Polyether-Modified Poly(acrylic acid): Synthesis and Applications

The Use of an Advanced Intelligent-Responsive Polymer for the Study of Dynamic Water-Carbon Dioxide Alternating Displacement

Addressing the issue of inadequate temperature tolerance in traditional polymers, in this study, we successfully executed a one-step synthesis of intelligent-responsive polymers which have excellent adaptability in water-gas alternating displacement scenarios. Utilizing the fatty acid method, we produced OANND from oleic acid (OA) and N,N-dimethyl-1,3-propanediamine (NND). Upon testing the average particle size in the aqueous solution both prior and subsequent to CO2 passage, it became evident that OANND assumes the form of a small-molecule particle in the aqueous phase, minimizing damage during formation. Notably, upon CO2 exposure, it promptly organizes into stable micelles with an average size of 88 nm and a relatively uniform particle distribution. This unique characteristic endows it with a rapid CO2 response mechanism and the ability to form a highly resilient gel. In the exploration of viscoelastic fluids, we observed the remarkable behavior of the AONND aqueous solution when CO2/N2 was introduced. This system displayed repeatable transitions between aqueous and gel states, with the highest viscosity peaking at approximately 3895 mPa·s, highlighting its viscosity reversibility and reusability properties. The rheological property results that we obtained indicate that an elongated micellar structure is present in the solution system, with the optimal concentration ratio for its formation determined as 0.8, which is the molar ratio of the OANND-NaOA system. In the sealing performance tests, a 1.0 wt% concentration of the gel system exhibited excellent injectability properties. At 80 °C, this gel effectively reduced the permeability of a sand-filled model to 94.5% of its initial value, effectively sealing potential leakage paths or gas fluxes. This remarkable ability to block leakage paths and reduce seepage capacity highlights the material's superior blocking effect and erosion resistance properties. Furthermore, even at a temperature of 90 °C and an injection pore volume (PV) of 3, this plugging system could reduce the permeability of a high-permeability sand-filled model to over 90% of its initial value.

Versatile Biodegradable Poly(acrylic acid)-Based Hydrogels Infiltrated in Porous Titanium Implants to Improve the Biofunctional Performance

This research work proposes a synergistic approach to improve implants' performance through the use of porous Ti substrates to reduce the mismatch between Young's modulus of Ti (around 110 GPa) and the cortical bone (20-25 GPa), and the application of a biodegradable, acrylic acid-based polymeric coating to reduce bacterial adhesion and proliferation, and to enhance osseointegration. First, porous commercially pure Ti substrates with different porosities and pore size distributions were fabricated by using space-holder techniques to obtain substrates with improved tribomechanical behavior. On the other hand, a new diacrylate cross-linker containing a reduction-sensitive disulfide bond was synthesized to prepare biodegradable poly(acrylic acid)-based hydrogels with 1, 2, and 4% cross-linker. Finally, after the required characterization, both strategies were implemented, and the combination of 4% cross-linked poly(acrylic acid)-based hydrogel infiltrated in 30 vol % porosity, 100-200 μm average pore size, was revealed as an outstanding choice for enhancing implant performance.

Development and Evaluation of pH-Responsive Pluronic F 127 Co-Poly- (Acrylic Acid) Biodegradable Nanogels for Topical Delivery of Terbinafine HCL

Research aimed to develop and evaluate biodegradable, pH-responsive chemically cross-linked Pluronic F127 co-poly- (acrylic acid) nanogels for dermal delivery of Terbinafine HCL (TBH) to increase its permeability and as a new approach to treat skin fungal infections. TBH-loaded nanogels were successfully synthesized from acrylic acid (AA) and Pluronic F127 by free-radical copolymerization technique using N,N′-methylene bisacrylamide (MBA) as crosslinker and ammonium persulphate (APS) as initiator. Prepared nanogels exhibited 93.51% drug entrapment efficiency (DEE), 45 nm particle size, pH-dependent swelling and release behavior. Nanogels were characterized using different physicochemical techniques. The ex-vivo skin retention studies through rat skin showed about 42.34% drug retention from nanogels while 1% Lamisil cream (marketed product) showed about 26.56% drug retention. Moreover, skin irritation studies showed that nanogels were not irritating. Nanogels showed improved in-vitro antifungal activity against Candida albicans compared to commercial product. In-vivo studies on rats infected with Candida albicans confirmed superiority of nanogels over 1% Lamisil for eradication of fungal infection. This confirms that TBH loaded in Pluronic F127 co-poly-(acrylic acid) nanogels provided greater targetibility and cure rates of poorly soluble TBH in animal model and hence nanogels could be a potential carrier for effective topical delivery of TBH for skin fungal infection treatment.

