US Patent 10561795 Convertible plungers, film coated plungers and related syringe assemblies

A convertible plunger is provided comprising an internal portion and a generally cylindrical exterior surface. At least a portion of the exterior surface is maintained in an initial expanded state by a property of the internal portion. The expanded state is reducible to a constricted state by an operation that is applied to the internal portion of the plunger to alter the property. A film coating may also be applied to a sidewall of the sleeve to reduce a sliding friction between the sleeve and barrel. A film coating may also be applied to a nose cone of the plunger to provide a barrier between the plunger and product in the barrel.