Magnetic drug-targeting carrier encapsulated with thermosensitive smart polymer: core-shell nanoparticle carrier and drug release response

A novel magnetic drug-targeting carrier consisting of magnetic nanoparticles encapsulated with a smart polymer with characteristics of controlled drug release is described. The carrier is characterized by functionalized magnetite (Fe₃O₄) and conjugated therapeutic agent doxorubicin, which is encapsulated with the thermosensitive polymer, dextran-g-poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) [dextran-g-poly(NIPAAm-co-DMAAm)]. The surface of magnetite nanoparticles was functionalized by chemical bonding with 3-mercaptopropionic acid hydrazide (HSCH₂CH₂CONHNH₂) via Fe–S covalent bonds. The anticancer therapeutic drug, doxorubicin, was attached to the surface of the functionalized magnetic nanoparticles through an acid-labile hydrazone-bond, formed by the reaction of hydrazide group of HSCH₂CH₂CONHNH₂ with the carbonyl group of doxorubicin. The dextran-g-poly(NIPAAm-co-DMAAm) smart polymer exhibits a lower critical solution temperature (LCST) of 38 °C, which is representative of a phase transition behavior. This behavior allows for an on–off trigger mechanism. At an experimental temperature lower than LCST, the drug release was very low. However, at a temperature greater than LCST, there was an initially rapid drug release followed by a controlled released in the second stage, especially, in the mild acidic buffer solution of pH 5.3. The release of drug is envisaged to occur by the collapse of the encapsulated thermosensitive polymer and cleavage of the acid-labile hydrazone linkage. The proposed carrier is appropriately suitable for magnetic targeting drug delivery system with longer circulation time, reduced side effects and controlled drug release in response to the change in external temperature.     

Incorporation and in vitro release of doxorubicin in thermally sensitive micelles made from poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide)-b-poly(D,L-lactide-co-glycolide) with varying compositions

Thermally sensitive block copolymers, poly(N-isopropylacrylamide-co-N, N-dimethylacrylamide)-b-poly(d,l-lactide-co-glycolide) [P(NIPAAm-co-DMAAm)-b-poly(D,L-lactide-co-glycolide) (PLGA)] with different compositions and lengths of PLGA block are synthesized and utilized to fabricate micelles containing doxorubicin (DOX), a model anticancer drug, by a membrane dialysis method for targeted anticancer drug delivery. The critical association concentration (CAC) of the polymers ranges from 4.0 to 25.0 mg/L. An increased length of core-forming block PLGA leads to a decrease in the CAC. The clearly defined core-shell structure of micelles is proved by 1H-NMR analyses of the micelles in CDCl3 and D2O. The morphology of the micelles is analyzed by transmission electron microscopy, showing a spherical structure of both blank and drug-loaded micelles. The results obtained from dynamic light scattering show that the blank and drug-loaded micelles have an average size below 200 nm. The lower critical solution temperature (LCST) of the micelles made from the various polymers is similar, around 39 degrees C in phophate-buffered solution (PBS). The presence of serum in PBS does not alter the LCST significantly. The drug loading capacity varies depending on the PLGA block. The polymers are degradable, and the degradation of PLGA-based polymers is faster than that of poly(lactide) (PLA)-based polymer. The DOX-loaded micelles are stable in PBS containing serum at 37 degrees C but deform at 39.5 degrees C above the normal body temperature, thus triggering DOX release. It is revealed by confocal laser scanning microscopy that free DOX molecules enter cell nuclei very fast and DOX-loaded micelles accumulate mostly in cytoplasm after endocytosis. At a temperature above the LCST, more DOX molecules release from the micelles and enter the nuclei as compared to the temperature below the LCST. DOX-loaded micelles show greater cytotoxicity at a temperature above the LCST. The P(NIPAAm-co-DMAAm)-b-PLGA micelles developed may be a good carrier for anticancer drug delivery.     

