On shelf stability of freeze-dried poly(methylidene malonate 2.1.2) nanoparticles

Abstract Freeze-dried poly(methylidene malonate 2.1.2) (PMM 2.1.2)-made nanoparticles were evaluated for their 12-month stability under various storage conditions of temperature and illumination. At different period of time after their preparation, nanoparticles were resuspended and tested for their size, and the molecular weight and reversed-phase HPLC profiles of their components. The suspension pH, its turbidity at 400 nm as well as its in vitro cytotoxicity on CEM T cell line were also measured. Generally, nanoparticles maintained at 40°C underwent significant alterations revealed by the suspension pH decrease, the progressive modification of the HPLC chromatogram and the decreased cytotoxicity. Degradation of the polymer side chains and generation of carboxyl moieties could account for these observations. From the 1 year measurements here reported, lyophilized PMM 2.1.2 colloidal nanoparticles conserved at room temperature or below, either in darkness or in daylight, may be assumed to have a satisfactory shelf-life.