Thermosensitive Block Copolymer Research Articles

Hyperthermia induced targeting of thermosensitive gene carriers to tumors

Locoregional hyperthermia (HT) can be used for site-directed activation of macromolecular drug delivery systems. We have developed a gene delivery system based on thermosensitive block copolymers (TSCs) with a phase transition temperature of 42 degrees C [Zintchenko, A., Ogris, M., and Wagner, E. (2006). Bioconjug. Chem. 17, 766-772], in which the statistical copolymer of vinylpyrrolidinone and N-isopropylacryamide is grafted on polyethylenimine (PEI). Here we applied polyplexes consisting of plasmid DNA and TSCs systemically in A/J mice bearing a syngeneic Neuro2A neuroblastoma tumor subcutaneously in each hind limb. One limb was selectively treated by HT at 42 degrees C, at the same time that polyplexes were injected via the tail vein. Hyperthermia led to increased accumulation of thermosensitive polymer and aggregation of thermosensitive polyplexes in HT-treated tumors, resulting in up to 10-fold increased DNA deposition compared with non-HT-treated tumor. The level of transgene expression induced by TSC polyplexes in HT-treated tumors was significantly higher and selective for tumor tissue. With nonthermosensitive PEI polyplexes HT did not influence transgene deposition or expression in tumor.

Synthesis and self-assembly behaviors of three-armed amphiphilic block copolymers via RAFT polymerization

The novel trifunctional reversible addition–fragmentation chain transfer (RAFT) agent, tris(1-phenylethyl) 1,3,5-triazine-2,4,6-triyl trithiocarbonate (TTA), was synthesized and used to prepare the three-armed polystyrene (PS3) via RAFT polymerization of styrene (St) in bulk with thermal initiation. The polymerization kinetic plot was first order and the molecular weights of polymers increased with the monomer conversions with narrow molecular weight distributions (Mw/Mn≤1.23). The number of arms of the star PS was analyzed by gel permeation chromatography (GPC), ultraviolet visible (UV–vis) and fluorescence spectra. Furthermore, poly(styrene-b-N-isopropylacrylamide)3 (PS-b-PNIPAAM)3, the three-armed amphiphilic thermosensitive block copolymer, with controlled molecular weight and well-defined structure was also successfully prepared via RAFT chain extension method using the three-armed PS obtained as the macro-RAFT agent and N-isopropylacrylamide as the second monomer. The copolymers obtained were characterized by GPC and 1H nuclear magnetic resonance (NMR) spectra. The self-assembly behaviors of the three-armed amphiphilic block copolymers (PS-b-PNIPAAM)3 in mixed solution (DMF/CH3OH) were also investigated by high performance particle sizer (HPPS) and transmission electron microscopy (TEM). Interestingly, the lower critical solution temperature (LCST) of aqueous solutions of the three-armed amphiphilic block copolymers (PS-b-PNIPAAM)3 decreased with the increase of relative length of PS in the block copolymers.

Association and Structure of Thermosensitive Comblike Block Copolymers in Aqueous Solutions

The structures and association properties of thermosensitive block copolymers of poly(methoxyoligo(ethylene glycol) norbornenyl esters) in D2O were investigated by small angle neutron scattering (SANS). Each block is a comblike polymer with a polynorbornene (PNB) backbone and oligo ethylene glycol (OEG) side chains (one side chain per NB repeat unit). The chemical formula of the block copolymer is (OEG3NB)79−(OEG6.6NB)67, where subscripts represent the degree of polymerization (DP) of OEG and NB in each block. The polymer concentration was fixed at 2.0 wt % and the structural changes were investigated over a temperature range between 25 and 68 °C. It was found that at room temperature polymers associate to form micelles with a spherical core formed by the block (OEG3NB)79 and corona formed by the block (OEG6.6NB)67 and that the shape of the polymer in the corona could be described by the form factor of rigid cylinders. At elevated temperatures, the aggregation number increased and the micelles became more...

