Direct In-Petri Dish Liquid Droplet Manipulation Based on Microscope and Ultrasonic Phased Transducer Array

Abstract

High-precision liquid droplet manipulation is widely used in life science, biomedical engineering, and industry. However, there still lacks a robotic approach supporting the direct in-petri dish manipulation of liquid droplets without the need of additives (such as magnetic beads) or other setup requirements (such as on hydrophobic or conductive surfaces). From the robotics perspective, this challenge concerns with designing an adequate robot end-effector capable of firmly holding and effectively moving droplet on hydrophilic surfaces. In this paper, we propose an automated robotic system for the direct in-petri dish liquid droplet manipulation based on ultrasonic phased transducer array (UPTA) and microscope, which can interact with users to selectively grasp droplet, follow user designated trajectories to transport droplet, and positioning droplet in high precision. The core working mechanism of the proposed system is to precisely generate an inclined single focal point, acting as a noncontact end-effector, inside the droplet under the guidance of microscope, which can induce sufficient hydrodynamic actuation forces on the peripheral contact line of the droplet to keep the droplet moving along the ultrasonic end-effector. Since it is additive free, our system is inherently compatible to medical, chemical and industrial protocols. Details regarding the system design and implementation, the ultrasound focusing strategy, and the visual servo control scheme are elaborated in this paper. Experiments validated the effectiveness of the proposed system.