Effect of molecular weight and polydispersity on kinetics of dissolution and release from ph/temperature-sensitive polymers

N-isopropylacrylamide (NIPAAm) polymers exhibit a lower critical solution temperature (LCST). Aqueous solutions of these polymers are soluble below their LCST and precipitate above their LCST. The LCST is dependent on pH for polymers with ionizable groups because of a change in hydrophilicity with ionization and electrostatic repulsion that cause a shift in the LCST. We have designed a novel polymeric delivery system that utilizes linear, pH/temperature-sensitive terpolymers of NIPAAm, butyl methacrylate (BMA) and acrylic acid (AA). This system allows the aqueous loading of drugs in polymeric beads with high loading efficiency while preserving the bioactivity of the protein drug. Furthermore, the unique properties of the pH/temperature-sensitive polymeric bead make it a potential system for oral drug delivery of peptide and protein drugs to different regions of the intestinal tract. This study aims at investigating the effect of polydispersity and molecular weight (MW) of terpolymers of poly(NIPAAm-co-BMA-co-AA) with feed mol ratio of NIPAAm/BMA/AA 85/5/10 on the polymer dissolution rate and on the release kinetics of a model protein, namely insulin. Varying the weight average MW (Mw) and polydispersity of the polymer modulated the polymer dissolution rate and the release rate of insulin from pH/temperature-sensitive polymeric beads. An increase in the polydispersity of the polymer through the addition of high MW polymer chains caused a decrease in the release rate of insulin and in the polymer dissolution rate. High MW polymer chains impose a certain degree of interaction between polymer chains due to chain entanglement. There is a limiting value of MW above which chain entanglement has no effect on drug release rate.     

Effect of molecular weight and polydispersity on kinetics of dissolution and release from pH/temperature-sensitive polymers

N-isopropylacrylamide (NIPAAm) polymers exhibit a lower critical solution temperature (LCST). Aqueous solutions of these polymers are soluble below their LCST and precipitate above their LCST. The LCST is dependent on pH for polymers with ionizable groups because of a change in hydrophilicity with ionization and electrostatic repulsion that cause a shift in the LCST. We have designed a novel polymeric delivery system that utilizes linear, pH/temperature-sensitive terpolymers of NIPAAm, butyl methacrylate (BMA) and acrylic acid (AA). This system allows the aqueous loading of drugs in polymeric beads with high loading efficiency while preserving the bioactivity of the protein drug. Furthermore, the unique properties of the pH/temperature-sensitive polymeric bead make it a potential system for oral drug delivery of peptide and protein drugs to different regions of the intestinal tract. This study aims at investigating the effect of polydispersity and molecular weight (MW) of terpolymers of poly(NIPAAm-co-BMA-co-AA) with feed mol ratio of NIPAAm/BMA/AA 85/5/ 10 on the polymer dissolution rate and on the release kinetics of a model protein, namely insulin. Varying the weight average MW (M_w) and polydispersity of the polymer modulated the polymer dissolution rate and the release rate of insulin from pH/temperature-sensitive polymeric beads. An increase in the polydispersity of the polymer through the addition of high MW polymer chains caused a decrease in the release rate of insulin and in the polymer dissolution rate. High MW polymer chains impose a certain degree of interaction between polymer chains due to chain entanglement. There is a limiting value of MW above which chain entanglement has no effect on drug release rate.     

Preparation and characterization of magnetic thermosensitive fluorouracil micelles

In this study, we synthesized P(NIPAM-co-DMAM)-b-PLA polymers with free radical polymerization and ring-opening addition polymerization, and immediately assembled ‘dextran magnetic layered double hydroxide fluorouracil’ (DMF) magnetic particles into the core of the amphiphilic polymer micelles with synchronous hydration and dialysis, to generate a magnetic thermosensitive fluorouracil drug delivery system. The basic properties of the micelle particles, such as the core–shell-type structure, size, and zeta potential, were studied with ¹H-NMR, FTIR, TEM, TGA, laser nanoparticle size analysis, and other characterization techniques. The thermosensitivity of the micelles was investigated by measuring parameters such as the lower critical solution temperature (LCST) and the relationship between the particle size variation and temperature. The drug release curves for the micelles at different temperatures were constructed with a dialysis method. The LCST of the triblock polymers was 42 °C. The particle sizes of the blank micelles and DMF-loaded micelles were 493.6 ± 1.8 nm and 464.9 ± 4.1 nm, respectively, at 25 °C. When the temperature was higher than LSCT, a contraction phase change in the micelle structure occurred, a significant characteristic of the core–shell-type structure, and reversible phase transition phenomena. The release behavior of the drug-loaded micelles showed obvious variations with temperature. Therefore, the magnetic thermosensitive fluorouracil drug delivery system has a good magnetic response and excellent temperature controlled release characteristics, so it can be used as a drug delivery system in magnetically and thermally targeted chemotherapy for tumors.     

