Properties of Aqueous Solutions and Gels of Poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide)-g-poly(acrylic acid)

Thermosensitive Poloxamer-graft-Carboxymethyl Pullulan: A Potential Injectable Hydrogel for Drug Delivery

A thermosensitive copolymer composed of amphiphilic triblock copolymer, poloxamer 407, grafted on hydrophilic pullulan with pendant carboxymethyl groups (CMP) was prepared and characterized. The structure of the new copolymer was assessed by Fourier transform infrared (FT-IR) and ¹H nuclear magnetic resonance (¹H NMR) spectroscopy. The content of the poloxamer in the grafted copolymer was 83.8% (w/w). The effect of the copolymer concentration on the gelation behavior was analyzed by the vertical method and rheological tests; the gel phase of the copolymer occurred at a lower concentration (11%, w/v) as compared with poloxamer (18%, w/v). The starting gelation time under the simulated physiological conditions (phosphate buffer with a pH of 7.4, at 37 °C) was sensitive on the rest temperature before the test, this being 990 s and 280 s after 24 h rest at 4 °C and 20 °C, respectively. The rheological tests evidenced a high elasticity and excellent ability of the copolymer to recover the initial structure after the removal of the applied force or external stimuli. Moreover, the hydrogel has proved a sustained release of amoxicillin (taken as a model drug) over 168 h. Taken together, the results clearly indicate that this copolymer can be used as an injectable hydrogel.

Formulation and evaluation of thermosensitive flurbiprofen in situ nano gel for the ocular delivery

The contemporary research implicates the formulation and evaluation of a thermosensitive in situ nano gelling method to improve solubility and ocular residence time of flurbiprofen. This study was carried out in two phases. In the first phase, an insolubility drug has been formulated in the form of a nanoparticulate system and evaluated for its characteristics. The nanoparticles obtained demonstrated an average size array of 150 to 250 nm in diameter, up to 79.35% encapsulation efficiency, and up to 93.42% drug release throughout 2 h. In the second phase, nanoparticulate systems were dispersed in aqueous solutions of Pluronic F 127 (14%) and various concentrations of Carbopol 934 in combination to form an in situ nano gel. The prepared in situ gel was investigated for its physicochemical properties like pH, flowability, sol-gel transition temperature, gelling capacity, and rheological properties. Carbopol 934 did not significantly affect sol-gel transition temperature in optimized concentration (<0.3%) but altered gelling capacity, pH, and transparency of the formulations. In vivo resident time and eye irritation test was evaluated in the rabbit eye. In optimized in situ gelling formulation (NIGF3), approximately 95% of in vitro drug release was observed after 6 h. NIGF3 increased precorneal residence time and high concentration in aqueous humor when paralleled to flurbiprofen eye drops. Greater concentration of drug in aqueous humor was due to its improved saturation solubility of the drug, and amplified residence time was attributed to the formation of gel matrix-embedded nanoparticles. This demonstrated that in situ nano gels (NIGF3) comprehending aqueous solutions of 0.3% w/v concentrations of Carbopol 934 with Pluronic F 127 may ominously persist the residence time and mend bioavailability of a water-insoluble drug.

Thermoreversible and Self-Protective Sol-Gel Transition Electrolytes for All-Printed Transferable Microsupercapacitors as Safer Micro-Energy Storage Devices

The safety issue caused by thermal runaway poses a huge threat toward the lifespan and application of high-density electrochemical energy storage devices, especially in the field of micro-energy, such as microsupercapacitors (MSCs). The heat accumulation is difficult to be eliminated, considering the narrow space inside integrated electronic devices attached to the MSC group. Active thermal management is of paramount importance to ensure the normal operation of electronic devices. However, existing one-time thermal protection strategies cannot fully meet current requirements. Herein, we report a promising thermoreversible temperature-responsive electrolyte system, which can shut down the current flow before thermal runaway occurs, thanks to the sol-gel transition of Pluronic [poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide)]-based graft copolymer solution. As the temperature rises to 80 °C, the self-protective electrolyte will change from the sol state to gel state. Meanwhile, the internal resistance increases and ionic conductivity decreases gradually as a result of the gelation of the sol electrolyte. The capacity of the energy storage device using the self-protective electrolyte is reduced by about 95%, and the ionic conductivity remains at only 1% at 80 °C compared with the initial value at room temperature, and it can be restored after cooling down. During 20 heating/cooling cycles, the electrochemical performance is substantially stable, demonstrating a potential approach to achieve repeatability and self-protection for micro-energy storage devices according to temperature changes. In addition, we integrated the as-prepared self-protective electrolyte into MSCs via three-dimensional printing technology to design an all-printed transferable micro-energy storage device with the dynamic reversible self-protection behavior, and the thermo-switchable protection mechanism under series and parallel conditions were studied under appropriate temperature window (25-80 °C). The strategy disclosed herein is expected to provide new insights into the new-generation smart MSCs for their wide applications in diverse fields such as microelectronics and wearable devices.