Effects of Substitution Groups on the RAFT Polymerization of N-Alkylacrylamides in the Preparation of Thermosensitive Block Copolymers

Reversible addition−fragmentation chain transfer (RAFT) polymerization was used to prepare a series of homo- and copolymers of N-alkyl-substituted acrylamides. The acrylamide monomers have similar chemical structures, but they all exhibit difference in reactivities, especially between N-monosubstituted and N,N-disubstituted acrylamides during the RAFT process. Results from size exclusion chromatography and matrix-assisted laser desorption ionization time-of-flight mass spectrometry indicate chain transfers to monomers are easier to occur for N-monosubstituted polyacrylamides, with negative deviations of the molecular weights from the theoretical values. The high transfer activity makes them good macro-chain transfer agents (CTAs). The stronger electron-donating conjugative effect renders the disubstituted acrylamides more reactive, meaning that they can react more readily with monosubstituted polyacrylamide−CTAs to form a sequent block. Tri- and tetrablock copolymers with multiple thermosensitivity have b...

Cell attachment to PET films coated with a thermo-sensitive block co-polymer with different chemical composition

This objective of this study is to characterize the surface of poly(ethylene terephthalate) (PET) films coated with the thermo-sensitive di-block co-polymers of 2-ethoxyethyl vinyl ether and 2-phenoxyethyl vinyl ether segments (EOVE-b-PhOVE) with a high polydispersity and evaluate the behavior of cell attachment on them at different temperatures. The EOVE segment possessed a low critical solution temperature at 20°C while the hydrophobic PhOVE segment functioned as the site to allow the co-polymer to adsorb onto the PET films. X-ray photoelectron spectroscopy and contact angle measurements revealed that the PET film was coated with the EOVE-b-PhOVE co-polymers. The density of co-polymers coated increased with the concentration of co-polymers used for coating. Irrespective of the co-polymer type, 3T3L1 cells attached on the surface of coated films at 37°C, while the cells showed a spread shape, which is similar to that of cells attached on the original non-coated film. However, when the temperature decreased from 37 to 4°C, the cell shape changed to be round, in contrast to that of the original PET film. The percent increase of round cells depended on the coating density and the polymerization degree of EOVE segment.

Biodegradability and biocompatibility of a pH- and thermo-sensitive hydrogel formed from a sulfonamide-modified poly(ε-caprolactone-co-lactide)–poly(ethylene glycol)–poly(ε-caprolactone-co-lactide) block copolymer

A pH- and thermo-sensitive block copolymer was synthesized by adding pH-sensitive sulfamethazine oligomers (SMOs) to either end of a thermo-sensitive poly(epsilon-caprolactone-co-lactide)-poly(ethylene glycol)-poly(epsilon-caprolactone-co-lactide) (PCLA-PEG-PCLA) block copolymer. The resulting pH- and thermo-sensitive SMO-PCLA-PEG-PCLA-SMO block copolymer solution did not form a gel at high pH (pH 8.0) or at increased temperatures (ca. 70 degrees C), but did form a stable gel under physiological conditions (pH 7.4 and 37 degrees C). The degradation rate of the pH- and thermo-sensitive block copolymer decreased substantially compared with the control block copolymer of PCLA-PEG-PCLA, due to the buffering effect of the SMO-PCLA-PEG-PCLA-SMO sulfonamide groups on the acidic monomer-induced rapid degradation of PCLA-PEG-PCLA. This suitable sol-gel transition and sustained biodegradability of the pH- and thermo-sensitive SMO-PCLA-PEG-PCLA-SMO block copolymer resolves two of the major drawbacks associated with thermo-sensitive block copolymers, namely premature gelation and rapid degradation. Interestingly, SMO-PCLA-PEG-PCLA-SMO showed no evidence of cytotoxicity in vitro. However, subcutaneous injection of the pH- and thermo-sensitive block copolymer solution (20wt% in PBS at pH 8.0) into Sprague-Dawley (SD) rats resulted in rapid, stable gel formation, with the injected hydrogel being completely degraded in vivo in just 6 weeks. The injected hydrogel in vivo presented a typical acute inflammation within 2 weeks, although chronic inflammation was not observed during the first 6-week period. As such, the pH- and thermo-sensitive hydrogel of the SMO-PCLA-PEG-PCLA-SMO block copolymer is a suitable candidate for use in drug delivery systems and cell therapy.

