Mini-human? Animal on a chip? No matter what you call it, the use of microfluidic circuitry to simulate human or animal tissue can creep some people out. But these tiny replications could have major market potential. "NASA is interested in using them to see if humans could survive in different environments," says Shuichi Takayama, an assistant professor at the University of Michigan's biomedical engineering department. "And drug companies love them." Using rubber chips with hollow circuits no wider than a human hair, Takayama has been able to create a self-contained circulatory system in which actual cells can be tested and observed. The liquid environment can be tightly controlled, unlike in the past when Petri dishes, subject to constant contamination, were scientists' best option. "When you take cells out of a person or animal, the exact same cells behave totally differently in a dish," says Takayama. "This way we can save animals and reagents, and work in a much more controlled environment.