Biomedical subjects

A V Delgado

Publications and source records attributed to A V Delgado.

At least 19 recordsLinked to original sources

PubMed2006

Ftorafur loading and controlled release from poly(ethyl-2-cyanoacrylate) and poly(butylcyanoacrylate) nanospheres.

In the present work, a method is described to prepare polymeric colloidal nanospheres, consisting of poly(ethyl-2-cyanoacrylate) (PE-2-CA) or poly(butylcyanoacrylate) (PBCA), loaded with the anticancer drug ftorafur. The method is based on the anionic polymerization procedure, often used in the synthesis of poly(alkylcyanoacrylate) nanospheres for drug delivery. A detailed investigation of the capabilities of both polymeric nanoparticles to load this drug is shown. The effect of synthesis residuals and degradation products on the absorbance of supernatants was considered in the loading and release measurement methodologies, because of their potential perturbing influence on the determination of ftorafur concentration in solution. We found the existence of two mechanisms of drug incorporation: absorption or entrapment in the polymeric network, and surface adsorption, detectable by means of zeta potential and spectrophotometric measurements. Among the factors affecting the drug incorporation to the polymer network, the type of polymer, the pH and the drug concentration are the main determining ones. Moreover, the acidity of the medium needs to be controlled in order to avoid the formation of macroaggregates of solids. The optimum loading conditions were used to perform ftorafur release evaluations from polymeric particles, and the influence of the mechanism of drug incorporation, the amount of drug loaded, and the type of polymer on the drug release were studied.

Absorption↗

PubMed2006

A simple model of the high-frequency dynamic mobility in concentrated suspensions.

Because electroacoustic techniques are gaining interest in many fields of colloid science, a number of theories dealing with the phenomenon of electrophoresis in high-frequency (on the order of the MHz) electric fields have been developed. In the present work we propose a straightforward derivation of a simple formula for the dynamic mobility of colloidal particles in mildly concentrated systems. Starting with a simple expression for the electrophoretic mobility in dilute suspensions, given as a function of the zeta potential and of the dipole coefficient, we introduce successive corrections related to: (i) the back flow of fluid induced by the electrophoretic motion of the particles; (ii) the electrostatic interactions among particles; (iii) the difference between the macroscopic and the external electric fields; (iv) the difference between the zero-momentum and the laboratory reference frames. Considering furthermore that the frequency dependence of the dipole coefficient is due to the Maxwell-Wagner-O'Konski double-layer relaxation, we obtain a mobility expression that compares well with other (semi)analytical models and (in proper conditions) with numerical cell-model calculations. However, its main merit is that it allows to understand, to a large extent, the physical origin of the frequency and volume fraction dependences of the dynamic mobility.

Journal Article↗

PubMed2006

Preparation and characterization of carbonyl iron/poly(butylcyanoacrylate) core/shell nanoparticles.

In this article a method is described to prepare composite colloidal nanoparticles, consisting of a magnetic core (carbonyl iron) and a biodegradable polymeric shell [poly(butylcyanoacrylate) or PBCA]. The method is based on the so-called anionic polymerization procedure, often used in the synthesis of poly(alkylcyanoacrylate) nanospheres designed for drug delivery. Interest of this investigation is based upon the fact that the heterogeneous structure of the particles can confer them both the possibility to respond to external magnetic fields and to be used as drug carriers. In order to investigate to what extent do the particles participate of this mixed properties, we compare in this work the physical characteristics (structure, chemical composition, specific surface area and surface electrical and thermodynamic properties) of the core/shell particles with those of both the nucleus and the coating material. This preliminary study shows that the mixed particles display an intermediate behavior between that of carbonyl iron and PBCA spheres. Electrophoretic mobility measurements as a function of pH and as a function of KNO3 concentration, show a great similarity between the core/shell and pure polymer nanoparticles. Similarly, a surface thermodynamic study performed on the three types of particles demonstrated that the electron-donor component of the surface free energy of the solids is very sensitive to the surface composition. In fact, a measurable decrease of such component is found for core/shell particles as compared to carbonyl iron. We also analyzed the influence of the relative amounts of polymer and carbonyl iron on the characteristics of the composite particles: data on the coating thickness, the amount of polymer bound to the magnetic nuclei, the redispersibility characteristics of the suspensions and the surface electrical and thermodynamic properties, suggest that the optimal synthesis conditions are obtained for a 4/3 initial monomer/carbonyl iron weight ratio.

