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PubMed2007

Drug release from pH-responsive thermogelling pentablock copolymers.

A novel pH-dependent injectable sustained delivery system was developed by utilizing a cationic pentablock copolymer that exhibits a thermoreversible sol-gel transition. Aqueous solutions of the pentablock copolymer, consisting of poly(2-diethylaminoethyl-methyl methacrylate)-poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)-poly(2-diethylaminoethyl-methyl methacrylate) (PDEAEM(25)-PEO(100)-PPO(65)-PEO(100)-PDEAEM(25)) exhibit temperature and pH dependent micellization due to the lower critical solution temperature of the PPO blocks and the polyelectrolyte character of the PDEAEM blocks, respectively. Aqueous solutions of the copolymers above 12 wt % are free flowing liquids at room temperature and form elastic physical hydrogels reversibly above 37 degrees C. Hydrophobic probe absorbance studies indicate that pentablock copolymer micelles increase the solubility of sparingly soluble drugs. Solutions of the pentablock copolymer that form gels at body temperature exhibit sustained zero-order release in in vitro experiments. The release rates of model drugs and proteins were significantly influenced by the pH of the release media, thereby making these polymers ideal candidates for modulated drug delivery.

Animals↗
PubMed2006

Novel pH responsive polymethacrylic acid-chitosan-polyethylene glycol nanoparticles for oral peptide delivery.

In present study, novel pH sensitive polymethacrylic acid-chitosan-polyethylene glycol (PCP) nanoparticles were prepared under mild aqueous conditions via polyelectrolyte complexation. Free radical polymerization of methacrylic acid (MAA) was carried out in presence of chitosan (CS) and polyethylene glycol (PEG) using a water-soluble initiator and particles were obtained spontaneously during polymerization without using organic solvents or surfactants/steric stabilizers. Dried particles were analyzed by scanning electron microscopy (SEM) and particles dispersed in phosphate buffer (pH 7.0) were visualized under transmission electron microscope (TEM). SEM studies indicated that PCP particles have an aggregated and irregular morphology, however, TEM revealed that these aggregated particles were composed of smaller fragments with size less than 1 micron. Insulin and bovine serum albumin (BSA) as model proteins were incorporated into the nanoparticles by diffusion filling method and their in vitro release characteristics were evaluated at pH 1.2 and 7.4. PCP nanoparticles exhibited good protein encapsulation efficiency and pH responsive release profile was observed under in vitro conditions. Trypsin inhibitory effect of these PCP nanoparticles was studied using casein substrate and these particles displayed lesser inhibitory effect than reference polymer carbopol. Preliminary investigation suggests that these particles can serve as good candidate for oral peptide delivery.

Administration, Oral↗
PubMed1981

Mitogenesis in normal human fibroblasts by polyinosinic . polycytidylic acid and other synthetic acidic polymers: enhancement of action by glucocorticoids.

The ability of specific synthetic polyelectrolytes to act as mitogens for quiescent normal human fibroblasts in cultures is described. Of several acidic polymers tested, polyinosinic acid .polycytidylic acid (poly I.poly C) and dextran sulfate were the most effective in stimulating 3H]thymidine incorporation (2-to 10-fold). The concentration for a half-maximal effect (ED50) was 0.4 microgram/ml (0.8 nM) for poly I.poly C, and 1.7 microgram/ml (3.4 nM) for dextran sulfate. Single-stranded polyinosinic acid or polycytidylic acid had no effect. The time course of stimulation of DNA synthesis by these acidic polymers was similar to that for naturally occurring mitogens such as epidermal growth factor, beginning at about 18 hours and reaching a maximum rate 26 to 30 hours after the addition of polymer. Glucocorticoids that have an 11-beta hydroxyl group (e.g., dexamethasone) had no effect on DNA synthesis alone, but enhanced several-fold the mitogenic activity of poly I.poly C or dextran sulfate; the ED50 for dexamethasone was 0.75 ng/ml (1.9 nM). Glucocorticoids with an 11-keto group were inactive in this respect. The labeling index following treatment of cultures with poly I.poly C and dexamethasone was 14%, compared with a labeling index of 25% following stimulation by fetal calf serum. The extent of stimulation of DNA synthesis by poly I.poly C and dexamethasone was comparable to that induced by epidermal growth factor. It appears that both the poly I.poly C and dexamethasone are required for only a short period of time (approximately 3 hours) in order to produce maximal stimulation of DNA synthesis 30 hours later.

