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Biomedical subjects

M M Vidal

Publications and source records attributed to M M Vidal.

4 recordsLinked to original sources
PubMed2000

Evaluation of poly(2-hydroxyethyl methacrylate) gels as drug delivery systems at different pH values.

Studies of dynamic and equilibrium swelling, structural characterisation and solute transport in swollen poly(2-hydroxyethyl methacrylate) gels (pHEMA) cross-linked with tripropyleneglycol diacrylate (TPGDA) were done for a wide range of TPGDA concentrations. The influence of the pH on these pHEMA properties was evaluated. In swelling studies it was found that in changing the pH from 6.5 to 12.0, a large increase in swelling occurred, from approximately 48 to 55%, for the lowest concentration of TPGDA (1 mol%), and from 40 to 80% for the highest concentration (10 mol%). Fourier transform infrared (FTIR) and differential scanning calorimetry (DSC) measurements were made after the equilibrium swelling of the gels at different pH values, to explain these results. The advantage of using these gels as controlled drug delivery systems is illustrated using salicylic acid (SA) as a model drug. The loading and the release of the SA were made at different pH values and the results obtained showed that it is possible to modulate the hydrogel performance by controlling an external factor, the pH at which the drug loading and release were performed.

Drug Delivery Systems↗
PubMed1999

Study of the thermal stability and enzymatic activity of an immobilised enzymatic system for the bilirubin oxidation.

In this work, we have studied the immobilisation of the haemoglobin/glucose oxidase coupled enzymatic system in poly(vinyl alcohol) membranes. These are to be used as a reagent phase either in the development of an optical sensor or as an efficient bilirubin (BR) removal reactor. Poly(vinyl alcohol) (PVA) was chosen as the support for this purpose, due to its good biocompatibility, hydrophilicity and non-thrombogenic effects. A hydrogel containing the enzymatic system, consisting of PVA crosslinked with glutaraldehyde, was prepared and characterised by DSC, enzyme activity measurements and release tests. Investigating protein conformational changes as a function of temperature and the enzymatic system activity we have found that, in spite of the destabilizing effect of the glutaraldehyde in the acidic medium, the PVA insolubilisation conditions seem do not perturb either the conformation of the 'native state' nor the enzymatic system activity. Moreover, it was found that PVA/glutaraldehyde membranes offer a simple way to hold enzymatic system, with the possibility of controlling the conditions to obtain either the effective prevention of leaching of the entrapped proteins or the in situ delivery of the haemoglobin.

Bilirubin↗
PubMed1996

Study of an enzyme coupled system for the development of fibre optical bilirubin sensors.

We have established an analytical procedure for bilirubin (BR) determination by following the variation of its yellow absorption band in the presence of the biocatalytic system haemoglobin/glucose oxidase/glucose. The influence of the pH of the medium, the haemoglobin/hydrogen peroxide ratio, and the concentration of the various components in the mixture on the system activity was evaluated. The solubility of the unconjugated BR was analysed. An anionic detergent in Tris buffer, in which it presents a high critical micellar concentration, was selected for the BR/bovine serum albumin cleavage. The Michaelis-Menten constant of the system (after the optimisation of the various parameters) was determined and compared with Km values reported in the literature for similar catalytic systems. Preliminary results obtained with the haemoglobin and glucose oxidase immobilised either in poly(vinyl alcohol) or by crosslinking with glutaraldehyde, show that this system is promising as a future biosensor.

Bilirubin↗