Absorbable Implants↗

PubMed2005

Influence of cell-model boundary conditions on the conductivity and electrophoretic mobility of concentrated suspensions.

In the last few years, different theoretical models and analytical approximations have been developed addressing the problem of the electrical conductivity of a concentrated colloidal suspension. Most of them are based on the cell model concept, and coincide in using Kuwabara's hydrodynamic boundary conditions, but there are different possible approaches to the electrostatic boundary conditions. We will call them Levine-Neale's (LN, they are Neumann type, that is they specify the gradient of the electrical potential at the boundary), and Shilov-Zharkikh's (SZ, Dirichlet type). The important point in our paper is that we show by direct numerical calculation that both approaches lead to identical evaluations of the conductivity of the suspensions if each of them is associated to its corresponding evaluation of the macroscopic electric field. The same agreement between the two calculations is reached for the case of electrophoretic mobility. Interestingly, there is no way to reach such identity if two possible choices are considered for the boundary conditions imposed to the field-induced perturbations in ionic concentrations on the cell boundary (r = b), deltan(i) (r = b). It is demonstrated that the conditions deltan(i)(b) = 0 lead to consistently larger conductivities and mobilities. A qualitative explanation is offered to this fact, based on the plausibility of counter-ion diffusion fluxes favoring both the electrical conduction and the motion of the particles.

Colloids↗

PubMed2005

Optical properties of dilute hematite/silicone oil suspensions under low electric fields.

Electrorheology (ER) is the name given to a set of phenomena related to the significant changes experienced by the rheological properties of certain fluids and suspensions upon application of external electric fields. It is mostly explained in terms of the formation of particle aggregates as a consequence of field-induced particle-particle interactions. In this work, we explore such structures by investigating the changes in optical absorbance of hematite/silicone oil suspensions associated to the application of an electric field. We have studied the effect of particle concentration, phi, electric field strength, E(0), and viscosity, eta(m), of the liquid medium on the absorbance-time behavior of the suspensions. Photographs of the electrified suspensions helped in elucidating the structures formed. At low phi values, the absorbance A of electrified suspensions dramatically decreases with time until a constant plateau is reached. The absorbance fall is faster the higher the field, although at long times curves corresponding to different fields tend to merge. In these dilute suspensions particles are observed to migrate toward the electrodes thus clarifying the medium and reducing A. When the concentration of particles is increased, fibrils stretching between the electrodes can be observed in addition to particle deposition on them, as long as the field is kept low. At high fields, migration of the particles to the electrodes occurs whatever the volume fraction. Two mechanisms producing particle-particle interactions are suggested by these data: the conductivity mismatch between the particles and the medium brings about an interfacial or Maxwell-Wagner polarization of the particles; in addition, solids can acquire a net charge provoked by injection from the electrodes. The first mechanism will produce attractive dipole-dipole interactions and hence columns or fibrils. The second one should lead to electrophoretic migration. Structural observations suggest that the latter predominates at high fields. If the viscosity of the fluid phase is increased, the critical electric field values separating both regimes also increase: the electrophoretic motion is hindered and the particle-particle aggregation is enhanced.

Journal Article↗

PubMed2005

Stability and magnetic characterization of oleate-covered magnetite ferrofluids in different nonpolar carriers.