Anions↗
PubMed2006

Preparation, characterization, and drug release in vitro of chitosan-glycyrrhetic acid nanoparticles.

A suitable carrier chitosan (CS) was used to prepare CS-Glycyrrhetic acid (GLA) nanoparticles under very mild conditions by polyelectrolyte complexation. These nanoparticles were well dispersed and stable in aqueous solution, and the physicochemical properties of which were investigated by FT-IR, dynamic light scattering, transmission electron microscope, fluorescence spectra and zeta potential. It was found that only when the weight ratio of CS to GLA was lower than 16.7, could the nanoparticles be formed. The prepared nanoparticles carried a positive charge and had the dried TEM-assessed size in the range from 20 to 30 nm. The mean hydrated diameter, size distribution and zeta potential of the nanoparticles could be controlled by some factors including the weight ratio of CS to GLA, the average molecular weight of CS and the pH value of the medium. It was also found that GLA encapsulation efficiency into the nanoparticles increased with the increase of the weight ratio of CS to GLA. The experiment of GLA release in vitro showed that the effect of CS encapsulation on GLA release was obvious and the CS-GLA nanoparticles system might be used to provide a continuous release.

Chemistry, Pharmaceutical↗
PubMed1975

Enhancing fluidity of concentrated antacid suspensions.

Highly concentrated antacid suspension can by fluidized by adding a colloidal polyelectrolyte to alter the charge on antacid particles from positive to negative. A deflocculated state is assumed to exist in such preparations, as supported by electrophoretic and viscometric analyses. When viscosity is directly correlated with the zota-potential, viscometry becomes particularly useful in confirming that the suspension has been maximally fluidized.

Aluminum Hydroxide↗
PubMed1994

Controlled release of albumin from chitosan-alginate microcapsules.

A polymeric delayed-release protein delivery system was investigated with albumin as a model drug. The polysaccharide chitosan was reacted with sodium alginate in the presence of calcium chloride to form microcapsules with a polyelectrolyte complex membrane. Variables believed to be important for membrane formation were examined; these included reaction time, chitosan molecular weight, alginate concentration, chitosan concentration, and solution pH. An alginate-chitosan reaction time, in the range of 10 to 45 min, had no effect on the release of albumin. Increasing the alginate concentration, however, resulted in a decreased rate of release of albumin (from 37% release at 4 h with 1.5% alginate to 20% release with 2.5% alginate). Another key variable was the chitosan molecular weight. The molecular weight of chitosan was varied from 1.25 x 10(6) to 0.25 x 10(6) through a nitrite oxidation reaction with sodium nitrite. Decreasing the molecular weight increased the release of albumin (from 37% release at 4 h with high molecular weight chitosan to 77% release with low molecular weight chitosan). The pH of the extracapsular environment was found to affect the release of albumin significantly (15% release over 24 h at a pH 3.0 and 73% release at pH 8.0). Capsules produced with high molecular weight chitosan and a combination of high and low molecular weight chitosan gave the best results for reducing elution of albumin in the first 4 h and increasing elution in the following 20 h.

Albumins↗
PubMed1994

Interaction of anionic compounds with gelatin. II: Effect on some physicochemical properties of gelatin.

The interaction of gelatin with four monosulfonated or monocarboxylated azo dyes was investigated by measuring the surface tension and intrinsic viscosity of gelatin solutions containing the dyes at different concentrations, the rigidity and melting point of their gels, and the moisture regain of their films. The dyes, which were used as models for anionic drugs, differed in the size of their aromatic hydrocarbon moieties. Surface tension measurements showed that the gelatin did not affect the critical micelle concentration of the free dyes and that the bound dyes increased the surface activity of the gelatin. The dyes reduced the intrinsic viscosity of gelatin by as much as 2/3. They also lowered the rigidity and the melting point of dilute gelatin gels and reduced the moisture regain of dry gelatin films. These changes became more pronounced with increasing dye concentrations. The effectiveness of the dyes in producing these changes increased with the size of their hydrocarbon moieties because, as had been shown in a previous study, increasingly larger hydrocarbon moieties increased the binding of the dyes to gelatin. At the pH of the measurements, which was 1.9 units below the isoelectric point of the gelatin, the gelatin was a cationic polyelectrolyte. Binding of the dye anions by ion pairing, hydrogen bonds, and other secondary valence forces rendered the gelatin less ionic and less hydrophilic, which accounts for the present observations.

