Mucoadhesive nanoparticles may disrupt the protective human mucus barrier by altering its microstructure

Mucus secretions typically protect exposed surfaces of the eyes and respiratory, gastrointestinal and female reproductive tracts from foreign entities, including pathogens and environmental ultrafine particles. We hypothesized that excess exposure to some foreign particles, however, may cause disruption of the mucus barrier. Many synthetic nanoparticles are likely to be mucoadhesive due to hydrophobic, electrostatic or hydrogen bonding interactions. We therefore sought to determine whether mucoadhesive particles (MAP) could alter the mucus microstructure, thereby allowing other foreign particles to more easily penetrate mucus. We engineered muco-inert probe particles 1 μm in diameter, whose diffusion in mucus is limited only by steric obstruction from the mucus mesh, and used them to measure possible MAP-induced changes to the microstructure of fresh human cervicovaginal mucus. We found that a 0.24% w/v concentration of 200 nm MAP in mucus induced a ～10-fold increase in the average effective diffusivity of the probe particles, and a 2- to 3-fold increase in the fraction capable of penetrating physiologically thick mucus layers. The same concentration of muco-inert particles, and a low concentration (0.0006% w/v) of MAP, had no detectable effect on probe particle penetration rates. Using an obstruction-scaling model, we determined that the higher MAP dose increased the average mesh spacing ("pore" size) of mucus from 380 nm to 470 nm. The bulk viscoelasticity of mucus was unaffected by MAP exposure, suggesting MAP may not directly impair mucus clearance or its function as a lubricant, both of which depend critically on the bulk rheological properties of mucus. Our findings suggest mucoadhesive nanoparticles can substantially alter the microstructure of mucus, highlighting the potential of mucoadhesive environmental or engineered nanoparticles to disrupt mucus barriers and cause greater exposure to foreign particles, including pathogens and other potentially toxic nanomaterials.     

Design of mucoadhesive polymeric films based on blends of poly(acrylic acid) and (hydroxypropyl)cellulose

Mixing of aqueous solutions of poly(acrylic acid) and (hydroxypropyl)cellulose results in formation of hydrogen-bonded interpolymer complexes, which precipitate and do not allow preparation of homogeneous polymeric films by casting. In the present work the effect of pH on the complexation between poly(acrylic acid) and (hydroxypropyl)cellulose in solutions and miscibility of these polymers in solid state has been studied. The pH-induced complexation-miscibility-immiscibility transitions in the polymer mixtures have been observed. The optimal conditions for preparation of homogeneous polymeric films based on blends of these polymers have been found, and the possibility of radiation cross-linking of these materials has been demonstrated. Although the gamma-radiation treatment of solid polymeric blends was found to be inefficient, successful cross-linking was achieved by addition of N,N'-methylenebis(acrylamide). The mucoadhesive potential of both soluble and cross-linked films toward porcine buccal mucosa is evaluated. Soluble films adhered to mucosal tissues undergo dissolution within 30-110 min depending on the polymer ratio in the blend. Cross-linked films are retained on the mucosal surface for 10-40 min and then detach.     

Potentiometric titration of poly(L-glutamic acid) in aqueous solutions and binding of divalent cations

The potentiometric titration of poly(L -glutamic acid) was performed under conditions of varied ionic strength and concentration of added divalent cations. From these titration curves, the amount of divalent cations, especially magnesium, bound to poly(L -glutamic acid) was determined using a new method of analysis based on polyelectrolyte theory. By comparison with the polyelectrolyte, poly(acrylic acid), it was found that there are no specific interactions between metal ion and poly(L -glutamic acid) in either the helical or random coil conformation. The effect of these divalent cations on the conformation of poly(L -glutamic acid) was also discussed.     

Synthesis of tethered-polymer brush by atom transfer radical polymerization from a plasma-polymerized-film-coated quartz crystal microbalance and its application for immunosensors

