Characterization of pH-Dependent Poly(acrylic Acid) Complexation with Phospholipid Vesicles

Electrophoretic deposition of collagen/chitosan films with copper-doped phosphate glasses for orthopaedic implants

Coatings with bioactive properties play a key role in the success of orthopaedic implants. Recent studies focused on composite coatings incorporating biocompatible elements that can increase the nucleation of hydroxyapatite (HA), the mineral component of bone, and have promising bioactive and biodegradable properties. Here we report a method of fabricating composite collagen, chitosan and copper-doped phosphate glass (PG) coatings for biomedical applications using electrophoretic deposition (EPD). The use of collagen and chitosan (CTS) allows for the co-deposition of PG particles at standard ambient temperature and pressure (1 kPa, 25 °C), and the addition of collagen led to the steric stabilization of PG in solution. The coating composition was varied by altering the collagen/CTS concentrations in the solutions, as well as depositing PG with 0, 5 and 10 mol% CuO dopant. A monolayer of collagen/CTS containing PG was obtained on stainless steel cathodes, showing that deposition of PG in conjunction with a polymer is feasible. The mass of the monolayer varied depending on the polymer (collagen, CTS and collagen/CTS) and combination of polymer + PG (collagen-PG, CTS-PG and collagen/CTS-PG), while the presence of copper led to agglomerates during deposition at higher concentrations. The deposition yield was studied at different time points and showed a profile typical of constant voltage deposition. Increasing the concentration of collagen in the PG solution allows for a higher deposition yield, while pure collagen solutions resulted in hydrogen gas evolution at the cathode. The ability to deposit polymer-PG coatings that can mimic native bone tissue allows for the potential to fabricate orthopaedic implants with tailored biological properties with lower risk of rejection from the host and exhibit increased bioactivity.

Synthesis and Properties of Targeted Radioisotope Carriers Based on Poly(Acrylic Acid) Nanogels

Radiation crosslinking was employed to obtain nanocarriers based on poly(acrylic acid)—PAA—for targeted delivery of radioactive isotopes. These nanocarriers are internally crosslinked hydrophilic macromolecules—nanogels—bearing carboxylic groups to facilitate functionalization. PAA nanogels were conjugated with an engineered bombesin-derivative—oligopeptide combined with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate chelating moiety, aimed to provide selective radioligand transport. 4-(4,6-Dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium (DMTMM) toluene-4-sulfonate was used as the coupling agent. After tests on a model amine—p-toluidine—both commercial and home-synthesized DOTA-bombesin were successfully coupled to the nanogels and the obtained products were characterized. The radiolabeling efficiency of nanocarriers with ¹⁷⁷Lu, was chromatographically tested. The results provide a proof of concept for the synthesis of radiation-synthesized nanogel-based radioisotope nanocarriers for theranostic applications.

Linking polymer hydrophobicity and molecular interactions to rheology and tribology in phospholipid-containing complex gels

HYPOTHESIS

The rheological behavior and frictional properties (macroscopic level) of systems containing a hydrophobically modified polymer and phospholipids depend on the hydrophobic association that occur between the hydrophobic moiety of the polymer and the phospholipid tails (molecular level). The hydrophobicity of the polymer can thus be used to control its interactions with phospholipids, and manipulate complex gel macroscopic behavior.

EXPERIMENTS

By using systems composed of a crosslinked hydrophobically modified polyacrylic acid (HMPAA) or a crosslinked polyacrylic acid polymer (PAA) and phospholipids, we examine the underlying mechanisms through which the components interact using isothermal titration calorimetry (ITC) and their effect on rheological and tribological characteristics of complex gels.

FINDINGS

We find the systems containing HMPAA and phospholipid exhibit gel-like behavior with the elastic modulus increasing substantially upon phospholipid addition due to hydrophobic interactions that result in a more interconnected network formation, as evidenced by ITC measurements. Similar experiments with a crosslinked polyacrylic acid polymer (PAA) show no interactions, lending credence to our hypothesis. In addition, soft tribological behavior shows lower friction coefficients at low entrainment speeds with HMPAA concentration and the addition of phospholipid, while no change in friction coefficient was observed in the case of increasing PAA concentration, indicating HMPAA and phospholipids to be interacting with the soft PDMS contacts.

