An example of ongoing work to make targeted cell-killing technologies economically practical: "For more than a decade, researchers have been trying to develop nanoparticles that would deliver drugs more effectively and safely. The idea is that a nanoparticle containing a drug compound could selectively target tumor cells or otherwise diseased cells, and avoid healthy ones. Antibodies or other molecules can be attached to the nanoparticle and used to precisely identify target cells. ... [Researchers] devised a method by which the building blocks of the nanoparticle and the drug self-assemble into a final product. Two types of polymer combine to form the tangled mesh of [a] drug-laden spherical nanoparticle. One of these polymers has two chemically and structurally distinct regions, or 'blocks': a water-insoluble block that forms part of the mesh that encapsulates the drug, and a water-soluble block that gives the final product a stealthy corona to evade the immune system. The other type of polymer has three blocks: the same two as the first, as well as a third region that contains a targeting molecule - the signal that will ensure the final particles attach to the desired cell types. The drug-carrying nanoparticles are formed by simply mixing these polymers together with the drug in the appropriate conditions. The self-assembling polymers can be produced in a repeatable and scalable fashion. But the method has an additional benefit ... The method by which the nanoparticles are built - from individual preparations of the two-block and three-block polymers - would also let researchers use high-throughput screening approaches, akin to how medicinal chemists design and test new drug compounds. Each block could be tweaked - extend one block, change the charge on another - and the relative amounts of each polymer could be varied. With so many parameters for tinkering, [scientists] can screen many combinations."