This study synthesizes a tethered surface-grafted poly(acrylic acid) with quartz crystal microbalance (QCM) surfaces and provides detailed analysis of their properties and application. A tethered polyelectrolyte brush of poly(acrylic acid) is generated by first covering the substrate with a plasma-polymerized allyl alcohol (pp-AA) film, changing the polymerization initiators (bromination), and then grafting through atom transfer radical polymerization (ATRP) of tert-butyl acrylate (t-BA); these initiators are immobilized on a surface and exposed to a monomer. Finally, we convert the poly(t-BA) brush into poly(acrylic acid) through hydrolysis. We use the QCM technique to measure configuration change of the tethered poly(acrylic acid) grafted chains with two different degrees of polymerization (DP=50,200) in aqueous solutions at three different pH values (4.0, 4.8, and 5.4). The tethered poly(acrylic acid) grafted QCM shows that repeatable frequency responses are induced by pH change of solution. These frequency responses of large DP for pH are 20 times larger than responses of lower DP for pH. The frequency response of antibody immobilization on tethered poly(acrylic acid) grafted QCM (DP=200) and its frequency response of immunoreaction are 10 times larger than conventional immobilization methods by cysteamine with glutalaldehyde coupling of the antibody. The tethered poly(acrylic acid) grafted QCM can increase the frequency response for pH, the immobilization amount of antibody, and immunosensor response.     

Synthesis, characterization, and bioavailability of mannosylated shell cross-linked nanoparticles

Saccharide-functionalized shell cross-linked (SCK) polymer micelles designed as polyvalent nanoscaffolds for selective interactions with receptors on Gram negative bacteria were constructed from mixed micelles composed of poly(acrylic acid-b-methyl acrylate) and mannosylated poly(acrylic acid-b-methyl acrylate). The mannose unit was conjugated to the hydrophilic chain terminus of the amphiphilic diblock copolymer precursor, from which the SCK nanoparticles were derived, by the growth of the diblock copolymer from a mannoside functionalized atom transfer radical polymerization (ATRP) initiator. Mixed micelle formation between the amphiphilic diblock copolymer and mannosylated amphiphilic diblock copolymer was followed by condensation-based cross-linking between the acrylic acid residues present in the periphery of the polymer micelles to afford SCK nanoparticles. SCKs presenting variable numbers of mannose functionalities were prepared from mixed micelles of controlled stoichiometric ratios of mannosylated and nonmannosylated diblock copolymers. The polymer micelles and SCKs were characterized by dynamic light scattering (DLS), electrophoretic light scattering, atomic force microscopy (AFM), transmission electron microscopy (TEM), and analytical ultracentrifugation (AU). Surface availability and bioactivity of the mannose units were evaluated by interactions of the nanostructures with the model lectin Concanavalin A via DLS studies, with red blood cells (rabbit) via agglutination inhibition assays and with bacterial cells (E. coli) via TEM imaging.     

Rational design of cytophilic and cytophobic polyelectrolyte multilayer thin films

Nanostructured polyelectrolyte multilayer thin films electrostatically assembled alternately from such polymers as poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) were investigated for their in vitro cell interactions. Not surprisingly, NR6WT cells, a highly adhesive murine fibroblast cell line, attached to many different multilayer combinations tested. However, PAH/PAA multilayers constructed at pH deposition conditions of 2.0/2.0 were completely bioinert. Analogous cell interactions were observed with PAH/poly(methacrylic acid) (PAH/PMA), PAH/sulfonated poly(styrene) (PAH/SPS), and poly(diallyldimethylammonium chloride)/SPS (PDAC/SPS) systems, thereby suggesting a general trend in the fibroblasts' response to multilayers. Specifically, highly ionically stitched films attracted cells, whereas weakly ionically cross-linked multilayers, which swell substantially in physiological conditions to present richly hydrated surfaces, resisted fibroblast attachment. Thus, by manipulating the multilayer pH or ionic strength assembly conditions or both, which in turn dictate the molecular architecture of the thin films, one may powerfully direct a single multilayer combination to be either cell adhesive or cell resistant.     

Cooperative effects involved in esterolytic reactions of cationic long chain esters catalyzed by benzimidazole-containing polymers

The solvolyses of positively charged esters with varying chain length catalyzed by benzimidazole, poly[5(6)-vinylbenzimidazole] and copolymers of 5(6)-vinylbenz-imidazole with acrylic acid were studied. Poly[5(6)-vinylbenzimidazole] showed a marked selectivity for the positively charged esters with varying aliphatic chain length but the catalytic activity was suppressed. In order to investigate the more detailed characteristics of the 5(6)-vinylbenzimidazole-acrylic acid copolymers in the solvolyses of these esters, the effects of copolymer composition on their catalytic activities were studied. In the solvolyses of every ester employed, the copolymer compositions affected their catalytic activities. In 40% 1-propanol-water the activities of the copolymers indicated a strong dependence on the carboxylatebenzimidazole-carboxylate triad. These effects were due to strong electrostatic interactions between these sequences and the substrates. The effects of solvent composition on the catalytic activities of the copolymer-catalyzed solvolyses were also investigated. The copolymers of 5(6)-vinylbenzimidazole with acrylic acid were found to have entirely different characteristics in methanol-water than in 1-propanol-water systems. The catalytic ability was found to be a function of the benzimidazole content and on the size of the substrate. Apolar interactions became a dominant force in the methanol-water system.     