Poly(N-isopropylacrylamide)-Based Polymers: Recent Overview for the Development of Temperature-Responsive Drug Delivery and Biomedical Applications

Temperature is a widely incorporated stimulus in pharmaceutical applications because of its efficiency as a therapeutic medium; thus, substantial evidence on temperature-responsive polymer applications is reported. Poly(N-isopropylacrylamide) (PNIPAAm) is a well-established, temperature-responsive polymer that exhibits a low critical solution temperature (LCST) at ≈ 32°C, which is close to physiological temperature. Hence, they are widely used in various pharmaceutical applications, such as drug delivery with nanocarriers and thermogels. Varying the LCST for different applications can be achieved by copolymerization with other hydrophobic or hydrophilic molecules, making it a favorable smart polymer. PNIPAAm is reported to enhance drug delivery by incorporation with nanocarriers and to facilitate prolonged drug delivery, thereby avoiding the burst release of drugs in temperature-responsive hydrogels. The application of PNIPAAm is not limited to drug delivery, and it is also applied in biomedical applications such as chromatography systems and cell culture applications, where its incorporation in cell culture media enhances cell production. The unique and versatile properties of PNIPAAm render it a promising smart polymer for various functional applications. Hence, this review focuses on the diverse applications of PNIPAAm.     

Synthesis and characterization of thermosensitive and pH-sensitive poly (N-isopropylacrylamide-acrylamide-vinylpyrrolidone) for use in controlled release of naltrexone

In this article N-isopropylacrylamide (NIPAAm)-acrylamide (AAm)-vinyl pyrrolidone (VP) terpolymers were prepared using free radical copolymerization method by varying feed ratios of monomers. The composition ratio and structure of polymer were determined by NMR and FTIR. The glass transition temperature was examined by DSC. The thermo-responsive behaviors of polymeric solutions were investigated by turbidimetry using UV-Visible spectroscopy. The sol-gel transition of the polymer solutions occurred reversibly within 1 min in response to the temperature. By alternating the monomer feed ratio, the synthesized terpolymers had their own distinctive lower critical solution temperature (LCST). In addition to the thermosensitivity, the terpolymers also showed a response to pH changes. The increase in ionic strength of the buffer solution with addition of salt lowered the LCST of the polymers. The ability to shift the phase transition temperature of the terpolymers provided excellent flexibility in tailoring transitions for specific uses. Swelling experiments were performed on the terpolymer disks in buffer solutions with different pH and ionic strength at varying temperature. We investigated naltrexone release as a model drug in phosphate buffer. Drug loading efficiency was varying from 8.75 to 55%. Gel composition, pH, and ionic concentration affected the drug loading. Finally in vitro drug release studies at 36-37 degrees C indicating 35-70% naltrexone release from terpolymers at the end of 30 days. In addition, these gels sustained naltrexone release for 30 days.     

Preparation of controlled release ophthalmic drops, for glaucoma therapy using thermosensitive poly-N-isopropylacrylamide.

In this study, controlled release ophthalmic agents for glaucoma therapy were developed based on the thermosensitivity of poly-N-isopropylacrylamide (PNIPAAm). The clear solution of PNIPAAm was known to undergo phase transition when the temperature was raised from the room temperature to about 32 degrees C. The drug was entrapped in the tangled polymer chains or encapsulated within the crosslinked polymer hydrogel at room temperature, and released progressively after topical application (i.e., at a higher temperature). Linear PNIPAAm and crosslinked PNIAAm nanoparticles containing epinephrine were prepared. The drug release rate and cytotoxicity were investigated in vitro. Ophthalmic formulations based on either linear PNIPAAm or the mixture of linear PNIPAAm and crosslinked PNIPAAm nanoparticles were administered to rabbits and the intraocular pressure (IOP)-lowering effect was evaluated. The decreased pressure response of the formulation based on linear PNIPAAm lasted six-fold longer than that of the conventional eye drop. Furthermore, for formulation based on the mixture of linear PNIPAAm and crosslinked nanoparticles, the pressure-lowering effect lasted eight times longer. These results suggest the use of thermosensitive polymer solutions or hydrogels is potential in controlled release antiglaucoma ophthalmic drugs.     