pH-Controlled Electrochemical Deposition of Polyelectrolyte Complex Films

Polyelectrolyte complex (PEC) films made from oppositely charged polymer chains have applications as drug-delivery vehicles, separation membranes, and biocompatible coatings. Conventional layer-by-layer techniques for polyelectrolyte coatings are low-throughput and multistep processes that are quite slow for building films on the order of micrometers. In this work, PEC films are electrochemically deposited using a rapid one-pot method, yielding thick (1 μm) films within short experimental time scales (5 min). This rapid electrodeposition is achieved by exploiting the reduction of hydrogen peroxide at mild electrode potentials that avoid water electrolysis yet trigger the pH-responsive self-assembly of a PEC film composed of poly(acrylic) acid and poly(allylamine) HCl. In situ rheology using an electrochemical quartz crystal microbalance quantified the shear modulus-density product of the deposited layer to be on the order of 10⁷ Pa g/cm³ at a frequency of 15 MHz, with a viscoelastic phase angle of approximately 50°. This electrodeposition scheme furthers the development of PEC coatings for more high-throughput applications, where a fast and efficient single-step approach would be desirable for obtaining coatings.

Cross-linked Pluronic-g-Polyacrylic acid microgel system for the controlled release of doxorubicin in pharmaceutical formulations

The binding of doxorubicin (DOX) to cross-linked Pluronic F127-g-PAA-EGDMA and L92-g-PAA-EGDMA microgels at different alpha (α) and salt concentrations was investigated using isothermal titration calorimetric (ITC), optical and scanning electron microscopic techniques (SEM). We seek to elucidate the mechanisms of interaction and the release of DOX from cross-linked microgels composed of Pluronic and poly(acrylic acid). The ITC results indicated a high binding affinity of DOX to the microgel, which is a function of salt concentrations due to the impact of electrostatic shielding on the DOX-binding process. Applying the polyelectrolyte theory allows the decoupling of the Gibbs free energy of binding that describes the role of non-electrostatic interaction of DOX and the microgel. The presence of DOX within the microgel resulted in the collapse of the microgel due to charge shielding, π-π interactions and self-association of polymer-bound DOX molecules. The diffusion of DOX through the microgel is controlled by the dissociation of COO^-/DOX⁺ coupling pairs.

Strategies to Maximize the Potential of Marine Biomaterials as a Platform for Cell Therapy

Marine biopolymers have been explored as a promising cell therapy system for efficient cell delivery and tissue engineering. However, the marine biomaterial-based systems themselves have exhibited limited performance in terms of maintenance of cell viability and functions, promotion of cell proliferation and differentiation as well as cell delivery efficiency. Thus, numerous novel strategies have been devised to improve cell therapy outcomes. The strategies include optimization of physical and biochemical properties, provision of stimuli-responsive functions, and design of platforms for efficient cell delivery and tissue engineering. These approaches have demonstrated substantial improvement of therapeutic outcomes in a variety of research settings. In this review, therefore, research progress made with marine biomaterials as a platform for cell therapy is reported along with current research directions to further advance cell therapies as a tool to cure incurable diseases.

Dual stimuli-responsive coating designed through layer-by-layer assembly of PAA-b-PNIPAM block copolymers for the control of protein adsorption

In this paper, we describe the successful construction, characteristics and interaction with proteins of stimuli-responsive thin nanostructured films prepared by layer-by-layer (LbL) sequential assembly of PNIPAM-containing polyelectrolytes and PAH. PAA-b-PNIPAM block copolymers were synthesized in order to benefit from (i) the ionizable properties of PAA, to be involved in the LbL assembly, and (ii) the sensitivity of PNIPAM to temperature stimulus. The impact of parameters related to the structure and size of the macromolecules (their molecular weight and the relative degree of polymerization of PAA and PNIPAM), and the interaction with proteins under physico-chemical stimuli, such as pH and temperature, are carefully investigated. The incorporation of PAA-b-PNIPAM into multilayered films is shown to be successful whatever the block copolymer used, resulting in slightly thicker films than the corresponding (PAA/PAH)n film. Importantly, the protein adsorption studies demonstrate that it is possible to alter the adsorption behavior of proteins on (PAA-b-PNIPAM/PAH)n surfaces by varying the temperature and/or the pH of the medium, which seems to be intimately related to two key factors: (i) the ability of PNIPAM units to undergo conformational changes and (ii) the structural changes of the film made of weak polyelectrolytes. The simplicity of construction of these PNIPAM block copolymer-based LbL coatings on a large range of substrates, combined with their highly tunable features, make them ideal candidates to be employed for various biomedical applications requiring the control of protein adsorption.

