In vitro sorption and desorption of basic fibroblast growth factor from biodegradable hydrogels

In vitro interaction of basic fibroblast growth factor (bFGF) with biodegradable gelatin hydrogels was investigated, focusing on its sorption into the hydrogels and desorption from them. Basic bFGF was sorbed to the hydrogel of acidic gelatin with an isoelectric point (IEP) of 5.0 over time at 4 degrees C, in contrast to that of basic gelatin with an IEP of 9.0 and type I collagen. The bFGF sorption was almost independent of the sorption temperature except for 4 degrees C and the hydrogel water content. Fluorescent microscopic observation revealed that bFGF was sorbed into the interior of the acidic gelatin hydrogel. The binding molar ratio of bFGF to the acidic gelatin was around 1.0. The bFGF sorption to the acidic gelatin hydrogel increased when gelatin was further carboxylated. bFGF was sorbed into the acidic gelatin hydrogel more slowly than into the poly(acrylic acid) (PAAc) hydrogel, probably because of the lower density of negative charge of gelatin. The bFGF sorption decreased with an increase in solution ionic strength, indicating that an electrostatic interaction was the main driving force for bFGF sorption to the acidic gelatin hydrogel. However, even at higher ionic strengths of solution, the sorbed bFGF was not desorbed from the acidic gelatin hydrogel, in contrast to the PAAc hydrogel.