A Miniaturized Ultrasonic Micro-Hole Perforator for Minimally Invasive Craniotomy.

Objective: Micro-hole perforation on skull is urgently desired for minimally invasive insertion of micro-tools in brain for diagnostic or treatment purpose. However, a micro drill bit would easily fracture, making it difficult to safely generate a micro-hole on the hard skull.

Methods: In this study, we present a method for ultrasonic vibration assisted micro-hole perforation on skull in a manner similar to subcutaneous injection on soft tissue. For this purpose, a high amplitude miniaturized ultrasonic tool with a 500 μm tip diameter micro-hole perforator was developed with simulation and experimental characterization. In-depth investigation of micro-hole generation mechanism was performed with systematic experiments on animal skull with a bespoke test rig; effects of vibration amplitude and feed rate on hole forming characteristics were systematically studied. It was observed that by exploiting skull bone's unique structural and material properties, the ultrasonic micro-perforator could locally damage bone tissue with micro-porosities, induce sufficient plastic deformation to bone tissue around the micro-hole and refrain elastic recovery after tool withdraw, generating a micro-hole on skull without material.

Results: Under optimized conditions, high quality micro-holes could be formed on the hard skull with a force (<1 N) even smaller than that for subcutaneous injection on soft skin.

Conclusion: This study would provide a safe and effective method and a miniaturized device for micro-hole perforation on skull for minimally invasive neural interventions.