As technology progresses, animal studies will be phased out more and more in favor of computer simulations. Currently however, animal studies are needed because there is no alternative. There are steps humans can take to reduce the ethical issues presented by using animals, but I do not believe an animal study can truly be ethically clean. For that to happen, you would need informed consent of the animal, which we cannot do. Computer simulations are powerful enough at the moment to complete non-biological simulations and some simple biological simulations (for instance Dr. Roman is using FEA to predict aneurysms). But until computers are powerful enough to hold the complexity of an organ and humans understand the organ enough to program it in, the most we can hope for is to minimize the ethical issues of animal research with the use of numbing agents, positive social interaction, and humane sacrificing methods. As it stands currently, it is our only option.