Freeze-Dried Human Platelet-Rich Plasma Retains Activation and Growth Factor Expression after an Eight-Week Preservation Period

STUDY DESIGN: Controlled laboratory study. PURPOSE: This study aimed to evaluate the efficacy of platelet-rich plasma (PRP) stored at room temperature (RT), frozen, or after freeze-drying. OVERVIEW OF LITERATURE: PRP enriches tissue repair and regeneration, and is a novel treatment option for musculoskeletal pathologies. However, whether biological activity is preserved during PRP storage remains uncertain. METHODS: PRP was prepared from blood of 12 healthy human volunteers (200 mL/person) and stored using three methods: PRP was stored at RT with shaking, PRP was frozen and stored at −80℃, or PRP was freeze-dried and stored at RT. Platelet counts and growth factor content were examined immediately after preparation, as well as 2, 4, and 8 weeks after storage. Platelet activation rate was quantified by flow cytometry. RESULTS: Platelet counts were impossible to determine in many RT samples after 2 weeks, but they remained at constant levels in frozen and freeze-dried samples, even after 8 weeks of storage. Flow cytometry showed approximately 80% activation of the platelets regardless of storage conditions. Almost no growth factors were detected in the RT samples after 8 weeks, while low but significant expression was detected in the frozen and freeze-dried PRP. Over time, the mean relative concentrations of various growth factors decreased significantly or disappeared in the RT group. In the frozen group, levels were maintained for 4 weeks, but decreased significantly by 8 weeks (p <0.05). The freeze-dried group maintained baseline levels of growth factors for the entire 8-week duration. CONCLUSIONS: Freeze-drying enables PRP storage while maintaining bioactivity and efficacy for extended periods.