PRF is an autologous fibrin-based (membrane, matrix, or scaffold), living biomaterial, derived from human blood and it is increasingly being used worldwide by clinicians.
Composition of PRF
The purpose of PRF technology is to extract from a patient’s blood sample the key elements and to prepare it in a clinically usable form such as a membrane or plug (A-PRF, L-PRF) or injectable liquid (i-PRF). The function of PRF is to connect the various elements within the fibrin matrix with local tissues (bone and soft tissue) to accelerate neoangiogenesis within the tissue and to enhance its healing and regeneration potential.
The future of PRF and its applications in clinical dentistry, especially in the field of soft tissue and bone regeneration, has enormous therapeutic implications.
The very strong fibrin matrix contains:
- a high concentration of platelets (± 90% of the platelets);
- ± 65% of leucocytes;
- a high concentration of growth factors – including platelet- derived (PDGF), vascular endothelial (VEGF), and transforming (TGF)
- a representative concentration of fibrin, fibronectin, vitronectin, and thrombospondin.
These components all act naturally and in synergy to stimulate, improve, and accelerate tissue healing and to regenerate soft or bone tissue (Dohan, et al., 2014), including cell proliferation and differentiation, extracellular matrix synthesis, chemotaxis, and angiogenesis (Kawase, 2015).
PRF can be easily prepared at chairside within a short period of time and provides the surgical wound area or defect not only with a matrix or scaffold permitting cell migration into the defect area, but also crucial biological signals or growth factors that can accelerate the wound healing and regeneration process.
There is no manipulation of the blood. And as there are no anticoagulants in the tubes, there is no need to use animal thrombin and calcium chloride for fibrin polymerisation.
After centrifugation, through the activation of autologous thrombin, a fibrin clot is created.
Three distinct layers can be seen in the tube: red blood corpuscles (RBCs) at the bottom of the tube, PPP (platelet-poor plasma) on the top of the tube, and the fibrin clot in the middle of the tube (containing most leucocytes and platelets).
Purpose of PRF technology
The purpose of PRF technology is to extract the essential elements that could be used to improve healing and promote tissue regeneration from a patient’s blood sample, and to prepare it in a clinically usable form such as a membrane (A-PRF, L-PRF or CGF) or injectable liquid (i-PRF).
PRF technology draws on the following three fundamental principles and biological processes of hemostasis and wound healing (Shah, et al., 2015):
- Principle one: The presence of a fibrin matrix at the surgical site acts as a scaffold for recruiting and migration of cells (epithelial, fibroblast, endothelial) throughout the wound-healing and reparation process
- Principle two: Platelets, neutrophil leukocytes, and monocytes within the fibrin matrix (release) secrete growth factors and chemotactic proteins that recruit epithelial, fibroblast, and endothelial cells to the surgical site to facilitate wound healing and reparation.
- Principle three: Angiogenesis (neovascularization) relies on a fibrin matrix (extracellular matrix) and stimulation of endothelial cell recruitment through growth factors (VEGF).
The slow polymerization mode confers upon the fibrin matrix its favorable physiologic architecture, loaded or seeded with platelets, leukocytes (B- and T-lymphocytes), monocytes, and neutrophilic granulocytes, and mesenchymal stem cells, which is required to support and enhance the healing process.
The 3D architecture provides the PRF membrane with great density, elasticity, flexibility, and strength that are excellently suited for handling, manipulation, and suturing. These autologous membranes (with a dense fibrin network) are strong – a single membrane can withstand a load of ± 500g. They also have excellent biological properties – they are rich in platelets, growth factors, and cytokines – which opens many new clinical avenues. PRF membranes remain solid and intact in vitro and continuously release large quantities of growth factors for between 10 and 14 days.
The strong three-dimensional fibrin network functions as an “adhesive” scaffolding material for endothelial cells involved in angiogenesis (new blood vessel formation) to adhere to, proliferate, and concentrate at the site of wound healing and tissue regeneration. It is these growth factors (i.e., vascular endothelial growth factor [VEGF]) that attract endothelial cells into the fibrin to stimulate formation of new blood vessels (Pradeep, et al., 2012).
Platelets in the fibrin matrix play a crucial role, not only in hemostasis, but also in the wound-healing process. Platelets are distributed throughout the entire clot and merged within the fibrin-rich scaffold or mesh like a cement (Panda, et al., 2014). After activation, they become trapped within the fibrin matrix and immediately start releasing growth factors (Inchingolo, et al., 2010; Krasny, et al., 2011).
Platelets are important reservoirs for growth factors since they release high concentrations of these biologically active proteins that support recruitment of cells from the surrounding host tissue, and stimulate growth and cell morphogenesis, thus promoting bone and soft tissue healing (Joseph, et al., 2014; Pradeep, et al., 2012; Lekovic, et al., 2012; Joseph, et al., 2012). Entrapped platelets release a broad spectrum of cytokines, chemokines, growth factors, and other mediators that facilitate angiogenesis and tissue healing and regeneration.
With these different growth factors, adhesion molecules, and other mediators, platelets have the ability to initiate and modulate host immune responsiveness through recruiting and influencing leukocytes, neutrophils, monocytes, and endothelial cells, as well as lymphocytes to sites of tissue damage or infection.
