Formulation and characterization of a plasma sterilized, pharmaceutical grade chitosan powder

• Chitosan was micronized by cryo-ball and cryo-jet milling.
• Mean particle size after cryo-jet mill (16.05 μm) was smaller than cryo-ball mill.
• Cryomilling reduced molecular weight by 26% and degree of deacetylation by 9.6%.
• Nitrogen plasma treatment produced sterile chitosan with endotoxins at <2.5 EU/g.
• Nitrogen plasma treatment also reduced molecular weight of chitosan.

Chitosan has great potential as a pharmaceutical excipient. In this study, chitosan flake was micronized using cryo-ball and cryo-jet milling and subsequently sterilized with nitrogen plasma. Micronized chitosan was characterized by laser diffraction, scanning electron microscopy (SEM), conductometric titration, viscometry, loss on drying, FTIR, and limulus amebocyte lysate (LAL) assays. Cryo-jet milling produced mean particle size of 16.05 μm, 44% smaller than cryo-ball milling. Cryomilled chitosan demonstrated increased hygroscopicity, but reduced molecular weight and degree of deacetylation (DD). SEM imaging showed highly irregular shapes. FTIR showed changes consistent with reduced DD and an unexplained shift at 1100 cm−1. Plasma treated chitosan was sterile with <2.5 EU/g after low-pressure plasma and <1.3 EU/g after atmospheric pressure plasma treatment. Plasma treatment decreased the reduced viscosity of chitosan flake and powder, with a greater effect on powder. In conclusion, pharmaceutical grade, sterile chitosan powder was produced with cryo-jet milling and plasma sterilization.