Design and Synthesis of Novel Podophyllotoxins Hybrids and the Effects of Different Functional Groups on Cytotoxicity

Development of novel anticancer therapeutic candidates is one of the key challenges in medicinal chemistry. Podophyllotoxin and its derivatives, as a potent cytotoxic agent, have been at the center of extensive chemical amendment and pharmacological investigation. Herein, a new series of podophyllotoxin-N-sulfonyl amidine hybrids (4a–4v, 5a–5f) were synthesized by a CuAAC/ring-opening procedure. All the synthesized podophyllotoxins derivatives were evaluated for in vitro cytotoxic activity against a panel of human lung (A-549) cancer cell lines. Different substituents’, or functional groups’ antiproliferative activities were discussed. The –CF₃ group performed best (IC₅₀: 1.65 μM) and exhibited more potent activity than etoposide. Furthermore, molecular docking and dynamics studies were also conducted for active compounds and the results were in good agreement with the observed IC₅₀ values.

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.

Podophyllotoxin: History, Recent Advances and Future Prospects

Podophyllotoxin, along with its various derivatives and congeners are widely recognized as broad-spectrum pharmacologically active compounds. Etoposide, for instance, is the frontline chemotherapeutic drug used against various cancers due to its superior anticancer activity. It has recently been redeveloped for the purpose of treating cytokine storm in COVID-19 patients. Podophyllotoxin and its naturally occurring congeners have low bioavailability and almost all these initially discovered compounds cause systemic toxicity and development of drug resistance. Moreover, the production of synthetic derivatives that could suffice for the clinical limitations of these naturally occurring compounds is not economically feasible. These challenges demanded continuous devotions towards improving the druggability of these drugs and continue to seek structure-optimization strategies. The discovery of renewable sources including microbial origin for podophyllotoxin is another possible approach. This review focuses on the exigency of innovation and research required in the global R&D and pharmaceutical industry for podophyllotoxin and related compounds based on recent scientific findings and market predictions.

Podophyllotoxin-polyacrylic acid conjugate micelles: improved anticancer efficacy against multidrug-resistant breast cancer

BACKGROUND

Podophyllotoxin (PPT) is a naturally occurring compound obtained from the roots of Podophyllum species, indicated for a variety of malignant tumors such as breast, lung, and liver tumors. This toxic polyphenol (PPT) exhibited significant activity against P-glycoprotein (P-gp) mediated multidrug-resistant (MDR) cancer cells. However, extremely poor water solubility, a narrow therapeutic window, and high toxicity have greatly restricted the clinical uses of PPT. Therefore, the present research was aimed to synthesize the water-soluble ester prodrug of PPT with polyacrylic acid (PAA), a water-soluble polymer by Steglich esterification reaction, and to screen it for assay, solubility, in vitro hemolysis, in vitro release, and in vitro anticancer activity.

RESULTS

The Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy results revealed the successful synthesis of podophyllotoxin-polyacrylic acid conjugate (PPC). The assay and saturation solubility of the prodrug is found to be 64.01 ± 4.5% and 1.39 ± 0.05 mg/mL (PPT equivalent) respectively. The PPC showed CMC (critical micelle concentration) of 0.430 mg/mL in distilled water at room temperature. The PPC micelles showed a mean particle size of 215 ± 11 nm with polydispersity index (PDI) of 0.193 ± 0.006. Further, the transmission electron microscope (TEM) results confirmed the self-assembling character of PPC into micelles. The PPC caused significantly less hemolysis (18.6 ± 2.9%) than plain PPT solution. Also, it demonstrated significantly (p < 0.01) higher in vitro cytotoxicity against both sensitive as well as resistance human breast cancer cells (MCF-7 and MDA MB-231) after 48 h of treatment.

CONCLUSION

The obtained study results clearly revealed the notable in vitro anticancer activity of PPT following its esterification with PAA. However, further in vivo studies are needed to ascertain its efficacy against a variety of cancers.