Preparation, properties and controlled release behaviors of pH-induced thermosensitive amphiphilic gels

Two pH-induced thermosensitive amphiphilic gels for controlled drug release were constructed with thermosensitive poly(N-isopropylacrylamide) (PNIPAm) and hydrophobic poly(ethyl acrylate) (PEA) by interpenetrating polymer network (IPN) technology. To obtain pH-induced thermosensitive functionality at physiological temperature, 5 mol % of acrylic acid (AAc) and N, N-dimethyl aminoethyl methacrylate (DMA) were incorporated into PNIPAm chain by their copolymerization. It is found that the IPN hydrogels show pH-induced thermosensitivity at physiological temperature. When the amphiphilic gels with IPN structure were immersed in water, the hydrophobic moieties formed by PEA have the potential to act as reservoirs for hydrophobic drugs, from which drug may be released slowly. Using drug daidzein (DAI) as a model molecule, controlled release behaviors of the IPNs were investigated. It is found that the presence of permanently hydrophobic PEA network can indeed slow the release rate of DAI and to some extent overcome disadvantageous burst effect of PNIPAm-based networks in hydration state. The release kinetics of DAI from the IPNs seems to follow pseudo-zero-order release character, regardless of the hydrogels in swollen or shrunken state.     

Possibility of active targeting to tumor by local hyperthermia with temperature-sensitive nanoparticles

Recently, the concept of drug delivery requires that the release of encapsulated drug be produced only at the diseased site with controllable rates. Given that thermosensitive hydrogels have been widely investigated for controlled delivery based on their phase transition, we speculate that nanoparticles with the novel polymers play a key role in tumor therapy respond to thermal activity. Therefore, we here hypothesize that enhanced delivery of therapeutics might be achieved by conjugation to thermosensitive polymers, in concert with targeted hyperthermia by precisely specifying the phase transition temperature of the thermosensitive polymer. By local hyperthermia at tumor site, a targeted drug delivery system could be obtained, exploiting both the temperature-sensitive and the site-specific behaviors. The proposition may provide a new strategy into the development of a novel drug delivery system for tumor therapy.     

Novel thermosensitive polymeric micelles for docetaxel delivery

Targeted delivery of antitumor drugs triggered by hyperthermia has significant advantages in clinical applications, since it is easy to implement and side effects are reduced. To release drugs site-specifically upon local heating often requires the drugs to be loaded into a thermosensitive polymer matrix with a low critical solution temperature (LCST) between 37 and 42 degrees C. However, the LCSTs of most thermosensitive materials were below 37 degrees C, which limits their application in clinic because they would precipitate once injected into human body and lost thermal targeting function. Herein, we prepared a novel thermosensitive copolymer (poly(N-isopropylacrylamide-co-acrylamide)-b-poly (DL-lactide)) that exhibits no obvious physical change up to 41 degrees C when heated. Docetaxel loaded micelles made of such thermosensitive polymer were prepared by dialysis method and the maximum loading content was found to be up to 27%. The physical properties, such as structure, morphology, and size distribution of the micelles with and without docetaxel were investigated by NMR, X-ray diffraction, dynamic light scattering, atomic force microscopy, etc. The efficacy of this drug delivery system was also evaluated by examining the proliferation inhibiting activity against different cell lines in vitro. After hyperthermia, the cytotoxicity of docetaxel-loaded micelles increased prominently. Our results demonstrated that this copolymer could be an ideal candidate for thermal targeted antitumor drug delivery.     

