Synthesis and Characterization of Biodegradable In Situ Forming Hydrogels via Direct Polycondensation of Poly(ethylene glycol) and Fumaric Acid

Currently, in situ forming polymeric gels and networks have attracted much attention due to their potential applications as injectable devices in drug delivery and tissue engineering. To this end, biodegradable hydrogels were developed based on poly (ethylene glycol)-co-fumaric acid macromers. These macromers were synthesized through direct polycondensation of poly (ethylene glycol) of different molecular weights and fumaric acid using dicyclohexylcarbodiimide (DCC) as an esterification promoting agent. They were fully characterized by spectroscopic methods (i.e., Fourier transform infrared and proton nuclear magnetic resonance spectroscopies) and gel permeation chromatography and thermal analysis (i.e., differential scanning calorimetry) techniques. Thermal characterization showed that the produced macromers have lower crystallinity than the original precursors. The molecular weight and the degree of oligomerization of the macromers were also substantially affected by the molecular weights of the initial PEGs. The macromers were cross-linked by redox mechanism in the presence of water soluble initiation system consisting of ammonium persulphate and N,N,N´,N´-tetramethylethylenediamine. The swelling properties of the cross-linked gels were also examined which showed a significant dependency to the initial molecular weight of PEGs. Our results have suggested that these biodegradable hydrogels are potentially applicable in drug delivery and tissue engineering applications.