Temperature Sensitization of Liposomes by Use of Thermosensitive Block Copolymers Synthesized by Living Cationic Polymerization: Effect of Copolymer Chain Length

We prepared block copolymers of (2-ethoxy)ethoxyethyl vinyl ether (EOEOVE) and octadecyl vinyl ether (ODVE) with the number average molecular weights of 6900, 9300, and 16 700 by living cationic polymerization. The poly(EOEOVE) block acts as a temperature-sensitive moiety, and the poly(ODVE) block acts as an anchor moiety. We also investigated the effect of chain length of the copolymer poly(EOEOVE) block on the ability to sensitize liposomes. The copolymers underwent a coil-globule transition at approximately 36 degrees C in the presence of a membrane of egg yolk phosphatidylcholine (EYPC), detected using differential scanning calorimetry (DSC). Liposomes encapsulating calcein, a water-soluble fluorescent dye, were prepared from mixtures of dioleoylphosphatidylethanolamine, EYPC, and the copolymers. While the copolymer-modified liposomes released little calcein below 30 degrees C, release was enhanced above 35 degrees C, indicating that dehydrated copolymer chains destabilized the liposome membrane. In addition, copolymers with a longer poly(EOEOVE) block induced a more drastic enhancement of contents release in a narrow temperature region near the transition temperature of the poly(EOEOVE) block. As a result, the copolymer with an average molecular weight of 16 700 generated highly sensitive liposomes that produced rapid and dramatic release of the contents in response to temperature.

Intelligent Crew‐Cut Aggregates Formed by Thermosensitive Block Copolymers and Their Multiple Morphologies

The thermosensitive block copolymer poly(2-cinnamoylethyl methacrylate)-block-poly(N-isopropylacrylamide) (PCEMA-b-PNIPAAm) can form crew-cut aggregates with multiple morphologies under various micellization conditions. Spherical, rod-like, vesicular, lamellar aggregates, and large compound micelles were obtained from the block copolymers. The effects of different conditions, such as the copolymer composition, the nature of the common solvent, the initial copolymer concentrations, and the water content on the morphologies of the aggregates were studied in detail. The thermosensitive property of the aggregates was investigated through measuring the change of the dimension of the aggregates with changing the external temperature.

The effect of the processing and formulation parameters on the size of nanoparticles based on block copolymers of poly(ethylene glycol) and poly( N-isopropylacrylamide) with and without hydrolytically sensitive groups

Block copolymers of poly(ethylene glycol) (PEG) as a hydrophilic block and N-isopropylacrylamide (PNIPAAm) or poly (NIPAAm- co- N-(2-hydroxypropyl) methacrylamide-dilactate) (poly(NIPAAm- co-HPMAm-dilactate)) as a thermosensitive block, are able to self-assemble in water into nanoparticles above the cloud point (CP) of the thermosensitive block. The influence of processing and the formulation parameters on the size of the nanoparticles was studied using dynamic light scattering. PNIPAAm- b-PEG 2000 polymers were not suitable for the formation of small and stable particles. Block copolymers with PEG 5000 and 10 000 formed relatively small and stable particles in aqueous solutions at temperatures above the CP of the thermosensitive block. Their size decreased with increasing molecular weight of the thermosensitive block, decreasing polymer concentration and using water instead of phosphate buffered saline as solvent. Extrusion and ultrasonication were inefficient methods to size down the polymeric nanoparticles. The heating rate of the polymer solutions was a dominant factor for the size of the nanoparticles. When an aqueous polymer solution was slowly heated through the CP, rather large particles (⩾200 nm) were formed. Regardless the polymer composition, small nanoparticles (50–70 nm) with a narrow size distribution were formed, when a small volume of an aqueous polymer solution below the CP was added to a large volume of heated water. In this way the thermosensitive block copolymers rapidly pass their CP (‘heat shock’ procedure), resulting in small and stable nanoparticles.

Thermosensitive polyalcohols: Synthesis via living cationic polymerization of vinyl ethers with a silyloxy group

AbstractThermosensitive homopolymers and copolymers with hydroxy groups were synthesized via the living cationic polymerization of Si‐containing vinyl ethers. The cationic homopolymerization and copolymerization of five vinyl ethers with silyloxy groups, each with a different spacer length, were examined with a cationogen/Et1.5AlCl1.5 initiating system in the presence of an added base. When an appropriate base was added, the living cationic polymerization of Si‐containing monomers became feasible, giving polymers with narrow molecular weight distributions and various block copolymers. Subsequent desilylation gave well‐defined polyalcohols, in both water‐soluble and water‐insoluble forms. One of these polyalcohols, poly(4‐hydroxybutyl vinyl ether), underwent lower‐critical‐solution‐temperature‐type thermally induced phase separation in water at a critical temperature (TPS) of 42 °C. This phase separation was quite sensitive and reversible on heating and cooling. The phase separation also occurred sensitively with random copolymers of thermosensitive and hydrophilic or hydrophobic units, the TPS values of which in water could be controlled by the monomer feed ratio. The thermal responsiveness of this polyalcohol unit made it possible to prepare novel thermosensitive block and random copolymers consisting solely of alcohol units. One example prepared in this study was a 20 wt % aqueous solution of a diblock copolymer consisting of thermosensitive poly(4‐hydroxybutyl vinyl ether) and water‐soluble poly(2‐hydroxyethyl vinyl ether) segments, which transformed into a physical gel above 42 °C. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3300–3312, 2003