This work describes the preparation and stability evaluation of suspensions consisting of hydrophobic magnetite nanoparticles dispersed in different organic solvents. The ferrite particles are covered by a shell of chemisorbed oleate ions following a procedure that is described in detail. The oleate-covered particles were dispersed in different organic solvents with dielectric constants, epsilon(r), ranging between 1.8 and 9, and the centrifugal field strength needed to remove particle aggregates formed during the synthesis was determined for the different liquid carriers used. A thermodynamic analysis demonstrated that the observed stability of the suspensions in liquids with epsilon(r) < 5 is well correlated with the very low lyophobic attraction between the particles. This can easily be surmounted by thermal agitation, since the van der Waals attraction is negligible. In contrast, for liquids with epsilon(r) > 9, the suspensions become unstable because of the combined action of the van der Waals and lyophobic attractions, the latter being dominant for very polar solvents. Finally, a complete magnetic characterization of the oleate-magnetite powder, as well as of several stable ferrofluids prepared with it, was carried out. From this characterization, the magnetic diameters and magnetic moments of the particles immersed in the different liquid carriers were estimated and compared to those corresponding to the dry magnetic particles. This made it possible to estimate the thickness of the nonmagnetic layer on the particles.

Journal Article↗

PubMed2005

Quasi-static electrorheological properties of hematite/silicone oil suspensions under DC electric fields.

In this work, a modified rheometer has been used to gain information on the "start-up" of the shear flow of an electrorheological (ER) fluid consisting of hematite particles dispersed in silicone oil. The results show that unelectrified suspensions behave essentially as fluids, continuously deforming upon application of shear. However, this behavior changes in the presence of an electric field. For low fields and low volume fractions of solids, a solidlike (drastic increase in shear stress after the strain is applied) behavior is observed for small deformations. If the strain is increased, the yield starts and a transition to a viscoelastic-plastic nature is observed. Finally, a plastic behavior is characteristic of the post-yield regime. If the field strength and solids content are high, a discontinuous flow profile develops. These results, together with direct structural observations, suggest that the observed behavior is compatible with the formation of layers of particles electrophoretically deposited on the electrodes; the layers turn into rings when the shear field is applied. It is the slip of the fluid between these rings that can be considered responsible for the ER effect in these suspensions.

Journal Article↗

PubMed2005

Stabilization of magnetorheological suspensions by polyacrylic acid polymers.

This work is devoted to the synthesis and stabilization of magnetorheological suspensions constituted by monodisperse micrometer-sized magnetite spheres in aqueous media. The electrical double-layer characteristics of the solid/liquid interface were studied in the absence and presence of adsorbed layers of high molecular weight polyacrylic acids (PAA; Carbopol). Since the Carbopol-covered particles can be thought of as "soft" colloids, Ohshima's theory was used to gain information of the surface potential and the charge density of the polymer layer. The effect of the pH of the solution on the double-layer characteristics is related to the different conformations of the adsorbed molecules provoked by the dissociation of the acrylic groups present in polymer molecules. The stability of the suspensions was experimentally studied for different pH and polymer concentrations, and in the absence or presence of a weak magnetic field applied. The stability of the suspensions was explained using the classical DLVO theory of colloidal stability extended to account for hydration, steric, and magnetic interactions between particles. Diagrams of potential energy vs interparticle distance show the predominant effect of steric, hydrophilic/hydrophobic, and magnetic interactions on the whole stability of the system. The best conditions to obtain stable suspensions were found when strong steric and hydrophilic repulsions hinder the coagulation between polymer-covered particles, simultaneously avoiding sedimentation by the thickening effect of the polymer solution. When a not too high molecular weight PAA was employed in a low concentration, the task of a long-time antisettling effect compatible with the desired magnetic response of the fluid was achieved.

Journal Article↗

PubMed2005

Determination of stagnant layer conductivity in polystyrene suspensions: temperature effects.

