Statement of Purpose: Osteoarthritis (OA), a disease caused by chronic inflammation and wearing of articular cartilage, affects more than 50 million Americans. Currently available clinical treatments for this disease fail to suppress cartilage degeneration or synovial inflammation, or to promote tissue regeneration. Platelet-rich plasma (PRP) therapy involves a direct injection of PRP into the joint cavity. PRP is obtained by drawing patients own blood and concentrating platelets, which release bioactive factors that are critical to tissue regeneration and cellular recruitment. However, current strategies utilizing bolus injections of PRP remain ineffective due to a rapid clearance of growth factors. A sustained-release injectable formulation of PRP would be beneficial by maintaining a steady amount of the bioactive factors at the site of injury. Thus, in this study, we test therapeutic effects of sustained-released PRP, encapsulated as lyophilized powder (PRGF), from polyethylene glycol (PEG) hydrogels in vitro on human chondrocytes and tissue explants.