Counterion binding in partially neutralized poly(D-glutamic acid) and poly(DL-glutamic acid)

Sodium counterion association with partially neutralized poly(D -glutamic acid) or poly(DL -glutamic acid) was measured by use of Wall's transference method with radioactive sodium. In the region where both polyacids are in completely random coil form, fractions of association were considerably less than that with poly(acrylic acid) in the same region of degree of neutralization. Even in the region where poly (D -glutamic acid) is in the helical form, the fraction of association was less than that with poly(acrylic acid) in the same region. No pronounced characteristics attributable to counterion association corresponding to the helix–coil transition could be found. The association phenomena were discussed on the basis of a rodlike model of polyelectrolyte.     

Activity and Stability of Native and Modified Subtilisins in Various Media

The activity and stability of native subtilisin 72, its complex with poly(acrylic acid), and subtilisin covalently attached to poly(vinyl alcohol) cryogel were studied in aqueous and organic media by hydrolysis of specific chromogenic peptide substrates. Kinetic parameters of the hydrolysis of Glp-Ala-Ala-Leu-pNA by native subtilisin and its complex with poly(acrylic acid) were determined. Based on the comparative study of stability of native and modified subtilisins in media of various compositions, it was established that covalent immobilization of subtilisin on poly(vinyl alcohol) cryogel is the most effective approach to improve enzyme stability in water as well as in mixtures with low water content.     

Precipitation with poly acrylic acid as a trypsin bioseparation strategy

Precipitation of enzymes with reversible soluble–insoluble polymers is a simple approach which can be easily scaled up. This work reports investigations aiming at verifying the existence of specific interactions and complex formation between porcine trypsin and poly acrylic acids using spectroscopy techniques. The trypsin–polymer complex was insoluble at pH lower than 5, with a stoichiometric ratio polymer mol per protein mol of 1:148. It took only a minute for the insoluble complex to form and it was redissolved modifying the pH of the medium. The enzymatic activity of trypsin was maintained even in the presence of the polymer and after precipitation poly acrylic acid presence protect the enzyme from itself degradation. The conditions of complex formation were studied using pure proteins that could be applied on porcine pancreas homogenates as an isolation strategy of trypsin.     

An efficient preparation of polyanionic affinity agent and its evaluation for the measurement of glycated hemoglobin

An efficient method was developed for the preparation of polyanionic affinity agent (3), a key component in the measurement of glycated hemoglobin (GHb). Glycated hemoglobin is an important clinical marker for diagnosis of patients with diabetes and useful to monitor the management of disease. The affinity agent (3) was prepared based on coupling reaction between poly(acrylic acid) (1) and 3-aminophenylboronic acid (2) in water. The critical features of this polymeric affinity agent (3), such as size, boronic acid incorporation ratio and concentration, on the measurement of glycated hemoglobin were evaluated. It was found that the agent (3) prepared using poly(acrylic acid) (1) with 225 kDa molecular weight gave optimal GHb measurement. The performance test results demonstrated that the boronic acid incorporation ratio and concentration of affinity agent (3) play a critical role in the assay and determines the precision of glycated hemoglobin measurement.     

Immobilization of Pseudorabies Virus in Porcine Tracheal Respiratory Mucus Revealed by Single Particle Tracking

