Gelation and
tissue adhesion of mixtures of
gelatin and poly (
L-glutamic acid) (PLGA) aqueous
solution were investigated in the presence of additives following the addition of a water-soluble
carbodiimide (WSC) that induced chemical cross linking between
gelatin and PLGA. To prevent spontaneous gelation of the mixed
solution through physical cross linking between
gelatin molecules at room temperature, additives were added to the mixed
solution. Among the additives studied,
starch and
urea were effective in preventing the spontaneous physical gelation. The mixed
gelatin and PLGA
solution set to a cross-linked
hydrogel within scores of second by WSC addition, irrespective of the presence of
urea, whereas the viscosity of the
solution with added
starch was too high to measure the gelation time. The cross-linked
gelatin-PLGA
hydrogels with and without
urea showed higher bonding strength to soft tissues than
fibrin glue. This was in marked contrast to
gelatin-PLGA
hydrogels with soluble
starch. Irrespective of the presence of
urea, the
gelatin-PLGA
hydrogels gradually biodegraded in the back subcutis of mice over 3 months and no severe inflammatory response to the
hydrogels was observed. These findings indicate that
urea is promising as an additive to prevent spontaneous physical gelation of the mixed
gelatin and PLGA aqueous
solution without changing the characteristics of WSC-induced cross linking and
tissue adhesion of the formed
hydrogel.