Magnetically Guided Release of Ciprofloxacin from Superparamagnetic Polymer Nanocomposites

Tailored with superparamagnetic properties the magnetic nanocomposites have been thoroughly investigated in recent past because of their potential applications in the fields of biomedicine and bioengineering such as protein detection, magnetic targeted drug carriers, bioseparation, magnetic resonance imaging contrast agents and hyperthermia. Magnetic drug targeting has come up as a safe and effective drug-delivery technology, i.e., with the least amount of magnetic particles a maximum of drug may be easily administered and transported to the site of choice. In the present work novel magnetic drug-targeting carriers consisting of magnetic nanoparticles encapsulated within a smart polymer matrix with potential of controlled drug release is described. To make such magnetic polymeric drug-delivery systems, both the magnetic nanoparticles and antibiotic drug (ciprofloxacin) were incorporated into the hydrogel. The controlled release process and release profiles were investigated as a function of experimental protocols such as percent loading of drug, chemical composition of the nanocomposite, pH of release media and strength of magnetic field on the release profiles. The structure, morphology and compositions of magnetic hydrogel nanocomposites were characterized by FT-IR, TEM, XRD and VSM techniques. It was found that magnetic nanocomposites were biocompatible and superparamagnetic in nature and could be used as a smart drug carrier for controlled and targeted drug delivery.     

Phase transition parameters of potential thermosensitive drug release systems based on polymers of N-alkylmethacrylamides

The phase separation and its thermohysteresis in dilute aqueous solutions of polymeric components of potential drug release systems (homopolymers and copolymers of N-isopropylacrylamide, N-isopropylmethacrylamide, N-propylmethacrylamide, N-sec-butylmethacrylamide, and N-(2-hydroxypropyl)methacrylamide) was studied, both on heating and cooling. Plots of light transmittance vs temperature were constructed and the parameters characterizing them were correlated with polymer structures. Qualitative information was obtained on the rate of formation of the concentrated phase on heating and its disappearance on cooling. Attention has been drawn to the improper identification of the cloud-point temperature, measured at an arbitrary concentration, with the lower critical solution temperature (LCST) as is frequently found in papers dealing with biomedical applications of thermosensitive polymers.     

Poly(vinyl alcohol) microspheres with pH- and thermosensitive properties as temperature-controlled drug delivery

One of the most important inconveniences of the pH- and temperature-sensitive hydrogels is the loss of thermosensitivity when relatively large amounts of a pH-sensitive monomer are co-polymerized with N-isopropylacrylamide (NIPAAm). In order to overcome this drawback, we propose here a method to prepare thermosensitive poly(vinyl alcohol) (PVA) microspheres with a higher content of carboxylic groups that preserve thermosensitive properties. Moreover, PVA possesses excellent mechanical properties, biocompatibility and non-toxicity. PVA microspheres were obtained by suspension cross-linking of an acidified aqueous solution of the polymer with glutaraldehyde. Poly(N-isopropylacrylamide-co-N-hydroxymethyl acrylamide) (poly(NIPAAm-co-HMAAm)), designed to have a lower critical solution temperature (LCST) corresponding to that of the human body, was grafted onto PVA microspheres in order to confer them with thermosensitivity. Then, the pH-sensitive functional groups (COOH) were introduced by reaction between the un-grafted OH groups of PVA and succinic anhydride. The pH- and temperature-sensitive PVA microspheres display a sharp volume transition under physiological conditions around the LCST of the linear polymer. The microspheres possess good drug-loading capacity without losing their thermosensitive properties. Under simulated physiological conditions, the release of drugs is controlled by temperature.     

Development of in situ thermosensitive drug vehicles for glaucoma therapy

The goal of this research was to design thermosensitive drug vehicles for glaucoma therapy. Thermosensitive ophthalmic drop was prepared by mixing linear poly(N-isopropylacrylamide-g-2-hydroxyethyl methacrylate) (PNIPAAm-g-PHEMA), PNIPAAm-g-PHEMA gel particles and antiglaucoma drug. This produced polymeric eyedrop containing the drug epinephrine was a clear solution at room temperature which became a soft film after contacting the surface of cornea. The drug entrapped within the tangled polymer chains was therefore released progressively after topical application. Evaluation of the drug release responded as a function of crosslinking density and PHEMA macromer contents. The in vivo studies indicated that the intraocular pressure (IOP)-lowering effect for a polymeric eyedrop lasted for 26 h, which is significantly better than the effect of traditional eyedrop (8 h). Hence our investigations successfully prove that the thermosensitive polymeric eyedrop with ability of controlled drug release exhibits a greater potential for glaucoma therapy.     