Pseudorabies virus (PRV) initially replicates in the porcine upper respiratory tract. It easily invades the mucosae and submucosae for subsequent spread throughout the body via blood vessels and nervous system. In this context, PRV developed ingenious processes to overcome different barriers such as epithelial cells and the basement membrane. Another important but often overlooked barrier is the substantial mucus layer which coats the mucosae. However, little is known about how PRV particles interact with porcine respiratory mucus. We therefore measured the barrier properties of porcine tracheal respiratory mucus, and investigated the mobility of nanoparticles including PRV in this mucus. We developed an in vitro model utilizing single particle tracking microscopy. Firstly, the mucus pore size was evaluated with polyethylene glycol coupled (PEGylated) nanoparticles and atomic force microscope. Secondly, the mobility of PRV in porcine tracheal respiratory mucus was examined and compared with that of negative, positive and PEGylated nanoparticles. The pore size of porcine tracheal respiratory mucus ranged from 80 to 1500 nm, with an average diameter of 455±240 nm. PRV (zeta potential: −31.8±1.5 mV) experienced a severe obstruction in porcine tracheal respiratory mucus, diffusing 59-fold more slowly than in water. Similarly, the highly negatively (−49.8±0.6 mV) and positively (36.7±1.1 mV) charged nanoparticles were significantly trapped. In contrast, the nearly neutral, hydrophilic PEGylated nanoparticles (−9.6±0.8 mV) diffused rapidly, with the majority of particles moving 50-fold faster than PRV. The mobility of the particles measured was found to be related but not correlated to their surface charge. Furthermore, PEGylated PRV (-13.8±0.9 mV) was observed to diffuse 13-fold faster than native PRV. These findings clearly show that the mobility of PRV was significantly hindered in porcine tracheal respiratory mucus, and that the obstruction of PRV was due to complex mucoadhesive interactions including charge interactions rather than size exclusion.     

Interaction of lysozyme with negatively charged flexible chain polymers

The complex formation between the basic protein lysozyme and anionic polyelectrolytes: poly acrylic acid and poly vinyl sulfonic acid was studied by turbidimetric and isothermal calorimetric titrations. The thermodynamic stability of the protein in the presence of these polymers was also studied by differential scanning calorimetry. The lysozyme-polymer complex was insoluble at pH lower than 6, with a stoichiometric ratio (polymer per protein mol) of 0.025-0.060 for lysozyme-poly vinyl sulfonic acid and around 0.003-0.001 for the lysozyme-poly acrylic acid. NaCl 0.1M inhibited the complex precipitation in agreement with the proposed coulombic mechanism of complex formation. Enthalpic and entropic changes associated to the complex formation showed highly negative values in accordance with a coulombic interaction mechanism. The protein tertiary structure and its thermodynamic stability were not affected by the presence of polyelectrolyte.     

Evaluation of mucoadhesive properties of chitosan microspheres prepared by different methods

The mucoadhesive properties of chitosan microspheres prepared by different method were evaluated by studying the interaction between mucin and microspheres in aqueous solution. The interaction was determined by the measurement of mucin adsorbed on the microspheres. A strong interaction between chitosan microspheres and mucin was detected. The intensity of the interaction was dependent upon the method of preparation of chitosan microspheres and the amount of mucin added. The extent of mucus adsorption was proportional to the absolute values of the positive zeta potential of chitosan microspheres. The zeta potential in turn was found to be dependent upon the method of preparation of microspheres. The adsorption of type III mucin (1% sialic acid content) was interpreted using Freundlich or Langmuir adsorption isotherms. The values ofr ² were greater for Langmuir isotherm as compared with Freundlich isotherm. The adsorption of a suspension of chitosan microspheres in the rat small intestine indicated that chitosan microspheres prepared by tripolyphosphate cross-linking and emulsification ionotropic gelation can be used as an excellent mucoadhesive delivery system. The microspheres prepared by glutaraldehyde and thermal cross-linking showed good stability in HC1 as compared with microspheres prepared by tripolyphosphate and emulsification ionotropic gelation.     

Adhesion of microorganisms to bovine submaxillary mucin coatings: effect of coating deposition conditions

The adhesion of Staphylococcus epidermidis, Escherichia coli, and Candida albicans on mucin coatings was evaluated to explore the feasibility of using the coating to increase the infection resistance of biomaterials. Coatings of bovine submaxillary mucin (BSM) were deposited on a base layer consisting of a poly(acrylic acid-b-methyl methacrylate) (PAA-b-PMMA) diblock copolymer. This bi-layer system exploits the mucoadhesive interactions of the PAA block to aid the adhesion of mucin to the substratum, whereas the PMMA block prevents dissolution of the coating in aqueous environments. The thickness of the mucin coating was adjusted by varying the pH of the solution from which it was deposited. Thin mucin coatings decreased the numbers of bacteria but increased the numbers of C. albicans adhering to the copolymer and control surfaces. Increasing the mucin film thickness resulted in a further lowering of the density of adhering S. epidermidis cells, but it did not affect the density of E. coli. In contrast, the density of C. albicans increased with an increase in mucin thickness.     

Location of fluorotryptophan sequestered in an amphiphilic nanoparticle by rotational-echo double-resonance NMR.

