Platelet gels

Platelet gels (PG) are blood-derived biomaterials that are generally obtained through the activation of a platelet-rich plasma or a platelet concentrate by thrombin or calcium chloride, resulting in the simultaneous conversion of fibrinogen into a fibrin gel and in the generation of a platelet releasate rich in a physiological cocktail of growth factors. To reinforce the physical strength of the fibrin network, a fibrinogen-rich fraction – generally cryoprecipitate – can be added to the platelet fraction prior to activation, resulting in the generation of platelet fibrin glue (PFG). PG and PFG, prepared from single donations, either autologous or allogeneic, are increasingly used, alone or in combination with grafting materials, in various field of regenerative medicine where the presence of growth factors is expected to stimulate the healing of soft or hard tissues. Being obtained from human blood, they are physiological and biodegradable preparations and do not induce tissue necrosis. So far, the viral safety of most allogeneic PG and PFG relies on donors selection and donation testing, as is the case for all non-virally inactivated blood components for transfusion. Major fields of clinical applications of PG and PFG in osseous tissue regeneration include maxillo-facial surgery, implantology, reconstructive and plastic surgery. Platelet gels are also used for enhancing the healing of soft tissues, most particularly recalcitrant lower extremity ulcers of various aetiologies, and burns. Newer promising indications include the treatment of osteo-arthritis and joint inflammation, and the repair of musculoskeletal tissue lesions in sports medicine. Autologous PG and PFG are mostly ‘home-made’ single-donor preparations prepared using medical devices. They suffer from the variability in donor characteristics and in isolation procedures of the platelet fraction. Clinical application methods are not standardized. Variability in autologous product characteristics is high, and optimal content of growth factors is unknown, confusing the analysis of product efficacy. The evidence of clinical benefits of these products based on controlled clinical studies is lacking in most indications, although many case studies do support an objective benefit in soft and probably hard tissues healing. Improvement in the standardization and formulation of PG and PFG is a mandatory step forward for improving the reliability and the predictability of clinical outcomes of these interesting blood preparations.