Physical forces are known to impact cell functions in a fundamental way. While the study dates back some 100 years, the scientific interests have significantly increased in the past decades. However, despite the extensive studies, obtaining precise force information in live animals remains an elusive task. Currently, a vast majority of, if not all, force sensing studies have only been carried out in cultured cells. Yet, it is well-documented that one of the most prominent differences between cell culture and intact tissues is the change of mechanical forces and cell- cell adhesion. Therefore, precise measurements of forces inside biological tissues of live animals are desperately needed to advance the field. The goal of this project is to develop a novel force sensing technique that allows non-invasive sensing of force distribution across 3D volume of biological tissue in a live animal. It promises highly sensitive force measurements with simple fluorescence measurements that can be conducted in a standard confocal microscope. The nanosensor is composed of metal nanodisk, upconversion nanoparticle and flexible polymer. Upconversion nanoparticle is excited by an infrared light and emits visible fluorescence. The infrared excitation provides many benefits including no background fluorescence and high sensitivity. The nanosensor produces fluorescence signal that is highly sensitive to local deformations, enabling detection of force as small as 1 nN and local deformation down to ~1 nm. Finally, we have established a state-of-art two-photon microscope system to perform fluorescence imaging in live mice. We have developed a number of fluorescence tagged mouse models that resolve epidermal and hair follicle lineages and monitor the adhesion, migration and proliferation of epithelial cells. This system will allow us to test and fine-tune our designs in a physiologically relevant condition.
It is widely recognized that physical forces strongly impact cell functions. However, there is no viable technique to reliably measure local forces in live animals and humans. This project will develop a new force sensing technique that enables force sensing in live animals and can eventually be used for humans.