The Thermoviscosifying Behavior of Water-Soluble Polymer Based on Graft Polymerization of Pluronic F127 with Acrylamide and 2-Acrylamido-2-methylpropane Sulfonic Acid Sodium Salt

A new concept of thermoviscosifying polymers is proposed to address the problems about decreasing viscosity of polymer solution under high temperatures. However, existing thermoviscosifying polymers have complicated synthesis processes and high costs, and both of them restrict the wide practical applications of thermoviscosifying polymers. Although polyethers have the characteristics of thermal gelatinization, they just display thermoviscosifying behaviors only under extremely high concentrations (>15 wt %). Therefore, the graft copolymerization of the commercialized Pluronic F127 (PEO₁₀₀-PPO₆₅-PEO₁₀₀) with acrylamide and 2-acrylamide-methylpropionic acid sodium salt was studied here. A series of graft modified polyether polymers were prepared and it was expected to get thermoviscosifying polymers with high molecular weights and low association temperatures. Several factors on thermoviscosifying behaviors were investigated, such as polymerization condition, polymer concentration, hydrophilic monomer, molecular structure and molecular weight. It was also proven that the apparent viscosity of polymer solution is influenced by polymer concentration, molecular weight of polymer, and content of anion groups.

Miscibility of poly(acrylic acid)/poly(methyl vinyl ketone) blend and in vitro application as drug carrier system

A series of poly(acrylic acid)/poly(methyl vinyl ketone) (PAA/PMVK) blends with different compositions were prepared by the solvent casting method. The miscibility of this pair of polymers was investigated by differential scanning calorimetry(DSC), Fourier transform infra-red (FTIR) and X-Ray diffraction (XRD) techniques. An in-vitro cytotoxicity test of the drug-carrier system via MTT (3-(4,5-demethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay revealed no significant cytotoxic effects at concentrations up to 100 µg· ml⁻¹. The STX/PAA-50 drug carrier systems were also prepared by solvent casting of solutions containing the sulfamethoxazole (STX) used as drug model and PAA/PMVK blend in N.N-dimethylformamide then crosslinked with acidified ethylene glycol. The release dynamic of STX from the prepared hydrogels was investigated in which the diffusion through the polymer matrix, the enhancement of the water solubility of STX, the influence of the initial drug concentration, the pH of the medium, and the effect of the degree of swelling of the polymer matrix on the release dynamic was evaluated. According to the total gastrointestinal transit time estimated by Belzer, the estimate distribution of STX released in the different organs indicated that the performance is obtained with the drug – carrier-system containing equal ratios of polymer and 10 wt% of STX (STX-10/PAA-50).

Assessment of the Efficiency of Aliquat 336+Rice Bran Oil for Separation of Acrylic Acid from Aqueous Solution Using Reactive Extraction

Biomass is an attractive target in process development for the emerging renewable resources based bio-refinery industry. Due to the ample range of application of acrylic acid, its production through bio-route received more awareness in scientific fraternity. In this view, an attempted was made to study the reactive extraction of acrylic acid with aliquat 336 in rice bran oil. Moreover, Box-Behnken matrix was employed to corroborate the effects of process variables viz. concentration of acrylic acid [CAA]aq, concentration of aliquat 336 [CR4N+Cl], and temperature on the extraction efficiency (η%). In physical extraction, average extraction efficiency was found in the order as: 43.55 > 35.36 > 29.14 at 303 K, 323 K, and 343 K respectively in rice bran oil. The correlation coefficient, R2 = 0.988 % indicates the appropriateness of proposed model to predict the extraction efficiency in terms of independent variables, and the predicted values were found in close agreement with that of experimental results. Further, R2(Pred) = 0.806 is in reasonable agreement with the R2(Adj) = 0.972. The optimum conditions for extraction of acrylic acid using aliquat 336 as an extractant in rice bran oil are [CAA]aq = 0.0.5 (mol/kg); [CR4N+Cl] = 1.98 (mol/kg); temperature = 323 K and the model predicted extraction efficiency 77.5 % was found to be an excellent fit with the experimental value 75 %. Further, number of theoretical stages was found to be 3 and S/F ratio 0.247.

Perspectives on: PEO-PPO-PEO Triblock Copolymers and their Biomedical Applications

Thermo-reversible polymeric gels represent an interesting class of materials that can be tailored for a wide range of applications. The triblock poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) based systems, PEO-PPO-PEO, show thermoreversible gelation around body temperature and, therefore, are particularly suitable for biomedical applications such as drug delivery, gene therapy and tissue engineering. The PEO-PPO-PEO tri-block copolymers have amphiphilic characteristics and self-assemble into micelles to form a variety of close packed structures. By varying the block composition (PEO/PPO ratio) and the molecular weight, it is possible to tailor the final properties of these systems to meet the specific application needs. In this report the thermodynamic basis of micellization of PEO-PPO-PEO systems is described. The factors influencing the micelles formation are discussed along with the methods used to investigate the micellization process and morphology as well as with the main applications of these systems in biomedical fields.