In the classical theory of electrokinetic phenomena, it is admitted that the whole electrokinetic behavior of any colloidal system is fully determined by the zeta potential, zeta, of the interface. However, both experimental data and theoretical models have shown that this is an incomplete picture, as ions in the stagnant layer (the region between the solid surface and the slip plane--the plane where the equilibrium potential equals zeta) may respond to the field. In this paper, we aim at the evaluation of this contribution by the estimation of both K(SL)(sigma) (the surface conductivity of the stagnant layer) and K(d)(sigma) (the conductivity associated with the diffuse layer). This will be done by measuring the high-frequency dielectric dispersion (HFDD) in polystyrene suspensions; here "high-frequency" means the frequency interval where Maxwell-Wagner-O'Konski relaxation takes place (typically at MHz frequencies). Prior to any conclusions, a treatment of electrode polarization effects in the measurements was needed: we used two methods, and both led to similar results. Simulating the existence of surface conductivity by bulk conductivity, we reached the conclusion that no consistent explanation can be given for our HFDD and additional electrophoresis data based on the existence of diffuse-layer conductivity alone. We thus show how K(SL)(sigma) can be estimated and demonstrate that it can be explained by an ionic mobility very close to that characteristic of ions in the bulk solution. Such mobility, and hence also the values of K(SL)(sigma), increases with temperature as expected on simple physical grounds.

Journal Article↗

PubMed2005

An experimental investigation of the stability of ethylcellulose latex: correlation between zeta potential and sedimentation.

This paper aims at explaining the experimental observations of the stability and redispersibility of an aqueous ethylcellulose latex through the electrokinetic characterization of the particles. The surface charge and the electrical double layer thickness play an essential role in the stability of the system, hence the need for a full characterization of the polymeric particles. The effect of both pH and ionic strength of the dispersion medium were investigated. It was found that at acid pH values the latex displays "delayed" or "hindered" sedimentation: in such conditions, the electrophoretic mobility and zeta potential are rather low, indicating a small electrokinetic charge on the particles. At alkaline pH, when the dissociation of ionizable surface groups must be complete, the zeta potential is high and negative. The electrostatic repulsion between polymer particles is responsible for the low sedimentation volume and poor redispersibility of the latex. The effect of NaCl and CaCl(2) concentration on both the zeta potential and stability of the latexes was also investigated: it was found that CaCl(2) has the greatest influence, yielding flocculated, easily re-dispersible systems when its concentration in the dispersion medium is high enough. There qualitative observations were ascertained by means of calculations of the potential energy of interaction between particles. In the case of NaCl solutions, a high and relatively wide potential energy barrier was predicted, that may prevent the particle aggregation. Above 5mM NaCl a shallow minimum in the potential energy curves must lead to the formation of aggregates. Similar results were found with CaCl(2) solutions, although in this case the secondary minima are deeper and appear at lower concentrations.

Calcium Chloride↗

PubMed2002

Electrokinetics of concentrated suspensions of spherical colloidal particles with surface conductance, arbitrary zeta potential, and double-layer thickness in static electric fields.

In this paper the electrophoretic mobility and the electrical conductivity of concentrated suspensions of spherical colloidal particles have been numerically studied under arbitrary conditions including zeta potential, particle volume fraction, double-layer thickness (overlapping of double layers is allowed), surface conductance by a dynamic Stern layer model (DSL), and ionic properties of the solution. We present an extensive set of numerical data of both the electrophoretic mobility and the electrical conductivity versus zeta potential and particle volume fraction, for different electrolyte concentrations. The treatment is based on the use of a cell model to account for hydrodynamic and electrical interactions between particles. Other theoretical approaches have also been considered for comparison. Furthermore, the study includes the possibility of adsorption and lateral motion of ions in the inner region of the double layers (DSL model), according to the theory developed by C. S. Mangelsdorf and L. R. White (J. Chem. Soc. Faraday Trans.86, 2859 (1990)). The results show that the correct limiting cases of low zeta potentials and thin double layers for dilute suspensions are fulfilled by our conductivity formula. Moreover, the presence of a DSL causes very important changes, even dramatic, on the values of both the electrophoretic mobility and the electrical conductivity for a great range of volume fractions and zeta potentials, specially when double layers of adjacent cells overlap, in comparison with the standard case (no Stern layer present). It can be concluded that in general the presence of a dynamic Stern layer causes the electrophoretic mobility to decrease and the electrical conductivity to increase in comparison with the standard case for every volume fraction, zeta potential, and double-layer thickness.

