Characterization of recombinant human bone morphogenetic protein‐2 delivery from injectable hyaluronan‐based hydrogels by means of 125I‐radiolabelling

This study presents a thorough in vitro and in vivo characterization of the delivery of bone morphogenetic protein 2 (BMP‐2) from a hyaluronan‐based hydrogel system. The in vitro release of BMP‐2 from similar hydrogels has previously been studied by enzyme‐linked immunosorbent assay (ELISA), by which only a fraction of the loaded protein is detected. In the current study, ¹²⁵I radiolabelling was used instead to monitor BMP‐2 in vitro and in vivo. To minimize protein loss during handling, ¹²⁵I‐BMP‐2 adsorption to different tubes was studied at different times and temperatures. The data showed that Protein LoBind tubes exhibited the lowest protein affinity. Furthermore, a biphasic release profile of biologically active BMP‐2 was observed both in vitro and in vivo, with the initial fast phase during the first week, followed by a slower release during the remaining 3 weeks. The initial fast‐release phase corresponded to the early bone formation observed after 8 days in an ectopic model in rats. Bone volume and mineral content increased until day 14, after which a decrease in bone volume was observed, possibly due to resorption in response to decreased amounts of released BMP‐2. Overall, the results suggested that cautious protein handling and a reliable quantification technique are essential factors for successful design of a BMP‐2 delivery system. Copyright © 2012 John Wiley & Sons, Ltd.