Spray-On Polyaniline/Poly(acrylic acid) Electrodes with Enhanced Electrochemical Stability

Polyaniline (PANI)-based electrodes are promising candidates for energy storage, but their cycle life remains poor. Recent work suggests that secondary interactions may enhance polyaniline's electrochemical stability and cycle life, but evidence to date is not conclusive. Here, we investigate spray-assisted layer-by-layer assemblies containing polyaniline nanofibers (PANI NFs) or conventional PANI and poly(acrylic acid) (PAA), which provides hydrogen bonding and electrostatic interactions. This spray-on approach may be suitable for the deposition of PANI onto a variety of surfaces. The effects of PANI type, PAA pH, and PAA molecular weight on the growth behavior, conductivity, and electrochemical performance are examined. It is shown that LbL films with PANI NFs, higher molecular weight PAA, and lower PAA pH yield the thickest films, whereas the thinnest films come from conventional PANI assembled under similar conditions. Electron microscopy imaging and density measurements show that LbL films containing PANI NFs are very porous, whereas those containing conventional PANI are very dense (0.28 vs 1.33 g/cm(3), respectively). The difference in density dramatically affects the electrochemical properties in terms of capacity and long-term cycling behavior. Upon extended cycling, PANI NFs alone rapidly lose their electrochemical activity. On the other hand, PANI NF-based LbL films exhibited somewhat enhanced stability, and PANI-based LbL films were exceptionally stable, maintaining 94.7% of their capacity after 1000 cycles when cycled up to 4.2 V vs Li/Li(+). These results show that secondary interactions from PAA enhance stability, as does the selection of PANI type and the electrode's density.

Near-Infrared Squaraine Dye Encapsulated Micelles for in Vivo Fluorescence and Photoacoustic Bimodal Imaging

Combined near-infrared (NIR) fluorescence and photoacoustic imaging techniques present promising capabilities for noninvasive visualization of biological structures. Development of bimodal noninvasive optical imaging approaches by combining NIR fluorescence and photoacoustic tomography demands suitable NIR-active exogenous contrast agents. If the aggregation and photobleaching are prevented, squaraine dyes are ideal candidates for fluorescence and photoacoustic imaging. Herein, we report rational selection, preparation, and micelle encapsulation of an NIR-absorbing squaraine dye (D1) for in vivo fluorescence and photoacoustic bimodal imaging. D1 was encapsulated inside micelles constructed from a biocompatible nonionic surfactant (Pluoronic F-127) to obtain D1-encapsulated micelles (D1(micelle)) in aqueous conditions. The micelle encapsulation retains both the photophysical features and chemical stability of D1. D1(micelle) exhibits high photostability and low cytotoxicity in biological conditions. Unique properties of D1(micelle) in the NIR window of 800-900 nm enable the development of a squaraine-based exogenous contrast agent for fluorescence and photoacoustic bimodal imaging above 820 nm. In vivo imaging using D1(micelle), as demonstrated by fluorescence and photoacoustic tomography experiments in live mice, shows contrast-enhanced deep tissue imaging capability. The usage of D1(micelle) proven by preclinical experiments in rodents reveals its excellent applicability for NIR fluorescence and photoacoustic bimodal imaging.

Electrospinning polyelectrolyte complexes: pH-responsive fibers

Fibers were electrospun from a solution comprised of oppositely charged polyelectrolytes, in efforts to achieve highly confined macromolecular packaging. A stoichiometric ratio of poly(allylamine hydrochloride) and poly(acrylic acid) solution was mixed in an ethanol-water co-solvent. Differential scanning calorimetry (DSC) analysis of electrospun fibers demonstrated no indication of glass transition, Tg. Infrared spectroscopy (FTIR) analysis of the fibers as a function of temperature, demonstrated an amidation process at lower temperature compared to cast film. Polarized FTIR indicated a preference of the functional groups to be perpendicular to the fiber axis. These results imply formation of mixed phase fibers with enhanced conditions for intermolecular interactions, due to the highly aligned and confined assembly of the macromolecules. The tunable intermolecular interactions between the functional groups of the polyelectrolytes, impact pH-driven, reversible swelling-deswelling of the fibers. The degree of ionization of PAA at pH 5.5 and pH 1.8 varied from 85% to 18%, correspondingly, causing transformation of ionic interactions to hydrogen bonding between the functional groups. The chemical change led to a massive water diffusion of 500% by weight and to a marked increase of 400% in fiber diameter, at a rate of 0.50 μm s(-1). These results allow for manipulation and tailoring of key fiber properties for tissue engineering, membranes, and artificial muscle applications.