Journal Article↗

PubMed2002

Stability of dispersions of colloidal hematite/yttrium oxide core-shell particles.

The colloidal stability of suspensions of hematite/yttria core/shell particles is investigated in this work and compared with that of the pure hematite cores. The different electrical surface characteristics of yttrium and iron oxides, as well as the diameters of both types of spherical particles, dominate the overall process of particle aggregation. The aggregation kinetics of the suspensions was followed by measuring their optical absorbance as a function of time. By previously calculating the extinction cross section of particle doublets, it was demonstrated that for both core and core/shell particles the turbidity of the suspensions should increase on aggregation. Such an increase was in fact found in the systems in spite of the ever-present tendency of the particles to settle under gravity. The authors used the initial slope of the turbidity increment time plots as a measure of the ease of aggregation between particles. Thus, they found that the essential role played by pH on the charge generation on the two oxides and the shift of one pH unit between the isoelectric points of hematite and yttria manifest in two features: (i) the stability decreases on approaching the isoelectric point from either the acid or basic side and (ii) the maximum instability is found for hematite at pH 7 and for hematite/yttria at pH 8, that is, close to the isoelectric points of alpha-Fe(2)O(3) and Y(2)O(3), respectively. The role of added electrolyte is simply to yield the suspensions of either type more unstable. Using the surface free energy of the particles, the authors could estimate their Hamaker constants in water. From these and their zeta potentials, the DLVO theory of stability was used to quantitatively explain their results.

Journal Article↗

PubMed2002

Analysis of the dielectric permittivity of suspensions by means of the logarithmic derivative of its real part.

Measurement of the dielectric permittivity of colloidal suspensions in the kilohertz frequency range (the so-called low-frequency dielectric dispersion) is a promising tool for the electrokinetic characterization of colloids. However, this technique is less used than would be desirable because of the difficulties associated with the measurements, the most important of which is the electrode polarization (EP). Recently (M. Wübbenhorst and J. Van Turnhout, Dielectrics Newsl. November (2000)) a method was proposed that appears capable of separating the unwanted electrode effects from the double-layer relaxation that we are interested in. The method, based on the logarithmic derivative of raw epsilon'(omega) data (epsilon'(omega) is the real part of the permittivity of the suspension for a frequency omega of the applied AC field), is first checked against the well-known theory of the AC permittivity of colloidal suspensions developed by DeLacey and White (E. H. B. DeLacey and L. R. White, J. Chem. Soc. Faraday Trans. 277, 2007 (1981)). We show that the derivative epsilon''(D)(omega)=-(pi/2)(partial differential epsilon'/partial differential ln omega) gives an excellent representation of the true imaginary part of the permittivity, epsilon''(omega). The technique is then applied to experimental data of the dielectric constant of polystyrene and ethylcellulose suspensions. We found that epsilon''(D) displays two separated behaviors when plotted against log omega in the frequency range 100 Hz-1 MHz: a monotonous decrease (associated with EP) followed by an absorption peak (associated with the double-layer relaxation, or alpha-relaxation). Interestingly, they are separated enough to make it possible to easily find the characteristic frequency of the alpha-relaxation. Fitting a relaxation function to epsilon''(D)(omega) after eliminating the part due to EP, we could calculate the real part epsilon'(omega) and compare it to the DeLacey and White (DW) theoretical predictions. A significantly better agreement between DW calculations and experimental epsilon'(omega) data is obtained when the logarithmic derivative method is used, as compared to the classical electrode-separation techniques.

Journal Article↗

PubMed2002

Aging effects in the electrokinetics of colloidal iron oxides.

