Preparation and characterization of poly(propylene fumarate-co-ethylene glycol) hydrogels

We describe the preparation and bulk characterization of a cross-linked poly(propylene fumarate-co-ethylene glycol), p(PF-co-EG), hydrogel. Eight block copolymer formulations were made varying four different design parameters including: poly(ethylene glycol) (PEG) molecular weight, poly(propylene fumarate) (PPF) molecular weight, copolymer molecular weight, and ratio of PEG to PPF. Two different cross-linking formulations were also tested, one with a cross-linking monomer and one without. The extent of the cross-linking reaction and the degree of swelling in aqueous solution were determined on copolymer formulations made without a cross-linking monomer. The values of molecular weight between cross-links, Mc ranged from 300 +/- 120 to 1190 +/- 320 as determined from swelling data (n = 3). The equilibrium volume swelling ratios, Q, varied from 1.5 +/- 0.1 to 3.0 +/- 0.1. This ratio was found to increase with increasing PEG content in the copolymer and decrease with increasing PPF molecular weight. The values for complex dynamic elastic moduli magnitudes of E*, ranged from 0.9 +/- 0.2 to 13.1 +/- 1.1 MPa for the formulations with the cross-linking monomer, N-vinyl pyrrolidinone (VP) (n = 3). The ultimate tensile stresses on the formulations made with VP ranged from 0.15 +/- 0.03 to 1.44 +/- 1.06 MPa, and tensile moduli ranged from 1.11 +/- 0.20 to 20.66 +/- 2.42 MPa (n = 5). All of the mechanical properties increased with increasing PPF molecular weight and decreased with increasing PEG content in the copolymer. These data show that the physical properties of p(PF-co-EG) hydrogels can be tailored for specific applications by altering the material composition.