Upon stimulation, platelets actively participate in pathogen detection, capturing, and sequestration. They can even induce the death of infected cellular targets (Joseph, et al., 2014; Bajaj, et al., 2013).
Release of growth factors
After platelets are activated, they start releasing high concentrations of growth factors (Inchingolo, et al., 2010; Panda, et al., 2014). The PRF membrane stays intact for at least 10 days and releases continuously large quantities of growth factors (such as transforming growth factor-β 1 [TGFβ β1], platelet-derived growth factor-AB [PDGF-AB], vascular endothelial growth factor [VEGF]), and key coagulation and healing matrix proteins or cytokines (thrombospondin-1, fibronectin, vitronectin, osteocalcin, osteonectin) (Kanayama, et al., 2016; Joseph, et al., 2014; Nacopoulos, et al., 2014; Patil, et al., 2014; Ranganathan and Chandran, 2014; Desarda, et al., 2013).
It is generally accepted that growth factors have an essential role in influencing processes of healing and tissue regeneration, including angiogenesis, chemotaxis, cell proliferation and differentiation, and the synthesis and degradation of extracellular matrix proteins (matrix remodeling) (Joseph, et al., 2014; Nacopoulos, et al., 2014; Pradeepet, et al., 2012b; Lekovic, et al., 2012; Simonpieri, et al., 2011; Dohan, 2009).
Platelets are not the only blood cells that release growth factors, but leukocytes and erythrocytes also contain TGF-β1 and VEGF (Dohan, et al., 2009; Moraschini, et al., 2015). The presence of these growth factors (TGF-β and VEGF) are important for stimulating cell proliferation, matrix remodeling, and angiogenesis during healing processes and tissue regeneration (Dohan, 2009; Del Corso, et al., 2009; Keceliet, et al., 2015).
Leukocytes are the cells of the immune system that are involved in protecting the body against infections or foreign bodies. Different types of leukocytes are concentrated in the fibrin matrix, namely lymphocytes (T-lymphocytes, B lymphocytes), monocytes, and neutrophilic granulocytes.
Leukocyte-enriched PRF (A-PRF and L-PRF) is reported to be an ideal provider of leukocytes (Joseph, et al., 2014). Leukocytes are enriched in A-PRF and L-PRF, primarily to exploit their antibacterial and osteoconductive actions (Kawase, 2015). Most leukocytes are found in the first 25%-30% proximal part of the clot (Joseph, et al., 2014). The leukocytes enmeshed into the dense fibrin network are alive and functional as an immune node that is able to stimulate defense mechanisms (Toeroek and Dohan, 2013; Panda, et al., 2014). Leukocytes living in the fibrin matrix are also involved in the production of significant amounts of growth factors, particularly TGFβ1 (Kanayama, et al., 2016; Troiano, et al., 2016; Patil, et al., 2014; Dohan, 2009; Eren and Atilla, 2014).
Neutrophilic granulocytes are considered to be early inflammatory cells due to their phagocytic capacity, participating in the process of wound debridement and revascularization (Aroca, et al., 2009; Aleksic, et al., 2010). Macrophages also support cell proliferation and tissue restoration following injury through expression of VEGF, PDGF, FGF, TGF-α, and TGF-β, and other biologically active molecules (e.g., BMP-2) (Jankovic, et al., 2010; 2012).
Neutrophils also facilitate trafficking of monocytes into the wound to phagocytize inflammatory remnants (necrotic and apoptotic cells) (Aroca, et al., 2009; Agarwal, et al., 2013).
Monocytes are in essence the “vacuum cleaners” of the body. They migrate into the wound or inflamed area after the influx of neutrophils, where they then become macrophages (Gupta, et al., 2015). The macrophages collect and remove all the dead, necrotic, bacterial, or foreign particles in the wound site. This function is essential for healing and regeneration of tissue.
Monocytes also have a beneficial effect on healing and tissue regeneration bone growth, the production of vascular endothelial growth factor (VEGF), and neovascularization (Gamal, et al., 2016; Shah, et al., 2015).
Mesenchymal stem cells (MSC)
PRF significantly stimulated MSC proliferation and osteogenesis in vitro. Studies has shown that MSC sheets injected with or without PRF formed new bone, but those with PRF produced significantly more and denser bone. PRF increases the osteogenic capacity of MSC sheets in vitro and in vivo.
The introduction of PRF as an autologous biomaterial has set in motion an exciting and promising era in the advancement of tissue healing and regeneration in the fields of implant dentistry, periodontology, oral surgery, and regenerative endodontics
The concept of generating a cell-seeded fibrin matrix, solely by drawing the patients’ own blood and centrifugation for a few minutes is truly revolutionary in terms of clinical practicability, as it can be made easily at chairside in a short period of time.
Dr Johan Hartshorne and Howard Gluckman examine the definition, development, biological characteristics, and function of PRF in all its many guises
Richard J Miron, Mark Bishara, Joseph Choukroun: Basics of platelet-rich fibrin therapy
Wang Z, Weng Y, Lu S, Zong C, Qiu J, Liu Y, Liu B.:Osteoblastic mesenchymal stem cell sheet combined with Choukroun platelet-rich fibrin induces bone formation at an ectopic site.