Polymeric micelles in mucosal drug delivery: Challenges towards clinical translation

Polymeric micelles are nanostructures formed by the self-aggregation of copolymeric amphiphiles above the critical micellar concentration. Due to the flexibility to tailor different molecular features, they have been exploited to encapsulate motley poorly-water soluble therapeutic agents. Moreover, the possibility to combine different amphiphiles in one single aggregate and produce mixed micelles that capitalize on the features of the different components substantially expands the therapeutic potential of these nanocarriers. Despite their proven versatility, polymeric micelles remain elusive to the market and only a few products are currently undergoing advanced clinical trials or reached clinical application, all of them for the therapy of different types of cancer and administration by the intravenous route. At the same time, they emerge as a nanotechnology platform with great potential for non-parenteral mucosal administration. However, for this, the interaction of polymeric micelles with mucus needs to be strengthened. The present review describes the different attempts to develop mucoadhesive polymeric micelles and discusses the challenges faced in the near future for a successful bench-to-bedside translation.

Scaling properties of the shear modulus of polyelectrolyte complex coacervates: a time-pH superposition principle

A novel time-pH superposition principle describes the complex shear moduli in polyelectrolyte complex coacervates.

Thermoresponsive polymers: insights into decisive hydrogel characteristics, mechanisms of gelation, and promising biomedical applications

Thermally induced gelling systems have gained enormous attention over the last decade. They consist of hydrophilic homopolymers or block copolymers in water that present a sol at room temperature and form a gel after administration into the body. This article reviews the main types of thermoresponsive polymers, with special focus on decisive hydrogel characteristics, mechanisms of gelation, and biocompatibility. Promising biomedical applications are described with a focus on injectable formulations, which include solubilization of small hydrophobic drugs, controlled release, delivery of labile biopharmaceutics, such as proteins and genes, cell encapsulation, and tissue regeneration. Furthermore, combinations of thermoresponsive hydrogels and various nanocarriers as promising systems for sustained drug delivery are discussed through selected examples from the literature. Finally, there is a brief overview of current progress in nano-sized systems incorporating thermoresponsive properties.

Non-invasive tumor detection in small animals using novel functional Pluronic nanomicelles conjugated with anti-mesothelin antibody

In this study QDs were encapsulated in carboxylated PluronicF127 (F127COOH) triblock polymeric micelles and conjugated with anti-mesothelin antibody for the purpose of alleviating potential toxicity, enhancing the stability and improving targeting efficiency of CdTe/ZnS quantum dots (QDs) in tumors. The amphiphilic triblock polymer of F127COOH contains hydrophilic carboxylated poly(ethylene oxide) (PEO) and hydrophobic poly(propylene oxide) (PPO) units. After encapsulating QDs into carboxylated F127 (F127COOH-QD) micelles, the particles were conjugated with anti-mesothelin antibodies to allow targeting of cancerous areas. The size of the monodispersed spherical QD-containing micelles was determined to be ∼120 nm by dynamic light scattering (DLS). The critical micelle concentration (CMC) was estimated to be 4.7 × 10(-7) M. In an in vitro study, the anti-methoselin antibody conjugated F127COOH (Me-F127COOH-QD) nanomicelles showed negligible cytotoxicity to pancreatic cancer cells (Panc-1). Confocal microscopy demonstrated that the Me-F127COOH-QD nanomicelles were taken up more efficiently by Panc-1 cells, due to antibody mediated targeting. An in vivo imaging study showed that Me-F127COOH-QD nanomicelles accumulated at the pancreatic tumor site 15 min after intravenous injection. In addition, the low in vivo toxicity of the nanomicellar formulation was evaluated by pathological assays. These results suggest that anti-mesothein antibody conjugated carboxylated F127 nanomicelles may serve as a promising nanoscale platform for early human pancreatic cancer detection and targeted drug delivery.

Copolymer hydrogels of acrylic acid and a nonionic surfmer: pH-induced switching of transparency and volume and improved mechanical stability

