Challenges facing colloidal delivery systems: From synthesis to the clinic

Improving therapeutic delivery to the body will have significant benefits for the treatment of a variety of diseases. Incorporating drugs inside engineered colloidal carriers is a promising approach that can lead to improved drug delivery. Such carriers offer a number of advantages, as they can protect therapeutic cargo from degradation by the body, limit potentially harmful side effects of the drug, and also allow targeted drug delivery to the desired site of action. Colloidal carriers have the potential to enable clinical use of a number of therapeutics, such as siRNA and peptides, which if administered in their naked form can degrade before demonstrating a viable therapeutic effect. A number of challenges, such as efficient therapeutic loading into the carrier, targeted and specific delivery in the body whilst evading biological defence mechanisms, and controlled release of therapeutically active cargo, must be met for these systems to be clinically relevant. In this review, we focus on recent advances and some of the pertinent challenges faced in developing clinically relevant colloidal drug carriers. We primarily focus on self-assembled carriers such as liposomes, polymer micelles and polymersomes, and carriers prepared through templated-assembly, for example, layer-by-layer assembled capsules and PRINT (particle replication in non-wetting templates) particles.