Platelet-rich fibrin (PRF), a self-clotted preparation of platelet-concentrated, blood-derived biomaterials, is prepared solely by contact activation of intrinsic coagulation pathways through centrifugation without addition of coagulation factors [1, 2]. Therefore, the preparation protocol is drastically simplified, and the resulting clot can be handled easily with forceps. PRF is further modified to two types: A-PRF, an advanced type that is expected to contain greater numbers of white blood cells [3] and concentrated growth factors (CGF), which is prepared under a facilitated intrinsic coagulation cascade [4]. Since these preparation protocols are similar and share the same principle of clot formation, A-PRF and CGF clots are not easy to differentiate either macroscopically or microscopically.

In clinical settings, both A-PRF and CGF preparations have been applied as barrier membranes and/or as carriers of growth factors to facilitate wound healing and tissue regeneration. However, their mechanical properties as barrier membranes have not been investigated sufficiently. For example, there is no available evidence as to which membrane is mechanically tougher. In addition, because the fibrin membranes degrade gradually at the implantation site in vivo, it is poorly understood how their mechanical properties change during the degradation process.

Degradability is also closely related to growth factor release, a phenomenon that is a key parameter in the efficacy at the implantation site. Recently, it has been demonstrated that growth factors are concentrated in A-PRF/CGF clots and released with time [5,6,7,8,9,10]. These experimental systems simulated the initial phase of growth factor release by simple diffusion; however, the simulation experiments were performed using conventional culture media in the absence of serum or proteases, which is not an appropriate simulation system of in vivo conditions. Therefore, it is apparent that growth factor release by degradation of fibrin fibers [11] is not well simulated. In the data obtained from our previous [12] and preliminary studies, fibrin clots can be maintained without substantial degradation under similar protease-free conditions for longer than a week. However, clinicians have frequently claimed based on their clinical experiences that fibrin clots applied to surgical sites, e.g., socket after tooth extraction, are almost completely degraded within a week or two. This observation is supported by several clinical review articles [13, 14].