Copolymer hydrogels were prepared from an aqueous micellar solution of the nonionic surfactant monomer (surfmer) ω-methoxy poly(ethylene oxide)40undecyl-α-methacrylate (PEO-R-MA-40) and acrylic acid (AA) in a one-step reaction using γ-irradiation. The hydrogels were transparent if the polymerization was carried out at pH ≥ 4, whereas turbid gels were obtained if the polymerization was carried out at lower pH. Exposure of the turbid gels to an aqueous solution of pH 11 led to swelling and clearing, whereas subsequent exposure to pH 1 had the reverse effect. Clear gels prepared at pH 4 became turbid, if exposed to an aqueous solution of lower pH and became clear again if reswollen at higher pH. The pH at which clouding set in increased with the amount of surfmer copolymerized in the gel. Pure poly(acrylic acid) (P-AA) hydrogels did not show any changes in transparency if the pH was varied. The presence of surfmer led to more pronounced shrinking and swelling, especially if the gels were prepared at pH 4. The mechanical stability of P-AA and copolymer hydrogels was studied using elongational flow measurements. The presence of surfmer led to increased mechanical stability of the hydrogels. The increase originates from copolymerized micellar aggregates acting as additional, stable cross-linking units in the gel. The true stress at break of copolymer hydrogels prepared at pH 2.4 (or 4) was 5.5 (or 3.4) times larger than for surfmer-free P-AA gels. Possible origins for the higher stability such as complex formation between P-AA and oxyethylene segments of copolymerized PEO-R-MA-40 are discussed.

Layer-by-layer assembly of salt-containing polyelectrolyte complexes for the fabrication of dewetting-induced porous coatings

The layer-by-layer (LbL) assembly of salt-containing nonstoichiometric polyelectrolyte complexes (PECs) with oppositely charged uncomplexed polyelectrolyte for the fabrication of dewetting-induced porous polymeric films has been systematically investigated. Salt-containing poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) complexes (noted as PAH-PAA) with a molar excess of PAH were LbL assembled with polyanion poly(sodium 4-styrenesulfonate) (PSS) to produce PSS/PAH-PAA films. The structure of the PAH-PAA complexes is dependent on the concentration of NaCl added to their aqueous dispersions, which can be used to tailor the structure of the LbL-assembled PSS/PAH-PAA films. Porous PSS/PAH-PAA films are fabricated when salt-containing PAH-PAA complexes with a large amount of added NaCl are used for LbL assembly with PSS. In-situ and ex-situ atomic force microscopy measurements disclose that the dewetting process composed of pore nucleation and pore growth steps leads to the formation of pores in the LbL-assembled PSS/PAH-PAA films. The present study provides a facile way to fabricate porous polymeric films by dewetting LbL-assembled polymeric films comprising salt-containing PECs.

Controlled Release Camptothecin Tablets based on Pluronic and Poly(acrylic acid) Copolymer. Effect of Fabrication Technique on Drug Stability, Tablet Structure, and Release Mode

Poly(ethylene oxide)-b-poly(propylene oxide)-b-(polyethylene oxide)-g-poly(acrylic acid), a graft-comb copolymer of Pluronic 127 and poly(acrylic acid) (Pluronic-PAA), was explored as an excipient for tablet dosage form of camptothecin (CPT). The tablets were prepared by either direct compression of the drug-polymer physical blend, suspension in ethanol followed by evaporation, or compression after kneading and characterized with respect to their physical structures, drug stability, and release behavior. Porosity and water uptake rate were strongly dependent on the fabrication procedure, ranking in the order: direct compression of physical blend > compression after suspension/evaporation in ethanol > compression after kneading. Tablets prepared by compression of physical blends swelled in water with a rapid surface gel layer formation that impeded swelling and disintegration of the tablets core. These tablets were able to sustain the CPT release for a period of time longer than those observed with the tablets made by either suspension/evaporation or kneading, which disintegrated within a few minutes. Despite the tablet disintegration, the CPT release was impeded for at least 6 hr, which was attributed to the ability of the Pluronic-PAA copolymers to form micellar aggregates at the hydrated surface of the particles. Physical mixing did not alter the fraction of CPT being in the pharmaceutically active lactone form, whilst the preparation of the tablets by the other two methods caused a significant reduction in the lactone form content. Tablets prepared from the physical blends demonstrated CPT release rates increasing with the pH due to the PAA ionization leading to the increase in the rate and extent of the tablet swelling. The results obtained demonstrate the potential of the Pluronic-PAA copolymers for the oral administration of chemotherapeutic agents.