Bioreducible cross-linked Pluronic micelles: pH-triggered release of doxorubicin and folate-mediated cellular uptake

Bioreducible are described here, cross-linked Pluronic micelles carrying doxorubicin (DOX) for folate-mediated cancer targeting. The amine-terminated Pluronic® F-127 was functionalized by grafting acrylic acid (AA) to the hydrophobic block (AA-Pluronic-NH2). Folic acid (FA), hydrazine (H), and cystamine (C) were sequentially conjugated to AA-Pluronic-NH2, followed by DOX conjugation via an acid-labile hydrazone bond (FA-Pluronic-C/H-DOX). The DOX content was approximately 143 µg/mg of polymer. We prepared bioreducible cross-linked micelles using FA-Pluronic-C/H-DOX, which had a diameter of 156.1 nm. After incubation for 24 h with 10 mM of dithiothreitol, the micelle size decreased dramatically to 87.6 nm with a broad distribution, indicating that disulfide bonds in the micelle core were reductively cleaved. In vitro release data showed that the conjugated DOX was released slowly from the FA-Pluronic C/H-DOX micelles at pH 7.4, whereas there was a rapid DOX release at pH 5.2. Confocal images of HeLa cells showed enhanced cellular uptake of FA-Pluronic-C/H-DOX micelles as compared to nontargeted Pluronic-C/H-DOX micelles. The FA-Pluronic-C/H-DOX micelles killed more cells than the nontargeted micelles, but the cytotoxic effect was not as significant as free DOX. Additionally, micelles without DOX were not cytotoxic. On the basis of these results, pH- and redox potential–responsive FA-Pluronic-C/H-DOX micelles could potentially function as cancer-targeted and controlled DOX delivery systems.

Effects of a novel poly (AA-co-AAm)/AlZnFe₂O₄/potassium humate superabsorbent hydrogel nanocomposite on water retention of sandy loam soil and wheat seedling growth

A novel poly(acrylic acid-co-acrylamide)AlZnFe₂O₄/potassium humate( )superabsorbent hydrogel nanocomposite (PHNC) was synthesized and its physical properties characterized using SEM, Energy Dispersive X-ray (EDX) and FTIR spectroscopic techniques. Air dried sandy loam soil was amended with 0.1 to 0.4 w/w% of PHNC to evaluate its soil moisture retention attributes. Effect of PHNC amendment on pH, electrical conductivity (EC), porosity, bulk density and hydraulic conductivity of sandy loam soil was also studied. The soil amendment with 0.1 to 0.4 w/w% of PHNC remarkably enhanced the moisture retention at field capacity as compared to the un-amended soils. Seed germination and seedling growth of wheat (Triticum aestivum L.) was considerably increased and a delay by 6-9 days in wilting of seedlings was observed in the soil amended with PHNC, resulting in improved wheat plant establishment and growth.

Synthesis and Characterization of Water Soluble Block Copolymers for pH-Sensitive Delivery

A novel, water-soluble AB-block copolymer of diethylaminoethyl methacrylate (DEAEM) and poly(ethylene glycol) (PEG) was synthesized by anionic polymerization. Poly(ethylene glycol) methyl ether (PEGME) was converted into the corresponding potassium salt by reacting with potassium metal. The PEG salt was used as a macroinitiator for the polymerization of DEAEM to yield a PEG-b-PDEAEM block copolymer. Carbon dioxide was used to terminate DEAEM polymerization with a carboxylic acid group. This polymer, loaded with dye, was tested for pH sensitivity by release studies into solutions of various pH.

Template-assisted synthesis of nanogels from Pluronic-modified poly(acrylic acid)

A series of novel polymeric nanogels with core-shell morphology was developed. Block ionomer complexes of comb-graft poly(ethylene oxide)-b-poly(polypropylene oxide)-b-poly(ethylene oxide)-g-poly(acrylic acid) copolymers (Pluronic-PAA) and divalent metal cations were utilized as micellar templates for the synthesis of nanogels with sizes ranging from 100 to 200 nm in diameter. The Pluronic-PAA nanogels were confirmed to possess ionic cross-linked PAA cores and flexible hydrophilic shells from the Pluronic copolymer chains. The ionic character of the core provided for pH-dependent swelling/collapse behavior of the nanogels. These prepared nanogels are expected to be of utility as carriers for charged therapeutic or diagnostic agents.