Towards a catheter-based impedimetric sensor for the assessment of intestinal histamine levels in IBS patients

In this work, we report on the development of a catheter-based sensor designed for measuring the concentration of histamine in the human duodenum. Certain gut disorders, such as the irritable bowel syndrome (IBS), are associated with elevated levels of intestinal histamine due to chronic immune activation. As it is still impossible to determine histamine concentrations in vivo, a nasointestinal catheter with histamine-sensing capabilities has the potential to become a valuable diagnostic instrument. Regarding the sensing principle, we selected impedance spectroscopy using voltages that are compatible with intra-body applications with molecularly imprinted polymers (MIPs) as recognition elements. MIPs are synthetic receptors that offer the advantages of robustness, high specificity and selectivity for histamine as a target. In this specific case, the MIPs were synthesized from acryclic acid monomers, which guarantees a uniform binding capacity within the pH range of intestinal fluid. We have validated the catheter sensor on human intestinal liquids spiked with histamine in a testing setup that mimics the environment inside the duodenum. The dose-response curves show an analytical range between 5 and 200 nM of histamine, corresponding to physiologically normal conditions while higher concentrations correlate with disease. The key output signal of the sensor is the resistive component of the MIP-functionalized titanium electrodes as derived from the equivalent-circuit modelling of full-range impedance spectra. Future applications could be catheters tailored to cardiovascular, urological, gastrointestinal, and neurovascular applications. This, in combination with the versatility of the MIPs, will make this sensor platform a versatile diagnostic tool.

Design and development of pH-responsive HSPC:C12H25-PAA chimeric liposomes

The application of stimuli-responsive medical practices has emerged, in which pH-sensitive liposomes figure prominently. This study investigates the impact of the incorporation of different amounts of pH-sensitive polymer, C12H25-PAA (poly(acrylic acid) with a hydrophobic end group) in l-α-phosphatidylcholine, hydrogenated (Soy) (HSPC) phospholipidic bilayers, with respect to biomimicry and functionality. PAA is a poly(carboxylic acid) molecule, classified as a pH-sensitive polymer, whose pH-sensitivity is attributed to its regulative -COOH groups, which are protonated under acidic pH (pKa ∼4.2). Our concern was to fully characterize, in a biophysical and thermodynamical manner, the mixed nanoassemblies arising from the combination of the two biomaterials. At first, we quantified the physicochemical characteristics and physical stability of the prepared chimeric nanosystems. Then, we studied their thermotropic behavior, through measurement of thermodynamical parameters, using Differential Scanning Calorimetry (DSC). Finally, the loading and release of indomethacin (IND) were evaluated, as well as the physicochemical properties and stability of the nanocarriers incorporating it. As expected, thermodynamical findings are in line with physicochemical results and also explain the loading and release profiles of IND. The novelty of this investigation is the utilization of these pH-sensitive chimeric advanced Drug Delivery nano Systems (aDDnSs) in targeted drug delivery which relies entirely on the biophysics and thermodynamics between such designs and the physiological membranes and environment of living organisms.

Programming the composition of polymer blend particles for controlled immunity towards individual protein antigens

In order for a more precise control over the quality and quantity of immune responses stimulated by synthetic particle-based vaccines, it is critical to control the colloidal stability of particles and the release of protein antigens in both extracellular space and intracellular compartments. Different proteins exhibit different sizes, charges and solubilities. This study focused on modulating the release and colloidal stability of proteins with varied isoelectric points. A polymer particle delivery platform made from the blend of three polymers, poly(lactic-co-glycolic acid) (PLGA) and two random pH-sensitive copolymers, were developed. Our study demonstrated its programmability with respective to individual proteins. We showed the colloidal stability of particles at neutral environment and the release of each individual protein at different pH environments were dependent on the ratio of two charge polymers. Subsequently, two antigenic proteins, ovalbumin (OVA) and Type 2 Herpes Simplex Virus (HSV-2) glycoprotein D (gD) protein, were incorporated into particles with systematically varied compositions. We demonstrated that the level of in vitro CD8(+) T cell and in vivo immune responses were dependent on the ratio of two charged polymers, which correlated well with the release of proteins. This study provided a promising design framework of pH-responsive synthetic vaccines for protein antigens of interest.

