Markus Faber
toolcraft internally cooled bone drill
Internally cooled bone drill.toolcraft C 1 Internally cooled bone drill
Precision part, mould and assembly manufacturer, toolcraft has collaborated with the Institute of Production Engineering and Machine Tools (IFW) at Leibniz University of Hannover to 3D print a surgical bone drill.
The bone drill is said to be capable of preventing possible tissue damage, often causing during operations that rely on the use of traditionally manufactured drills. Damage to tissue occurs when the heat produced in the cutting process reaches 48 degrees C and higher. The Leibniz University IFW division approached toolcraft while carrying out a research and development project which explored the production of a machining tool capable of cutting bone without causing thermal-induced osteonecrosis.
To combat this, drilling processes have had to be interrupted at regular intervals, in order to ensure the temperature is kept as low as possible. toolcaraft and the IFW group, however, have harnessed metal laser melting to manufacture drills with integrated cooling ducts. Thanks to the cooling ducts, there is a constant flow of coolant inside the tool, along the helix and back to the tool holder, without coming into contact with the wound. toolcraft also developed a non-rotating pre-spindle attachment with an inflow and outflow function for the coolant. Attached, a coolant tank and pump ensures the continuous supply of coolant.
The engineers working on the drill prototyped a model with a diameter of 6mm, with the shape, designed by Schmidt WFT using Materialise's Magics CAD software, maintained to ensure ease-of-use for users. Of more importance was that the material used to build the drill was well tolerated by patients – the group used biocompatible material 1.4404. Then, there was the point of the research: the reduction of temperature, and thus the cooling ducts. The internal circular cooling ducts had a diameter of 1.2mm, while horizontal drilled holes were added to link the cooling circuit to the drill. This allowed the coolant to be supplied and taken away as and when necessary.
At the outset of the project, the cooling capacity was determined, measuring volumetric flow rate, temperature and thermal capacity of the coolant. A method was developed, which would maintain tool stability and ensure the tool was functional and capable, to bring a closed cooling circuit into the tool substrate.
Once the researchers were sure of the material, and confident in the design, the drill was printed on a Concept Laser machine and machined to its final size. Practical tests were then carried out at IFW. Using water as a coolant, IFW drilled and measured the process temperature in artificial and bovine bone, measuring reference temperatures at higher and lower feed rates, as well as when the tool cooling system was turned on and off.
The IFW group and toolcraft, having conducted several tests, say the drill has seen a 70% reduction in the temperature produced during a bone-cutting process, thanks to the internal cooling system. The engineers working on the project also believe it results in a considerably improved surgery, since excessively high temperatures put bones at risk of damage in virtually all bone-cutting procedures.
