Investigation of propellant-free aqueous foams as pharmaceutical carrier systems.

Due to their light consistency and good spreadability, aqueous foams are considered as convenient and highly accepted drug carrier systems that are of great importance in the field of topical drug delivery. The production of a stable, easy to dose, preferably environmentally harmless foam formulation is challenging. Therefore, foam characterisation requires a complex approach: several tests are to be performed throughout the formulation. Our study primarily aims to investigate the quality attributes of propellant-free foam-forming additives. Throughout the research, we focused on acquiring knowledge about the properties of pharmaceutical excipients suitable for foam formulations and their effect on foam characteristics. Not only were the relative foam density, actuated foam weight and the foam collapse tendencies studied, but also the initial liquid properties. Along with surface tension determination, bubble-forming experiments were carried out. The bubble size and rate of formation, standardised by using a texture analyser, were followed by image analysis. Analysing the bubble-forming properties of dilute surfactant solutions allows assumptions on the properties of foam formed from the more concentrated solutions. The size and number of bubbles in the produced foams are related to the kinetics of single bubble formation. For comparison, commercially available medicated foams were studied.