We analyze in this contribution the effect of aging on the electrokinetic properties of magnetite (Fe(3)O(4)) and hematite (alpha-Fe(2)O(3)). In both cases, high-purity commercial samples and monodisperse synthetic particles were studied. Commercial magnetite showed a rather erratic dependence of its electrophoretic mobility u(e) with the concentration of NaCl. Furthermore, sufficient concentrations of the latter were able to change the sign of the mobility. When KNO(3) solutions were used, although no such change was observed, no clear effect of [KNO(3)] on the mobility was found, and, in addition, an intense aging effect was detected, as the mobility became increasingly positive in suspensions that were stored over 1 day. The picture was radically different with synthetic magnetite spheres, as the expected overall decrease of u(e) with either NaCl or KNO(3) concentration was measured. However, also in this case the aging effect was clearly observed: u(e) tended in this case to more negative values upon suspension storage, and a steady value of the mobility was reached only after 5 days in NaCl (and even longer in KNO(3) solutions). Because of the crystal structure similarities between magnetite and maghemite (gamma-Fe(2)O(3)), it has been shown that the final step of magnetite oxidation is maghemite. This is confirmed in the present study, as the mobility-pH trends of magnetite progressively approach those of maghemite after about 7 days of storage. Since hematite is chemically more stable than magnetite, our study focused in this case on the comparison between commercial and synthetic particles. The former showed a negative mobility at pH 5.5 under all conditions, suggesting an isoelectric point well below the value accepted for hematite (>/=7). The effect of aging on commercial samples was again very significant, as u(e) decreased in absolute value, apparently without limit as the time since preparation was longer. In contrast, synthetic hematite showed a more predictable dependence on ionic strength, and more limited aging effects, as u(e) reached equilibrium values after around 5 days in NaCl; longer times were required in KNO(3) solutions.

Journal Article↗

PubMed2001

Synthesis and characterization of poly(ethyl-2-cyanoacrylate) nanoparticles with a magnetic core.

A method is described to prepare composite colloidal nanoparticles, consisting of a magnetic core (magnetite) and a biodegradable polymeric shell (poly(ethyl-2-cyanoacrylate) or PE-2-CA). The method is based on the so-called anionic polymerization procedure, often used in the synthesis of PE-2-CA nanospheres designed for drug delivery. In the present work, the heterogeneous structure of the particles can confer both magnetic-field responsiveness and potential applicability as a drug carrier. In order to investigate to what extent this target is achieved, we compare the structure, chemical composition, and surface properties of the core/shell particles with those of both the nucleus and the coating material. This preliminary study shows that the synthetic new material displays an intermediate behavior between that of magnetite and PE-2-CA spheres. Thus, electrophoresis measurements as a function of pH and as a function of KNO3 concentration, show great similarity between the core/shell and pure polymer nanoparticles. A similar conclusion is reached when a surface thermodynamic study is performed on the three types of particles: the electron-donor component of the surface free energy of the solids is the quantity that appears to be most sensitive to the surface composition. The fact that PE-2-CA is close to being a non-polar material gives rise to a measurable decrease in the electron-donor component of the surface free energy of core/shell particles as compared to magnetite.

Contrast Media↗

PubMed2001

Different hypotensive responses to intravenous bovine and human thrombin preparations in swine.

BACKGROUND: Accidental intravenous introduction of commercial bovine thrombin (BT) during use of fibrin glue may result in profound hypotension. Commercial human thrombin (HT) is now available. This study compared the effects of intravenous BT versus HT in swine. METHODS: Swine received 30 U/kg BT, 60 U/kg BT, 30 U/kg HT, or 60 U/kg HT intravenously. Mean arterial pressure (MAP) and survival were monitored for 30 minutes. Thrombin purities and in vitro activities were examined. RESULTS: MAP nadir was lower (p < 0.05) after BT, 27.7 +/- 3.3% (mean +/- SEM) of pretreatment MAP, compared with 41.1 +/- 3.7% after HT. Five of six animals died after 60 U/kg BT, whereas all others survived (p < 0.05). Histology suggested more severe disseminated intravascular coagulation after BT. HT was purer than BT. In vitro activities were similar. CONCLUSION: Both BT and HT produced hypotension. HT appeared safer, because of higher purity. Regardless of source and purity, thrombin must be used with caution.