Poly(N-isopropylacrylamide-co-acrylamide) cross-linked thermoresponsive microspheres obtained from preformed polymers: Influence of the physico-chemical characteristics of drugs on their release profiles

Poly(N-isopropylacrylamide-co-acrylamide) copolymer was synthesized as an interesting thermoresponsive material possessing a phase transition temperature of around 36 degrees C in phosphate buffer, pH 7.4 (PB); the concentration was 10%, w/v. The copolymer maintains a sharp phase transition at a relatively high percentage of acrylamide. The lower critical solution temperature (LCST) of the copolymer is influenced by the concentration of copolymer solution in PB. The copolymer was transformed in thermoresponsive microspheres by chemical cross-linking of amide groups with glutaraldehyde. The key factors for the successful preparation of microspheres are the use of a concentrated polymer solution, a temperature (38 degrees C) that is high enough but lower than LCST, and a long reaction time (48h). The microspheres were characterized by optical and scanning electron microscopy, swelling/deswelling kinetics, swelling degree, and PB retention at different temperatures. Finally, the influence of hydrophilicity/hydrophobicity and the molecular weight of the drugs (propranolol, lidocaine, vitamin B(12)) on their release profile from thermoresponsive microspheres were examined. Above LCST the hydrogel matrix is in the dehydrated state and hydrophobic interactions between the hydrophobic drugs and the polymer occur, modulating the release rate of the drugs. For hydrophilic drugs, the release rate is modulated mainly by the steric interaction between the drug molecule and the matrix.     

Synthesis, characterization and controlled drug release of thermosensitive IPN-PNIPAAm hydrogels

A method was developed to prepare thermosensitive poly(N-isopropylacrylamide) (PNIPAAm) hydrogels with an interpenetrating polymer network (IPN) structure for the purpose of improving its mechanical properties, response rate to temperature and sustained release of drugs. Although the differential scanning calorimetry data exhibited similarly lower critical solution temperature (LCST) between IPN- and non-IPN-PNIPAAm hydrogels, an increase in the glass transition temperature (Tg) of the IPNs relative to the normal PNIPAAm hydrogel was observed. In addition, the mechanical properties of the IPNs were greatly improved when compared with the normal PNIPAAm hydrogel. The interior morphology of the IPN-PNIPAAm hydrogels was revealed by scanning electron microscopy (SEM); the IPN hydrogels showed a fibrillar-like porous network structure that normal PNIPAAm did not have. Furthermore, by measuring the temperature dependence of the swelling ratio and deswelling kinetics, these IPN hydrogels also exhibited improved intelligent characteristics (e.g., controllable faster response rate) that depended on the composition ratio of the two network components. From the applications viewpoint, the effects of a shrinking-reswelling cycle around the LCST on the properties of the IPN hydrogels were examined to determine if these properties would be stable for potential applications. Bovine serum albumin was chosen as the model protein for examining its release from the IPNs at different temperatures. The release data suggested that an improved controlled release could be achieved by the IPN-PNIPAAm hydrogels without losing their intelligent properties.     

