Although the growth factor contents in PRF and CGF preparations and their bioactivities have been demonstrated in in vitro studies by several independent groups [8–11, 13–20], many clinicians still believe that the regenerative effects of PRF/CGF are solely due to fibrin clots. We speculate that this discrepancy may be caused by two major factors. First, the initial report on PRF by Choukroun and his co-workers showed that PDGF-BB, TGF-β1, or IGF-I is not significantly concentrated in PRF preparations [21]. Second, the preparation protocols of PRF extraction are not fully disclosed in several articles and likely varied with the individual groups. In the previous study [7], we demonstrated that intense compression of PRF preparations, which is designated as CGF preparations in this study, with dry gauze fully removes PRF exudate and substantially reduces the content of growth factors. Therefore, we concluded that the major source of growth factors in PRF preparations is its exudate; however, as a minor source, growth factors are thought to be secured by fibrin fibers.

To confirm these observations, we recently examined the angiogenic activity of PRF/CGF preparations in endothelial cell cultures and the chick embryo chorioallantoic membrane (CAM) assay [22]. As a result, it was demonstrated that PRF/CGF preparations are somewhat more potent in angiogenesis than PRP preparations. To further assure the growth factor contents in the self-clotted PRP derivatives, in this study, we compared the growth factor contents in four types of PRP derivatives (PRP, PRGF, A-PRF, CGF) prepared from the same donors. The main finding of this study was that both A-PRF and CGF preparations contained TGF-β1, PDGF-BB, VEGF, IL-1β, and IL-6 at levels similar to or higher than PRP preparations. The expected proliferative effects of both A-PRF and CGF extracts were demonstrated in the in vitro assay using human periosteal cells, which give rise to osteoblasts involved in periodontal skeletal regeneration. Therefore, as do PRP preparations, these self-clotted PRP derivatives are expected to function not only as a scaffolding material but also as a reservoir to deliver certain growth factors and pro-inflammatory cytokines at the implantation sites.