**3.4 Platelet-rich fibrin (PRF)**

Platelet-rich fibrin belongs to the second generation of platelet concentrates. It was patented by Joseph Choukroun in 2000. In contrast to the previous platelet concentrates, this one does not require the use of anticoagulants or bovine thrombin as procoagulants. The principle behind preparing this autologous biomaterial starts with physiologically triggered coagulation processes. The equipment required is a phlebotomy pack, vacuum test tubes, and a centrifuge with a fixed angle [12].

The authentic PRF protocol is the leukocyte (L-PRF) or Choukroun's protocol (**Figure 3**), which contains the phases listed below:


#### **Figure 3.**

*L-PRF protocol. (A) Vacutainer with clot activator. (B) PRF clots. (C) Centrifuge with chosen protocol. (D) PRF membranes. (E) PRF plug.*


Apart from the PRF membranes, PRF plugs can also be made from the PRF clots. For this purpose, PRF clots need to be put into cylinders of the PRF box. On the top, stainless steel weights need to be placed to eliminate the residual liquid. By using this approach, clots are turned into plugs or disks of desired height.

PRF clots contain 100% platelets and the growth factors from the patient's blood sample. Additionally, they contain 65% leukocytes, which are the growth factor source, especially for PDGF and VEGF.

Besides platelets and leukocytes, PRF contains fibrin too. There are multiple roles of fibrin in PRF:


PRF membrane and PRF disks or plugs are also called solid PRF.

Numerous protocols have been invented to obtain advanced PRF forms. Most of them are based on the change in velocity and time required for centrifugation. The objective was to obtain PRF with the best characteristics possible—uniform platelet distribution along the clot and prolonged growth factor release.

In the text below, we will further be discussing different types of PRF.

#### *3.4.1 Leukocyte-platelet-rich fibrin (L-PRF)*

L-PRF is the original version of solid PRF. It was first prepared by centrifuging samples at rcf of 400 g for 12 minutes [13]. The end product was a PRF clot that was used for PRF membrane and plug preparation. The research has shown that the majority of the growth factors could be found at the bottom of a membrane or plug rather than them being evenly distributed across the structures. This can also be considered a disadvantage of L-PRF.

#### *3.4.2 Advanced platelet-rich fibrin (A-PRF)*

Advanced platelet-rich fibrin came to light in 2014 [14]. It was a result of a newly introduced slow centrifugation concept, objective of which was to prevent cell loss and increase the number of viable cells. A-PRF has a greater number of leukocytes, platelets, neutrophils, and lymphocytes and has been suggested to have a prolonged growth factor release [13]. It is obtained by centrifuging samples at the rcf of 208 g for 14 minutes [13]. In comparison to the L-PRF membrane, the A-PRF membrane is shorter, has a greater cell-retaining capacity, and it releases larger amounts of growth factors [9, 15].

#### *3.4.3 Advanced A-PRF+*

A-PRF+ is a variant of the A-PRF obtained by decreasing the time needed to centrifuge samples while remaining a constant relative centrifugation force of 208 g. Instead of centrifuging samples for 14 minutes, this protocol requires one to do so for 8 minutes [16]. In comparison with the A-PRF and L-PRF, A-PRF+ has been shown to release even greater amounts of growth factors, especially TGF-β1, VEGF, PDGF, EGF, and IGF1 [13, 17].

#### *3.4.4 Advanced liquid PRF (A-PRF liquid)*

A-PRF liquid can be prepared by centrifuging samples at 1300 rpm for 5 minutes. The end-product is in a liquid state, which allows it to be mixed with bone grafts, whereby so-called sticky bone is obtained. It can also be used for large membrane preparation.

#### *3.4.5 Injectable PRF (i-PRF)*

Injectable PRF is a liquid form of PRF intended for a variety of purposes including but not limited to tissue injections, mixing with grafts to obtain sticky bone, skin injections in the facial region to achieve rejuvenation, joint injections, and large membrane preparation. Choukroun has patented several types of i-PRF:

#### *3.4.5.1 i-PRF*

i-PRF can be considered a universal protocol for injectable PRF. The protocol instructs blood sample centrifugation at 700 rpm for 3 minutes.

#### *3.4.5.2 i-PRF M*

This protocol is intended for males since they naturally have a greater number of erythrocytes. Consequently, the centrifugation time needs to be longer compared to protocols addressing i-PRF preparation for women to ensure larger quantities of centrifuged i-PRF. In short, it should be centrifuged at 700 rpm for 4 minutes.

#### *3.4.5.3 i-PRF+*

The i-PRF+ protocol requires centrifuging blood samples at 700 rpm for 5 minutes. Its purpose lies in obtaining a liquid PRF that is oftentimes used for facial esthetic procedures as well as in orthopedic surgeries.

*PRF and Sticky Bone as Regenerative Materials in Oral Surgery DOI: http://dx.doi.org/10.5772/intechopen.108807*

A novel protocol introduced in 2019 (1300 rpm for 14 minutes) by Choukroun covered both solid and liquid PRF preparation and simplified the preparation process. Namely, this protocol allows us to place test tubes for solid (A-PRF) and liquid PRF (S-PRF, i-PRF+) immediately upon taking blood samples in the very same centrifuge and spinning them according to the same protocol. Consequently, this protocol amnesties us from using different protocols for solid and liquid PRF preparation.
