Mathematical models involving ordinary and partial differential equations and corresponding convergent numerical algorithms for computing their solutions can be used to create simulation packages to study physical phenomena. The mathematical approach can offer guidance for running laboratory experiments, creating specific drugs, and developing tools. In this talk, I will focus on models and numerical simulations used to study the following problems: the colonization of Vibrio cholerae in a human host, the detection of recurrent brain tumors, the development of medical devices, tracking nuclear transport in porous media, and more.