Ultrasonic vibration-assisted micro-hole forming on skull

Abstract

In minimally invasive neurosurgery, there is a gap between the need for a micro-burr hole to be opened on the skull to expose the enclosed brain for further operation and the proper technology available. Conventionally, a burr hole is generated by a drilling perforator, which usually causes damage to the vital soft tissue beneath skull. Besides, because of the extremely low mechanical strength of a micro-drilling bit, a micro-hole cannot be generated on the hard skull by the conventional drilling method. To bridge this gap, an ultrasonic vibration-assisted micro-burr hole forming technique has been developed in this study and its effectiveness has been proved through in vitro experiment on cat skull. With the assistance of ultrasonic vibration (29.7 kHz), a micro-hole has been successfully formed on skull with a 300 µm diameter conically tipped tool. Ultrasonic vibration of a large amplitude is found beneficial because the thrust force can be greatly reduced by increasing the vibration amplitude. Moreover, the micro-hole forming is free of cutting and chips. The ultrasonic vibration is found to have a hammering effect similar to shot peening, and a layer of dense tissue is formed around the hole and no chip is generated in the hole forming process. Besides, since the ultrasonic vibration tool can only fragment hard bone tissue without causing damage to the soft tissue beneath skull, a safe micro-hole forming technique can be enjoyed. Based on the findings from this study, a micro-burr hole perforator can be developed for the next-generation minimally invasive neurosurgery.