Polymeric micelles in oral chemotherapy

Oral administration of anticancer agents is preferred by patients for its convenience and potential for use in outpatient and palliative setting. In addition, oral administration facilitates a prolonged exposure to the cytotoxic agents. Enhancement of bioavailability of emerging cytotoxic agents is a pre-requisite for successful development of oral modes of cancer treatment. Over the last decade, our studies have focused specifically on the utilization of large (MW>10(5)) and non-degradable polymers in oral chemotherapy. A family of block-graft copolymers of the poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) Pluronic(R) polyethers and poly(acrylic acid) (PAA) bound by carbon-carbon bonds emerged, wherein both polymeric components are generally recognized as safe. Animal studies with Pluronic-PAA copolymers demonstrated that these molecules are excreted when administered orally and do not absorb into the systemic circulation. The Pluronic-PAA copolymers are surface-active and self-assemble, at physiological pH, into intra- and intermolecular micelles with hydrophobic cores of dehydrated PPO and multilayered coronas of hydrophilic PEO and partially ionized PAA segments. These micelles efficiently solubilize hydrophobic drugs such as paclitaxel and steroids and protect molecules such as camptothecins from the hydrolytic reactions. High surface activity of the Pluronic-PAA copolymers in water results in interactions with cell membranes and suppression of the membrane pumps such as P-glycoprotein. The ionizable carboxyls in the micellar corona facilitate mucoadhesion that enhances the residence time of the micelles and solubilized drugs in the gastrointestinal tract. Large payloads of the Pluronic-PAA micelles with weakly basic and water-soluble drugs such as doxorubicin and its analogs, mitomycin C, mitoxantrone, fluorouracil, and cyclophosphamide are achieved through electrostatic interactions with the micellar corona. Mechanical and physical properties of the Pluronic-PAA powders, blends, and micelles allow for formulation procedures where an active is simply dispersed into an aqueous Pluronic-PAA micellar formulation followed by optional lyophilization and processing into a ready dosage form. We review a number of in vivo and in vitro experiments demonstrating that that the oral administration of the cytotoxics formulated with the Pluronic-PAA copolymer micelles results in enhanced drug bioavailability.

Pluronic F127-g-poly(acrylic acid) copolymers as in situ gelling vehicle for ophthalmic drug delivery system

To prolong the precorneal resident time and improve ocular bioavailability of the drug, Pluronic F127-g-poly(acrylic acid) copolymers were studied as in situ gelling vehicle for ophthalmic drug delivery system. The rheological properties and in vitro drug release of Pluronic-g-PAA copolymer gels were investigated. The rheogram and in vitro drug release studies indicated that the drug release rates decreased as acrylic acid/Pluronic molar ratio and copolymer solution concentration increased. But the drug concentration had no obvious effect on drug release. The release rates of the drug from such copolymer gels were mainly dependent on the gel dissolution. In vivo resident experiments showed the drug resident time and the total resident amount in rabbit's conjunctiveal sac increased by 5.0 and 2.6 folds for in situ gel, compared with eye drops. The decreased loss angle at body temperature and prolonged precorneal resident time also indicated that the copolymer gels had bioadhesive properties. These in vivo experimental results, along with the rheological properties and in vitro drug release studies, demonstrated that in situ gels containing Pluronic-g-PAA copolymer may significantly prolong the drug resident time and thus improve bioavailability. Pluronic-g-PAA copolymer can be a promising in situ gelling vehicle for ophthalmic drug delivery system.

Fabrication of ultrathin polyelectrolyte fibers and their controlled release properties

Ultrathin fibers comprising 2-weak polyelectrolytes, poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) were fabricated using the electrospinning technique. Methylene blue (MB) was used as a model drug to evaluate the potential application of the fibers for drug delivery. The release of MB was controlled in a nonbuffered medium by changing the pH of the solution. The sustained release of MB in a phosphate buffered saline (PBS) solution was achieved by constructing perfluorosilane networks on the fiber surfaces as capping layers. Temperature controlled release of MB was obtained by depositing temperature sensitive PAA/poly(N-isopropylacrylamide) (PNIPAAM) multilayers onto the fiber surfaces. The controlled release of drugs from electrospun fibers have potential applications as drug carriers in biomedical science.

Synthesis and aggregation behavior of pluronic F87/poly(acrylic acid) block copolymer in the presence of doxorubicin

Poly(acrylic acid) (PAA) was polymerized on both termini of Pluronic F87 copolymer using the atom transfer radical polymerization technique to produce a novel block copolymer, PAA-b-F87-b-PAA (F87PAA). The loading of a cationic anticancer drug, doxorubicin (DOX), to F87PAA at different pH values was investigated using isothermal titration calorimetry (ITC), laser light scattering techniques, and UV-vis spectroscopy. At pH of 4.3-7.1, the ITC profile exhibited a significant exothermic peak, which indicated that the drug loading is an enthalpically driven process. At a pH of 4.3, the enthalpy maximum was significantly reduced in the presence of 2 M urea, indicating the existence of hydrogen bonds between the DOX and F87PAA copolymer. At a pH of 7.1, the fraction of bound DOX was close to the stoichiometric proportion of 1:1 to the molar concentration of carboxyl groups in the copolymer, where the drug loading is governed by electrostatic and stacking interactions. The TEM image of the complex indicated the formation of large compound micelles induced by the binding of DOX to the PAA segments.

