Electrophoretic mobility and colloidal stability of PLGA particles coated with IgG.

Drug delivery systems based on polymeric nanocarriers have been widely exploited during the last years. However, one of the basic problems that is still not totally solved in this kind of systems is the ability of delivering drugs to specific target cells. Coating the nanocarrier with reactive antibodies against specific molecules presented in the external membrane of the target cells is a usual recommendation. In this paper, an ideal delivery system has been studied. Nanoparticles made of poly(d,l-lactic acid/glycolic acid) 50/50 (PLGA) polymers have been coated with polyclonal IgG. In the first part of the paper, some basic characteristics of these IgG-PLGA complexes have been analysed (i.e. size, electrophoretic mobility and colloidal stability). Then, the immunoreactivity of the immobilized IgG molecules was tested by using an optical device, monitoring the binding of a standard molecule (C-reactive protein, CRP) to the antibody (antiCRP-IgG) adsorbed on the PLGA particles. This allowed us to estimate the percentage of active IgG molecules on the PLGA particles by applying a simple kinetic model to the immunoreactivity results. According to this model, the PLGA-IgG particles supply a good immunoresponse even if only less than 5% of the total IgG molecules on the surface were active. Despite the simplicity of the system, the results may be of potential interest for developing more realistic nanocarriers with targeting ability. That is, it can be inferred that it is possible to obtain a high targeting specificity in IgG-sensitized nanocarriers even working with a low coverage of active antibody molecules. The results have been compared with those similarly obtained with polystyrene (PS) particles used as a reference system.

Colloidal stability of pluronic F68-coated PLGA nanoparticles: a variety of stabilisation mechanisms.

Poloxamers are a family of polypropylene oxide (PPO) and polyethylene oxide (PEO) tri-block copolymers that are usually employed in the micro- and nanoparticulate engineering for drug delivery systems. The aim of this work is to study the electrophoretic mobility (mu(e)) and colloidal stability of complexes formed by adsorbing a poloxamer (Pluronic F68) onto poly(d,l-lactic-co-glycolic acid) (PLGA) nanoparticles. A variety of stabilisation mechanisms have been observed for the Pluronic-coated PLGA nanoparticles, where DLVO interactions, solvent-polymer segment interactions and hydration forces play different roles as a function of the adsorbed amount of Pluronic. In addition, the mu(e) and stability data of these complexes have been compared to those obtained previously using a PLGA-Pluronic F68 blend formulation. As both the mu(e) and the stability data are identical between the two systems, a phase separation of both components in the PLGA-Pluronic blend formulation is suggested, being the PLGA located in the core of the particles and the Pluronic in an adsorbed shell.

Hofmeister effects on the colloidal stability of an IgG-coated polystyrene latex.

The effect of various ions related to the Hofmeister series (HS) on different properties of a cationic latex covered with a protein (IgG) is analyzed in this study. NaNO3, NH4NO3, and Ca(NO3)2 were used to compare the specificity of the cations, and NaCl, NaSCN, NaNO3, and Na2SO4, to compare the specificity of the anions. Two pH values, 4 and 10, were chosen to analyze the behavior of these ions acting as counter- and co-ions. At pH 4, the total surface charge is positive, whereas at pH 10 it is negative. Three different phenomena have been studied in the presence of these Hofmeister ions: (1) colloidal aggregation, (2) electrophoretic mobility, and (3) colloidal restabilization. The specific effect of the ions was clearly observed in all experiments, obtaining ion sequences ordered according to their specificity. The most important parameter for ion ordering was the sign of the charge of the colloidal particle. Positively charged particles displayed an ion order opposite that observed for negatively charged surfaces. Another influential factor was the hydrophobic/hydrophilic character of the particle surface. IgG-latex particle surfaces at pH 10 were more hydrophilic than those at pH 4. The SCN- ion had a peculiar specific effect on the phenomena studied (1)-(3) at pH 10. With respect to the restabilization studies at high ionic strengths, new interesting results were obtained. Whereas it is commonly known that cations may provoke colloidal restabilization in negative particles when they act as counterions, our experiments demonstrated that such restabilization is also possible with positively charged particles. Likewise, restabilization of negative surfaces induced by the specific effect of chaotropic anions (acting as co-ions) was also observed.

