Recently, Professor Guang-Zhong Yang, Dean of the Institute of Medical Robotics from Shanghai Jiaotong University, published a research paper "Liquid seal for compact micro piston operation at the capacitive tip" (DOI: 10.1126 / sciadv. Aba5660) in Science Advances.

With increasing demand for targeted therapy and cell-based intervention, there is a growing interest in the development of new microtools that can be used for in situ and in vitro applications. Actuators at the tip of a sub-millimetric catheter could facilitate in vivo interventional procedures at cellular scales by enabling tissue biopsy and manipulation or supporting active micro-optics. However, the dominance of frictional forces at this scale makes classical mechanism problematic. Improvement is an urgent need.

To provide actuation at the scale of a few hundreds of micrometers, the paper proposed the combination of pneumatic actuation and surface tension to drive a piston that was attached to the distal end of a 140-μm-diameter glass capillary. An oil drop method was used to create a seal between the piston and the cylinder that prevented any leakage below 185-mbar pressure difference while providing lubricated friction between moving parts. This piston generated forces that increase linearly with pressure up to 130 μN without breaking the liquid seal. With a maximum dimension of 150 μm, the microscale piston was fabricated with two-photon lithography. The practical value of the design was demonstrated with its integration with a microgripper that can grasp, move, and release 50 μm microspheres. Such a mechanism opens the way to micrometer-size catheter actuation.

Fig. 1. Principle of operation of the proposed micropiston, microscopic pictures and SEM of the micropiston actuation.

Fig. 2. Microgripper that can grasp, move, and release 50 μm microspheres.

Full text link:

https://advances.sciencemag.org/content/6/22/eaba5660