Handling of micro objects using phase transition of thermoresponsive polymer

In this paper, we achieve a handling of micro objects using a phase transition of thermoresponsive polymer solution. The phase transition was controlled by a microheater which is embedded in a tip of probe device. In general, probe devices are one of the important devices for micromanipulation, especially for cell manipulation such as handling of egg cells, stiffness measurement, and patch clamping. However, conventional probe devices have some limitations: difficulties in releasing the handled objects by the effect of surface force and damages to the handled cells by the direct contact. As one solution of those problems, we use phase transition of thermoresponsive polymer solution to control handling and releasing of micro objects. The microheater embedded in the probe tip can generate the thermoresponsive gel. Micro objects can be handled by the generated gel and released by returning the gel to sol again. The manipulation of micro objects and assembly of three dimensional structures were demonstrated by the probe. The thermoresponsive gel generated μN force to fix handled objects in the gel. The multi-scale handling from a yeast cell (less than 10 μm in diameter) to a liposome (more than 100 μm in diameter) was also demonstrated. The handling of micro objects in pure water (not containing thermoresponsive polymer) was finally conducted using a theta tube. Those results validate that the probe can achieve the soft handling by the thermoresponsive gel and the precise positioning by reducing the effect of surface force.