Interaction of nicotine with magnesium aluminum silicate at different pHs: characterization of flocculate size, zeta potential and nicotine adsorption behavior

The purposes of this study were to prepare dispersions in various ratios of nicotine (NCT) and magnesium aluminum silicate (MAS) at different pHs and to investigate interaction of NCT with MAS by characterizing microscopic morphology, particle size and zeta potential of MAS-NCT flocculates. Moreover, the NCT adsorption onto MAS at different pHs were also investigated. At basic medium, incorporating NCT into MAS dispersion brought about a small decrease in the zeta potential of MAS, leading to a loose flocculate formation of MAS. This is likely to be due to an adsorption of unionized form of NCT onto MAS via intermolecular hydrogen bonding. The lower zeta potential, denser matrix structure and larger size of the flocculates was found at neutral and acidic media because the protonated species of NCT could interact with the negatively charged MAS by electrostatic force. In addition the flocculates formed at pH 4 possibly possessed a higher density than those formed at pH 7, suggesting that the diprotonated species of NCT at pH 4 caused stronger interaction with MAS. The adsorption isotherms of NCT onto MAS at different pHs can be described not only using the Langmuir model, but also using the Freundlich model. The higher affinity of NCT adsorption onto MAS at neutral and acidic media was found. However, the adsorption capacity to form NCT monolayer reduced with decreasing the pH of the dispersions because of an adsorption of hydronium ions and a decrease in surface area of adsorption site by flocculation. These findings suggested that the flocculation of MAS dispersion could be induced by incorporation of NCT. The characteristics, such as particle size and zeta potential, of the NCT-MAS flocculates and the adsorption isotherms of NCT onto MAS were depended upon pH of dispersion, in which the different charged species of NCT were formed.     

Effect of dispersion pH on the formation and stability of Pickering emulsions stabilized by layered double hydroxides particles

Using positively charged plate-like layered double hydroxides (LDHs) particles as emulsifier, liquid paraffin-in-water emulsions stabilized solely by such particles are successfully prepared. The effects of the pH of LDHs aqueous dispersions on the formation and stability of the emulsions are investigated here. The properties of the LDHs dispersions at different pHs are described, including particle zeta potential, particle aggregation, particle contact angle, flow behavior of the dispersions and particle adsorption at a planar oil/water interface. The zeta potential decreases with increasing pH, leading to the aggregation of LDHs particles into large flocs. The structural strength of LDHs dispersions is enhanced by increasing pH and particle concentration. The three-phase contact angle of LDHs also increases with increasing pH, but the variation is very small. Visual observation and SEM images of the interfacial particle layers show that the adsorption behavior of LDHs particles at the planar oil/water interface is controlled by dispersion pH. We consider that the particle-particle (at the interface) and particle-interface electrostatic interactions are well controlled by adjusting the dispersion pH, leading to pH-tailored colloid adsorption. The formation of an adsorbed particle layer around the oil drops is crucial for the formation and stability of the emulsions. Emulsion stability improves with increasing pH and particle concentration because more particles are available to be adsorbed at the oil/water interface. The structural strength of LDHs dispersions and the gel-like structure of emulsions also influence the stability of the emulsions, but they are not necessary for the formation of emulsions. The emulsions cannot be demulsified by adjusting emulsion pH due to the irreversible adsorption of LDHs particles at the oil/water interface. TEM images of the emulsion drops show that a thick particle layer forms around the oil drops, confirming that Pickering emulsions are stabilized by the adsorbed particle layers. The thick adsorbed particle layer may be composed of a stable inner particle layer which is in direct contact with the oil phase and a relatively unstable outer particle layer surrounding the inner layer.     

Hydrogen‐Bonded Complexes and Blends of Poly(acrylic acid) and Methylcellulose: Nanoparticles and Mucoadhesive Films for Ocular Delivery of Riboflavin

Poly(acrylic acid) (PAA) and methylcellulose (MC) are able to form hydrogen‐bonded interpolymer complexes (IPCs) in aqueous solutions. In this study, the complexation between PAA and MC is explored in dilute aqueous solutions under acidic conditions. The formation of stable nanoparticles is established, whose size and colloidal stability are greatly dependent on solution pH and polymers ratio in the mixture. Poly(acrylic acid) and methylcellulose are also used to prepare polymeric films by casting from aqueous solutions. It is established that uniform films can be prepared by casting from polymer mixture solutions at pH 3.4–4.5. At lower pHs (pH < 3.0) the films have inhomogeneous morphology resulting from strong interpolymer complexation and precipitation of polycomplexes, whereas at higher pHs (pH 8.3) the polymers form fully immiscible blends because of the lack of interpolymer hydrogen‐bonding. The PAA/MC films cast at pH 4 are shown to be non‐irritant to mucosal surfaces. These films provide a platform for ocular formulation of riboflavin, a drug used for corneal cross‐linking in the treatment of keratoconus. An in vitro release of riboflavin as well as an in vivo retention of the films on corneal surfaces can be controlled by adjusting PAA/MC ratio in the formulations.     