Physicochemical characterization of chitosan nanoparticles: electrokinetic and stability behavior.

Some physical properties of nanogel particles formed by chitosan ionically cross-linked by tripolyphosphate (TPP) have been studied. Electrokinetic properties and colloidal stability were analyzed as a function of pH and ionic strength of the medium. Chitosan particles showed volume phase transitions (swelling/shrinking processes) when the physicochemical conditions of the medium were changed. Experimental data were mainly obtained by electrophoretic mobility measurements and by photon correlation spectroscopy and static light scattering techniques. Chitosan chains possess glucosamine groups that can be deprotonated if the pH increases. Therefore, modification of pH from acid to basic values caused a deswelling process based on a reduction of the intramolecular electric repulsions inside the particle mesh. Electrophoretic mobility data helped to corroborate the above electrical mechanism as responsible for the size changes. Additionally, at those pH values around the isoelectric point of the chitosan-TPP particles, the system became colloidally unstable. Ionic strength variations also induced important structural changes. In this case, the presence of KCl at low and moderate concentrations provoked swelling, which rapidly turned on particle disintegration due to the weakness of chitosan-TPP ionic interactions. These last results were in good agreement with the predictions of gel swelling theory by salt in partially ionized networks.

Nanoparticles made from novel starch derivatives for transdermal drug delivery.

The goal of this paper was aimed to the formulation of nanoparticles by using two different propyl-starch derivatives - referred to as PS-1 and PS-1.45 - with high degrees of substitution: 1.05 and 1.45 respectively. A simple o/w emulsion diffusion technique, avoiding the use of hazardous solvents such as dichloromethane or dimethyl sulfoxide, was chosen to formulate nanoparticles with both polymers, producing the PS-1 and PS-1.45 nanoparticles. Once the nanoparticles were prepared, a deep physicochemical characterization was carried out, including the evaluation of nanoparticles stability and applicability for lyophilization. Depending on this information, rules on the formation of PS-1 and PS-1.45 nanoparticles could be developed. Encapsulation and release properties of these nanoparticles were studied, showing high encapsulation efficiency for three tested drugs (flufenamic acid, testosterone and caffeine); in addition a close to linear release profile was observed for hydrophobic drugs with a null initial burst effect. Finally, the potential use of these nanoparticles as transdermal drug delivery systems was also tested, displaying a clear enhancer effect for flufenamic acid.

Insulin-loaded PLGA nanoparticles for oral administration: an in vitro physico-chemical characterization.

The aim of this work was to study poly(d,l-lactic-co-glycolic) acid (PLGA) nanoparticles--formulated by a modified solvent diffusion technique--applied as model nanocarriers for insulin in potential oral administrations. These nanostructures consisted of a blend matrix formed by PLGA copolymer and polyoxyethylene derivatives. Two types of blend formulations, PLGA:poloxamer (Pluronic F68) and PLGA:poloxamine (Tetronic T904), were analyzed, and the results compared to those obtained with pure PLGA nanoparticles. The work has been divided into two parts. (a) Firstly, the stability of the unloaded nanoparticles in simulated gastric and intestinal fluids was studied. Degradation studies reflected a strong interaction between the pure PLGA nanoparticles and the digestive enzymes. However, this interaction was considerably reduced in the blend formulations, although the PLGA:poloxamine system became colloidally unstable in the simulated gastric fluid. (b) Secondly, the effect of the net charge of the encapsulated macromolecule in the final properties of the blend formulations was studied by encapsulating insulin below and above its corresponding isoelectric point. The net charge of the encapsulated protein showed a clear effect in the final size of the nanoparticles, while the encapsulation efficiency was controlled by the polyoxyethylene derivative presents in the blend formulation. The obtained results show that those carriers formed with encapsulated insulin in PLGA-Pluronic F68 particles are capable, at least in vitro, to overcome the gastrointestinal barrier. Therefore, these nanocarriers seem to be appropriate for oral administration of insulin, although performing in vivo studies becomes necessary to corroborate such statement.

