Temperature and polymer crosslinking degree influence on drug transfer from α,β-polyasparthydrazide hydrogel to model membranes. A calorimetric study
ABSTRACT A non-steroidal anti-inflammatory drug, diflunisal, has been chosen as drug model to be incorporated in α,β-polyasparthydrazide (PAHy) matrices to study the effect of polymer crosslinking degrees on the release processes from hydrogel (X=0.4 and X=0.8) to a model membrane represented by unilamellar vesicles of dipalmitoylphosphatidylcholine. The technique employed to monitor these processes was differential scanning calorimetry that appears to be particularly suitable to follow the transfer kinetics of a drug from a controlled release system to void biomembrane model. The drug release from the two PAHy hydrogels differently crosslinked by glutaraldehyde to the lipidic model was compared with that from the drug solid form, by examining the effects exerted on the thermotropic behaviour of unilamellar vesicles. The diflunisal (DFN) is able to interact with unilamellar vesicles by causing a decrease of the transitional (gel-to-liquid crystal phase transition) temperature characteristic of lipidic bilayer. The amount of DFN transferred and interacting with the dipalmitoylphosphatidylcholine (DPPC) unilamellar vesicles was quantified by comparing the effects caused on the thermodynamic parameters of bilayer (transitional temperature, Tm, and enthalpy variation, ΔH) with the effects obtained from increasing molar fractions of drug. The release kinetics of the drug from PAHy hydrogels were followed at different temperatures (25, 37 and 50°C) to determine the influence of temperature on the drug release and successive transfer at a biological membrane. Particularly, it appears evident that by increasing the polymer crosslinking degree the total amount of transferred drug and the release velocity are decreased. This behavior may be caused by the increase of the number of cruciate bonds in the hydrogels, which causes a free volume reduction obstructing the drug passing. The obtained results suggest that PAHy hydrogels constitute an innovative delivery system able to slightly release water-soluble drugs and to modulate their uptake by biomembrane.
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ABSTRACT: An overview of the current pharmaceutical applications of calorimetric measurements is discussed with an emphasis on providing references supporting various techniques. Areas where recent reviews of the techniques are available will be noted. In the context of the outlined current utilities, future areas of advancement will be discussed.Thermochimica Acta 07/2000; · 2.11 Impact Factor
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ABSTRACT: The process parameters typically reported in the literature for the encapsulation of aroma compounds via coacervation are reviewed and their effects on capsule formation discussed. We then report on our approach to produce coacervates [liquid (limonene or medium chain triglycerides) or solid core (menthol)] using gum acacia/gelatin as wall materials. Manufacturing parameters were optimized to allow the production of consistent batches of coacervate microcapsules. Capsules were cross-linked with glutaraldehyde and freeze-dried. Coacervates were characterized for their structure and shape, size distribution, flavour load and water uptake rate. In addition, a brief storage study compared the ability of coacervate capsules and spray-dried capsules (using modified starch as carrier material) to protect limonene from oxidation. No detectable increase in limonene oxide could be detected in capsules made by coacervation over 25 days in storage at 45 °C, whereas a significant increase in limonene oxide was detected in spray-dried powder over the same period. Encapsulation by coacervation (as described in this paper) appears to be an effective technique for encapsulating aroma compounds and provides a good barrier against oxidation of sensitive material. Copyright © 2008 John Wiley & Sons, Ltd.Flavour and Fragrance Journal 12/2008; 24(1):17 - 24. · 1.82 Impact Factor
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ABSTRACT: A new dissolution microcalorimeter that can measure enthalpies of dissolution of slightly soluble solids was developed by Ingemar Wadsö at Lund University, and the prototype as well as the commercial vessel were tested in our laboratory. Recently we did report the testing of the prototype and we are now extending the previous investigation to measurements with an organic solvent in the commercial vessel. The instrument performance was found to be as good with formamide as with water.The vessel was calibrated chemically (dissolution of KCl in water) and electrically, by means of a permanent and an insertion heater. The results obtained from the three methods are compared and discussed.The enthalpy of dissolution of α-cyclodextrin, dry and hydrated with six water molecules, was determined in water and in formamide. The results are discussed in terms of the difference between water and formamide as regarding dissolution and binding to the cyclodextrin molecule.Thermochimica Acta 10/2004; 420:111-117. · 2.11 Impact Factor