Membrane permeation of testosterone from either solutions, particle dispersions, or particle-stabilized emulsions

We derive a unified model that accounts for the variation in extent and rate of membrane permeation by a permeating species with the type of donor compartment formulation (aqueous and oil solutions, particle dispersions, and oil-in-water and water-in-oil emulsions stabilized by particles) initially containing the permeant. The model is also applicable to either closed-loop or open-flow configurations of the receiver compartment of the permeation cell. Predictions of the model are compared with measured extents and rates of permeation of testosterone across an 80 μm thick polydimethylsiloxane (PDMS) membrane from donor compartments initially containing testosterone dissolved in either aqueous or isopropylmyristate (IPM) solutions, aqueous or IPM dispersions of silica nanoparticles or IPM-in-water or water-in-IPM emulsions stabilized by silica nanoparticles. Using a single set of input parameters, the model successfully accounts for the wide variations in permeation behavior observed for the different donor formulation types with either closed-loop or open flow configurations of the permeation cell receiver compartment.     

Structure and flow behavior of crosslinked ethyl acrylate–methacrylic acid copolymer dispersion particles

 Changes in viscosity, pH and static light scattering behavior on alkali addition of model dispersions of statistical copolymers of ethyl acrylate with 15 and 50 wt% of methacrylic acid prepared by semicontinuous emuslion copolymerization and crosslinked with various amount of N,N′-methylenebisacrylamide were investigated. It was found that about 1% of crosslinking agent was sufficient to prevent unpredictable disintegration of dispersion particles and gauranteed reproducible flow behavior of alkalinized dispersions. The viscosity of alkalinized dispersions of crosslinked particles at low concentration is controlled by the effective hydrodynamic volume of swelled particles which decreases with the crosslinking degree of copolymer. On the other hand, at higher particle concentration close to critical concentration at which the space is filled up by swelled particles the influence of particle interaction prevails and due to lower deformability of crosslinked particles viscosity increases with a crosslinking degree. In comparison with similar dispersions prepared without a crosslinking agent these results indicated much uniform structure of dispersion particles and suppression of influence of random crosslinking due to chain transfer reactions. The study shows that dispersions of crosslinked copolymers of this type could be considered as thickners of latex binders with stable and reproducible thickening properties. Received: 23 February 1998 Accepted: 11 June 1998     

Stable aqueous film coating dispersion of zein

The effects of plasticizers, pH, and electrolytes on film formation and physical stability of aqueous film coating dispersions (pseudolatexes) of zein were evaluated. The influence of plasticizer on film formation mechanism and minimum film-formation temperature (MFT) were monitored by means of hot stage microscopy (HSM). Furthermore, the effects of pH and electrolytes on the short-term physical stability of pseudolatexes were investigated by measuring relative absorbance, zeta potential, and particle size of the dispersions. With aqueous coating dispersions of zein, stages of film formation were identified. The dispersions plasticized with 20% (w/w) PEG 400 or glycerol formed mechanically strong and flexible films with the lowest glass transition temperature (T(g)). Physical stability of the aqueous zein dispersions was dependent on both pH and electrolyte content. At a pH ranging from 3 to 4, the aqueous dispersions of zein were stable for at least 2 months exhibiting the highest values for zeta potential, the smallest particle size, and a low volume of aggregates. The stable dispersion could be obtained containing a lower concentration of electrolytes (e.g., 10(-5) M). The physical stability of aqueous zein dispersions can be determined by the combined measurements of relative absorbance, zeta potential, and particle size.     

Preparation and characterization of complexes of liposomes with gold nanoparticles

Gold nanoparticles (Au NPs), which are extremely useful materials for imaging and photothermal therapy, typically require a drug delivery system to transport them to the affected tissue and into the cells. Since liposomes are approved as drug carriers, complexes of liposomes with Au NPs were considered ideal solutions to deliver Au NPs to the target site in vivo. In this study, we prepared complexes of various liposomes with Au NPs via physical absorption and characterized them. The time dependency of the surface plasmon resonance of this complex, which is a unique property of Au NPs, shows that the liposomes promote the formation of stable dispersions of Au NPs under isotonic conditions, even though intact Au NPs aggregate immediately. From a release assay of calcein from liposomes and transmission electron microscopy analysis, the Au NPs were complexed with liposomes without membrane disruption. These complexes could be formed by using cationic liposomes and polyethylene glycol-modified liposomes, as well as by using phosphatidylcholine liposomes, which are useful for drug and gene delivery. We proposed this kind of complex as a nanomedicine with diagnostic and therapeutic ability.     

