Encapsulation of basic fibroblast growth factor in thermogelling copolymers preserves its bioactivity

In this paper, we present a new approach of using thermogelling copolymers for the encapsulation of basic fibroblast growth factor and the preservation of its bioactivity without the need for stabilizing agents. Thermogelling poly(ether urethane)s consisting of poly(ethylene/butylene) (PEB), poly(ethylene glycol) (PEG), and poly(propylene glycol) (PPG) segments were investigated as potential encapsulation and delivery agents for basic fibroblast growth factors (bFGFs). Thermogels form when micelles aggregate as the temperature increases. This leads to the formation of gels without the need for crosslinking. The mobility of the protein encapsulated within the gel matrix was found to be closely related with the rheological property of the copolymer gel. Lysozyme and BSA release studies were conducted to understand the effects of gel concentration, protein size and protein concentration on the kinetics of protein release. Based on the calculated diffusion coefficients, the mobility of the protein within the gel matrix was determined. Finally, basic fibroblast growth factor (bFGF) was encapsulated in the gels. The immunoreactivities and bioactivities of the cytokines encapsulated in the gel were well preserved for up to 5 days, as determined by enzyme-linked immunosorbent assay (ELISA) measurements as well as cell culture assays. This finding suggests that thermogelling polymers could potentially be used as an injectable gel depot for the release of bioactive cytokines for tissue repair and other related applications.