Lab on a chip systems have often focused on diagnostic, chemical, and cell analysis applications, however, more recently the scale and/or precision of micro-engineered systems has been applied in developing new therapies. In this issue we highlight recent work using microfluidic and micro-engineered systems in therapeutic applications. We discuss two approaches that use microfluidic precision to address challenges in filtering blood--to both remove unwanted pathogens and toxins and isolate rare cells of interest that have therapeutic potential. In both cases chemically-modified surfaces, a bioengineered mannose binding lectin on magnetic particles and antibody-functionalized reversibly degradable alginate film, provide the functionality to remove (or isolate) target cells of interest. The third paper we highlight generates microscale gels as protective niches for cell-based therapies. Importantly, the microgels are designed to have controlled porosity but also mechanical rigidity to protect housed therapeutic cells, like mesenchymal stem cells. We expect continued progress in micro- & nano-enabled therapies facilitated by the fabrication of new microstructured materials, precise separations, and closed-loop sensing and drug delivery.