Pharmaceutical nanocrystals: A promising approach for improved topical drug delivery.

The barrier function of skin and the non-optimal physicochemical properties of drugs present challenges to the skin penetration of many drugs, thus motivating the development of novel drug delivery systems. Recently, nanocrystal-based formulations have been investigated for topical drug delivery and have demonstrated improved skin penetration. This review highlights barriers in skin penetration, current techniques to improve topical delivery and application of nanocrystals in conquering obstacles for topical delivery. Nanocrystals can improve delivery through the skin by mechanisms including the creation of a higher concentration gradient across skin resulting in increased passive diffusion, hair follicle targeting, formation of diffusional corona, and adhesion to skin. The recent research would be of interest for formulation scientists seeking to develop products involving molecules that are 'difficult-to-deliver' topically.