Identifying a certain cell type based on a specific signature, separating cell mixtures according to cellular differences, and studying changes in a specific signature with cell environments are important techniques in biological research. While various biochemical markers of cells have been extensively used for decades, biomechanical properties such as cell stiffness are increasingly recognized as an important indicator of cell type and physiological state. The mechanical properties of cells are defined by the membrane, cytoskeleton and the volume of the cell, and are likely associated with basic characteristics including type, growth, stage of differentiation, and response to the environment. Existing mechanical characterization tools, however, can only examine a few cells at a time, severely limiting their utility and application due to the low throughput associated with the sequential isolation and probing of individual cells. Here, a high-throughput method will be developed, where optical-based mechanical ?stretching? forces are applied to cells in microfluidic devices. By the end of this 3-year project, a device capable of the rapid measurement of cell mechanical properties will be built and tested on bovine blood cells, vascular cells, and human HeLa cells. A number of broader impacts are expected including providing new research opportunities for undergraduate students, new teaching opportunities at the high-school level, and new recruitment efforts for underrepresented groups within the state of Colorado.
Recent studies have shown that cell stiffness is a clear indicator of disease, with examples including sickle cell anemia, malaria infection, and cancer. The goals of this project were to develop new technologies using low cost lasers for stretching cells in a high speed device. This technology is designed to aid biomedical researchers as well as medical doctors for eventual clinical applications such as detecting and diagnosing disease. In this work, we developed methods for machining appropriate devices and assessed various approaches for measuring cell stretchiness. Specifically, 1. We found that laser micromachining of complex microfluidic structures with short pulses of light (less than 1 millionth of 1 millionth of a second) enables fabrication of microdevices with features such as fluidic channels and light guides that are unattainable with previous microfabrication techniques. 2. It was found that simple, efficient, sharp focusing of compact laser diode beams into glass microchannels can be achieved with a simple four-lens geometry, thus enabling inexpensive light sources to be employed for cell-stretching studies. 3. The time-dependence of cell-stretch was observed by temporally varying the power of an optical trap. It was found that employing the ability of the cell to keep up with the varying force by stretching and relaxing in response enables reliable cell identification. This technique is more reliable than measurement of cell stretch in response to a constant force. We tested this method on red blood cells infected with malaria, and we anticipate that this type of elasticity measurement will be generally useful for classifying cell types and assessing cell health. 4. Our feasibility studies indicated that an electrical techniques are the best option for high-speed detection of the small (<5%) magnitude of stretching likely to be observed in most cell types. Furthermore, it will be straightforward to employ these electrical signals to trigger elasticity-based cell sort.