Gas transport across hyperthin membranes

The use of organic polymeric membranes to separate gaseous mixtures provides an attractive alternative to other methods such as selective adsorption and cryogenic distillation. The primary advantages of membrane-based separations are their relative energy efficiency and lower costs. Because the flux of a gas across a membrane is inversely proportional to the membrane's thickness, this method relies on fabricating membranes that are as thin as possible. However, as researchers have tried to produce "hyperthin" membranes (less than 100 nm), these membranes often form defects and lose their permeation selectivity. In this Account, we review some of the progress in our laboratories at Lehigh University to create hyperthin membranes with high permeation selectivities. We focus special attention on gaseous permeants that are relevant for the production of clean energy (H2 and CO2 formed from CH4) and the reduction of global warming (CO2 and N2, the major components of flue gas). Our studies make extensive use of Langmuir-Blodgett (LB) methods and porous surfactants derived from calix[6]arenes. We specially designed each surfactant to form cohesive monolayers and multilayers, and we introduced a "gluing" technique, where we cross-link porous surfactants containing quaternary ammonium groups ionically with polymeric counterions. Using ellipsometry, atomic force microscopy, X-ray photoelectron spectroscopy, monolayer isotherm, surface viscosity, and permeation measurements, we have characterized these hyperthin films. While molecular sieving appears to make a significant contribution to the permeation selectivity of some of these membranes, solution-diffusion pathways predominate. We also describe initial studies in which we formed hyperthin films from poly(ethylene glycol)-based polyelectrolytes using layer-by-layer deposition (LbL) methods. We have found remarkably high H2/CO2 and CO2/N2 permeation selectivities with these LB- and LbL-based hyperthin membranes. These results suggest that such materials may lead the way to materials that researchers can exploit to purify hydrogen produced from CH4 and to capture CO2 from flue gas.

Customization of copolymers to optimize selectivity and yield in polymer-driven antibody purification processes

This manuscript describes customization of copolymers to be used for polymer-driven protein purification in bioprocessing. To understand how copolymer customization can be used for fine-tuning, precipitation behavior was analyzed for five target antibodies (mAbs) and BSA as model impurity protein, at ionic strength similar to undiluted cell culture fluid. In contrast to the use of standardized homopolymers, customized copolymers, composed of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and 4-(acryloylamino)benzoic acid (ABZ), exhibited antibody precipitation yields exceeding 90%. Additionally, copolymer average molecular weight (Mw ) was varied and its influence on precipitation yield and contaminant coprecipitation was investigated. Results revealed copolymer composition as the major driving force for precipitation selectivity, which was also dependent on protein hydrophobicity. By adjusting ABZ content and Mw of the precipitant for each of the mAbs, conditions were found that allowed for high precipitation yield and selectivity. These findings may open up new avenues for using polymers in antibody purification processes.

Active drug encapsulation and release kinetics from hydrogel-in-liposome nanoparticles

Herein, we demonstrate for the first time the use of hydrogel-in-liposome nanoparticles (lipogels) as a promising drug delivery vehicle for the active encapsulation of the anticancer drug 17-DMAPG, a geldanamycin (GA) derivative. This model drug was chosen due to its improved aqueous solubility (4.6 mg/ml) compared to the parent GA (<0.01 mg/ml), and presence of a tertiary amine which readily protonates at low pH. For the design of lipogels, a PAA hydrogel core was formed inside liposomes through UV-initiated DEAP activation and polymerization of AA and BA. We have demonstrated here that electrostatic interactions between drug and gel are critical for active encapsulation and sustained release of 17-DMAPG. We found that optimal loading conditions could be obtained (88% loading efficiency) through control of pH, temperature and incubation time. Dramatic sustained drug release from lipogels was achieved independent of the external solution pH (ca. 54 h to 50% drug release) and confirmed that the lipid bilayer was intact in the presence of the gel core. In vitro cell culture studies revealed that at the highest concentration tested, which corresponded to approximately 0.4 mg/ml of material, lipogels did not exert cytotoxicity to cells.