Polyurethane-polymethacrylic acid multiblock copolymer dispersions through polyurethane macroiniferters

Polyurethane-polymethacrylic acid multiblock copolymers have been prepared from tetraphenylethane-based polyurethane macroiniferters. Aqueous dispersions of these block copolymers and their anionomers have been prepared. Anionomeric dispersions have smaller particle size and higher viscosity when compared to their corresponding block copolymeric dispersions. Particle size decreases whereas viscosity increases when the degree of neutralization is increased. Tensile strength and initial modulus are higher for films derived from anionomeric dispersions than for the corresponding block copolymeric films. Received: 13 March 1998 Accepted in revised form: 13 November 1998     

接枝环氧树脂/硅溶胶杂化水分散液的制备与表征

利用原位分散法制备了接枝环氧树脂 硅溶胶杂化水分散液 ,并通过红外光谱和 ζ电位测定 ,表征了接枝环氧树脂与硅溶胶之间的杂化作用 .实验结果表明 ,与接枝环氧树脂水分散液相比 ,杂化水分散液的粒径和粘度均减小 .按此探讨了形成杂化水分散液的历程 .初步测定了杂化水分散液成膜后的表面性能 ,发现它们具有更高的硬度和更好的疏水性能 ,与成膜过程中硅溶胶在膜表面的富集效应有关     

Effect of pore former on the properties of casted film prepared from blends of Eudragit NE 30 D and Eudragit L 30 D-55

The casted films of aqueous dispersions of Eudragit NE30 D and Eudragit L30 D-55 containing pore former were prepared. The study investigated the influence of pore former on basic model drug clarithromycin release, water uptake and water vapor permeability from casted film prepared from the blends of neutral polymer dispersion of Eudragit NE30 D and enteric polymer dispersion of Eudragit L30 D-55. This study was concluded that pore former hydroxypropyl methyl cellulose, lactose, polyethylene glycol (PEG) and polyvinyl pyrrolidon (PVP) was released at the beginning of the release process, the rate and extent of water uptake of the polymeric films were much higher in phosphate buffer pH 6.8 than in pH 5.0 and the concentration of pore former have a significant influence on the permeability to water vapour.     

Design and evaluation of bioadhesive in-situ nasal gel of ketorolac tromethamine

The present study was aimed at developing safe and effective bioadhesive gelling systems of ketorolac tromethamine, a potent non-narcotic analgesic with moderate anti-inflammatory activity for nasal systemic delivery. Chitosan and pectin based gelling systems were prepared with variables like polymer concentration and type. These systems were characterized in terms of their physical properties, in vitro bioadhesion, in vitro drug release and long-term stability. The anti-inflammatory activity and mucosal irritancy of selected gels were also evaluated in rats and these results were compared with per oral, intraperitoneal and nasal solution administration of ketorolac tromethamine. All the prepared formulations gelled immediately at the nasal mucosal pH and showed longer contact time. Addition of hydroxypropyl methylcellulose (HPMC) in both chitosan and pectin based gelling systems increased the viscosity and gel strength. All the formulated gels exhibited pseudoplastic rheology and diffusion-controlled drug release. The results from stability studies revealed that the prepared thermogels showed marginal decrease in viscosity but at the same time, no significant difference in drug content, and in vitro release characteristics were observed before and after accelerated studies. The developed gelling systems produced only mild to negligible irritant effect to nasal mucosae as compared to control group.     

Studies on bioadhesive granules I: granules formulated with Prosopis africana (prosopis) gum

Prosopis gum (PG) extracted from Prosopis africana was investigated for bioadhesive delivery of theophylline (TPL). Bioadhesive granules containing TPL were formulated and the bioadhesive properties evaluated using adhesion of the granules onto a porcine intestinal mucus surface. The bioadhesion of the gum dispersion was also evaluated using coated glass beads and the strength of the films formulated from the gums was also determined. The release properties of the TPL-containing granules were assessed by diffusion of TPL from the granules through porcine intestinal wall into a sink solution. Sodium carboxymethylcellulose (SCMC) was used as the standard bioadhesive polymer. Results indicated that PG is highly bioadhesive compared to SCMC. The result of the release studies also showed that PG could be used to deliver TPL in a bioadhesive dosage form.     

