We are exploiting unique physics, microenvironment control, and the potential for automation associated with miniaturized systems for applications in basic biology, medical diagnostics, and cellular engineering.
1. Quantitative Cell Biology and Mechanics of Cancer Metastasis
Metastasis of cancer to secondary sites, not the primary tumor is responsible for 90% of cancer-related deaths, representing over 500,000 deaths per year in the United States alone. Consequently, metastases are among the most important biological problems to address in cancer research. Although a link between the primary tumor and secondary sites has been discovered in the form of cancer cells circulating in the blood (CTCs – circulating tumor cells), little is known about the mechanism by which cancer cells pass through the barrier of endothelial cells and extracellular matrix lining vessel walls, migrate through the confined environment, and detach to circulate freely in the peripheral blood. An understanding of this process of intravasation could lead to novel therapies targeted at the initial stages leading to metastases. However, direct observation of the process has been mostly unsuccessful because of the technical difficulty of visualization in a 3-D living organism. Microfabricated in-vitro systems that can replicate particular aspects of the tumor environment quantitatively and allow observation of the process of intravasation can yield critical insights into this problem.
2. Nonlinear Microfluidics
In microfluidic systems, inertial, nonlinear terms of the Navier-Stokes equations describing fluid flow are often neglected. This is because of the widely-held notion that because of the small length scales the Reynolds number in these systems is concurrently small. This is not necessarily the case, especially when microfluidic systems are operated at high flow velocities. In these finite inertia systems, particles in a fluid under laminar flow migrate across streamlines in a predictable and precise manner. Ordering of particles into regular trains along the longitudinal direction of the channel can also be observed in these systems. The physical basis of focusing and ordering phenomena in inertial flows has been explored briefly, but an intuitive understanding is still elusive. Further understanding and intuition for these systems would allow application to a broad base of engineering and biological problems. A particularly good match for this technology is in developing novel flow cytometry systems with massive throughput, enabled by ordering and focusing without added sheath fluids. These systems should be useful in rare cell detection from clinical samples, with principle uses in cancer diagnostics. Inertial microfluidics for concentration of rare cells or particles in large volumes of bodily fluids is also promising, since centrifugation based techniques are especially lossy for large sample volumes.
3. Microfluidic Directed Cellular Evolution
Directed evolution of improved proteins and enzymes for applications in biotechnology, food science, and medicine has been very successful over the last few decades. Selection processes have been implemented that select for thermostability, substrate specificity, kinetics, and other properties in evolved enzymes. In most cases evolutionary processes have been applied to optimize a particular protein’s characteristics but not a bulk cellular behavior that has contributions from a system of interacting proteins. This may be partly because of a lack of suitable selection techniques for particular cellular behaviors. Microfluidic technologies may offer advantages in creating new useful selection criteria for cellular evolution. Examples include cell migration speed, proteolytic activity, deformability, shear-stress stability, and osmotic tolerance. Besides gaining an understanding of dominant molecular pathways in controlling these behaviors, the resultant evolved cell populations and genetic modifications may be useful for therapeutic applications. For example, fast migrating and proteolytically active cells and the underlying genetic circuits may be used in aiding and speeding wound healing, as cell migration into the wounded site can be a rate limiting step for further healing. Additionally, directed evolution in prokaryotic cells may assist in the understanding of chemotaxis, adherence, and sporulation and be therapeutically useful in designing pharmaceuticals, antisense, or gene therapies to disrupt these important behaviors.