Nanoparticle layers controlling drug release from emulsions.

The influence of interfacial layers of silica nanoparticles on the release kinetics of a model lipophilic drug (di-butyl-phthalate (DBP)) from polydimethylsiloxane droplets in water is reported. The nanoparticle layers are formed by self-assembly from solution and their structure is controlled by nanoparticle hydrophobicity and the solution conditions. For DBP loading levels resulting in released concentrations below the solubility limit, release is rapid from uncoated droplets whereas significant sustained release is facilitated by rigid interfacial layers of hydrophobic silica nanoparticles. Activation energies for release are in the range 580-630kJmol(-1), which is ten times greater than for barriers introduced by typical polymeric stabilisers. In contrast, at higher DBP loading levels (total concentration greater than the solubility level), both hydrophilic and hydrophobic nanoparticle layers increase the rate and extent of dissolution compared with uncoated droplets and pure DBP solutions. Nanoparticle layers are shown to significantly influence the release kinetics of lipophilic drugs from oil in water emulsions: either sustained or enhanced release properties can be introduced depending on the nanoparticle layer type and drug loading level. Thus, nanoparticle layers may be engineered to facilitate a range of release behaviours and offer great potential in the delivery of poorly soluble drugs.