Preparation and Properties of Non-ionic Polyurethane Crosslinkers from 2-Ethoxyethanol/ϵ-caprolactam-Blocked Diisocyanate

A series of novel water-based non-ionic blocked polyurethane crosslinker (n-BPUC) dispersions have been synthesized by the reaction of toluene 2,4-diisocyanate (TDI), isophorone diisocyanate (IPDI), polyethylene glycol (PEG), 1,1,1-trimethylolpropane (TMP), 2-Ethoxyethanol (2-Et) and ?-caprolactam (CL). The physical properties of prepared n-BPUC dispersions such as viscosity, pH, and storage stability are measured and compared. The chemical structure of the prepared n-BPUC dispersions is confirmed by Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC). Deblocking temperatures of the n-BPUC dispersions are analyzed by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) techniques. The thermal analysis reveals that deblocking temperature obtained by DSC and TGA techniques is compared and found to be in the order DSC < TGA. Based on DSC and TGA data, it is shown that deblocking of n-BPUC dispersions based on 2-Et start at lower temperatures compared to that of the ones based on CL. The TDI-based n-BPUCs show higher reactivity than the ones based on IPDI. Hydroxyl-terminated polyurethane (HPU) is introduced to estimate the crosslinking effect of the prepared n-BPUCs. The better tensile properties and water resistance of n-BPUC modified HPU films compared to pure HPU film demonstrate the good crosslinking effect of the prepared n-BPUCs.     

聚合物多元醇分散体的流变特性

聚合物多元醇分散体(以下简称分散体)是接枝聚醚多元醇、聚醚多元醇和乙烯基单体聚合物的混合物,直接用于制备高回弹、高负载和阻燃的软质和半软质聚氨酯泡沫体,是新一代聚醚多元醇产品[1].分散体用于聚氨酯工业中各种产品的生产,除要求有良好的稳定性外,其最为重要的指标是粘度应小于3000mPa·s和乙烯基单体聚合物的含量(固含量)应大于40%.但分散体的粘度,随固含量的增加呈指数性增加[2].近年来,已有既具高固含量和良好稳定性,又有较低粘度的分散体的研究报道[3].本文在不同的反应条件下,合成了分散体,测定了其流变特性和体系中微粒的大小…     

Controlled drug release through poly(L-leucine) and its copolymer

The release behavior of a water-soluble drug through membranes made of poly(L-leucine) and its copolymer with different hydrophilic properties was studied. The effect of casting methods on the release rate was also investigated. It was found that the membrane with a higher hydrophilic property resulted in a higher permeation rate. The capsule was prepared as a composite sheet from a poly(L-leucine)-prednisolone 21-sodium succinate sponge and a poly(L-leucine) membrane. Release of the water-soluble drug from the capsule was found to be effectively governed by the hydrophilic character and thickness of the outer membrane. Biocompatibility studies carried out by implanting the poly(L-leucine) sponge subcutaneously in the dorsal surface of the rat showed that the sponge had a good biocompatibility and slow biodegradation. It was concluded from these results that poly(L-leucine) should be a suitable material for preparing a controlledrelease drug device for long-term dosage.     

pH and ionic sensitive chitosan/carboxymethyl chitosan IPN complex films for the controlled release of coenzyme A

pH and ionic sensitive interpenetrating polymer network (IPN) complex films based on chitosan (CS) and carboxymethyl chitosan (CM-CS) were prepared by using glutaraldehyde as crosslinking agent. Its structure was characterized by FT-IR, which indicated that the IPN was formed. The films were studied by swelling, weight loss with time, and release of coenzyme A (CoA). It was found that the IPN films were sensitive to pH and ionic strength of the medium. The cumulative release rate of CoA decreased with CoA loading content, ionic strength or crosslinking agent increasing. The composition of the IPN films and pH of release medium also had significant effect on the release of CoA. The differences in the rates and amounts of released CoA may be attributed to the swelling behavior, the degradation of films, and interaction between drug molecule and polymer matrix. These results suggested CS/CM-CS IPN films could be used as drug delivery carrier.     

