Biomedical subjects

B Seijo

Publications and source records attributed to B Seijo.

5 recordsLinked to original sources

PubMed2005

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.

Chemical Phenomena↗

PubMed2001

Colon-specific delivery of budesonide from microencapsulated cellulosic cores: evaluation of the efficacy against colonic inflammation in rats.

Budesonide (BDS) is a potent corticosteroid that has important implications in the pharmacotherapy of inflammatory bowel disease, especially in the treatment of ulcerative colitis and Crohn's disease. BDS is available on the market in the form of enteric-coated preparations. However these products, similar to other available site-specific dosage forms, are not sufficiently selective to treat colonic inflammatory bowel disease. The objective of this study was to evaluate the efficacy of a new microparticulate system containing BDS, to treat experimentally induced colitis in rats. This microparticulate system consisted of BDS-containing hydrophobic cores, microencapsulated within an enteric polymer, which solubilizes at above pH 7, thus combining pH-sensitive and controlled-release properties. Colonic injury and inflammation were assessed by measuring colon/bodyweight ratio, myeloperoxidase (MPO) activity, and by scoring macroscopic and histological damage in colitic rats. Rats were treated orally with BDS, included in the developed system, once a day for 4 days after the induction of inflammation. A BDS suspension and BDS-containing enteric microparticles were included as control formulations in the experimental design. The administration of the new BDS delivery system significantly reduced the colon/bodyweight ratio compared with the administration of control formulations. Similarly, MPO activity and macroscopic and histological damage of the inflamed colonic segments decreased significantly when the BDS formulation was administered, compared with the results obtained after oral administration of the drug suspension. There were no significant differences, however, when the new treatment was compared with the control formulation consisting of simple enteric microparticles.

Administration, Oral↗

PubMed2000

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.

Adsorption↗

PubMed1995

Surface pressure-area isotherms of mixed cyclosporin-poly(isobutylcyanoacrylate) monolayers spread at the air/water interface.

The pi-A isotherms of mixed monolayers of cyclosporin and poly(isobutylcyanoacrylate) (PIBCA) show that the molecular areas of cyclosporin and PIBCA are additive regardless of the pH of the substrate or the physical state of the monolayers. All these mixed films collapse at the same surface pressure; therefore, application of the two-dimensional phase rule implies that cyclosporin and PIBCA are immiscible at the interface. This conclusion may have important implications with regard to the formulation of PIBCA-cyclosporin nanoparticles for cyclosporin administration, though further research in this direction will require consideration of the role played by the coadjuvants used for PIBCA polymerization during nanoparticle formation.

Cyanoacrylates↗

PubMedDate not supplied

Joint effects of monomer and stabilizer concentrations on physico-chemical characteristics of poly(butyl 2-cyanoacrylate) nanoparticles.

A rotatable central composite design was applied to the formulation of poly(butyl 2-cyanoacrylate) nanoparticles with the aim of modifying some physico-chemical properties of these carriers in a controlled way. The joint effect of stabilizer concentration and monomer concentration on the mean particle size, on the electrophoretic mobility and on the polymer molecular weight has been investigated. The results demonstrate that the particle size is only dependent on the stabilizer concentration, nevertheless the electrophoretic mobility and the molecular weight distribution were affected simultaneously by the monomer and the stabilizer concentrations. Moreover, using the response surface diagrams it is possible to deduce the experimental conditions to design particles with the desired properties. Finally, the degradation rates for two different molecular weight formulations were compared, showing the relevance of this property.

Capsules↗