5. Injectable platelet-rich fibrin (i-PRF)

2. Pure platelet-rich fibrin (P-PRF)

material for several applications [3].

Pure platelet-rich fibrin (P-PRF) in other terms leukocyte-poor platelet-rich fibrin is a preparation without leukocytes having a high-density fibrin network. This platelet concentrate exists in a strongly activated gel form. It cannot be injected and used like traditional fibrin glues. On the other hand, with its strong fibrin matrix facility, P-PRF can be handled like a real solid

During preparation, only very low amounts of leucocytes are collected because of the specific separator gel, which is used to obtain P-PRF. However, the platelet collection level is high, and the preservation of the platelets during the procedure seems to be acceptable [4]. The main disadvantage of this platelet concentrate protocol is its cost and complex procedure if it is

The second platelet concentrate type is leukocyte and platelet-rich fibrin (L-PRF), which is known as leukocyte and platelet-rich fibrin concentrate, called Choukroun's PRF. This product was invented by Choukroun in 2000 [1, 2]. The main concept of this technique differs from the other protocols. Patient's blood is taken and immediately softly centrifuged. This provides the formation of a fibrin clot in the middle of the tube, between the red blood cell base at the bottom and the acellular plasma at the top. This clot includes nearly all the platelets and more than 50% of the leukocytes from the initial blood harvest [5, 6]. The high quantity of leukocytes provides immune and antibacterial properties, wound healing and growth factor regulation. But, it depends on which leukocytes, in which quantity and in which state the centrifugation process can softly activate the white blood cells [7]. This product therefore only exists in an activated form and cannot be injected like a suspension. Therefore, L-PRF is a practical solid material with strong fibrin scaffold and used in oral and maxillofacial surgery, periodontology,

The amount of WBCs effect vascularization and bone remodeling. As a result, researchers made new modifications in the centrifugation speeds and times to prevent cell loss within the PRF matrix [8]. These recent modifications of the PRF protocol have led to the improvement of advanced platelet-rich fibrin (A-PRF), which uses lower G-forces to gain higher growth factors compared to PRF [9]. It maintains higher amount of WBCs in the fibrin matrix and has special glass tubes, which are designed to make clotting faster. After the centrifugation, the tubes are removed and placed in their holders and left for 5 min to start clot formation. The fibrin clot which is rich with WBCs provides higher growth factors and recent research emphasizes that

A-PRF enhances collagen matrix synthesis and supplement of progenitor cells [8].

compared to the other forms of PRF, which are available nowadays [3].

96 Bone Grafting - Recent Advances with Special References to Cranio-Maxillofacial Surgery

3. Leukocyte and platelet-rich fibrin (L-PRF)

implant dentistry and ear nose throat surgery [6].

4. Advanced platelet-rich fibrin (A-PRF)

One of the recent developments in the PRF technology is injectable PRF (i-PRF). Standard PRF is prepared as a gel which is inconvenient to inject [10]. i-PRF protocol necessitates short centrifugation period in order to produce a liquid platelet concentrate, which includes primarily liquid fibrinogen and thrombin prior to fibrin formation [11]. The plastic tubes with hydrophobic surface are used, and therefore coagulation process does not effectively start. Hence, all the blood components reach the top of the tube under the centrifugation force with short centrifugation time (i.e., 2–4 min). The light yellow-colored layer, which is the combination of plasma and platelets, is aspirated from the top of the tube to obtain i-PRF. Nowadays, it is used with bone grafts to keep graft particles tightly encapsulated in the fibrin matrix. With the coagulation process, i-PRF forms a gel consistency holding bone graft together. Also, the release of growth factor is beneficial for the graft. This has the potential to convert any osteoconductive graft to osteopromotive, which would provide faster and better bone formation. Another type of graft prepared with i-PRF is the PRF block. For its preparation, i-PRF is mixed with a combination of bone graft and shredded PRF clot [10].
