In this study, we found no apparent differences between A-PRF and CGF clot microstructures, especially in fibrin fiber thickness or crosslink density. However, in PPTF clots, which were prepared through direct conversion of fibrinogen by thrombin, fibrin fiber thickness and their crosslink density were substantially thinner and higher, respectively, than those of either A-PTF or CGF clots. This finding was supported by the water content data, which revealed that significantly less amounts of water were contained in PPTF clots. These data are summarized along with the centrifugal conditions in Table 3.

Since the ratio of surface area to volume is known to be a significant factor for degradation of polymer material [20], these structural characteristics can be correlated to their degradability. As expected, we demonstrated that PPTF membranes degraded faster than other self-clotted fibrin membranes and A-PRF and CGF degradation rates were almost identical. However, it has not yet been clarified if those structural characteristics are correlated to mechanical properties.

In the tensile test, we again found no significant difference in any parameters evaluated among A-PRF, CGF, and PPTF membranes. However, in the strain at break, PPTF membranes were broken by a significantly weaker tensile force. The order of this parameter from high to low was CGF ≈ A-PRF > PPTF. As described above, the order of degradability was PPTF > CGF ≈ A-PRF, which is the reverse of the mechanical strength. Despite higher crosslink density, fibrin fibers formed in PPTF clots were substantially thinner and therefore they are probably not capable of bearing higher tensile forces. The manufacturer explains that the difference between PRF and CGF is related to the centrifugation techniques; programmed switching between acceleration and deceleration facilitates both conversion of fibrinogen to fibrin and their polymerization more efficiently than centrifugation at fixed speeds. However, as far as we examined, CGF is identical to A-PRF in terms of mechanical and degradable properties.