Pluronic-poly (acrylic acid)-cysteine/Pluronic L121 mixed micelles improve the oral bioavailability of paclitaxel

The aim of the study is to synthesize a thiolated Pluronic copolymer, Pluronic-poly (acrylic acid)-cysteine copolymer, to construct a mixed micelle system with the Pluronic-poly (acrylic acid)-cysteine copolymer and Pluronic L121 (PL121) and to evaluate the potential of these mixed micelles as an oral drug delivery system for paclitaxel. Compared with Pluronic-poly (acrylic acid)-cysteine micelles, drug-loading capacity of Pluronic-poly (acrylic acid)-cysteine/PL121 mixed micelles was increased from 0.4 to 2.87%. In vitro release test indicated that Pluronic-poly (acrylic acid)-cysteine/PL121 mixed micelles exhibited a pH sensitivity. The permeability of drug-loaded micelles in the intestinal tract was studied with an in situ perfusion method in rats. The presence of verapamil and Pluronic both improved the intestinal permeability of paclitaxel, which further certified the inhibition effect of thiolated Pluronic on P-gp. In pharmacokinetic study, the area under the plasma concentration-time curve (AUC0→∞) of paclitaxel-loaded mixed micelles was four times greater than that of the paclitaxel solution (p < 0.05). In general, Pluronic-poly (acrylic acid)-cysteine/PL121 micelles were proven to be a potential oral drug delivery system for paclitaxel.

Interaction of a poly(acrylic acid) oligomer with dimyristoylphosphatidylcholine bilayers

We studied the influence of 5 kDa poly(acrylic acid) (PAA) on the phase state, thermal properties, and lateral diffusion in bilayered systems of dimyristoylphosphatidylcholine (DMPC) using (31)P NMR spectroscopy, differential scanning calorimetry (DSC), (1)H NMR with a pulsed field gradient, and (1)H nuclear Overhauser enhancement spectroscopy (NOESY). The presence of PAA does not change the lamellar structure of the system. (1)H MAS NOESY cross-peaks observed for the interaction between lipid headgroups and polyion protons demonstrated only surface PAA-biomembrane interaction. Small concentrations of PAA (up to ∼4 mol %) lead to the appearance of a new lateral phase with a higher main transition temperature, a lower cooperativity, and a lower enthalpy of transition. Higher concentrations lead to the disappearance of measurable thermal effects. The lateral diffusion coefficient of DMPC and the apparent activation energy of diffusion gradually decreased at PAA concentrations up to around 4 mol %. The observed effects were explained by the formation of at least two types of PAA-DMPC lateral complexes as has been described earlier (Fujiwara, M.; Grubbs, R. H.; Baldeschwieler, J. D. J. Colloid Interface Sci., 1997, 185, 210). The first one is characterized by a stoichiometry of around 28 lipids per polymer, which corresponds to the adsorption of the entire PAA molecule onto the membrane. Lipid molecules of the complex are exchanged with the "pure" lipid bilayer, with the lifetime of the complex being less than 0.1 s. The second type of DMPC-PAA complex is characterized by a stoichiometry of 6 to 7 lipids per polymer and contains PAA molecules that are only partially adsorbed onto the membrane. A decrease in the DMPC diffusion coefficient and activation energy for diffusion in the presence of PAA was explained by the formation of a new cooperative unit for diffusion, which contains the PAA molecule and several molecules of lipids.

Facile One-Pot Synthesis of Polymer-Phospholipid Composite Microbubbles with Enhanced Drug Loading Capacity for Ultrasound-Triggered Therapy

This paper reports the one-pot synthesis of perfluorocarbon microbubbles with crosslinked shells of poly(acrylic acid) and phospholipid that boast excellent ultrasound contrast enhancement, enhanced loading capacity, and the ability to retain or release their contents through variation in the level of ultrasound exposure.