Anions↗
PubMed2004

High activity of enzymes immobilized in colloidal nanoreactors.

We present a novel type of nanoreactor suitable for the immobilization of enzymes. The particles used consist of a polystyrene core onto which long chains of poly(acrylic acid) are grafted ("spherical polyelectrolyte brush"). Proteins adsorbed spontaneously onto these particles from aqueous solutions if the ionic strength is low. We immobilized glucoamylase on these particles and showed that this enzyme keeps nearly its full activity. This is shown by analyzing the enzymatic activity in terms of the Michaelis-Menten kinetics. No leaching out of the enzyme takes place during the reaction and the colloidal stability is not impeded by the adsorbed biomolecules. The data presented here suggest that the principle of immobilizing enzymes on these particles may be of general use.The Figure shows a schematic representation of the colloidal nanoreactors.

Acrylic Resins↗
PubMed2005

Microstructure formation and property of chitosan-poly(acrylic acid) nanoparticles prepared by macromolecular complex.

We report here a study on the microstructure formation process of polymeric nanoparticles based on polyelectrolyte complexes. When polyanion poly(acrylic acid) (PAA) was dropped into polycation chitosan (CS) solution, CS-PAA nanoparticles with diverse microstructure would be formed under different experimental conditions. The microstructure of CS-PAA nanoparticles changed from solid spherical nanoparticles to core-shell separative ones and turned back to solid spherical ones with the variation of preparation conditions. The influence of molecular weight of CS and PAA, shell cross-linking, dropping temperature on the size, stability and morphology of CS-PAA nanoparticles were also studied. The nanoparticle size was affected by the molecular weight of CS and PAA, the ratio of amino group to carboxyl group (na/nc) and the incubation temperature as well. The shell-cross-linking provides a means to stabilize these nanoparticles. These nanoparticles can encapsulate plasmid DNA very well, which makes them have great potential in gene delivery.

Acrylates↗
PubMed2005

Ternary complex formation in aqueous solution between a beta-cyclodextrin polymer, a cationic surfactant and DNA.

Polyelectrolyte complexes have been elaborated by mixing in water neutral poly(beta-CD), a cationic surfactant (DTAC) and herring sperm DNA fragments. The driving forces for the poly(beta-CD)/DTAC/DNA association in aqueous solution are, on the one hand, reversible inclusion interactions between the CD cavities of poly(beta-CD) and the alkyl group of DTAC, leading to the formation of a polycation and, on the other hand, electrostatic interactions between the opposite charges of the cationic surfactant and anionic DNA. Viscometry and SANS have been used to prove the occurrence of such ternary complexes in dilute aqueous solutions.

Carbohydrate Sequence↗
PubMed2005

Multilayer microcapsules as anti-cancer drug delivery vehicle: deposition, Sustained release, and in vitro bioactivity.

A drug delivery system based on spontaneous deposition of soluble, low-molecular-weight therapeutic agents has been developed for the purpose of sustaining drug release. Layer-by-layer assembly of oppositely charged polyelectrolytes onto melamine formaldehyde (MF) colloidal particles, followed by removal of the cores at low pH has yielded intact hollow microcapsules having the ability to induce deposition of various water-soluble substances. Dynamic observation by confocal laser scanning microscopy provided direct evidence of such deposition. Dependence of loading rate on molecular weight was investigated. Efficient loading of an anti-cancer drug, daunorubicin (DNR), was confirmed by transmission electron microscopy (TEM). Its release was quantified by fluorometry. The results indicated that loading, and subsequent release, could be tuned by factors such as feeding concentrations, temperature, and salt concentrations. The intrinsic mechanism of loading and release was discussed taking into account the interaction between the drugs and the poly(styrene sulfonate)/MF complex existing in the hollow capsules. With culture of the HL-60 cell line, a kind of human leukemia cell, the presence of DNR-loaded capsules was seen to steadily decrease the cyto-viability. Fluorescence intensity averaged from inside the circles as a function of incubation time.

