Stability of bacteriophages in spray‐dried polymeric formulations: Effect of excipient polyvinylpyrrolidone glass transition temperature and molecular weight

Abstract Effective dry‐state stabilization of bacteriophages is crucial for expanding their therapeutic use. This study builds on previous findings that saccharide‐based formulations maintain phage stability when the glass transition temperature (Tg) exceeds the storage temperature (Ts) by approximately 50°C. We investigated polymer‐based matrices for long‐term stabilization by spray‐drying PEV1 phage with polyvinylpyrrolidone (PVP) of varying molecular weights (K15, K25, K40, K100) and storing for 180 days at temperatures (4, 22, and 40°C) and relative humidity (15%, 33%, 43%, and 53% RH). All formulations achieved minimal titre losses (≤1 log 10 ) at 4 and 22°C under 15% RH. Differential scanning calorimetry (DSC) demonstrated Tg increased with PVP molecular weight but decreased substantially with humidity (30–50°C reduction per 20% RH increase). At 33% RH, long‐term stability was achieved with high‐molecular‐weight PVPs (K40, K100), which maintained thermal offsets between Tg and Ts (ΔT ≥ 100°C), while lower‐weight (K15, K25) showed 2–3 log 10 titre loss. Water activity ( aw ) analysis revealed a critical threshold at aw 0.43, above which degradation kinetics increased by approximately a tenfold rate. Arrhenius analysis confirmed that phage degradation rates increased with temperature, consistent with thermally activated destabilization mechanisms. Under higher stress conditions (40°C/≥43% RH), water absorption plasticized the PVP matrix and depressed the Tg while elevated temperature simultaneously accelerated degradation kinetics, resulting in substantial titre losses even when ΔT exceeded 100°C. In conclusion, at mild humidity ( aw ≤ 0.33) and ambient temperature (≤22°C), high‐molecular‐weight PVP‐based formulations can offer enhanced storage flexibility and reduced cold‐chain dependency for optimal therapeutic viability.