A fairly long time is required for in vivo bone formation, which means that rhBMP-2 needs to be released continuously [27]. The results of the present study showed that a collagen carrier gave an initial burst of released rhBMP-2 in a period of 1 day, whereas the hyaluronic acid-based powder gel released rhBMP-2 continuously for up to 7 days. A previous report on bone healing revealed that the sustained release of growth factor is more favorable than a burst release [28].