Hydrogen-bonded layer-by-layer temperature-triggered release films

A hydrogen-bonded layer-by-layer (LbL) technique was used to build multilayers of neutral, temperature-responsive polymers such as poly(N-isopropylacrylamide) (PNIPAM), poly(N-vinylcaprolactam) (PVCL), poly(vinyl methyl ether) (PVME), or poly(acrylamide) (PAAm) with a polycarboxylic acid such as poly(acrylic acid) (PAA), poly(methacrylic acid) (PMAA), or poly(ethacrylic acid) (PEAA). For all multilayers involving temperature-responsive polymers, the temperature used during or after self-assembly had a significant effect on film stability with pH changes. The proximity of the self-assembly or post-self-assembly temperature to the critical temperature of phase separation of a neutral polymer from solution resulted in a higher pH stability of multilayers. However, for polymers with a lower critical solution temperature (LCST) such as PNIPAM, PVCL, or PVME within PNIPAM/PMAA, PVCL/PMAA, or PVME/PMAA multilayers, the critical pH of film disintegration (pH(crit)) increased in the temperature range from 10 to 37 degrees C, whereas for polymer films with an upper critical solution temperature (UCST), such as PAAm within PAAm/PMAA, the film showed the opposite trend. Using a hydrogen-bonded polyvinylpyrrolidone (PVPON)/PMAA system, which is not responsive to temperature changes, we constructed hybrid films with lower [PNIPAM/PMAA](n) and higher [PVPON/PMAA](m) strata and obtained free-floating [PVPON/PMAA](m) films by temperature-triggered dissolution of the PNIPAM/PMAA layers at a constant pH value. The kinetics of [PVPON/PMAA](m) film release was strongly dependent on the number of bilayers within the PNIPAM/PMAA stratum, indicating significant interpenetration between PNIPAM/PMAA and PVPON/PMAA bilayers. Importantly, the use of PEAA instead of PAA or PMAA in film assembly enabled the construction of hydrogen-bonded LbL films that can be released by applying temperature as a trigger at near-physiological pH values. This feature makes such release layers attractive candidates for future tissue engineering applications.

Membrane deformation under local pH gradient: mimicking mitochondrial cristae dynamics

Mitochondria are cell substructures (organelles) critical for cell life, because biological fuel production, the ATP synthesis by oxidative phosphorylation, occurs in them driven by acidity (pH) gradients. Mitochondria play a key role as well in the cell death and in various fatigue and exercise intolerance syndromes. It is clear now that mitochondria present an astonishing variety of inner membrane morphologies, dynamically correlated with their functional state, coupled with the rate of the ATP synthesis, and characteristic for normal as well as for pathological cases. Our work offers some original insights into the factors that determine the dynamical tubular structures of the inner membrane cristae. We show the possibility to induce, by localized proton flow, a macroscopic cristae-like shape remodeling of an only-lipid membrane. We designed a minimal membrane system (GUV) and experimentally showed that the directional modulation of local pH gradient at membrane level of cardiolipin-containing vesicles induces dynamic cristae-like membrane invaginations. We propose a mechanism and theoretical model to explain the observed tubular membrane morphology and suggest the underlying role of cardiolipin. Our results support the hypothesis of localized bioenergetic transduction and contribute to showing the inherent capacity of cristae morphology to become self-maintaining and to optimize the ATP synthesis.