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.

New biodegradable thermogelling copolymers having very low gelation concentrations

New biodegradable multiblock amphiphilic and thermosensitive poly(ether ester urethane)s consisting of poly[(R)-3-hydroxybutyrate] (PHB), poly(ethylene glycol) (PEG), and poly(propylene glycol) (PPG) blocks were synthesized, and their aqueous solutions were found to undergo a reversible sol-gel transition upon temperature change at very low copolymer concentrations. The multiblock poly(ether ester urethane)s were synthesized from diols of PHB, PEG, and PPG using 1,6-hexamethylene diisocyanate as a coupling reagent. The chemical structures and molecular characteristics of the copolymers were studied by GPC, 1H NMR, 13C NMR, and FTIR. The thermal stability of the poly(PEG/PPG/PHB urethane)s was studied by thermogravimetry analysis (TGA), and the PHB contents were calculated based on the thermal degradation profile. The results were in good agreement with those obtained from the 1H NMR measurements. The poly(PEG/PPG/ PHB urethane)s presented better thermal stability than the PHB precursors. The water soluble poly(ether ester urethane)s had very low critical micellization concentration (CMC). Aqueous solutions of the new poly(ether ester urethane)s underwent a sol-gel-sol transition as the temperature increased from 4 to 80 degrees C, and showed a very low critical gelation concentration (CGC) ranging from 2 to 5 wt %. As a result of its multiblock architecture, a novel associated micelle packing model can be proposed for the sol-gel transition for the copolymer gels of this system. The new material is thought to be a promising candidate for injectable drug systems that can be formulated at low temperatures and forms a gel depot in situ upon subcutaneous injection.

Poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)-g-poly(vinylpyrrolidone): association behavior in aqueous solution and interaction with anionic surfactants

In this work, we aimed to study the association and interaction behavior of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) block copolymers grafted with poly(vinylpyrrolidone). Critical micellization concentrations were determined using fluorescent probes (pyrene) and critical micellization temperatures characterizing temperature-dependent transitions from monomers to multimolecular micelles were measured. The thermal responsiveness of the copolymer is not affected by the grafting. The hydrodynamic radius of the graft copolymer micelles is found to be greater than that of the original copolymer micelles. The graft copolymer is found to form anisotropic aggregates. The structure of the graft copolymer micelles is less disrupted by the anionic surfactant sodium dodecyl sulfate, compared to the ungraft copolymer.

Poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide)-g-poly(vinyl pyrrolidone): synthesis and characterization

Pluronic poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers are grafted with poly(vinyl pyrrolidone) by free radical polymerization of vinyl pyrrolidone with simultaneous chain transfer to the Pluronic in dioxane. This modified polymer has both thermal responsiveness and remarkable capacity to interact with a wide variety of hydrophilic and hydrophobic pharmaceutical agents which is very attractive for medical applications. The chemical structure of the graft copolymers was characterized by FTIR and 1H NMR spectroscopy. Polymerization conditions such as initiators, feed ratio, and reaction times are studied to obtain the ideal graft copolymer.

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.

Adhesion of polyether-modified poly(acrylic acid) to mucin

Pluronic-PAA, a thermogelling copolymer composed of side chains of poly(acrylic acid) (PAA) grafted onto a backbone of Pluronic copolymer, is of interest as a vehicle for the controlled release of compounds. An important feature of such a vehicle is its bioadhesive/mucoadhesive properties, which in the case of Pluronic-PAA are significant due to the presence of the PAA side chains. An atomic force microscopy (AFM) method has been developed and utilized to investigate the interactions between a Pluronic-PAA-modified microsphere and mucous substrates. The bioadhesive force was successfully measured, and trends were observed under conditions of varying pH and ionic strength. Pluronic-PAA exhibits significant mucoadhesion over a range of pH values, with mucoadhesion being optimal at pH 4-5 (adhesive force approximately 80 mN/cm(2)) and dropping sharply at higher pH, to a value of approximately 20 mN/cm(2) at pH 8. The mucoadhesive force decreased with increasing ionic strength, from a value of approximately 80 mN/cm(2) in 0.025 M NaCl to approximately 25 mN/cm(2) in 1.0 M NaCl. These results have been interpreted in terms of the effect of changing pH and ionic strength on electrostatic interactions and swelling of the polymer and mucin layers. Tensiometric force measurements indicated that hydrophobic interactions, as well as hydrogen bonding and electrostatic interactions, were significant in the mucoadhesion of Pluronic-PAA copolymers. Experiments with a range of Pluronic-PAA copolymers with varying PPO contents in the Pluronic segments showed that increasing the overall PPO content increased the hydrophobicity of the polymer solutions. This was reflected in the increases in the advancing contact angles with the mucin layer, indicating that hydrophobic interactions play a role in the adhesion of Pluronic-PAA to mucin.