Hofmeister effects in the restabilization of IgG--latex particles: testing Ruckenstein's theory.

The hydration interaction is responsible for the colloidal stability observed in protein-coated particles at high ionic strengths. The origin of this non-DLVO interaction is related not only to the local structure of the water molecules located at the surface but also to the structure of those molecules involved in the hydration of the ions that surround the colloidal particles. Ruckenstein and co-workers have recently developed a new theory based on the coupling of double-layer and hydration interactions. Its validity was contrasted by their fitting of experimental data obtained with IgG-latex particles restabilized at high salt concentration. The theory details the important role played by the counterions in the stability at high salt concentrations by proposing an ion pair reaction forming surface dipoles. These surface dipoles are responsible of repulsive interactions between two approaching surfaces. This paper checks the theory with recent data where some ions associated with the Hofmeister series (NO(3)(-), SCN(-) and Ca(2+)) restabilize the same kind of IgG-latex systems by means of hydration forces. Surprisingly, these ions induce stability acting even as co-ions, likely by modifying the water structure at the surface, but not forming surface ion pairs. Therefore, this experimental evidence would question Ruckenstein's theory based on the surface dipole formation for explaining the observed restabilization phenomena.

A review of factors affecting the performances of latex agglutination tests.

The present review describes the different strategies followed to improve the performance of latex agglutination tests. The analysis is mainly focused on the diverse parameters that affect the final colloidal stability of the immunoprotein-latex system. These parameters include: the surface properties of polymer carriers; the different kind of antibodies usually employed; the use of BSA as stabilizer; the co-adsorption of various macromolecules (BSA, surfactants and lipids) and antibodies; recent approaches to colloidal stability at high ionic strengths due to hydration forces; and the covalent coupling of antibodies on functionalized latex particles. Special emphasis is given to the relation between electrophoretic mobility and the colloidal stability of the sensitized particles and how this knowledge can be utilized for a better understanding of the immunoagglutination kinetic.

Colloidal stability of IgG- and IgY-coated latex microspheres.

The stabilization of antibody-latex complexes at high salt concentration is an event that cannot be explained by the widespread DLVO theory. Adsorption of antibodies on polystyrene latex usually leads to a loss in colloidal stability. However, after the expected particle aggregation induced by an increase in ionic strength, an 'anomalous' restabilization occurs when the electrolyte concentration increases even more. This non-DLVO behaviour can be explained taking into account the hydration forces, which become significant in hydrophilic surfaces. This restabilization has already been observed in different protein latex complexes. In the present work, a study on the stability patterns of polystyrene particles covered independently by mammalian and chicken antibodies has been performed. This study reveals that avian antibodies present a more hydrophobic surface than that of mammalian antibodies. In addition, it has been possible to obtain some information about the molecular orientation of the adsorbed antibodies from the stability experiments. This information has been corroborated by an immunoreactivity study.

A comparative study between the adsorption of IgY and IgG on latex particles.

The use of egg yolk antibodies (IgY) instead of IgG from mammalian species may present several advantages in the development of routine diagnostic immunoassays. On the one hand, the animal suffering is reduced, as antibodies are obtained directly from the egg. On the other hand, the use of IgY avoids the rheumatoid factor interference. The rheumatoid factor interacts with IgG molecules in many immunoassays causing false positive results. Despite these advantages, IgY antibodies are scarcely used. As part of an aim to develop a diagnostic test based on IgY-latex agglutination, a preliminary study on some characteristics of the IgY-latex complexes is carried out. In this work, protein adsorption and desorption, isoelectric point, electrokinetic mobility, and colloidal stability are analysed. Results are compared to those obtained by IgG. Interesting differences are observed (which mainly arise from the difference in molecular structure between IgY and IgG), suggesting that IgY is a more hydrophobic molecule than IgG. In addition, colloidal dispersions of IgY-covered latex particles are more stable (at pH 8) than those sensitized by IgG.