The influence of cellulosic coacervate composition on the flux of an entrained agent through a coacervate/sebum barrier
Complex coacervation is the primary mechanism used in rinse-off formulations to deliver topical agents to the skin and hair; this process produces polycation-surfactant anion coacervates that entrain the agent and enhance its substantivity at these sites. This study investigates the relationship between the transport of agents released from a coacervate vehicle into artificial sebum and the coacervate's composition and properties. The flux of a model compound, kinetin, through a variety of cellulosic coacervate/sebum composite barriers prepared on cell culture inserts was determined. These values were interpreted according to a semi-empirical model based on the composition of the coacervate, polymer properties, and the material stiffness. A multivariate analysis using composition and polymer descriptors yielded a strong correlation (r2 = 0.72) to the experimental kinetin transport data. Variables that describe the degree of entanglement of the surfactant-linked polymer chain web (specifically, the molar ratio of anions to cations and wt% water) emerged as important predictive variables for kinetin transport. According to the developed model, compositional or ingredient manipulations that expand and untangle the web favor a more rapid release of entrained agents from the coacervate into sebum and, consequently, higher bioavailability on the skin surface.