Synthesis of in Situ Cross-Linkable Macroporous Biodegradable Poly(propylene fumarate-co-ethylene glycol) Hydrogels

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Abstract
This study describes a synthesis method of biodegradable macroporous hydrogels suitable as in situ cross-linkable biomaterials. Macroporous hydrogels were based on poly(propylene fumarate-co-ethylene glycol) and prepared via coupled free radical and pore formation reactions. Cross-linking was initiated by a pair of redox initiators, ammonium persulfate and l-ascorbic acid. Pores were formed by the reaction between l-ascorbic acid and sodium bicarbonate, a basic component, which evolved carbon dioxide. Sol fraction of the hydrogels was varied from 0.06 ± 0.01 to 0.64 ± 0.01. A stereological approach was used to analyze the morphological properties of the macroporous hydrogels by relating the morphological properties of thin sections to the original three-dimensional macroporous hydrogel. Prepared macroporous hydrogels had porosities between 0.43 ± 0.08 and 0.84 ± 0.02 and surface area densities between 55 ± 3 and 108 ± 7 cm-1. Sodium bicarbonate concentration had the greatest effect on both the porosity and surface area density. The effect of copolymer formulation on the porosity and surface area density was insignificant. From thin sections of the macroporous hydrogels, the profile size distributions were determined as an estimate of the pore size distribution. Two formulations synthesized with varying l-ascorbic acid concentration of 0.05 and 0.1 M had median profile sizes of 50−100 and 150−200 μm, respectively. This novel synthesis method allows for the in situ cross-linking of biodegradable macroporous hydrogels with morpholological properties suitable for consideration as an injectable tissue engineering scaffold.