Effect of hydrophilicity and agmatine modification on degradation of poly(propylene fumarate‐co‐ethylene glycol) hydrogels

Abstract We synthesized positively charged biodegradable hydrogels with different poly(propylene fumarate‐co‐ethylene glycol) [P(PF‐co‐EG)] block copolymers and agmatine‐modified poly(ethylene glycol)‐tethered fumarate [Agm‐PEGF] by radical crosslinking and investigated the effect of copolymer composition and agmatine modification on their degradation. Hydrogels were incubated in phosphate‐buffered saline (PBS) at 37°C with periodic PBS changes. All hydrogels experienced a slight mass loss over 4 weeks, ranging from 10–20%. Hydrogels with a molar ratio of ethylene glycol repeating units to propylene fumarate repeating units (EG/PF) of 9.3 degraded faster than hydrogels with an EG/PF ratio of 0.6. Agmatine‐modified hydrogels degraded faster than unmodified hydrogels. The weight swelling ratio of the hydrogels at pH 7 increased over 4 weeks while increases in the EG/PF ratio and agmatine modification showed greater swelling. After 2 weeks, degraded hydrogels swollen at pH 3 demonstrated significantly lower weight swelling ratios than at pH 5, 7, and 9. Our results suggest that the hydrophilicity of the P(PF‐co‐EG) copolymer and agmatine modification have a small effect on the degradation of P(PF‐co‐EG) hydrogels. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 67A: 1148–1154, 2003