Creating effective targeted drug delivery strategies is an integral component of the overall process of drug development. The four key requirements of an effective drug delivery system are retain, evade, target and release. Increasing the therapeutic index (TI) of a delivered compound by selectively delivering it to target areas is a goal that has many obstacles. Some of these concerns have been addressed by recent developments in areas such as liposomes, prodrugs, external targeting, controlled gene expression and antibodies. An analysis of some of the relevant inventions is discussed below. In order to present these inventions in a new light, materials science and engineering approaches have been used to examine the patents and help discuss their advantages and disadvantages. Patents concerning the manipulation of genes and proteins are at the core of this research and are an integral part of its future. Very specific targeting is possible when working at this level. The most exciting developments combine targeting strategies for delivery systems with many layers of specificity, increasing their targeting potential. It is also important to understand (and possibly exploit) the area to which a delivery system is being targeted and to learn from nature's own delivery systems. Examples of these systems, including the red blood cell, the neutrophil and the secretory granule, are discussed using a materials engineering approach. This analysis reveals numerous characteristics that nature has designed into its delivery systems, and how these are important when creating man-made products. Working with these kinds of ideas, a true 'magic bullet' may be discovered.