Animals↗

PubMed2000

Effects of heme proteins on nitric oxide levels and cell viability in isolated PMNs: a mechanism of toxicity.

Isolated human PMNs served as a model to determine oxyhemoglobin (oxyHb) binding and the effects of oxymyoglobin (oxyMb) or oxyHb on production of both nitric oxide (NO*) and superoxide (O2*-) and the resulting cytotoxicity. Physiologically relevant concentrations of NO* and H2O2 oxidized, to a similar extent, 2,7-dichlorodihydrofluorescein (DCFH) loaded into polymorphonuclear neutrophils (PMNs). Activation of PMNs with phorbol 12-myristate 13-acetate (PMA) markedly increased the internalization of extracellular oxyHb (10-250 microg/mL). OxyMb (10-300 microg/mL) or oxyHb (30-300 microg/mL) enhanced DCFH oxidation by a concentration-dependent mechanism in unstimulated, lipopolysaccharide (LPS) and tumor necrosis factor alpha (TNF-alpha)-, and PMA-stimulated PMNs. This increased DCFH oxidation was eliminated by NO* synthase inhibitors, glutathione and ascorbate, and was reduced by albumin. Nitrite accumulation in PMN filtrates mirrored NO*-induced DCF fluorescence. OxyMb-induced increases in NO* levels paralleled alterations in DNA and cell membrane damage and ATP levels in PMNs and co-cultured lymphocytes, and were attenuated by NO* synthase inhibitors. OxyMb eliminated extracellular O2*- at protein concentrations 100- to 1000-fold above those of superoxide dismutase. These results suggest that heme proteins bind and internalize into PMNs and increase NO*-induced damage in neighboring cells by inhibiting O2*(-)-scavenging of NO*. We propose a mechanism whereby heme protein-induced NO* levels may contribute to immunosuppression and increased infection rates associated with transfusions and cellular damage during inflammation.

Adenosine Triphosphate↗

PubMed1996

Adsorption of betamethasone disodium phosphate on ethylcellulose latex: an electrokinetic study.

The use of polymer latexes as vehicles for drug transport and controlled delivery in the body is a very active research field in applied colloid science. In this work, the polymer chosen is a commercially available ethylcellulose-based material, Aquacoat. We report electrokinetic (electrophoresis) data on this polymer in the presence of the soluble glucocorticoid betamethasone disodium phosphate (BMP). The electrophoretic mobility of the particles becomes more negative as the concentration of BMP in the medium is increased between 10(-5) and 10(-3) M, this demonstrating that the negative species produced upon dissolution of BMP adsorb on the particles; this trend is reversed for higher concentrations due to the phenomenon of double layer thickness. When pH is increased at constant BMP concentration, the negative mobility increases in absolute value, but it reaches lower values than attained in the absence of BMP. This is interpreted as another consequence of adsorption, since the ionization constants of the phosphate and sulfate groups are different. Such adsorption is confirmed and measured by spectrophotometric analysis of the supernatants after centrifugation of the suspensions; it is found that the adsorption density increases with the initial concentration of BMP in the medium, an almost vertical isotherm being obtained for concentrations above 5 x 10(-3) M, possibly due to bidimensional aggregation of the adsorbed molecules and multilayer adsorption at higher concentrations. It is found that the adsorbed amount increases with the ionic strength of the medium as a consequence of screening of the particle and BMP charges, whereas these electrostatic contributions to adsorption manifest also in the pH dependence of adsorption. IR analysis of the particles after equilibration with BMP solutions of increasing concentration agrees well with adsorption data.

Adsorption↗