Effect of transferrin as a ligand of pH-sensitive fusogenic liposome-lipoplex hybrid complexes

We previously developed potent nonviral vectors based on complexation of lipoplexes and pH-sensitive fusogenic liposomes, which achieve efficient transfection through membrane fusion with intracellular acidic compartments such as endosomes. Because transferrin receptor is known to be overexpressed in cancer cells, in this study, we investigated the effect of transferrin as a ligand for transfection of various cancer-derived cell lines mediated by the liposome-lipoplex hybrid complexes. Results showed that these hybrid complexes with transferrin exhibited higher transfection efficiency toward these cells than complexes without transferrin, but the extent of the transferrin-induced enhancement was dependent on the cell line. Conjugation of transferrin increased their transfection activity for HeLa and KB cells, although it only slightly enhanced transfection for HT1080, HepG2, and K562. Transferrin receptors in HT1080, HepG2, and K562 cells were internalized slowly, whereas those in HeLa and KB cells were internalized quickly and actively. These results indicate that transfection mediated by the ligand-attached hybrid complex does not correlate with the amount of transferrin receptor in the cell surface but correlate with the activity of internalization of transferrin receptor into the cells.

Hydrotropic polymer micelles containing acrylic acid moieties for oral delivery of paclitaxel

Hydrotropic polymers (HPs) and their micelles have been recently developed as vehicles for delivery of poorly water-soluble drugs, such as paclitaxel (PTX), by oral administration. The release of PTX from HP micelles, however, was slow and it took more than a day for complete release of the loaded PTX. Since the gastrointestinal (GI) transit time is known to be only several hours, pH-sensitive HP micelles were prepared for fast release of the loaded PTX responding to pH changes along the GI tract. Acrylic acid (AA) was introduced, as a release modulator, into HPs by copolymerization with 4-(2-vinylbenzyloxy)-N,N-(diethylnicotinamide) (VBODENA). The AA content was varied from 0% to 50% (in the molar ratio to VBODENA). HPs spontaneously produced micelles in water, and their critical micelle concentrations (CMCs) ranged from 31 microg/mL to 86 microg/mL. Fluorescence probe study using pyrene showed that blank HP micelles possessed a good pH sensitivity, which was clearly observed at relatively high AA contents and pH>6. The pH sensitivity also affected the PTX loading property. Above pH 5, the PTX loading content and loading efficiency in HP micelles were significantly reduced. Although this may be primarily due to the AA moieties, other factors may include PTX degradation and polymer aggregation. The PTX release from HP micelles with more than 20% (mol) AA contents was completed within 12 h in a simulated intestinal fluid (SIF, pH=6.5). The HP micelles without any AA moiety showed very slow release profiles. In the simulated gastric fluid (SGF, pH=1.6), severe degradation of the released PTX was observed. The pH-dependent release of PTX from HP micelles can be used to increase the bioavailability of PTX upon oral delivery.

Tuning swelling pH and permeability of hydrogel multilayer capsules

We report on tuning swelling pH transitions of hydrogel hollow capsules that were derived from hydrogen-bonded multilayers via chemical cross-linking. The capsules were either of a single component - a weak poly(carboxylic acid), such as poly(acrylic acid) (PAA), poly(methacrylic acid) (PMAA), or poly(ethacrylic acid) (PEAA) - or contained two hydrogen-bonding polymers, such as in poly(carboxylic acid)/poly(N-vinylpyrrolidone-co-NH2) (PVPON-co-NH2) or in poly(carboxylic acid)/poly(N-vinylcaprolactam-co-NH2) (PVCL-co-NH2) systems. By varying the acidity of weak polyelectrolytes, the capsule swelling can be tuned over a wide pH range from 5 to 10. We show that differently from one-component capsules, the swelling amplitude of two-component capsules is limited by the number of cross-links provided by amino-containing units of a PVCL-co-NH2 copolymer. For two-component capsules with the same degree of cross-linking, permeability at the minimum swelling pH was decreased for PMAA-neutral copolymer capsules as compared to those of PAA-neutral copolymer. We also demonstrate that swelling pH of one-component capsules in the acidic region can be modulated via reversible association with a polycation. The fine control over the swelling pH transitions and permeability of hydrogel capsules enables their use in biomedical applications.

