BIOARTIFICIAL POLYMERIC MATERIAL - POLY(ETHYLENE GLYCOL) CROSS-LINKEDWITH ALBUMIN - II - MECHANICAL AND THERMAL-PROPERTIES

A family of hydrogels based on the crosslinking of bovine serum albumi n (BSA) and activated poly(ethylene glycol) (PEG), were characterized. The swelling process was found to be dependent on the molecular weigh t of the PEG used and on the OH/NH2 molar ratio of the reagents. These hydrogels performed a volume expansion from 266 to 554% when PEG with molecular weights from 3,350 to 20,000 were used. The volume expansio n was greater when the OH/NH2 molar ratio increased. Some anisotropy o ccurred during swelling since thinner devices swelled more than thicke r ones, due to the difference of constraints in the hydrogels structur e. Mechanical studies showed that these hydrogels were highly deformab le and presented good elastic behavior since they broke only after 80% deformation. At this point, they needed a compression force ranging f rom 165 to 456 g/cm(2) to break. The differentiation of two kinds of w ater in these highly swollen hydrogels was performed using DSC studies at low temperature. Free water (i.e., bulk water) was found to be the predominant form which filled the network, and bound water (i.e., wat er engaged in interactions with PEG) tended to form a trihydrate compl ex (three molecules of water per ethylene oxide repeated unit). Three forms of water with different evaporating rates were detected by DSC s tudies at high temperature. This other form of water may be important for maintaining the hydrogel's form.