Heat-Induced Self-Assembling of Thermosensitive Block Copolymer. Rheology and Dynamic Light Scattering Study

The dynamic aspects of the thermoreversible morphological transition of poly(2-ethoxyethyl vinyl ether)-b-poly(2-hydroxyethyl vinyl ether) (PEOVE-b-PHOVE) in aqueous solutions have been investigated by dynamic light scattering (DLS) and rheological measurements. A sample-position-dependent DLS study, employed here, allowed us to resolve two transitions, i.e., (1) molecular dispersion-to-micelle transition and (2) micelle-to-macrolattice transition, which were not clearly resolved by small-angle neutron scattering studies in the previous work. These transitions are characterized by (1) an abrupt increase in the scattered intensity and (2) an appearance of speckle patterns. The temperature where the abrupt increase in intensity was observed was a few degrees lower than that the speckle pattern appeared. Rheological behaviors also supported the two transitions as (1) Newtonian-to-non-Newtonian transition and (2) non-Newtonian-to-plastic flow transition. It is concluded that a pseudo-sol-to-gel transition wit...

Heat-Induced Self-Assembling of Thermosensitive Block Copolymer. 1. Small-Angle Neutron Scattering Study

The sharp and thermoreversible morphological transitions of poly(2-ethoxyethyl vinyl ether-b-2-hydroxyethyl vinyl ether) (poly(EOVE-b-HOVE)) in aqueous solutions have been investigated by means of small-angle neutron scattering. The poly(EOVE-b-HOVE), synthesized by living cationic polymerization, had the number-average degree of polymerizations of the constituent blocks of 200 and 400, respectively, and a polydispersity index of 1.07. The poly(EOVE-b-HOVE) underwent a disorder−order transition around 17−21 °C, depending on the polymer concentration. This is a micellization with a poly(EOVE) core of ca. 20 nm in radius and a poly(HOVE) corona. When the polymer concentration was high enough, e.g., 17 wt %, a macrolattice formation with body-centered cubic symmetry was also observed. This transition took place in a narrow temperature window of less than a degree centigrade. The origin of this sharp transition was found to be a dissociation of hydrophobically associated structure, such as an iceberg structur...

Dissolution and Aggregation of a Poly(NIPA-block-sulfobetaine) Copolymer in Water and Saline Aqueous Solutions

Thermal properties of the novel, double thermosensitive block copolymer, poly(N-isopropyl acrylamide)-block-poly(3-[N-(3-methacrylamido-propyl)-N,N-dimethyl]-ammonio propane sulfonate) (PNIPA-b-PSPP) have been studied in pure and saline (NaCl) aqueous solutions by dynamic laser light scattering. The block copolymer [Mn(PNIPA) = 10 800 g/mol and Mn(PSPP) = 9700 g/mol] exhibits both upper (UCST about 9 °C) and lower (LCST about 32 °C) critical solution temperatures in pure water. The addition of NaCl enhances the solubility of the zwitterionic block, PSPP, leading to the disappearance of the UCST. On the other hand, the solubility of PNIPA in water decreases as NaCl is added. At 20 °C, the copolymer shows a bimodal size distribution through the NaCl concentration range of 0−0.93 M above a certain limiting polymer concentration. The slow and fast components of the diffusion coefficients of the polymer have been calculated. A gradual addition of salt turns the mutual interactions from zwitterionic attractions between PSPP blocks to hydrophobic attractions between PNIPA blocks. The formation of the aggregates and the aggregate sizes at T < UCST and T > LCST are influenced by polymer and salt concentrations. Below the UCST, the aggregates in saline polymer solutions are somewhat larger than those in pure polymer solutions. Above LCST, the aggregate size is determined by the salt concentration.