Influence of different parameters on drug release from hydrogel systems toa biomembrane model. Evaluation by differential scanning calorimetry technique

A comparative study on the drug release capacity of four water swellable po lymeric systems was carried out by differential scanning calorimetry (DSC). The polymeric systems chosen were alpha,beta-polyaspartahydrazide (PAHy) c rosslinked by glutaraldehyde (GLU) (PAHy-GLU) or by ethyleneglycoldiglycidy lether (EGDGE), (PAHy-EGDGE), polyvinylalcohol (PVA) crosslinked by glutara ldehyde (PVA-GLU) and alpha,beta-poly(N-hydroxyethyl)-DL-aspartamide (PHEA) by gamma irradiation (PHEA-gamma matrices). The degree of crosslinking for PAHy-GLU, PAHy-EGDGE and PVA-GLU samples was about 0.4 and 0.8. These hydr ogels were characterized as free of drugs and were loaded with diflunisal ( DFN) (approximate to 2.5% w/w). Diflunisal, a non-steroidal anti-inflammato ry drug, has been chosen as a model drug to be incorporated into polymeric matrices to follow the release processes of a drug from these hydrogels to a model membrane made by unilamellar vesicles of dipalmitoylphosphatidylcho line (DPPC). Differential scanning calorimetry appears to be a suitable tec hnique to follow the transfer kinetics of the drug from the controlled rele ase system to the biomembrane model. The drug releases from all the conside red polymeric hydrogels, were compared with the release observed from the d rug solid form by examining the effects on the thermotropic behaviour of DP PC unilamellar vesicles. The release kinetics of the drug from hydrogels we re followed at 25, 37 and 50 degrees C to evidence the influence of tempera ture on the drug release and on the successive transfer to biological membr ane model. Particularly, it appears evident that the total amount of drug t ransferred and the release rate are affected by the polymer crosslinking de gree (it increases with crosslinking decrease) as well as by the nature of crosslinking agent. In fact, the drug release profiles from PAHy-GLU sample s are more differentiated than those from PAHy-EGDGE. The effect of paramet ers correlating with the properties of starting polymer, such as water-affi nity, crystallinity, glass-to-rubber transition temperature and affinity to wards drug molecules, has been also evaluated. (C) 2000 Elsevier Science Lt d. All rights reserved.