The structure and properties of materials used in advanced drug delivery systems

The various requirements placed on materials that might serve as suitable components in drug delivery systems are discussed. Special attention is paid to the interactions between the drug delivery constructs and the biological environment, using the interactions in the vascular compartment of the body as an example. Two alternative general approaches are compared: (a) “controlled drug release”, which aims to reduce or eliminate side effects by producing a steady therapeutic concentration of drug in the body; (b) “site-selective drug delivery”, which aims to ensure that the drug is delivered to the site of its biochemical and disease-related site of action, at the same time maintaining the drug inactive elsewhere in the body. It is concluded that materials for delivering drugs to selected sites of disease within the body must be designed to utilise the unique features (structure, function, rhythm) of the main elements involved in the disease. Equally important is to design drug carriers that do not interact non-specifically within the body so that their specific action would be prevented. It is difficult to see how this could be achieved using materials entirely “foreign” to the body. Utilising the primary structures used by the biological systems (proteins, glycoproteins, carbohydrates) and creating novel higher structures (secondary, tertiary, quartenary) that mimic the native material is the logical way forward in the search for new drug delivery systems, and we need to turn more and more to the molecular basis of biology for guidance and inspiration.