Rotational-echo double-resonance (REDOR) 13C NMR spectra (with 19F dephasing) have been obtained of 6-fluorotryptophan complexed by a polymeric amphiphilic nanosphere consisting of a polystyrene core covalently attached to a poly(acrylic acid)-polyacrylamide shell. The REDOR spectra show that aromatic carbons from the polystyrene core and oxygenated carbons in the poly(acrylic acid)-polyacrylamide shell are both proximate to the 19F of 6-fluorotryptophan. Molecular modeling restrained by distances inferred from the REDOR spectra suggests that all of the 6-fluorotryptophans are in the shell but within 10 A of the core-shell interface.     

Light scattering of aqueous solutions of DNA, poly(acrylic acid), and tobacco mosaic virus under alternating electric field

Two new techniques, amplitude modulation (AM) and frequency modulation (FM) of an electric field, are developed for the light-scattering study of polymer solutions under ac electric fields. The AM technique makes it possible to observe accurately the frequency dependence of the intensity changes of scattered light due to the electric field. The FM one allows us to obtain directly the frequency derivative of the intensity change. The techniques are applied to DNA, poly(acrylic acid), and tobacco mosaic virus in the frequency range from 10 Hz to 100 kHz. A low-frequency relaxation is found for both DNA and poly(acrylic acid). The obsersved relaxation time of DNA agrees with that in the dielectric relaxation of DNA, which has been attributed to the rotation of the molecule with a quasipermanent dipole. In the case of poly(acrylic acid), the relaxation strength increases with increasing degree of neutralization. TMV at a concentration of 0.1% exhibits a negative relaxation at low frequencies, which indicates the rotation of TMV aggregate with a permanent dipole along its minor axis.     

Light scattering from solutions of a semi-flexible polymer and a polyelectrolyte both having sharp molecular weight distributions

The particle scattering factor in light scattering is determined for poly(tert-butyl crotonate) in n-butyl chloride and also for partially neutralized poly (acrylic acid) in aqueous solution in the presence of added neutral salt (NaBr). The former is a wormlike chain which is extended due to stiffness of the polymer chain, while the latter is extended due to the electrostatic repulsive force which is a kind of excluded volume effect. A clear difference is found between P(theta) of both polymers.     

Novel insulin thiomer nanoparticles: in vivo evaluation of an oral drug delivery system

It was aim of the study to investigate the in vivo potential of a novel insulin-thiomer complex nanoparticulate delivery system. Insulin loaded nanoparticles were obtained by the formation of hydrogen bonds between poly(vinyl pyrrolidone) (PVP) and poly(acrylic acid)-cysteine (PAA-Cys) or poly(acrylic acid) (PAA), respectively, in the presence of insulin. Dissolution behavior of insulin from tablets as well as nanoparticulate suspensions was evaluated in vitro. Serum insulin concentrations and reduction of blood sugar values were determined after oral administration of nanoparticles formulated as enteric coated tablets and suspensions. Results displayed a low serum insulin concentration and pharmacological efficacy in terms of blood sugar reduction after oral administration of enteric coated tablets. On the contrary, nanoparticulate suspensions led to significant serum insulin concentrations. Furthermore a 2.3-fold improvement of the AUC of insulin could be achieved due to the use of thiolated PAA instead of unmodified PAA. In addition, a blood sugar reduction of 22% was observed. Results demonstrate that this novel complex nanoparticulate formulation is an encouraging new attempt toward the noninvasive delivery of peptide drugs.     

Structure and characterization of amphoteric semi-IPN hydrogel based on cationic starch

A series of semi-interpenetrating polymer network (semi-IPN) materials were prepared by blending polymerization of acrylic acid (AA) in cationic starch (CS) and poly(methacryloyloxyethyl trimethylammonium chloride) (PDMC) solution. The crosslinker concentration, the feed ratio of the CS-g-AA to PDMC was discussed in term of the swelling capacity, and hydrogel properties were evaluated by network parameters M_c, morphological and compressive load tests. The semi-IPN hydrogels were also characterized by FT-IR spectroscopy to confirm the interactions between CS-g-AA and PDMC. Electron microscopy involved to staining of the anionic phases using CsF showed a transition from two-phase to compatible structure with the increasing content of PDMC, and further confirmed that the semi-IPN structure in hydrogels along with DSC. The resultant semi-IPN hydrogels were found to possess appreciable compatibility, good swellability and mechanical strength.