Entrapment and release of drugs by a strict "on-off" mechanism in pullulan microspheres with pendant thermosensitive groups

Here, we report a new method to predict the appropriate size of drugs which can be entrapped in and released from a hydrogel with pendant thermosensitive units by a strict "on-off" mechanism. Moreover, the valve-type action of the thermosensitive arms has been investigated. Inverse size exclusion chromatography (ISEC) and environmental scanning electron microscopy (ESEM) have been used to characterize the extension and collapse of the pendant thermosensitive units, below and above the lower critical solution temperature (LCST) under physiological conditions, confirming the hypothesis postulated by the "arid" theoretical models. The functionalized pullulan (Pul) microspheres, here prepared, were coupled with thermoresponsive oligomers by reaction between the -NH? end-group of oligomers and chlorine present on Pul microspheres. The Pul microspheres with temperature sensitive moieties were packed in a glass column and the elution volume of standard molecule with well-known molecular weights (radius of gyration) was determined below and above the LCST. FITC-Dextran 4000 diffused through the pores of Pul microspheres with short thermosensitive arms (Mw = 1500 g/mol) both below and above the LCST of the thermosensitive units. In contrast, Pul microspheres with long thermosensitive arms (Mw = 3300 g/mol) allowed the diffusion of FITC-Dextran 4000 only above the LCST of the thermosensitive units. Indeed, the long thermosensitive arms are extended below the LCST and FITC-Dextran 4000 is completely excluded from the pores. The loading/release profile of this model molecule follows an "on-off" mechanism, confirming the results obtained by ISEC. ESEM was used as a new technique, taking images of the surface of the thermosensitive pullulan microspheres in their natural swollen state, with no prior specimen preparation, below and above the LCST. The low toxicity of pullulan microspheres observed below and above the LCST of thermosensitive units at high concentrations (10 mg/ml) recommends their potential use for controlled drug delivery applications.     

A pH and thermosensitive choline phosphate-based delivery platform targeted to the acidic tumor microenvironment

Solid tumors generally exhibit an acidic microenvironment which has been recognized as a potential route to distinguishing tumor from normal tissue for purposes of drug delivery or imaging. To this end we describe a pH and temperature sensitive polymeric adhesive that can be derivatized to carry drugs or other agents and can be tuned synthetically to bind to tumor cells at pH 6.8 but not at pH 7.4 at 37 °C. The adhesive is based on the universal reaction between membrane phosphatidyl choline (PC) molecules and polymers derivatized with multiple copies of the inverse motif, choline phosphate (CP). The polymer family we use is a linear copolymer of a CP terminated tetraethoxymethacrylate and dimethylaminoethyl (DMAE) methacrylate, the latter providing pH sensitivity. The copolymer exhibits a lower critical solution temperature (LCST) just below 37 °C when the DMAE is uncharged at pH 7.4 but the LCST does not occur when the group is charged at pH 6.8 due to the ionization hydrophilicity. At 37 °C the polymer binds strongly to mammalian cells at pH 6.8 but does not bind at pH 7.4, potentially targeting tumor cells existing in an acidic microenvironment. We show the binding is strong, reversible if the pH is raised and is followed rapidly by cellular uptake of the fluorescently labeled material. Drug delivery utilizing this dually responsive family of polymers should provide a basis for targeting tumor cells with minimal side reactions against untransformed counterparts.     

Self-assembled, fluorescent polymeric micelles of a graft copolymer containing carbazole for thermo-controlled drug delivery in vitro

A novel thermosensitive amphiphilic graft copolymer PNIPAAm-g-PCbzEA appending carbazole group was successfully designed and synthesized by the free radical copolymerization of N-isopropylacrylamide with hydrophobic precursor polymers of vinyl-functionalized poly(2-(N-carbazolyl)ethyl acrylate) (PCbzEA) in DMF. The PNIPAAm-g-PCbzEA copolymer was characterized by FTIR, (1)H NMR, GPC analysis, UV-vis spectroscopy and fluorescence spectroscopy. The TEM observation shows that the graft copolymer may self-assemble into polymeric micelles exhibiting a nanospheric morphology within a narrow size range of 30-60 nm in aqueous solution. From the (1)H NMR and FTIR analysis, the polymer micelles are composed of hydrophobic PCbzEA segments as the cores and the hydrophilic PNIPAAm segements as outer shells. The resulting micelles exhibited the temperature sensitivity with a lower critical solution temperature (LCST) of 31.5 degrees C and a critical micelle concentration (CMC) of 12.9 mg/L in water. In the study of drug release, an "on-off" drug release profile was found in response to stepwise temperature changes between 20 and 40 degrees C. The cytotoxicity assays for vero cells shows good biocompatibility of the graft copolymer in vitro.