Properties of acrylic–polyurethane hybrid emulsions synthesized by the semibatch emulsion copolymerization of acrylates using different polyurethane particles

Aqueous acrylic–polyurethane hybrid emulsions were prepared by the semibatch emulsion copolymerization of methyl methacrylate and butyl acrylate in the presence of eight polyurethane dispersions. The polyurethane dispersions were synthesized with isophorone diisocyanate, 1000 and 2000 molecular weight polyester polyols, 1000 molecular weight polyether polyol, butanediol, and dimethylol propionic acid. Acrylic monomers were added in the monomer emulsion feed. We studied the effect of the use of different polyurethane seed particles and the effect of different weight ratios of methyl methacrylate to butyl acrylate on the emulsion properties, microphase structure, and mechanical properties of hybrid films. The average particle size and distribution were determined by photon correlation spectroscopy. The rheological properties of polyurethane dispersions and hybrid emulsions were tested under destructive conditions by an examination of flow curves and under nondestructive conditions of oscillatory shear in a range of linear viscoelastic responses. Differential scanning calorimetry was performed to characterize the thermal‐response properties of polymeric films. The relative average molecular weights were determined by gel permeation chromatography. The interactions between the acrylic and polyurethane components in hybrid particles and particle structure were studied with infrared spectroscopy and nuclear magnetic resonance spectroscopy. Mechanical properties such as the Koenig hardness, tensile strength, elongation at break, and Young's modulus were measured. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4050–4069, 2005     

Effect of electrostatic interaction on the adsorption of globular proteins on octacalcium phosphate crystal film

The electrostatic effect on the adsorption of globular proteins, such as bovine serum albumin (BSA), hen egg white lysozyme (LZM), and beta-lactoglobulin (beta-Lg), on octacalcium phosphate (OCP)-like crystal thin films was investigated. A poorly crystalline thin film was synthesized on a tissue culture polystyrene (TCP) surface and used as a model surface in this study. The solution pH clearly affected the electrostatic properties of both proteins and surface. The adsorbed amounts obtained at quasi-steady state were readily related to the solution pH for each protein. The adsorption rate is fast during the initial period and levels off gradually. The maximum adsorbed mass occurred at pH 7 for BSA and at pH 9 for LZM. beta-Lg adsorbed similar amounts at pHs lower than 9, but the adsorbed mass decreased at pHs higher than 9 where electrostatic repulsion exists. The pH values where the maximum adsorbed mass occurred may be considered as the conditions where electrostatic attraction is most favorable. The adsorbed mass of beta-Lg was the greatest among the proteins of interest while BSA adsorbed the least despite its greater molecular mass. LZM falls into the intermediate region. According to these observations, BSA has undergone conformational changes that prevent further adsorption to a greater extent than the others. A simple relationship between the adsorption rate and the electrostatic properties was not established. However, the order of magnitude of the adsorption rate at the initial period tends to be the same as that of maximum adsorbed mass for each protein.     

Competition of hydrogen-bonding and electrostatic interactions within hybrid polymer multilayers

Using a layer-by-layer sequential adsorption technique, we report the construction of hybrid films in which layers of hydrogen-bonded polymers are embedded within electrostatically associated polyelectrolytes. The components of the hybrid film include a neutral hydrogen-bonding polymer, a weak polycarboxylic acid, and a strong polycation. Depending on the pH value used for the deposition of the electrostatic film, we found two distinctive regimes of film growth. At pHs lower than a critical value, deposition of electrostatic layers occurred on top of hydrogen-bonded stacks to produce hybrid, three-component films. At pHs higher than a critical value, neutral, hydrogen-bonded chains were displaced by the adsorbing chains of the polycation, producing two-component films. The property of the hydrogen-bonded stacks of hybrid films to be selectively dissolved by exposing them to a high pH makes these films promising candidates for producing free polyelectrolyte films.     

Ionically crosslinked alginate/carboxymethyl chitin beads for oral delivery of protein drugs

Complex beads composed of alginate and carboxymethyl chitin (CMCT) were prepared by dropping aqueous alginate-CMCT into an iron(III) solution. The structure and morphology of the beads were characterized by IR spectroscopy and scanning electron microscopy (SEM). IR confirmed electrostatic interactions between iron(III) and the carboxyl groups of alginate as well as CMCT, and the binding model was suggested as a three-dimensional structure. SEM revealed that CMCT had a porous morphology while alginate and their complex beads had a core-layer structure. The swelling behavior, encapsulation efficiency, and release behavior of bovine serum albumin (BSA) from the beads at different pHs were investigated. The BSA encapsulation efficiency was fairly high (>90%). It was found that CMCT disintegrated at pH 1.2 and alginate eroded at pH 7.4 while the complex beads could effectively retain BSA in acid (>85%) and reduce the BSA release at pH 7.4. The results suggested that the iron(III)-alginate-CMCT bead could be a suitable polymeric carrier for site-specific protein drug delivery in the intestine.