Determination of surface free energy of interactive dry powder liposome formulations using capillary penetration...

The surface free energy of interactive dry powder formulations consisting of varying ratios of lactose plus liposomal ciprofloxacin were determined using capillary penetration technique. Powder is produced by jet-milling after mixing with lyophilized liposomal ciprofloxacin with inhalation grade lactose powder (Pharmatose 325M). Measurement of the weight gained during intrusion of different liquids in a packed column of powder is combined with dynamic considerations to give the surface free energy, gamma(sv). Confidence in methodology was gained by determining gamma(sv) for PMMA microspheres and comparing to literature values. Values of gamma(sv) are then obtained for unmilled Pharmatose 325M powder (gamma(sv)=54.2 mJ m(-2)), milled Pharmatose 325M (gamma(sv)=54.2 mJ m(-2)) and lipid:lactose formulations with weight ratios of 1:5, 1:10 and 1:20. All the powder liposomal formulations are found to have the same gamma(sv)=48.0 mJ m(-2), suggesting that adhesive forces in the three interactive powders should be similar barring any confounding roughness effects.