Most deaths from breast cancer occur because the cancer becomes metastatic and spreads to one or more organs. Brain metastatic breast cancer (BMBC) is very aggressive. The prognosis for patients with brain metastases from breast cancer remains poor, often because of resistance to treatment. The environment of BMBC includes tumor cells, immune cells and extracellular matrix (ECM), which is the network of molecules secreted by cells that surround and support them within tissues. Hyaluronic acid (HA) is a primary component of the brain ECM. The immune cells in the BMBC environment are mainly microglia (brain resident immune cells) and macrophages (from blood-derived monocytes). It is not known how these immune cells influence BMBC response to treatment. The goal of this project is to engineer an experimental model incorporating BMBC cells, human microglia, and macrophages as microtumors in HA hydrogels. The model will be used to study how microglia and macrophages influence BMBC cell characteristics and response to treatment. The model may also serve as a platform for the development of new treatment strategies for BMBC or be used for fundamental studies of neurological disorders where disease progression is influenced by immune cells. The project will contribute to training the next generation of the science and engineering workforce by engaging high school students and teachers, as well as undergraduate and graduate students in cancer bioengineering research and enhancing und