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.

Optimization of a thermally reversible W/O/W multiple emulsion for shear-induced drug release

PURPOSE

The present work aimed at improvement of the formulation of a previously developed thermo-reversible W/O/W multiple emulsion by increasing the emulsion stability and reaching a higher fraction of an encapsulated drug released under shear. The emulsion was based on high molecular weight graft-copolymers of poly(acrylic acid) and Pluronic F127 as stabilizing agents.

METHODS

Once a stable W/O/W thermo-reversible multiple emulsion was obtained via a fine-tuning of the formulation, rheological, granulometric and conductometric tests were performed to assess the thermo-reversible behavior and the fragmentation-release characteristics of the new W/O/W multiple emulsion.

RESULTS

The emulsion exhibited a 10(3) fold increase in viscosity over a range of temperatures from 20 to 40 degrees C. At moderate shearing, a complete release of the marker encapsulated in the internal aqueous phase was observed (99.6%) at 35 degrees C, whereas only 30% was released at 20 degrees C. Under similar conditions at 35 degrees C, slightly more than 50% was released for the initial formula.

CONCLUSION

Additionally, the ease of fabrication of the thermo-reversible W/O/W multiple emulsion combined with the complete release under shear at body temperature and the superior emulsion stability suggest numerous applications in the controlled release of drugs.

Effects of polyether-modified poly(acrylic acid) microgels on doxorubicin transport in human intestinal epithelial Caco-2 cell layers

Novel microgels composed of cross-linked copolymers of poly(acrylic acid) and Pluronics were evaluated as possible permeation enhancers for doxorubicin transport using Caco-2 cell monolayers as a gastrointestinal model. Pluronic, triblock copolymers of ethylene oxide (EO) and propylene oxide (PO), were chosen to represent the most hydrophobic (Pluronic L61 and L92 with average compositions of EO(3)PO(30)EO(3) and EO(8)PO(52)EO(8), respectively) and the relatively hydrophilic (Pluronic F127 with average formula EO(99)PO(67)EO(99)) extremes of this class of block copolymers. The weight ratio of Pluronic to poly(acrylic acid) in the microgels was set at 45:55. By inhibiting the P-glycoprotein (P-gp)-mediated doxorubicin efflux from the cells and enhancing the passive influx, the microgels were shown to enhance the overall cell absorption of doxorubicin. The enhancement effect was more pronounced than with a known penetration enhancer, Pluronic L61, and was comparable to that of Pluronic L92. Microgels exhibited synergism of the doxorubicin transport enhancement with Verapamil, a known inhibitor of the P-gp. The effects of the microgels were studied using the hydrophilic marker ([14C]mannitol) test and the MTT assay. Transepithelial electrical resistance (TEER) studies demonstrated that the microgels decreased TEER to about 80% of initial values, but these minor effects were fully reversible, indicating viability of the cells after incubation with microgels. No significant enhancement of [14C]mannitol transport by microgels was observed, relative to Carbopol 934NF (control polymer). Cytotoxicity studies confirmed that the transport-enhancing properties of the microgels were not due to damage of the Caco-2 cell monolayers.

Lessons from nature: stimuli-responsive polymers and their biomedical applications

Response to stimulus is a basic process of living systems. Based on the lessons from nature, scientists have been designing useful materials that respond to external stimuli such as temperature, pH, light, electric field, chemicals and ionic strength. These responses are manifested as dramatic changes in one of the following: shape, surface characteristics, solubility, formation of an intricate molecular self-assembly or a sol-to-gel transition. Applications of stimuli-responsive, or 'smart', polymers in delivery of therapeutics, tissue engineering, bioseparations, sensors or actuators have been studied extensively and numerous papers and patents are evidence of rapid progress in this area. Understanding the structure-property relationship is essential for the further development and rational design of new functional smart materials. For example, kinetic and thermodynamic control of the coil-to-globule transition could be achieved through changes in polymer composition and topology.