Antibiotics, Antineoplastic↗
PubMed2006

Cytocompatibility and antibacterial activity of a PHBV membrane with surface-immobilized water-soluble chitosan and chondroitin-6-sulfate.

A water-soluble chitosan (WSC)/chondroitin-6-sulfate (ChS) polyelectrolyte complex (PEC) is covalently immobilized onto the surface of poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) (PHBV) membranes via ozone-induced oxidation and poly(acrylic acid) (PAA) graft polymerization. To characterize the modified membranes, X-ray photoelectron spectroscopy (XPS) and water contact angle measurements are performed. It is shown that by coupling WSC as a spacer, the amount of ChS immobilized can be significantly increased. The water contact angle decreases with the amount of PAA, WSC, and ChS immobilized, which indicates the improving hydrophilicity. After WSC- and PEC-immobilization modification, the PHBV membranes possess antibacterial activity against S. aureus, E. coli, P. aeruginosa, and Methicilin resistant Staphylococus aureus (MRSA). According to the L929 fibroblast cell growth inhibition index, the as-prepared PHBV membranes are non-cytotoxic. In addition, the in-vitro evaluation of L929 fibroblast attachment, proliferation, and viability of PEC-immobilized PHBV membranes are ascertained to be superior to those of immobilized WSC or ChS alone. The overall results demonstrate that WSC/ChS PEC immobilization can not only improve the hydrophilicity and cytocompatibility of the PHBV membrane, but also endows antibacterial activity. [GRAPH: SEE TEXT] The bacterial survival ratio of as-prepared PHBV membranes (n=3).

Animals↗
PubMed2006

Non-covalent interactions in polysaccharide systems.

[Chemical structure: see text] This paper describes the behavior of some polysaccharides with well-known chemical structures and in which the influence of cooperative secondary interactions play an important role. The roles played by hydrophobic and ionic interactions (including ionic selectivity) on polysaccharide conformation and gelation are discussed. Electrostatic attractions are also important in the complexes formed between surfactants and polyelectrolytes of opposite charge. Finally, van der Waals dipolar interactions and particularly hydrogen-bond formation are examined. The role of hydrogen bonds in solubility, conformation, and especially the local stiffness of polysaccharides, but also in polymer-polymer complexes frequently obtained with polysaccharides, is developed. Repeat unit for a number polysaccharides.

Carbohydrate Conformation↗
PubMed2004

Magnetic relaxation dispersion of lithium ion in solutions of DNA.

The magnetic field dependence of the nuclear spin-lattice relaxation rate constant defines the magnetic relaxation dispersion (MRD) and provides a direct characterization of the molecular dynamics that cause fluctuations in the magnetic couplings in the system and may also indicate the dimensional constraints on the motion. The counterion cloud surrounding a linear polyelectrolyte ion, such as DNA in solution, provides an interesting opportunity for ion confinement that helps in understanding the thermodynamics and the dynamics of the interactions between the polyion and other solutes. The MRD profiles of lithium ion and tetramethylammonium ion were recorded in dilute aqueous solutions of native calf thymus DNA, which provides a long, charged rod that reorients slowly. The 7Li ion relaxes through the nuclear electric quadrupole coupling and the proton-lithium dipole-dipole coupling; the protons of the tetramethylammonium ion relax by dipole-dipole coupling. MRD profiles of the 7Li+ ion are dominated by transient interactions with the DNA that yield a linear dependence of the spin-lattice relaxation rate constant on the logarithm of the Larmor frequency. This magnetic field dependence is consistent with diffusive ion motions that modulate two spatial coordinates that characterize the relaxation couplings in the vicinity of the polyion. Motions around the rod and fluctuations in the ion distance from the rod are consistent with these constraints for lithium. The magnetic field dependence of the tetramethylammonium ion proton relaxation rate constant is weak, but also approximately a linear function of the logarithm of the Larmor frequency, which implies that the field dependence is caused in part by local order in the DNA solution.

