐from route. The molecular weights of both the backbone and the side chains were controllable and the molecular weight distributions kept narrow (M_w/M_n ≤ 1.20). This kind of double hydrophilic copolymer was found to be stimuli‐responsive to both temperature and ion (0.3 M Cl^? and SO). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 647–655, 2010