A novel rotationally oscillating micro drill for microinjection operations

Abstract

Since their invention, microinjection tools have been widely used for cellular micromanipulation operations including intracytoplasmic sperm injection, gene injection, drug development, transgenic animal development and clone creation. Currently, microinjection for mice and some other species is performed with the piezo-driven actuators. In these type of drills, a very small segment of mercury in the proximal end of the pipette is used to increase the success rate. However, the toxicity of mercury causes a serious risk factor both for the operator and the injected organisms. Therefore, there is a demand for mercury-free microinjection devices. This thesis presents a novel mercury-free rotationally oscillating micro drill device based on the same principle of Ros-Drill© for single living organisms. The drilling motion is generated using a hollow shaft brushless direct current motor with an integrated pipette holder in its shaft. The device creates high frequency and small amplitude rotational oscillations at the sharp tip of the injection pipette for piercing. The position of the motor is controlled to track the desired sinusoidal trajectory with a wide range of frequencies and amplitudes to achieve successful piercing with different organisms. A novel control method for the brushless motor is developed and validated with both simulation and experimental studies. Also, high speed camera images show that the design reduces the unwanted lateral vibrations. The biological experimental studies with the new device are conducted on mouse oocytes and Caenorhabditis elegans worms. The experiments reveal that the drill is suitable for piercing mouse zona pellicuda and oolemma considering the minimal damage and acceptable success rates. In microinjection experiments on Caenorhabditis elegans worms, the cuticles of worms are pierced much more easily than the conventional method and all worms survived after injection. The thesis also presents a novel sensorless measurement method for angular displacements of oscillation assisted micro drill device. It requires a mechanical motion limiter for motor and a modification in motor energizing topology. The method utilizes the back-emf voltage and generates analog signals for angular displacements. Simulations and experimental studies reveal that the method is viable for the measurement during cellular piercing operation. It presents fair performance for frequencies up to 1000 Hz. As a conculusion, the novel rotationally oscillating micro drill device presents good performance in terms of successful microinjection operations with different organisms, ease of usage, mercury-free structure, compactness and compatibility with different manipulation systems.