The local delivery of nitric oxide (nitrogen monoxide, NO) by thermal or photochemical means to target cells or organs has a great potential in several biomedical applications, especially if the NO donors are incorporated into non-toxic viscous matrices. In this work, we have shown that the NO donors S-nitrosoglutathione (GSNO) and S-nitroso-N-acetylcysteine (SNAC) can be incorporated into F 127 hydrogels, from where NO can be released thermally or photochemically (with lambda(irr) > 480 nm). High sensitivity differential scanning calorimetry (HSDSC) and a new spectrophotometric method, were used to characterize the micellization and the reversal thermal gelation processes of the F 127 hydrogels containing NO donors, and to modulate the gelation temperatures to the range 29-32degreesC. Spectral monitoring of the S-NO bond cleavage showed that the initial rates of thermal and photochemical NO release (ranging from 2 to 45 mumol 1(-1) min(-1)) are decreased in the hydrogel matrices, relative to those obtained in aqueous solutions. This stabilization effect was assigned to a cage recombination mechanism and offers an additional advantage for the storage and handling of S-nitrosothiols. These results indicate that F127 hydrogels might be used for the thermal and photochemical delivery of NO from S-nitrosothiols to target areas in biomedical applications. (C) 2003 Elsevier Science Ltd. All rights reserved.242035433553