Dynamics of short as compared with long poly(acrylic acid) chains hydrophobically modified with pyrene, as followed by fluorescence techniques

New low and high molecular weight poly(acrylic acid), PAA, 2000 g mol(-1) and 450,000 g mol(-1), respectively, were tagged with pyrene (low and high contents of probe) and its behaviour in solution was investigated using absorption and fluorescence (steady-state and time-resolved) techniques. Fluorescence data shows that the degree and level of intramolecular association strongly depends on the molecular weight. With the short pyrene-labeled PAA chains in aqueous solution, the excimer-to-monomer fluorescence ratio I(E)/I(M) decreases with the increase of pH, oppositely to the increase in the I(E)/I(M) ratio with the increase in pH previously observed with the long chain PAA. Time-resolved data suggest that excimer formation with the short pyrene-labeled PAA polymers (ca. 28 acrylic acid monomers per chain) in water is largely due to excitation of Ground State Dimers, GSD. The increment of pH, and the consequent gradual ionization of the carboxylic groups in the chain, initially increases the fraction of GSD, possibly due to the occurrence of special micelle-like chain conformations, inside which the pyrene units are accommodated. A further increase of the pH above the pK(a) values, resulting in the full ionization of carboxylic groups, apparently destabilizes such chain conformations, which leads to a pH effect on the photophysical properties identical to that of the long chain polymers. In water, the dynamic data shows the existence of two excimers coexisting with two monomer classes. In methanol and dioxane (good solvents for the pyrene probe) at room temperature, where one excimer and two monomers are present, all rate constants could be obtained, as well as the fractions of ground-state species. It is thus shown that different types of interactions are produced with small- and long-sized PAA polymers, i.e., the size of the polymer matters.

Novel O-palmitoylscleroglucan-coated liposomes as drug carriers: Development, characterization and interaction with leuprolide

Polysaccharide-coated liposomes have been studied for their potential use for peptide drug delivery by the oral route because they are able to minimize the disruptive influences on peptide drugs of gastrointestinal fluids. The aim of this work was to synthesize and characterize a modified polysaccharide, O-palmitoylscleroglucan (PSCG), and to coat unilamellar liposomes for oral delivery of peptide drugs. To better evaluate the coating efficiency of PSCG, also scleroglucan (SCG)-coated liposomes were prepared. We studied the surface modification of liposomes and the SCG- and PSCG-coated liposomes were characterized in terms of size, shape, zeta potential, influence of polymer coating on bilayer fluidity, stability in serum, in simulated gastric and intestinal fluids and against sodium cholate and pancreatin. Leuprolide, a synthetic superpotent agonist of luteinizing hormone releasing hormone (LHRH) receptor, was chosen as a model peptide drug. After polymer coating the vesicle dimensions increased and the zeta potential shifted to less negative values. These results indicate that both SCG- and PSCG-coated liposomes surface and DSC results showed that PSCG was anchored on the liposomal surface. The stability of coated-liposomes in SGF, sodium cholate solution and pancreatin solution was increased. From this preliminary in vitro studies, it seems that PSCG-coated liposomes could be considered as a potential carrier for oral administration.

Cyclodextrin-grafted poly(phenylene ethynylene) with chemically-responsive properties

Water-soluble poly(phenylene ethynylene) carrying beta-cyclodextrin was prepared; the polymer exhibited a fluorescence color change or quenching, depending on the kind of guest.

Interactions between liposomes and hydroxypropylmethylcellulose

The characteristics of the adsorption process of hydroxypropylmethylcellulose (HPMC) of molecular weight 35400 Da and nominal viscosity 100 cps onto liposomes prepared with different egg lecithin-cholesterol molar ratios were examined. Adsorption isotherms were constructed and analysed to investigate the mechanisms implicated in the incorporation of the polymer to the interface. Only the isotherms obtained with cholesterol-free liposomes were fitted with Langmuir model. When cholesterol is present in the composition they present a sigmoidal slope. The mechanism of adsorption depends on liposome composition being the main force that drives polymer adsorption of hydrophobic nature. The apparent volumes of HPMC indicate that the conformation of the adsorbed macromolecules depends on liposome composition. Hydration enthalpy values show that adsorbed polymers do not give more hydrophilic systems after freeze-drying as expected with the hydrophilic characteristics of the HPMC.