Block ionomer complexes as prospective nanocontainers for drug delivery

Nanosized environmentally responsive materials are of special interest for various applications, including drug delivery. Block ionomer complexes (BIC) composed of graft-comb copolymers of Pluronic and poly(acrylic acid) (Pluronic-PAA) and a model cationic surfactant, hexadecyltrimethylammonium bromide (HTAB), were synthesized by mixing the polymer and surfactant in aqueous media. According to TEM, the resulting BIC represented spherical particles of nanoscale size (50 to 100 nm). The stability of the BIC in the aqueous dispersion depended on the lengths of the hydrophilic poly(ethylene oxide) and hydrophobic poly(propylene oxide) chains in Pluronic molecules as well as on the surface charge of the resulting complexes. The latter was controlled by changing the ratio of the Pluronic-PAA and HTAB in the BIC and by changing the pH due to reversible ionization of the PAA chains. The acidification of the media below pH 6.0 resulted in the appearance of a strong positive charge on the BIC, which in the intracellular environment can trigger interaction of such BIC with the cell membranes. An efficient solubilization of a model hydrophobic molecule, Sudan III, and a drug, Etoposide, in such BIC was demonstrated with the loading capacities of about 6 to 15% by weight of the dispersed complex. Overall, these BIC wield a promise as environmentally responsive nanocarriers for pharmaceuticals.

Pluronic-g-poly(acrylic acid) copolymers as novel excipients for site specific, sustained release tablets

Potential utility of copolymers comprising Pluronic (PEO-PPO-PEO) surfactants covalently conjugated with poly(acrylic acid) (PAA) as excipients for sustained-release tablets was explored. Apparent particle density, particle size distribution, Carr index, thermal stability, and compression behavior of the Pluronic-PAA copolymers were characterized. Tablets prepared by direct compression of blends of Pluronic-PAA copolymers were evaluated on the basis of their thermomechanical profile, crushing strength, friability, and drug release properties. Small molecular weight drugs of aqueous solubility decreasing in the order theophylline>hydrochlorothiazide>nitrofurantoin were incorporated to the tablets. For comparison purposes, tablets were also prepared from PAA of Carbopol 71G (C71G), and mixtures of C71G and Pluronic F127, with each of the above three drugs. The Pluronic-PAA aggregates are stabilized by hydrophobic associations between poly(propylene oxide) (PPO) segments in aqueous solutions, and thus require higher ionization of the carboxylic groups to overcome the associations and swell. The swelling pattern of the Pluronic-PAA copolymers is more dramatically pH-dependent than that of Carbopol lacking any hydrophobic associations. The drug retention in and release from the Pluronic-PAA based tablets is profoundly pH-dependent and hence specific to the pH exceeding that of the pK(a)>5 of these copolymers. Theophylline- and hydrochlorotiazide-containing tablets made with Pluronic-PAA copolymers showed a reduced release rate under acidic conditions compared to the neutral or alkaline conditions, while the opposite pattern was observed with the Carbopol-based tablets due to the different pH-dependent swelling behavior of the polymers. Nitrofurantoin-containing tablets showed a remarkably low drug release rate owing to the strong hydrophobic character of nitrofurantoin and of its complexes with the copolymers. Integrity of the nitrofurantoin-containing tablets was maintained during the 24h release test. Zero-order kinetics of the cumulative release profile of all drugs under study was observed with the Pluronic-PAA as a tablet excipient. Adequate mechanical properties, the self-assembling behavior, and the pH-sensitiveness of the Pluronic-PAA copolymers make them promising excipients for tablets with preferential delivery into a neutral to alkaline pH environment.

In situ-forming hydrogels--review of temperature-sensitive systems

In the past few years, an increasing number of in situ-forming systems have been reported in the literature for various biomedical applications, including drug delivery, cell encapsulation, and tissue repair. There are several possible mechanisms that lead to in situ gel formation: solvent exchange, UV-irradiation, ionic cross-linkage, pH change, and temperature modulation. The thermosensitive approach can be advantageous for particular applications as it does not require organic solvents, co-polymerization agents, or an externally applied trigger for gelation. In the last 2 decades, several thermosensitive formulations have been proposed. This manuscript focuses on aqueous polymeric solutions that form implants in situ in response to temperature change, generally from ambient to body temperature. It mainly reviews the characterization and use of polysaccharides, N-isopropylacrylamide copolymers, poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) (poloxamer) and its copolymers, poly(ethylene oxide)/(D,L-lactic acid-co-glycolic acid) copolymers, and thermosensitive liposome-based systems.

