Mechanical forces play an important role in cell morphology, motility, proliferation, and physiology. Despite their importance, the current knowledge on the role of mechanical forces on cell biology is still limited, especially for cells in a three-dimensional (3D) environment, which behave very differently compared with those on two-dimensional (2D) substrates. One of the reasons is lack of suitable techniques and tools to non-invasively apply well characterized forces to and precisely measure mechanical response from cells in 3D environments. The proposed studies aim to develop and use a novel tool entitled ?optical chopsticks,? which would enable simultaneous force application and cell response measurements in a nonlinear heterogeneous 3D environment, breaking the limitation of existing techniques. The developed optical chopsticks will be portable, easy to work with, and supported by a broad spectrum of commercialized fiber optic components. The outcome of this research will not only have a significant impact to multiple areas such as cellular biophysics, mechanobiology, and biophotonics, but also shed further light on pathological mechanisms and diagnosis. The research project will provide interdisciplinary training and education for a broad audience of students ranging from high school to graduate school.
Cell mechanics have been quantitatively investigated with different methods, including fluorescence imaging-based traction force microscopy, atomic force microscopy (AFM), and optical tweezers. However, no work has been shown so far to both apply and measure 3D forces in a 3D environment, which is much closer to the in vivo environment. AFM is limited by the resolution of lateral force measurements, while conventional optical tweezers are not suitable for measurements on cells in a 3D matrix due to limited working distances. The proposed optical chopsticks are based on fiber optical tweezers that can create 3D optical traps for non-contact force exertion and measurements. Fiber optical tweezers can reach anywhere inside the medium as long as the medium is transparent, which is especially important for force measurements on cells embedded in a 3D matrix. Moreover, a fiber optic modulation and detection system will be implemented to facilitate dynamic control of optical forces with desired waveforms on cells in a 3D matrix. With these capabilities, optical chopsticks will be integrated with fluorescence imaging techniques for spatiotemporal characterization of force propagation in cytoskeletons of cells on 2D substrates. More importantly, optical chopsticks will be used to precisely measure cell forces in a nonlinear heterogeneous 3D matrix. In the meantime, 3D forces with controllable directions and magnitudes will be applied to cells to study cell migration under external mechanical stimuli. Four specific aims are proposed. 1) To develop the optical chopstics. 2) To implement the optical chopsticks and model the optical force generation. 3) To perform cell mechanics studies on 2D substrates. 4) To perform cell mechanics studies in 3D matrices. The outcome of this research is expected to have a significant impact on multiple areas, including cellular biophysics, mechanobiology, and biophotonics, and also shed further light on pathological mechanisms and diagnosis.