Complex Mixtures↗
PubMedDate not supplied

A method for imaging single clay platelets by scanning electron microscopy.

A method for preparing and observing clay platelets for size and shape analysis using scanning electron microscopy (SEM) was developed. Samples of the clay platelets were prepared by polyelectrolyte-assisted adsorption onto a pyrolytic graphite surface. The use of graphite as a substrate was advantageous because of the low number of secondary electrons emitted from it during imaging by SEM. The resulting low background noise allowed the emission from the approximately 1 nm thick clay sheets to be clearly visualized. Images of centrifuged montmorillonite showed large exfoliated platelets with lateral dimensions between 200 and 600 nm. In contrast, uncentrifuged montmorillonite appeared to contain a large amount of unexfoliated clusters. Although it was not possible to obtain high-quality images of the smaller sheets of Laponite RD, the images of this material did contain size features comparable to the approximately 30 nm2 size reported previously using light scattering, as well as transmission electron and atomic force microscopies.

Journal Article↗
PubMed2005

Tunable whispering gallery mode emission from quantum-dot-doped microspheres.

We describe the synthesis of quantum-dot (QD) doped silica microspheres and a method by which it is possible to fine-tune the position of the whispering gallery modes (WGMs) produced by the fluorescence emission of CdSe@ZnS doped silica microspheres (5.06 mum in diameter). The method is based on small perturbations to the sphere's refractive index caused by adsorption of thin layers of polyelectrolytes and modification of the radial position of the nanocrystals within the microsphere by means of deposited silica shells.

Adsorption↗
PubMed2006

Soft lithographic printing of patterns of stretched DNA and DNA/electronic polymer wires by surface-energy modification and transfer.

Aligned and stretched lambda DNA is directed to specific locations on solid substrates. Surface-energy modification of glass substrates by using patterned polydimethylsiloxane (PDMS) stamps is used to direct DNA onto the surface-energy-modified micrometer-scale pattern through molecular combing. As an alternative, patterned and nonpatterned PDMS stamps modified with polymethylmethacrylate (PMMA) are utilized to direct the stretched DNA to the desired location and the results are compared. The DNA is elongated through molecular combing on the stamp and transfer printed onto the surfaces. PMMA-modified stamps show a more defined length of the stretched DNA, as compared to bare PDMS stamps. A combination of these two methods is also demonstrated. As an application example, transfer printing of DNA decorated with a semiconducting conjugated polyelectrolyte is shown. The resulting patterned localization of stretched DNA can be utilized for functional nanodevice structures, as well as for biological applications.

DNA↗
PubMed1997

Three-way curve resolution applied to the study of solvent effect on the thermodynamic and conformational transitions related to the protonation of polycytidylic acid.

Solvent effect on the acid-base behavior of polycytidylic acid [poly(C)] is studied by means of potentiometric and spectrometric (UV and CD) procedures. Low-polarity biological environments are mimicked by using a 30% (v/v) dioxane-water mixture. Experiments performed in this medium are compared with previously reported results in aqueous solution in order to determine changes in both thermodynamic and structural aspects associated with modifications of the biomolecular surroundings. Potentiometric and spectrometric studies reveal the presence of a nonlinear polyelectrolytic effect associated with the protonation of poly(C) in the hydroorganic mixture, different from the analogous effect in aqueous solution. The curve resolution method alternating least squares is applied to the poly(C) spectrometric data. Concentration profiles and spectra of both deprotonated poly(C) and half-protonated [poly(C).poly(CH+)] are thus obtained. The fully protonated species poly(CH+) precipitates in the hydroorganic medium at pH values lower than 4. Evidence for the ordered structure of both poly(C) and [poly(C).poly(CH+)] species is seen through the comparison of the macromolecule spectra with those of the cytidine-3',5'-cyclic monophosphate monomer. Polarity decreases around the macromolecule produce significant hypochromicity in the CD spectra and hyperchromicity in the UV spectra, both signs of a disordering effect in the macromolecular structure due to the weakening of base stacking interactions.

Acid-Base Equilibrium↗