Solubilization and stabilization of camptothecin in micellar solutions of pluronic-g-poly(acrylic acid) copolymers

The capability of a family of copolymers comprising Pluronic (PEO-PPO-PEO) surfactants covalently conjugated with poly(acrylic acid) (Pluronic-PAA) to enhance the aqueous solubility and stability of the lactone form of camptothecin (CPT) was studied. The unprotected lactone form of CPT, which possesses cytotoxic activity, is rapidly converted to the ring-opened carboxylate form under physiological conditions. Firstly, surfactant properties such as critical micellization concentration (CMC) of Pluronic-PAA copolymers were characterized. Then, the equilibrium solubility partitioning and hydrolysis of the lactone form of CPT in the presence of Pluronic-PAA in water and in human serum were analyzed. CPT solubility in polymer micellar solutions was ca. 3- to 4-fold higher than that in water at pH 5. The amount of CPT solubilized per PPO was considerably greater in the Pluronic-PAA solutions than in the parent Pluronic solution, which suggests that the drug is not only solubilized by the hydrophobic cores and also by the hydrophilic POE-PAA shells of the micelles. The equilibrium partition coefficient of the CPT lactone between Pluronic-PAA solutions and water exceeded (2-3) x 10(3). The complete solubilization of CPT and the absence of chemical interactions between CPT and Pluronic-PAA were confirmed by modulated temperature differential scanning calorimetry (MTDSC), infrared spectroscopy, and X-ray diffraction of films. The loading of CPT into the Pluronic-PAA micelles was able to prevent the hydrolysis of the lactone group of the drug for 2 h at pH 8 in water. When compared to the unprotected CPT, the kinetics of the CPT hydrolysis in human serum was about 10-fold slower in the Pluronic-PAA formulations.

Bioadhesive properties and rheology of polyether-modified poly(acrylic acid) hydrogels

Transient rheological properties and mucoadhesion of hydrogels composed of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO-PPO-PEO, or Pluronic) block copolymers and poly(acrylic acid) were explored. Nine Pluronic copolymers ranging in nominal molecular weight and PPO/PEO content were grafted to PAA through C-C bonds, with or without the use of divinyl cross-linker, ethylene glycol dimethacrylate (EGDMA). The hydrogel elasticity increased with the PPO content in the copolymers, as well as in the presence of EGDMA. Tensile tests were conducted to measure the fracture strength and the work of adhesion between the hydrogels and rat intestinal tissue. The fracture strength was proportional to the gel pseudoequilibrium modulus and depended on the nominal length of the PPO segments in the parent Pluronic copolymer. The work of mucoadhesion and gel cohesion declined with the loss angle measured in oscillatory shear experiments. The length of the PEO segments in Pluronic affected the work of adhesion. Applications of the Pluronic-PAA gels as vehicles in oral drug delivery are discussed. The longest Pluronic copolymers bonded to PAA resulted in copolymeric gels with strongest mucoadhesive properties.

Thermodynamics of temperature-sensitive polyether-modified poly(acrylic acid) microgels

The temperature-induced structural changes and thermodynamics of ionic microgels based on poly(acrylic acid) (PAA) networks bonded with poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO-PPO-PEO) (Pluronic) copolymers have been studied by small-angle neutron scattering (SANS), ultra-small-angle neutron scattering (USANS), differential scanning calorimetry (DSC), and equilibrium swelling techniques. Aggregation within microgels based on PAA and either the hydrophobic Pluronic L92 (average composition, EO8PO52EO8; PPO content, 80%) or the hydrophilic Pluronic F127 (average composition, EO99PO67EO99; PPO content, 30%) was studied and compared to that in the solutions of the parent Pluronic. The neutron scattering results indicate the formation of micelle-like aggregates within the F127-based microgel particles, while the L92-based microgels formed fractal structures of dense nanoparticles. The microgels exhibit thermodynamically favorable volume phase transitions within certain temperature ranges due to reversible aggregation of the PPO chains, which occurs because of hydrophobic associations. The values of the apparent standard enthalpy of aggregation in the microgel suspensions indicate aggregation of hydrophobic clusters that are more hydrophobic than the un-cross-linked PPO chains in the Pluronic. Differences in the PPO content in Pluronics L92 and F127 result in a higher hydrophobicity of the resulting L92-PAA-EGDMAmicrogels and a larger presence of hydrophobic, densely cross-linked clusters that aggregate into supramolecular structures rather than micelle-like aggregates such as those formed in the F127-PAA-EGDMA microgels.

Smart Polymeric Materials

Smart polymeric materials respond with a considerable change in their properties to small changes in their environment. Environmental stimuli include temperature, pH, chemicals, and light. "Smart" stimuli-sensitive materials can be either synthetic or natural. This review discusses the application of smart materials as tools to solve biological problems such as bioseparation, drug delivery, biosensor design, tissue engineering, protein folding, and microfluidics. The goal for these endeavors is to mimic the "smartness" of biological systems and ultimately moderate complex systems such as immune responses at desired levels. The versatility and untapped potential of smart polymeric materials makes them one of the most exciting interfaces of chemistry and biology.