The main purpose of this research is to engineer the bone marrow niche microenvironment in vitro for metastatic cancer studies using micro-technologies. In the original plan, we proposed to include cancer cells, osteoblasts, and endothelial cells in the system. During the process, we learned about the importance of mesenchymal stem cells and pursued to create three-dimensional (3D) microenvironments from mesenchymal stem cells (MSCs). Initially, multipotent dedifferentiated fat (DFAT) cells that possess similar differentiation abilities as MSCs were used. DFAT cells were encapsulated in the core region of alginate shell fibers using a microfluidic double co-axial device to make 3D cell fiber constructs and differentiated into the smooth muscle cell lineage. Subsequently MSCs derived from adipose tissue, adipose-derived stem cells (ADSCs), were cultured as cell fiber constructs using the same cell fiber technology and differentiated into adipocytes. The conditioned media from the differentiated ADSC fibers was further used to culture MCF-7 breast cancer cells to study its effect on breast cancer cell proliferation.